Radiological factors affecting decision-making in a nuclear attack: Recommendations of the National Council on Radiation Protection and Measurements

NCRP REPORT No. 42

RADIOLOGICAL FACTORS AFFECTING DECISION-MAKING IN A NUCLEAR ATTACK

Recommendations of the NATIONAL COUNCIL O N RADIATION PROTECTION AND MEASUREMENTS

Issued November 16, 1074 National Council on Radiafion Protection and Measurements 7910 WOODMONT AVENUE / WASHINGTON, D.C. 20014

Copyright @ National Council on Radiation Protection and Measurements 1974

All rights reserved. This publication is rotected by copyright. No a r t of this

publication may be reproduced in any Ern or by any mems, i n c l u h s photocopying, or utilized by a.ny information storage and retrieval system wlthout wrltten permission from the copyright owner, except for brief quotation in critical articles or reviews. Library of Congress Catalog Card Number 74-20064 International Standard Book Number 0-913392-243

Preface In 1954 the Federal Civil Defense Administration (FCDA) informally requested that the National Committee on Radiation Protection and Measurements (NCRP) provide information as to the radiation exposures that might be acceptable in several categories of civil defense work in emergency conditions. In response to this request an ad hoc group appointed by the NCRP furnished the FCDA with the information then available. In response to a formal recluest to undertake a broader study of the problems in emergency exposures that might result from nuclear weapon attack, the NCRP, in 1955, established a subcommittee for this purpose. Attention was focused on the extent to which whole-body exposure to gamma radiation resulted in: (a) early injury; (b) impaired capacity to work; (c) reduced fertility; (d) late somatic (body) effects such as leukemia, cancer, cataracts, and life shortening; and (e) genetic injury. Initially, the subcommittee examined in detail the problem of stipulating values for permissible dose for selected personnel engaged in tasks of varying priority during the post-attack period. However, it became apparent that this approach-however commendable in the case of a radiation accident in peacetime-was not realistic in a nuclear war. The subcommittee became convinced that the primary problem was national survival, i.e., the question of how much radiation a society could survive, rather than how much is individually acceptable or permissible. The subcommittee shared with many others the enormous psychological difficulty of coming to grips with the concept of nuclear war as a disasler that may be experienced and from which there may be recovery. After considerable debate, the subcommittee decided to prepare an information base for the decision-making that might be required in civil defense operations during and after a nuclear attack. The result was NCRP Report No. 29, Exposure to Radiation in an Emergency, which was published in 1961. NCRP Report No. 29 dealt with radiation emergencies in general and included some aspects not necessarily associated with nuclear war. I t has been widely distributed and many of its recommendations have been incorporated into the civil defense programs of the United States and other countries. New information developed since the publication iii

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PREFACE

of that Report has stjmulated its revision, however. In 1968 the NCRP reactivated the subcommittee that had been responsible for the drafting of Report No. 29, as Scientific Committee 14, to revise Report No. 29. The intent was to produce a new report on radiological problems associated with nuclear attack, using data from accidental human radiation exposures and contemporary experimental radiobiological information to evaluate how fractionation and protraction of radiation exposure might influence the effectiveness of total-body radiation exposure. Report No. 29 had attempted to provide a means of predicting recovery from radiation injury by introducing the concept of Equivalent Residual Dose (ERD). The ERD formula, based largely on results of experiments on mice, was modified empirically to predict human recovery rates. The ERD formula is considered to be an adequate basis for making large scale pre-attack radiation casualty predictions, but leaves unfulfilled the need for some guidance scheme on which those in charge could base their decisions concerning exposed individuals or groups of persons under operational conditions during and after a nuclear attack. The NCRP has attempted to provide this more practical base in this revision of R e ~ o rNo. t 29. This report was prepared to assist in preparedness activities for large disasters in which exposure of many people t o nuclear radiation is of primary concern. In particular, those officially responsible for civilian preparedness against nuclear attack should find this report a basic resource for their task. It is an attempt t o describe the important characteristics of radiation, with emphasis on radioactive fallout, and radiation injury so that they can be understood by people who will be responsible for decision-making in civil defense ope&ions in a nuclear attack. The recommendatiom must be regarded as reflecting the NCRP1s best effort t o evaluate information presently available; they may be modified as more knowledge becomes available. The present report was prepared by Scientific Committee 14 on Radiological Factors Affecting Decision-Making in a Nuclear Attack. Serving on the Committee during the preparation of this report were: G. V. LEROY, Chairman (198&1870) G . W . CASARETT, Chairman (1970) Members

E. L. ALPEN J. L. BATEMAN H. A. B L A I R ~ J. T. BRENNAN R. J. HASTERLIK

C. C. Lus~sanoa J. H. RUBT f Deceased.

Consullant J. C. GREENE

PREFACE

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v

The Council wishes to express its appreciation to the members and consultant for the time and effort devoted to the preparation of this report. LAURNTON S. TAYLOR President, NCRP Washington, D. C. August 16,1974

Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . .

1

.

2

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3

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4

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5

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Introduction . . . . . . . . . . . . . . . . . . . . . . 1.1 The Problem . . . . . . . . . . . . . . . . . . . . 1.2 Assumptions . . . . . . . . . . . . . . . . . . . . 1.3 Limitations of the Report . . . . . . . . . . . . . . 1.4 Radiation Exposure and Dose Units Used in This .Report . . . . . . . . . . . . . . . . . . . . . . . . General Aspects of Nuclear Weapons . . . . . . . . . . 2.1 Introduction . . . . . . . . . . . . . . . . . . . . 2.2 Types of Nuclear Explosions . . . . . . . . . . . . 2.3 Nuclear Reactions (Fission and Fusion) . . . . . . . . Residual Nuclear Radiation and Fallout . . . . . . . . 3.1 Introduction . . . . . . . . . . . . . . . . . . . . 3.2 Residual Nuclear Radiation From Fission Products . . . . 3.3 Fallout . . . . . . . . . . . . . . . . . . . . . . 3.4 Measurement of Gamma Radiation . . . . . . . . . . 3.5 Exposure and Exposure Rate Calculations . . . . . . . . 3.6 Radiation Monitoring Instruments . . . . . . . . . . Effects of Radiation o n Man . . . . . . . . . . . . . . 4.1 General . . . . . . . . . . . . . . . . . . . . . . 4.2 Biological Features of Acute Radiation Injury . . . . . . 4.3 Statistical Features of Radiation Injury . . . . . . . . 4.4 Clinical Features of Radiation Injury . . . . . . . . . . 4.5 The Problem of Protracted Exposure . . . . . . . . . . 4.6 System for Predicting Outcome of Human Exposure . . 4.7 Prediction of Number of Persons Requiring Hospitalization . . . . . . . . . . . . . . . . . . . . . . 4.8 Work Capacity . . . . . . . . . . . . . . . . . . 4.9 Infection . . . . . . . . . . . . . . . . . . . . . . The Process of Decision-Making . . . . . . . . . . . . 5.1 The Relation of Exposure t o Effect . . . . . . . . . . 5.2 Predicting the Outcome . . . . . . . . . . . . . . 5.3 The Population a t Risk . . . . . . . . . . . . . . . . 5.4 Distinction Between Causes of Injuries . . . . . . . .

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CONTENTS

5.5 The Probable Outcome . . . . . . . . . . . . . . . . 5.6 Summary . . . . . . . . . . . . . . . . . . . . . . APPENDIX A . Glossary . . . . . . . . . . . . . . . . . . APPENDIX B . The Use of the "Penalty" Table in DecisionMaking (Dose-Time Considerations) . . . . The NCRP . . . . . . . . . . . . . . . . . . . . . . . . NCRP Reports . . . . . . . . . . . . . . . . . . . . . . .......................... Index

42 43

45 51 54 60 63

1. Introduction 1.1 The Problem

The National Council on Radiation Protection and Measurements (NCRP) has developed sets of criteria for the maximum permissible exposure of radiation workers and the general public to ionizing radiations, for the purpose of minimizing the possibility of deleterious effects of radiation on lifespan and heredity. All such criteria are designed to deal with situations in which there is control of the source of radiation, of the exposure of persons to the radiation, or of both. Radiation exposure levels considered in the criteria are very low. For most conditions encountered in everyday uses of radiation, the criteria are considered to be adequate and reasonable. Emergency situations in which large numbers of people may be heavily or intensely exposed to radiation under circumstances essentially beyond their control can occur, however. Such exposure may result from nuclear detonations and consequent radioactive fallout material. In disasters of this sort, the concept of permissible exposures described above cannot be applied. The formulation of recommendations dealing with intense and uncontrolled radiation exposures represents a departure from the usual considerations in radiation protection in which the principal emphasis has been upon the prevention of significant radiation injury from exposures extending over long periods of time. Here we are concerned with possible exposures much greater in magnitude and intensity than those encountered in normal radiation work, and with a high likelihood that many people will be killed or severely injured. I t is most likely that the initial exposure in a nuclear war will be under little or no control, although later exposure may be subject to some degree of control and prediction. In addition, operations such as rescue, salvage, reconstruction, movement from and re-occupation of contaminated areas, must be conducted so that control of exposure is exercised. In any disaster involving intense and uncontrolled exposure of many people to nuclear radiation, the objective must be to minimize the number of lives lost, the number of people with incapacitating sickness, the long-term biological effects, and impediments to industrial, agri-

2

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INTRODUCTION

cultural and social recovery of the area. Because problems of radiation exposure are apt to be accompanied by other aspects of any disaster and also by other requirements of the populace and the govenment, many complex decisions must be made in which additional radiation exposure to sets of individuals for specific purposes must be considered in conjunction with radiation doses which they have already received and in relation to the requirements of the situation.

1.2 Assumptions a. This report is intended to be applicable to nucIear disasters, ranging in size t o full-scale, nationwide nuclear attack. The NCRP is firmly convinced that appropriate actions would reduce the toll of casualties from radiation exposure in nuclear warfare. The Council is confident that even the widespread fallout after an attack with high-yield nuclear weapons need not create a hopeless situation. Enough is known about radiation physics and about the medical and biological effects of radiation to go far toward reducing radiation casualties, if tthe knozuledge i s properly applied. However, the effective application of existing knowledge for civil defense requires that many preparations are made well in advance of the disaster. These include the development of: (1) shelters adequately stocked with food and water; (2) a capability for radiation monitoring; (3) an effective civil defense organization, including an adequate number of people having a t least a basic knowledge of radiation hazards and safeguards; and (4) an informed public. b. The text has been prepared so that it can be read and used by oficials responsible for disaster preparedness, mitigation and recovery, and also by educated citizens concerned with, or involved in, disasters of this kind. c. The NCRP assumes that survival of the people and thus the nation has the first priority in a major nuclear disaster. In the event of such a disaster, until national survival is assured, the possibility that late somatic (body) effects might impair the health of some of the survivors must be disregarded. I t should be realized, however, that many measures which may be chosen to reduce casualties may also be effective in reducing late effects. Consequently, early decisions based primarily on survival need not, in general, be in serious conflict with judgments made a t more leisure in which late effects are also considered. Whenever there is a possibility for making distinctions, persons who may be expected to

LIMITATIONS OF THE REPORT

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3

reproduce later should receive special protection. In addition to lessening the genetic risk in this way, this also protects the persons who have the longest life expectancy and therefore the greatest risk of radiation induction of delayed somatic effects of long latency, such as cancer.

1.3 Limitations of the Report a. The biological effects of radiation which are considered in this report are: (1) the effects of total-body irradiation from external sources of gamma radiation; (2) the effects of deposition of radioiodines in the thyroid gland, particularly in the glands of children; and (3) injury to skin by beta radiation. The acute clinical consequences of radiation injury, which may appear in various forms and degrees of seve~ity from minutes to weeks after irradiation, will be responsible for most of the early casualties. What is known about the quantitative aspects of acute radiation injury comes mostly from analysis of clinical experience with radiation therapy, from studies of radiation accidents, and from the study of the Japanese who were exposed to radiation from atomic bombs. However, it must be emphasized that most of the available information about acute radiation injury is based on experience with brief, intense, large radiation exposures. Much less is known about the effects on man of repeated exposure to amounts of radiation which individually would not cause significant sickness or disability. Repeated exposure can occur; recommendations about effects of such exposures are necessarily based to a large extent on informat,ion obtained from animal experiments. b. Neutron dose due to nuclear bursts is not considered in this report; however, the reader should be aware that for some circumstances, such as small bursts together with relatively light shielding, the neutron dose can be large. Even so; this report is more narrowly focused, for the following reasons: (1) Current weapon sizes tend to be large enough that the contribution to the dose by prompt neutrons tends to be m a l l relative to the gamma-ray component. (2) Despite the fact that the relative contribution by delayed neutrons increases with weapon size, current information is that this component likewise tends to be less important than gamma dose for current weapons.

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INTRODUCTION

(3) Nearly all of the report holds equally well if "dose" is interpreted to include a neutron component. (4) In cases in which the neutron dose is the largest constituent of the prompt radiation in the open, an individual exposed to it would often-though by no means always-be killed by other weapon effects, while a well-shielded individual would often be exposed mainly to the gamma rays. This last is because neutron dose is reduced relative to gamma,-ray dose by heavy shieldmg. (5) Inclusion of a section on neutron dose would require the introduction of additional concepts. For this report, the added complexity would decrease the readability enough that i t would be preferable to discuss neutron dose separately. c. The limited experience of the Marshall Island children exposed to fallout suggests that the combination of gamma radiation from external sources and beta radiation from internal deposit of radioiodines in the thyroid gland may seriously affect the development of this gland as the child matures. Accordingly, this report offers recommendations for countermeasures. The radiation doses and effects from the internal deposition of other radioactive materials are considered to be relatively minor and outside the scope of this report, and must be the subjects of other guides. Food and water are unlikely to be seriously contaminated, and water can be easily decontaminated. d. The recommendations ofered in this report are limited in their application to the 3 r d three to four months after an attmk. It is the opinion of the Council that experience gained during this period will be a more reliable guide to later decision-making than any judgments that can be offered here on the basis of information presently available. e. This report does not contain data or recommendations relating to food crops, domestic animals or wildlife. This type of information may be found in other reports.'

1.4 Radiation Exposure and Dose Units Used in This Report

After a nuclear attack the information received from monitors concerning gamma-radiation exposures will be those measured in free air in terms of the roentgen (R). For this reason, the roentgen (R) is chosen, for the practical purposes of this report, m the generic term or unit for gamma-radiation exposure or dose, rather than the unit of absorbed radiation dose, the rad. On the other hand, determination of dose to Survival o j Food Crops and Livestock in the Eveni o j Nuclear W ~ TAEC , Symposium Series 24, U.S. Atomic Energy Commission, Washington, 1071.

RADIATION EXPOSURE AND DOSE UNITS USED

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5

specific tissues from the less penetrating beta radiation is more complex and not achieved directly from monitoring instruments, but is calculated in terms of the rad. Therefore, the rad is used in this report .as the unit for beta-radiation dose, with specification of the tissue receiving the dose. Incidentally, this arbitrary use of the roentgen (in air) for gamma-radiation exposure or dose to the body and the rad for betaradiation dose to specified tissues can serve to emphasize that 1,000 roentgens of highly penetrating gamma radiation measured in air at the surface of the skin may give a dose of somewhat less than 1,000 rads to the skin and also substantial but diminishing doses to tissues a t increasing depth in the body, while 1,000 rads of lowly penetrating beta radiation to the skin does not indicate substantial doses to tissues deep in the body. The reader is referred to the Glossary (Appendix A) for definitions of the terms used in the report.

2. General Aspects of Nuclear Weapons 2.1 Introduction For reference, this section includes limited information on nuclear explosions and reactions. A comprehensive coverage may be found in The E f c t s of Nuchar Weapons?

2.2 Types of Nuclear Explosions

2.2.1 General. The phenomena associated with the detonation of nu-

clear weapons vary with respect to the relationship between the point of detonation and the surface of the earth. For convenience, nuclear bursts are sometimes categorized in two distinguishing types-air bursts and surface bursts. 2.2.2 Air Bursts. An air burst is a nuclear detonation at an altitude at which the fireball, a t maximum diameter, does not touch the surface of the earth. The quantitative aspects of an air burst depend upon the yield of the weapon as well as the burst height. Most of the energy appears as blast, but thermal radiation would be of sufficient intensity to cause severe burns and fires at relatively large distances from ground zero. Exposures to initial nuclear radiation will occur in regions where there are also intense blast and thermal effects. If the air burst occurs a t a high altitude, the residual nuclear radiation arising from the fission products generally will be of no immediate consequence on the ground, since the fission products would be losing much of their activity while widely dispersed a t high altitude. 2.2.3 Surface Bursts. A surface burst occurs when a nuclear weapon is detonated on the surface of the earth, or at such a height above the earth that the fireball makes contact with the surface. A large-yield detonation The E'ects of Nuclear Weapons, S. Glasstone (Editor). Department of Defense and Atomic Energy Commission, Revised Edition, February 1964 (U.S. Government Printing Office, Washington, 1964). 6

NUCLEAR REACTIONS

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7

near the surface of shallow water would produce fallout having about the same characteristics as tha.t from a land-surface burst. The general phenomena are essentially the same as for an air burst. However, much of the energy quickly induces ground shock and causes major deformation and cratering of the surface of the earth. Of particular importance to the radiation hazard is the enormous quantity of material from the earth's surface that is fused with t,he radioactive fission products. This debris then serves as a vehicle for bringing down the radioactive fission products. Severe radiation emergencies of long duration can result from this radioactive fallout.

2.3 Nuclear Reactiom (Fission and Fusion)

Two nuclear processes that release energy are the fission process and the fusion process. Fission takes place when heavier nuclei such as those of certain isotopes of uranium or plutonium split. The fusion process takes place when light nuclei, e.g., those of the hydrogen isotopes, tritium and deuterium, join. In the fision reaclion, a free neutron enters the nucleus of a fissionable atom causing the nucleus to split into two smaller nuclei which are called fission fragments. In addition to the release of energy, two or more neutrons are released. Neutrons released in this manner are able to induce fission of other fissionable nuclei. This results in the release of more energy and more free neutrons. The number of nuclei involved, and the amount of energy released, increases very rapidly. Some of the neutrons escape from the reaction and others are absorbed in non-fission reactions. Fusion reactions occur when the reactants are heated to very high temperatures--of the order of several million degrees. Reactions obtained under these circumstances are referred to as thermonuclear reactions. Because a fission reaction produces temperatures of great magnitude, a fission device can be combined with quantities of certain light elements and, under the proper conditions, initiate a thermonuclear reaction. The Jission process is not only the fundamental process for nuclear weapons, and basic to the production of much of the initial pulse of nuclear radiation emitted in a nuclear explosion, but is also basic to the production of residual nuclear radiation from fission products in fallout.

3. Residual Nuclear Radiation and Fallout 3.1 Introduction

This section is primarily a description of the residual radiation from nuclear weapons, in particular the gamma rays which are emitted in the process of the decay of the fission products or the decay of elements made radioactive by the neutrons released at the time of the explosion, together with beta-particle radiation from decaying fission products. The amount of radioactivity associated with alpha-particle emitters, e.g., non-fissioned uranium or plutonium, would be negligible compared to that of the other radioactive elements, so that for the purposes of this document, the alpha radiation is regarded as insignificant and is not considered.

3.2 Residual Nuclear Radiation from Fission Products

In the fission process, there are many different ways in which a uranium or plutonium nucleus can split. Thus, a nuclear explosion gives rise to approximately 400 types of fission fragments, all of which are nuclides (or isotopes) of lower mass than uranium or plutonium and most of which are radioactive, i.e., unstable isotopes which decay by emitting radiations. Radioactivity associated with these fragments usually is manifested by the emission of beta particles and, almost always, gamma radiation. These radiations are the means by which the excess energy "stored" in the fission products is carried off. When a negatively charged beta particle is emitted, the radioactive element (radionuclide) is changed into another nuclide called a decay or daughter product. The decay products may be unstable (radioactive) and, in turn, decay by the further emission of beta particles and gamma rays. A chain of decays may take place before a stable (nonradioactive) form is reached. At any given time after the explosion, the fission product mixture will be very complex. The half-lives (decay half-times) for 8

FALLOUT

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these nuclides range from a fraction of a second to infinity (stable). The initial mixture of fission products will ultimately result, through decay, in about 95 stable isotopes of about 36 elements. The high-energy gamma rays from some of the fission products are highly penetrating, so that they pass through the human body with only moderate intensity reduction. In air, the intensity of gamma radiation decreases as the distance from the radiation source increases; from a point source this decrease is in proportion to the inverse of the square of the distance. Beta particles penetrate only a few millimeters of tissue, so that a source on the skin irradiates only the skin and subcutaneous layers of tissue and not the internal organs. Alpha particles have very low penetration in tissue, such that they would not penetrate through the superficial horny cell layers of the epidermis. The beta-particle emitters in fallout produce radiation burns if they are in contact with exposed skin for a sufficient period of time (see Section 4.4.2). I n the early fallout period, some beta particle emitters also may be hazardous if ingested or inhaled, e.g., isotopes of iodine, which concentrate in the thyroid gland. Radioiodines are the chief gaseous isotopes of concern after nuclear explosions. Because most of the fission products would be associated uith particles too la.rge to be suspended in the air or to be drawn into the nostrils and, thence, into the lungs, the inhalation problems with fission products other than iodine are minor.

3.3 Fallout

3.3.1 Formation. In a nuclear explosion all nearby material is vaporized, including remaining fissionable material, components of the device, and fission fragments. If the explosion is inside or near the ground, great; quantities of nearby solid or liquid materials will also be pulverized or vaporized and will mingle with the radioactive material from the device. As the resulting cloud of debris ascends and cooling takes place, these vapors condense, forming solid particles ranging in diameter from less than a micrometer to several millimeters. These particles may be composed only of debris material from the earth, or may be a mixture of such debris and the radioactive fission products, or may be composed primarily of condensed fission products. 3.3.2 Early and Delayed Fallout. Early fallout is defined as that which returns to earth within a period of about 24 hours following an explosion.

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RESIDUAL NUCLEAR RADIATION AND FALLOUT

The particles are comparatively large, hence the rapid fall; and the intensity of the radiation emitted is high so as to give rise to an immediate hazard to health. Reduction of exposure to early fallout is the principal function of fallout shelters. Delayed fallout-that which arrives after the first day-consists of the very fine, invisible particles which will accumulate slowly in low concentrations over a considerable portion of the surface of the earth. During the long time in which such radioactive particles are aloft, the process of decay materially reduces the itensity of radiation that comes from them. This lengthy period of decay while aloft, together with the wide geographic dispersion of the fallout of these particles, reduces radiation exposure rates to levels where dose accumulation is too slow and too small to be immediately haziardous to health, but may be sufficient to cause delayed or late effects. 3.3.3 Distribution of Early Fallout. Factors affecting the distribution of early fallout particles on the surface of the earth include the height of the atomic cloud, quantity and size distribution of fallout particles, wind speeds and directions a t various levels of the atmosphere through which the particles must fall, the density of the atmosphere, and other aspects of weather. Accurate predictions of fallout deposition are impossible. Localized wind currents may give rise t o "hot spots" and "cool spots" in unexpected places, mperimposed on a larger pattern which features a general decrease in intensity with distance from ground zero. Rain or snow may also influence distribution of fallout deposition. Studies of hypothetical nuclear attacks have utilized standard or idealized fallout patterns based on assumed detonation times and locations and assumed weather patterns. Such studies have established that no location in the United States can be considered free from a potential fallout radiation hazard in the event of a major nuclear attack. Since fallout particles descend from the atomic cloud, which may reach heights of over 30 miles, a point on the ground just far enough from the explosion to permit survival from immediate effects may not receive any fallout for a period of as much as 20 to 30 minutes after the burst. This interval of time or delay is an important factor from the standpoint of moving people to shelter and for improvisation of protection. Points farther removed would not begin to receive fallout for even longerperiods of time; the amount of this delay is influenced largely by distance from ground zero and by wind velocity. Once fallout reaches a specific location, it may continue to build up for a period of several hours. Since i t arrives as solid particles and with

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MEASUREMENT OF GAMMA RADIATION

11

an average size of fine beach sand, it can be observed by the naked eye as a fine, dusty mist in the air or as a sheen of dust accumulating on smooth surfaces. Being relatively heavy, fallout tends to remain where it is deposited, except under rain or wind conditions which may cause some drifting. The area contaminated by significant amounts of fallout from a single explosion could cover several thousand square miles. Figure 1 shows representative fallout patterns expressed the radiation exposures (calculated to infinite time) to unshielded objects a t various distances and directions from point of detonation.

3.4

Measurement of Gamma Radiation

3.4.1 The Roentgen. The unit generally used to express exposure to gamma radiation is the roentgen (R). In general, and for the practical purposes of this document, the roentgen will be considered as the generic term and unit for gamma-radiation exposure or dose, and the rad will be used for beta-radiation dose to specified tissues (see Appendix A for definitions of terms). o

50

1w

200

360

400

500

600

1

1

I

I

I

I

I

I

I 50

I

I

I

I

I

I

100

200

300

400

500

600

1 MEGATON Max dose 3,000~

25 MEGATON

0

Scale:Slalule Miles

Fig. 1. Unshielded fallout radiation exposure contours, 60 percent fimion50 percent fusion (average wind speed 26 nlph).

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RESIDUAL NUCLEAR RADIATION AND FALLOUT

3.4.2 Gamma Radiation Exposure Rate and Exposure. Gamma radiation exposure rate is measured in roentgens per hour (R/h); but exposure rate is commonly determined relative to that for a reference location and a reference time. The former is the exposure rate measured a t a point three feet above the ground. The latter is a hypothetical rate which would exist one hour after the explosion if all the fallout were assumed to have arrived by then. The (one-hour) rate can readily be calculated after cessation of fallout; and it is used to predict radiation levels a t later times. Exposure cumulates with time according to exposure rate. Biological effects depend on both the total exposure and the rate a t which the exposure occurs.

3.5

Exposure and Exposure Rate Calculations

3.5.1 Decay of Radioactivity. In the fission products from a nuclear detonation, the radionuclides have half-lives ranging from a fraction of a second to thousands of years. The rate a t which fallout radioactivity declines can be estimated by adding the contributions of all radioactive components contributing. A reasonable approximation of the rate of decay can be expressed by the following equation plotted in Figure 2: where: exposure rate a t time 1, exposure rate a t H 1 unit of time (hour, for example), with If = time of explosion. 1 = time after explosion (same units as above). This expression is precise enough, for all practical purposes, for times from about 10 seconds up to about six months after the explosion, assuming that all the fallout has been completely deposited by time t = H 1, and that subsequently it is not removed or added to as a result of wind, rain or decontamination. Values for use in Equation (I) are given in Table 1. The following is an example of dose rate prediction using Table 1 and Equation (1): (2

=

dl

=

+

+

Suppose the fallout dose rate at some point, measured 18 hours after the explosion that produced the fallout, is 15 R/h and that one wants to know when the dose rate will be about 0.5 R/h: First, find d l .

EXPOSURE AND EXPOSURE RATE CALCULATIONS

10

20

30

50

100

200 300 400 500

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1000

TIME AFTER EXPLOSION (HOURS)

Fig. 2 Approximate rate of decay of radioactivity from fallout. For times from 0.1 to 10 hours, use upper curve and right hand scale. For times more than 10 hours, use lower curve and left hand scale.

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RESIDUAL NUCLEAR RADIATION AND FALLOUT

TBLE 1-Values for use i n exposure rate formulas

hours

hours

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.o 1.5 2.0 2.5 3.0 4.0 5.0 6.0 7 .O 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15 .O 16 .O 17.0 18.0 19.0 20.0 21 .o 22.0 23.0 24.0

25 26 27 28 29 30 32 34 36 38 40 42 44 46 48 50 55 60 05 70 75 80 85 90

95 100 120 140 160 180 200 250 300 336 720

Since d

=

dl

=

dlt-1,2 =

15

x (18)l.2 = 15 x 32 (from Table 1)

Second, find the time when t,he R/h will be 0.5 f1.2 =

dl/d (from above)

=

t = 300 h (from Table 1)

480/0.5

=

960

=

480 R/h

EXPOSURE AND EXPOSURE RATE CALCUTAATIONS

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A useful approximation, called the Seven-Ten rule, is that for every seven-fold increase in time, as measured from the time of explosion, there is an approximate ten-fold decrease in exposure rate. As an ex1 hour is taken as 1,000 R/h, ample, if the reference rate for H seven hours after the explosion the exposure rate would be 100 R/h. Forty-nine hours (i.e., about 2 days) after the explosion the exposure rate would be 10 R/h, and 2 weelcs after explosion it would be one R/h. 3.5.2 Accumulated Exposure. Based on the egposure rate equation given in Section 3.5.1, the following expression will yield the total accumulated exposure to which an exposed point or body will be subjected in a given time interval:

+

In this expression : D = exposure accumulated from ti to tr dl = exposure rate (R/h) at H 1 hour (as before) ti = time of beginning of exposure (in hours after the explosion) t f = time of end of exposure (in hours after the explosion) If ti is 1 and tt is infinity, the above equation reduces to D = 5dl. Thus, according to this equation the total accumulated exposure to infinity is approxirnatcly fivc times the exposure ovcr thc onc-hour period centered a t time (H 1) hours (as noted above, the t rate of decay is only an approximation and the actual number is somewhat less than 5). Table 1 which is given as an aid in solving exposure and exposure rate problems may be used to show that of this infinity exposure of 5 dl, a point would accumulate, beginning a t H 1, about 40 percent in 12 hours; or 50 pcrccnt in 30 hours; or 60 perccnt in 4 days; or 70 percent in 2 weeks. The radiation exposure accumulated in periods of time shortly after detonation (at high rates) is of extreme importance in determining the incidence or degree of an expected biological effect. The following is an example of an exposure calculation using .Table 1

+

+

+

and Equation (2) :

Supposc one wants to know the total exposure (D) between tl~etwo times of the above example, namely 18 hours and 300 hours: D = 5dI (t i-0.9 - t p . 2) =

5 X 480 (18-0.2 - 3 W 0 . 2 )

=

2400 (0.560 - 0.319) (from the table)

= 578 R

I

16

/

RESIDUAL NUCLEAR RADIATION AND FALI,OUT

3.6 Radiation Monitoring Instruments 3.6.1 General. Although the fallout particles to be expected after a nuclear attack most probably could be observed directly by sight or touch, the degree of hazard represented by these particles can be evaluated only through the use of special instruments. Such instruments have been developed and are now widely available. I t should be noted that the radiation monitoring equipment normally used in places such as hospitals and research laboratories may not always have the same range or suitability of design for rough handling, and may not be available in large numbers, as compared with the standard civil defense instruments. In the event, however, that standard instruments were not available in a particular location when needed, such hospital or research instruments could be used t o some advantage. There is no history of nuclear war or of major nuclear accident experience upon which t o base requirements for civil defense radiation instruments. However, extensive tests of nuclear weapons under known conditions have indicated the kinds and extent of residual radiation that could result froiri use of nuclear weapons. The design and development of civil defense radiation instruments have been based on this experience and on the knowledge of the kinds of information about radiation required to enable the correlation of biological effects to radiation exposure and exposure rate. Radiological monitoring instruments are of two general types: survey meters and dosimeters. 3.6.2 Survey Meters. The survey meters measure the exposure rate in roentgens per hour (R/h) a t the point being metered. Survey meters developed by the Defense Civil Preparedness Agency have a useful operating range of from less than 0.1 R/h to 500 R/h. Certain of the instruments have a special provision to allow an assessment of the relative amount of beta radiation present in the radiation field. The properly calibrated instrument, if operating correctly, will indicate exposure rate to within f25 percent. 3.6.3 Dosimeters. Dosimeters memure the total accumulated radiation exposure in roentgens (R). Although several models are available, the most common one has a top range of 200 R. These dosimeters are direct reading. They require an auxiliary electric charger. These instruments (properly calibrated and operating correctly) will indicate accumulated exposure to within f20 percent. 3.6.4 Availability of Civil Defense Radiological Equipment. As of early 1973, about one million survey meters and three million dosimeters

MONITORING INSTRUMENTS

/

17

procured by the federal government are in operational condition, or could quickly become so, and are available in case of emergency. Most have been distributed to the States and their political subdivisions. Maintenance and calibration facilities, supported by federal funds, are available throughout the country. Some 200,000 people have been trained as radiological monitors to be available to use the instruments and advise civil defense officials.

4. Effects of Radiation on Man 4.1 General Large-scale release of fission products and other radioactive material into the environment (see Section 3) creates both immediate and delayed hazards for everyone exposed to the fallout field and to contaminated agricultural products and water. In addition to the immediate effects of large exposures a t high dose rates, the delayed effects of these and/or protracted exposure for long periods of time at low dose rates must be prevented when possible. Radiation injury is a collective term used to describe all kinds of biological effects varying in severity from the barely detectable or minor to the fatal. The term also includes genetic effects in descendants of irradiated persons as well as early and late somatic effects in irradiated persons. The nature of the radiation injury, its severity, and its outcome depend on such factors as the type of radiation (e.g., gamma and/or beta), the parts of the body irradiated, the uniformity of body exposure, the rate and the duration of exposure, the magnitude and duration and/or number of exposures, the duration of radiation-free intervals between exposures, the level of contamination of the skin, the body burden of radionuclides deposited internally (types and distributions), and the age and sex of the irradiated person. The quantitative relationships between radiation dose or exposure and effect are not as well documented in man as in experimental animals. There is still great uncertainty in predicting the consequences of a particular eqosure or dose of radiation for any individual in a group of people. In order to avoid over- or under-estimation of the immediate and delayed dangers t o the population, decision-making in a radiation emergency must be based on estimates, as realistic as possible, of the radiosensitivity of human biological systems.

4.2

Biological Features of Acute Radiation Injury

The biological action of ionizing radiation3 is related in a complex fashion to the parts of the body irradiated, total dose absorbed, the dose a T h e various theories t h a t have been proposed to explain the primary damaging mechanisms of ionizing radiations a r e beyond the scope of this report.

18

BIOLOGICAL FEATURES

/

19

rate, and the radiation quality. Broadly speaking, radiation causes effects that mimic more closely those of cumulative chemical poisons than those of purely physical causes of injury such as blast, missiles, and heat. The characteristics of clinical effects shared by radiation and cumulative chemical poisons include the following: (a) Large single doses can cause severe acute sickness or death immediately (less than two days) or within 60 days, depending upon dose and individual susceptibility. (b) Small daiiy doses can be tolerated over extended periods of time without causing serious acute illness if the rates of exposure are such that the production of injury and its repair are nearly in balance. When this state of equilibrium exists, the total dose can exceed the size of the prompt single dose for acute lethality by several fold without being acutely fatal. The ability of. the body to recover from large single radiation doses and t o tolerate much larger total doses received from protracted exposure or as repeated small doses depends on the rate and efficiency of biological repair processes. These biological repair processes are modified by irradiation in ways that are poorly understood. A total-body radiation exposure of 600 R probably will be lethal without medical treatment when received as a single exposure or during a period of 4 days or less. The same accumulated exposure protracted over a period of 20 years and delivered in equal dally amounts (that is, less than 0.1 R/day) will probably not cause any clinically recognizable injury, although there may be signs of significant effects that can be detected by sensitive laboratory tests. When a portion of the total 600 R exposure-one half, for example-is received as a brief exposure and the remainder is received in protracted fashion (for example, a t the rate of 1.0 R/week), the following symptoms have a strong likelihood of occurring: the chances are 9 out of 10 that the person will become sick and vomit during or within two or three hours after the brief exposure; approximately 3 4 weeks later, he will develop symptoms of moderately severe damage to blood-forming organs. The chances are about even that the acute syrnptoms would warrant hospitalization for treatment if such facilities are available. In otherwise healthy adults, the likelihood of death following a brief exposure of 300 R may be about 1 in 10, possibly somewhat greater. After recovery from the acute radiation syndrome, there will be no overt symptoms or signs of residual damage. So far as is known a t present, fractionated or protracted exposures at the overall rate of 1 R/week for 6 years (about 300 R total) have little chance of causing any acute symptoms, although it is possible that some signs of significant radiation effect can be demonstrated by means of laboratory methods. In evaluating acute injury an unqualified report of a total exposure

20

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EFFECTS OF RADIATION ON MAN

(300 R, in this case) is of Little medical value for predicting outcome, without exposure-rate information. The details concerning the part of the body irradiated and the rate and duration of the exposure are necessary for predicting the expected outcome and expressing the level of injury in terms of probability of various consequences. The uniformity or lack of uniformity of irradiation of the body is important in this respect because localized irradiation of parts of the body is usually better tolerated than uniform irradiation of the torso or whole body with similar or even lesser amounts of exposure.

4.3

Statistical Features of Radiation Injury

The same radiation exposure will not have the same effect on everyone. Biologic variation in susceptibility between individuals is characteristic of all living organisms. For thls reason, in assessing the lethal effects of radiation and toxic chemicals in experimental animals, the dose-response relationship is often measured in statistical ternls. The usual term for indicating such response is the dose that is expected to kill half the animals exposed; this measurement is known as the median lethal dose (MLD) or 50 percent lethal dose (LD60).4This term implies that the probability of dying is 50 percent, or the chances of surviving or of dying as a result of this dose are 1 of 2. In suitably designed animal experiments, the probability of lethality for other doses can be estimated, e.g., the 25 percent lethal dose (amount that kills 1 out of 4). The same data can be used to calculate the statistical confidence limits of the estimate of the LD60. Such experiments provide a dose-response relationship for predicting the expected incidence of death and include a statement of the uncertainty of the prediction under the conditions of the experiment. For this uncertainty to be chiefly biological, the uncertainty of the dosage measurement must be minimized. Statistical studies of the lethal effects of a brief, single, whole-body exposure of healthy animals demonstrate a farily consistent pattern in all species, as follows: (1) The dose which causes few deaths (e.g., the 5 percent lethal dose; chances of surviving = 19 of 20) is about half the LDso. It is customary t o qualify the LDao by the period of time after exposure within which t h e deaths occur. I n smaller experimental animals, this time for acute hematopoietic death is usually 30 days: LDso/~o;with large animals (pigs, burros) the interval is60 days: LDoo/ap. I n man, deaths due to acute hematopoietic damage are rare later than 8-10 weeks after exposure to large brief exposures and, therefor, the LDbo/so is used.

STATISTICAL FEATURES

/

21

TABLE 2--Estimated single radiation exposures that will cause 60 percent incidence of prodromal responses (early symptoms) i n mann Level of Radiation Sickness

Single Radistion Exposure

Anorexia (loss of appetite for food) Nausea Fatigue Vomiting Diarrhea

180 280 280 320 360

95 Percent Confidence

Ram

150-210 220-290

230-310 290-360 310-410

This table was derived from Table 9, page 81, in Radiobiological Factors i n Manned Space Flight, Edited b y W . Langham, National Academy of Sciences Publication 1487 (National Academy of Sciences-National Research Council, Washington, 1967). b Measured in air.

(2) The 95 percent lethal dose (chances of surviving = 1 of 20) is slightly less than twice the LDbo. (3) The uncertainty of the LDGO is expected to be f 10 percent, implying that the actual dose required to kill half the animals exposed may be from 10 percent larger to 10 percent smaller than the estimated LDso computed from the data. The LD60 is not the same for all species, but varies from about 800 R in the rabbit to less than 300 R in the dog.6 There is little statistically valid information for any species on dose-effect relationship for nonlethal physiologic effects, such as acute gastrointestinal distress (for example, vomiting) and impaired capacity to work. Our best statistical information on the amount of radiation required to cause various levels of early acute radiation siclcness (known clinically as prodromal gastrointestinal distress) has been derived largely from an analysis of clinical data obtained from the histories of therapeutically and accidentally irradiated persons. The radiation exposures predicted to cause 50 percent probabilities of loss of appetite, nausea, vomiting, diarrhea and fatigue in such patients are listed in Table 2. The times of occurrence of, these and other factors in acute radiation sickness (or in the various syndromes) are given in Section 4.4. The human population is heterogeneous with respect to age as well as other factors, and, therefore, the spread of susceptibility is expected to be greater than that found in experiments using relatively homogeneous groups of laboratory animals. Man responds to brief doses of radiation in the same fashion as do animals, however; and so it may be as-

' Values cited are for brief, total-body exposure.

22

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E F F E C T S OF RADIATION ON

MAN

surned for practical purposes that in man also the 5 percent lethal dose (few deaths expected) should be approximately half the LD60. However, the 90 percent lethal dose (few survivors expected) for man should be much less than twice the LD6O, as will be discussed below. There have been no known human survivors 60 days after a brief total-body exposure to 650 R Gthout medical treatment. The human LD60160 has not, of course, been determined experimentally. A value for the LD60/60 accepted by many is 450 R (measured in air). The value 450 R is the median of a number of educated guesses made by a group of U.S. experts in 1949.6Since 1949, there have been many attempts to estimate the human LD60 objectively, using data from: (a) the Atomic Bomb Casualty Commission study of Japanese atomic bomb casualties; (b) studies of the Marshall Island natives inadvertently irradiated in a nuclear bomb test fallout field; (c) studies of cancer patients being irradiated therapeutically; and (d) studies of radiation accident victims. The estimates derived from these studies are all somewhat lower than the 1949 estimate of 450 R,7 and perhaps 400 R (measured in air) for brief gamma exposure may be a reasonable compromise. I t should be emphasized that the LD60/60value of 450 R (measured in air) is an estimate related to medically nontreated human populations which are heterogeneous with respect to sex, age, and condition of health. The LDso,ao values for the old or the very young or the ill may well be 1 ~than s 450 R, perhaps 50 to 100 R less, while the values for the healthy adults of intermediate age may well be somewhat greater than 450 R. It is possible, therefore, that LD60values estimated from data on irradiated adult patients may be underestimations as compared with that for healthy adults, for example. On the other hand, a person receiving 600 R in a brief exposure may recover if well treated medically. I t should also be pointed out here that estimates of LD60 in units of absorbed dose (rads) a t the midline of the body are lower numerically than the L D ~ o in roentgens mcasured in air. Thus, 450 R gamma radiation (e.g., from cobalt-60) measured in air would give on the average a t the midpoint of the adult body an absorbed dose of about 315 rads, with a range of about 270 to 340 rads, depending on the thickness of the body. On the basis of the high incidence of death among irradiated sick per~ be sons, it has sometimes been assumed that doubling of the L I I 6 may used to extrapolate to the 90 percent incidence of death in an exposed Warren, S . and Bowers, J. Z., "The acute radiation syndrome in man," Ann. I n t . Med. 32, 207 (1950). 'See Table 11, page 106, in Radiobiological Faclors in Manned Space Flight, Edited by W . Langham, National Academy of Sciences Publication 1487 (National Academy of Scieuces--National Research Council, Washington, 1967).

STATISTICAL FEATURES

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23

fictitious human population. This assumption is unwarranted by clinical facts derived from study of persons irradiated with more than 450 R . In ,addition, the steep regression lines that depict the changes in lethal probabilites among healthy large animals, such as dogs and monkeys, indicate to some investigators that the human single exposure level for 90 percent lethality may be between 500 and 600 R instead of a t 900 R (2 X 450 R). As mentioned earlier, no person is known to have survived an evenly distributed torso or whole-body exposure greater than 650 R without medical treatment. The statistical problem is more complicated when exposure is protracted. Available data on the ratio of the LDso value for protracted exposure to the L D ~for o brief exposure to gamma radiation have shown among several species a considerable variability that is independent of body size. This variability among species is best explained by differences in the efficiency of their recovery mechanisms. For example, the ratio of LD60 a t 50 R/day to LDsofor brief exposure is about 3 for sheep and about 20 for pigs. The ratios for other species are intermediate between those for sheep and pig. Experience with the effects of prolonged irradiation in persons involved in a radiation accident in Mexico8suggests that man resembles the sheep rather than the pig in the ability to recover from radiation injury. The evaluation of the risk of genetic injury and of late somatic effects of irradiation in human populations is entirely statistical and consists of the measurement of changes in the incidence of biological phenomena (Section 4.4.2) which occur in some incidence in the populations whether or not there has been exposure to radiation. Large groups of people, exposed and non-exposed, must be studied to obtain data from which to determine accurately the relationship between dose and such late effects. The extent to which radiation dose increases the risks of developing leukemia or other cancers has been estimated on the basis of data on Japanese atomic bomb survivors, persons irradiated for various medical reasons, and some groups of people exposed to radiation inadvertently in industrial activities or nuclear bomb tests (fallout). Itecent studies have demonstrated chromosome abnormalities in progeny of irradiated women, particularly an increase in incidence of Klinefelter's disease (see Glossary, Appendix A). The statistical uncertainties surrounding the effects of radiation exMartinez, G. R., Cassab, H. G., Ganem, G. G., Gultman, K. G., Lieberman, L. M., Vater, B. L., Linares, M. M. and Rodriguez, M. H., "Accident from radiation. Observations on an accidental exposure of a family to a source of cobalt-60," Rev. Med. Inst. Mex. Seguro Social, Suppl. 1, Vol. 3, p. 14 (1964).

24

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EFFECTS OF RADIATlON ON MAN

posure are large enough to make for considerable uncertainty in predicting or calculating risk quantitatively in an emergency. 4.4

Clinical Features of Radiation Injury

4.4.1 General. All that is known quantitatively about the immediate effects of various radiations on humans comes from analysis of experience with radiation therapy of patients, from studies of accidental radiation exposures, and from the study of Japanese exposed to atomic bomb radiation. In an emergency due to radioactive fallout, t.he casualty rate for any group of exposed people as a whole can be predicted with about f25 percent confidence if the radiation exposure estimates are combined with a medical evaluation of the acute reactions of a representative sample of persons in the group. A syste~nof prediclim has been evolved from the correlations of the classifications of radiation injuries, their clinical manifestations and prognoses, the exposure estimates and confidence limits, and the duration of exposure responsible for each category of radiation-induced illness. 4.4.2

ClassiJlcalim~of Radiation Injury.

Asymptomatic Radiation Injury.

This class of injury, not apparent to the victim and undetectable by the physician, occurs after brief exposure of less than 60 R. The effects of a single, brief exposure of less than 50 R on blood cells can be detected only in retrospect by statistical analysis of the blood cell counts or chromosomes of cells obtained from a large group of exposed people. Clinically, some normal persons irradiated in this dose range will show mild signs and symptomsg of gastrointestinal distress such as loss of appetite and nausea, easily confused with the effects of anxiety and fear. Acute Radiation, Synclrome'o This class of radiation injury may be caused by brief irradiation of the whole body or major portions of the torso or head by gamma or x Symptoms are the feelings the patient complains about, e.g., headache and weakness; signs are the manifestations of various levels of radiation damage observed by an examiner, e.g., hemorrhage and loss of hair. 'D A radiation syndrome is described as acute when clinical manifestations other than local burns occur early and do not last longer than 60 days after exposure.

CLINICAL FEATURES

/

25

radiations from external or internal sources. Local irradiation of an extremity does not cause generalized symptoms or signs. Clinical manifestations of the acute radiation syndrome include general "toxic" symptoms, such as weakness, nausea, vomiting, and easy fatigue, and specific symptoms and signs caused by damage to the gastrointestinal tract, the blood-forming organs and the central nervous system. The signs of systemic radiation damage include loss of hair (epilation) and s tendency to bleed easily, for example. Laboratory tests may detect low white blood cell count, for example. The clinical response to extensive radiation damage, although usually severe, can sometimes be so slight that it is manifested by little more than loss of appetite, a decrease in the white blood cell count, and slight fatigue. Conversely, the clinical response to mild radiation damage, although u s u d y mild, may sometimes be severely debilitating. Usually, however, when radiation damage is severe the clinical response is also severe and, depending on dose, death may result within hours or days of the onset of exposure. Five clinical levels of severity of acute radiation effects are distinguished m d correlated with the size of brief exposure. Level I: This level of illness has been seen after brief whole-body exposures to gamma or x radiation in the range of 50-200 R. Less than half the persons exposed experience nausea and vomit within 24 hours. There are either no subsequent symptoms or, a t most, only increased fatigability, a slight decrease in total white blood cell count (princip d y due to a fall in number of lymphocytes), and later a fall in the blood platelet count. Fewer than 5 percent (1 out of 20) require medical care for their gastric distress. All can perform tasks, even when sick. Any deaths that occur subsequently are due t o complications such as intercurrent infections, debilitating diseases, and traumatic injuries such as those from blast and thermal burns. Level 11: This level of illness has been seen after brief whole-body exposures to gamma or x radiation in the range of 200-4150R. More than half of this group experience nausea and vomit soon after the onset of exposure and are ill for a few days. This acute illness is followed by a period of 1-3 weeks when there are few if any symptoms. During this latent period, typical changes occur in the blood cell counts that can be used for diagnosis. At the end of this latent period, epilation (loss of hair) is seen in more than half; a moderately severe illness develops, due primarily to infection often characterized by sore throat and to loss of defensive white blood cells resulting from damage to the blood-forming organs. Most of the people in this group require medical care. More than half will survive without therapy, and

26

/

EFFECTS OF RADlATlON ON MAN

the chances of survival are better for those who received the smaller doses and improved for those receiving medical care. Level 111: This level of illness has been seen after brief whole-body exposure to gamma radiation in excess of 450 R (460 R to 900 R). This is a more serious degree of the illness described for Level 11. The initial period of acute gastric distress is more severe and prolonged. The latent period is shortened to one or two weeks. The main episode of illness is characterized by extensive oral, pharyngeal, and dermal hemorrhages. Infections such as mre throat, pneumonia and enteritis, are commonplace. People in this group need intensive medical care and hospitalization t o survive. Fewer than half will survive in spite of the best care, with the chances of survival being poorest for those who received the largest exposures. Level ZV: This level of illness has been seen after brief whole-body exposure to gamma radiation in excess of 600 R (600 R 20 1,000 R). This is an accelerated version of the illness described for Level 111. All in this group begin to vomit soon after the onset of exposure. Without medication this gastric distress can continue for several days or until death. D a m g e t o the gastrointestinal tract is the predominant lesion. It is manifested by intense cramps and an intractable diarrhea, which usually becomes bloody. Changes in the blood cell counts occur early. Usually the white cell count immediately increases several fold, as in an infection, but within a few days the count may be less than 500 per cubic millimeter. There is an early almost complete loss of lymphocytes from the blood. Death can occur anytime during the second week without the appearance of hemorrhage or epilation. All persons in this group require care for or relief of the gastrointestinal symptoms, but it is unlikely even with extensive medicaI care that many can survive. During a protracted exposure to this amount of gamma radiation, it is unlikely that this type of gastrointestinal distress mrould be the first evidence of injury. What little clinical evidence exists indicates that any clinical problems resulting from this exposure at a low rate would be related to failure of the bone marrow. Level V: This level or type of illness has been seen after brief wholebody doses of fission neutrons and gamma rays in excess of several thousand rads. This level is an extremely severe illness in which hypotensive shock secondary to vascular damage predominates. Symptoms and signs of rapidly progressing shock come on almost as soon as the dose has been received. Death occurs within a few days.

CLINICAL FEATURES

/

27

Chronic Radiation Illness."

There is little information about the effects of protracted external exposure of man. Some radium chemists and radiologists who worked with radioactive materiala before the hazards were recognized developed a progressively refractory anemia and died from either the anemia or complicating infections. In recent history, this kind of symptomless aplastic anemia was found in a lone male survivor among five persons unknowingly exposed to cobalt-60 gamma radiation for about 116 days. His total exposure during this time was estimated to have been between about 980 and 1200 R. Animal experiments (e.g., beagles a t Argonne National Laboratory receiving continuous gamma irradiation) show that with daily exposures in the 10-4-0 R range, anemia is the major cause of death, and with daily exposures of 50 R or greater, infection is the major cause of death. With protracted exposure below 10 R/day, myeloproliferative diseases, potentially leukemic, are causes of death.

Radiation I n j u r y to the Skin. (1) Epilation, or loss of hair, is caused by irradiation when doses in excess of 300 rad are absorbed by hair follicles. Radiation exposures (in roentgens) causing epilation vary greatly with radiation quality. Regardless of the dose, epilation is unusual before the second week after exposure. Epilation is a reliable indicator of the existence of radiation injury in persons exposed to mixed radiation from fallout or to the initial nuclear radiations. It seldom occurs when the dermal dose is 1e.s~than 200 rads. Beta-ray irradiation due to radioactive fallout particles falling on the scalp is additive with gamma-ray (and neutron) exposure so that epilation may be frequent and severe in individuals so exposed during fallout deposition unless the fallout particles are soon removed. Certain single "hot" particles containing fission products lodging in the hair are capable of causing a bald spot up to one-half inch in diameter. The hair grows back, however, unlem the dose has exceeded about 600 rads. (2) Radiation dermatitis is caused by skin irradiation of various kinds. Beta-ray burns result most commonly from radioactive fallout particles that are retained on the skin. The skin of the hands may be damaged by even brief handling of objects heavily contaminated by fresh fission products. The reactions of the skin depend on the size of dose absorbed, l1 The illness is described as chronic when the symptoms and signs are delayed in developing and/or persist beyond 6 months.

28

/

EFFECTS OF RADIATION ON MAN

the type and energy of the radiation, and its depth of penetration. Four clinical types of radiation-inducedskininjurycan be recognized (in order of increasing severity) : T y p e I : Erythema (only), is equivalent to a first degree thermal burn like mild sunburn. Some time after exposure, a sensation of warmth or itching may occur; the redness, however, can appear as late as 2-3 weeks after exposure; the length of the symptomless interval depends on the dose. Medical care is not necessary and ability to work is no more impaired than after a similarly severe sunburn. Dry desquamation (scaling) occurs. Brief doses of several hundred rads to skin can cause delayed erythema. In two fatal radiation accidents where skin dose was several thousand rads, erythema developed within 15 to 30 minutes after exposure. Type II: Transepidermul injury (wet desquamation), is equivalent to the injury seen in a thermal burn of the second degree. After the erythema develops, blisters form and break open, leaving raw, painful wounds vulnerable to infection. After exposure, itching and pain are experienced. The symptom-free latent period is shorter than in the Type I lesions and blisters appear within 1-2 weeks depending on the dose. Recognizable injury of this grade requires a brief skin dose between 1,000 and 2,000 rads. The need for medical care and the ability to work depend on the size, location and severity of the lesion. These lesions usually heal with proper cue, but the new skin is usually pigmented, thin and easily injured. Type III: D m 1 radionecrosis (radiation-induced skin death), is a more serious degree of the Type I1 lesion, caused by prompt doses of radiation in excess of 2,000 rads. Injury of this sort has been observed in persons who handled fresh fission product material or ta.rgets in which radioactivity was induced during laboratory experiments by neutron or electron bombardment, and also after accidental exposure of hands to the direct beam of an electron accelerator. The lesions resemble those caused by a severe scalding or chemical burn. Pain occurs promptly and is intense. Medical abatement of pain is urgently needed. T y p e IV: frequently repeated or continuous exposure of the skin t o x rays, gamma rays, or beta rays over a period of months to years causes an eczema-like condition. Once it hras developed, it seldom heak completely and ulceration frequently occurs. Skin cancer occurs in a large (but unknown) proportion of such cases of chronic rcldiatian dermatitis. In the case of persons working with x rays during a lifetime (30 years), the effective dose levels for skin cancer production are thought to be in the region of several thousand rads when accumulated at rates of about one rad per day.

+

Radiation Injury From Internally-Deposited Radioisotopes. Radioiodines are the primary internal radiation hazard during the first few weeks after atomic bomb fallout. Bone-seeking radionuclides, particularly strontium, are the predominant long-term internal radiation hazards. It is unlikely that swallowed and inhaled fission products from nuclear weapon fallout can occur in sufficient quantities to cause acute radiation illness. If this level of contamination were to occur it is most likely that a lethal dose of gamma radiation from external sources would also be received. Such symptoms as loss of appetite, nausea, vomiting and diarrhea are conceivably possible from the effects of ingested radioisotopes on the gastrointestinal mucosa, but when such symptoms occur they probably would represent acute radiation sickness from the whole-body external gamma radiation. Sublethal exposures to external gamma radiation could be accompanied by significant internal absorption of radionuclides. These exposures may act together to cause delayed effects without having caused any acute symptoms or signs except changes in white blood cell counts. In the fallout exposure of the Marshall Islanders, for example, the combined effects of radiation from external sources and radiation from radioisotopes of iodine produced in the atomic explosion constituted a major medical hazard.* The radioiodines were concentrated and stored in the thyroid gland where resulting local radiation exposure was many times that of the whole body. While the Marshallese people received an estimated average total-body gamma dose of about 175 rads, the radiation doses to thyroid from radioiodiies were estimated to have varied in the children from 500 to 1,400 rads and to have averaged in adults about 334 rads. The higher uptake of iodiies per unit weight, and the smaIler thyroids of the exposed children, combine to result in larger doses to their thyroids than to thyroids of adults exposed to similar levels. Furthermore, the thyroid glands of children may be more susceptible to acute radiation damage than those of adults because of greater growth rate (mitotic activity) of the glands of children. Ten to fifteen years after the fallout exposure, 17 to 19 Marshdese children exposed at less than ten years of a.ge have developed thyroid tumors, and two of these children also have shown somatic growth retardation from hypothyroidism which was essentially restored by replacement therapy. Thyroid cancer has been found in a t least one chid and two adults. From this and sparse Conard, R. A., Dobyns, B. M. and Sutow, W. W., "Thyroid neoplaeia as late effect of exposure to radioactive iodine in fallout," JAMA 214, 316 (1970). See also, Richard Cole, Inhalation. of Radioiodine from Fallout: Hazards and Countermmures (Environmental Science Associates, Burlingame, Cal., 1972).

30

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EFFECTS OF RADIATION ON MAN

clinical experience, large doses of radioiodines are suspected of being potentially carcinogenic for the thyroid gland, as axe external x or gamma radiations. A slight increase in incidence of thyroid neoplasia has been associated with whole-body exposure to atomic bomb radiations in the survivors a t Hiroshima and Il'agasaki. X-ray exposure of the neck region (including thyroid) in young children has been shown to increase the incidence of benign and malignant thyroid tumors later in life. The oral administration of nonradioactive iodine in the form of potassium iodide is a relatively safe prophylactic means of reducing absorption of radioactive iodine by the thyroid and thus reducing radiation exposure of the gland. The resulting large amount of nonradioactive iodine in the blood reduces the absorption of radioiodine by the thyroid. The oral administration of potassium iodide can be continued until environmental contamination has been reduced to an insignificant Icvel. The recommended dosage of potassium iodide is 10 mg/day for persons over ten years of age (including pregnant women), 5 mg/day for ages 1-10 years, and 2.5 mg/day for infaats younger than one year. When exposure to heavy fallout contamination is anticipated, larger doses of the nonradioa.ctive iodide are advisable initially, i.e., 100-200 mg for adults and proportionately smaller doses for children. During the fallout period, in view of the pathway of iodine via grass to cow to milk to man, consumption of contaminated milk can be avoided: (a) by use of previously canned or powdered milk; (b) by feeding cows on uncontaminated fodder and curtailing grazing;and (c) by processing contaminated milk for later use when radioactivity of the iodines present has decayed to negligible amounts. Genetic Efects of Radiation. Radiation exposure of sexual reproductive cells of the ovary and testis (i.e., ova and sperm and cells producing them) causes gene mutations18 and chromosome abnormalities (mutations) in excess of the spontaneous mutation rate. This genetie injus-y does not affect the health of the exposed individuals in any way and is detectable only by changes in their descendants. The expression of genetic effects in children whose parents (one or both) were exposed to radiation might consist of: (1) a change in the sex ratio (i.e., number of male versus femalebabies born) ; la A mutation is a change in the properties of a gene, which is the fundamental unit of heredity. Individual genes "control" specific biochemical reaations, and any deleterious change may be expressed as abnormal development or abnormal function. Factors other than radiation are known to cause mutations.

CLINICAL FEATURES

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31

(2) an increased incidence of abortions and stillbirths; (3) an increased incidence of malformed babies; (4) an increased rate of infant mortality; (5) an increased incidence in some specsc inherited diseases; and (6) questionably, subsequent life shortening in other offspring, due to inherited disorders. It is not possible, a t present, to predict the amount of genetic injury that will result in human populations from a given dose of radiation with the degree of coddence applicable to predictions of the incidence of acute radiation sickness or injury to the skin. The statistical term used to describe the dose-effect relationship for radiation-induced mutations is the doubling dose, the amount of radiation that causes an iucrease in mutation equal to the spontaneous mutation rate. Based on experimental animal data and on fragmentary data on man, the doubling dose for brief gamma irradiation for man may lie between 8 and 75 R, and for protracted (low rate) irradiation may be several times greater (e.g., 2&200 R). There is no satisfactory way to check these very uncertain estimates for use in planning operations because specific information on man is inadequate. Because other circumstances of nuclear war and of post-attack reconstruction are likely to increase infant mortality to a greater extent than the genetic effects of irradiation, sorting out those instances of fatal genetic injury due to irradiation would not be possible. It is recommended that the probability of genetic injury not be used as a principal determining factor in decision-making during a war emergency. It should be emphasized, however, that such genetic injury can and should be minimized by keeping controllable exposures as m a l l as possible for all people who are likely to produce children at a later time, and by counseling such persons concerning avoidance of conception during the f i s t few months after exposure when genetic risks are highest.

Late Somatic Eflects of Radiation. The effects in this clam of radiation injury are defined as those that occur many months or years after exposure. They include leukemia, cancer of any organ, sterility, cataracts, permanent and delayed degenerative effects in various organs, and, in the case of the irradiated embryo and fetus, a variety of developmental defects. A late effect may (but &dl not necessarily) develop in a person who has recovered from acute radiation illness or in a person who was never ill during protracted low-rate exposure. None of these late effects is specific (unique) to radiation. Additional radiation is expected to increase the probability of these late effects (e.g., leukemia) above the standard rates for persons of the same

32

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EFFECTS OF RADIATION ON MAN

ages. Some of these late effects presumably result in a reduced lifespan in irradiated humans, as has already been demonstrated in animal experiments. (1) Cancer Production. Studies of human populations exposed to radiation (mainly the atomic bomb survivors of Hiroshima and Nagasaki, certain groups of patients irradiated therapeutically, and groups of people who were exposed occupationally) have shown increasing incidence of leukemia and several other types of cancer with increasing radiation dose. The radiation doses and dose rates involved in these effects were usually relatively high, i.e., ranging from doses equivalent to 50 R or rads to much higher doses, and dose ratea ranging high above 1 R or rad per minute. Accurate assessment of the risks of radiation carcinogenesia in human populations are beset by many difficulties, including: presently insufficient precision and data on doses to tissue of cancer origin and on excess incidence over a wide enough range of doses and dose rates to permit accurate determination of the shapes of the dose-effect relationships; presently insufficient data on variation of natural incidence of cancers and of susceptibility to radiation induction of cancers according to quality, quantity and rate of irradiation, age, sex, genetic influence, diet, and environmental and clinical variables; present incompleteness of follow-up of study populations for complete ascertainment of lifetime incidence of cancers (in both irradiated and nonirradiated control populations) for statistical determination of the excess lifetime incidence as compared with early occurrence of cancers which would have developed later without irradiation; and the present uncertainty as to the influence of conditions or diseases requiring the medicd irradiation, the influence of treatments other than the radiation, and the lack of ideal control groups in the studies of medically irradiated populations. Recently, the National Academy of Sciences Advisory Committee on the Biological Effects of Ionizing Radiations (the BEIR Committee) reviewed the data on cancer incidence and radiation dose in the available human population studies and issued a report." The BEIR Committee estimated the risks of radiation induction or deaths from cancers per rad from the data a t the relatively high doses and dose rates on the basis of the assumption of linear (straight line) dose-effect relationship, which means that the relationship between the effect per rad and the dose rel4 National Academy of Sciences Advisory Committee on the BiologicaI Effects of Ionizing Radiations, The Effects on Populalions of Ezposure to Low Levek of Ionizing Radiation (National Academy of Sciences-National Research Council, Wnshington, 1972).

mains the same (proportional), regardless of differences .&.dosesize and dose rate. The BEIR Committee also estimated the risks of radiation induction of cancers or deaths from cancer per rad a t low levels of radiation exposure by extrapolation on the basis of this linear dose-effect relationship derived a t higher dose and dose rate and the assumptions that (I) any radiation dose can cause an excess incidence of cancer in a population and (2) such estimates are applicable to m y human population. The BEIR Committee report gave cogent radiobiological reasons, both theoretical and factual (from experimental animal data), for doubting that the dose-incidence relationships for cancer induction does remain constant (linear) over the whole range of dose and dose rate. The BEIR Committee stated: "Hence, expectations based on linear extrapolation from the known effects in man of larger doses delivered a t high dose rates in the range of rising dose-incidence relationship may well overestimate the risks of low-LET radiation a t low dose rates and may, therefore, be regarded as upper limits of risk for low-level low-LET irradiation. The lower limit, depending on the shape of the dose-incidence curve for low-LET radiation and the efficiency of repitir processes in counteracting carcinogenic effects, could be appreciably smaller (the possibility of zero is not excluded by the data). On the other hand, because there is greater killing of susceptible cells at high doses and high dose rates, extrapolation based on effects observed under these exposure conditions may be postulated to underestimate the risks of irradiation a t low doses and low dose rates." On the basis of linear extrapoIation, the BEIR Committee estimated the risks of radiation-induction of various cancers, in terms of excess cases or deaths per million exposed persons per year per rad (of gamma radiation) to pertinent tissue of cancer origin, as follows: leukemia deaths, 1 (perhaps several times higher in persons irradiated in the uterus, during childhood, or late in adult life, than in persons irradiated a t intermediate age); thyroid cancer in children (cases, not deaths), 6.6-9.9 (risk in children appears to be several times greater than in adults) ;and the less reliable estimates (much more limited data), as follows; lung cancer deaths, 1; breast cancer deaths (women), 3; skeleton cancer death, 0.9; gastroir~testinal cancer death, 1; and possibly 1 for death from cancer at other sites not included above. Although cancers have been observed to occur in other tissues heavily irradiated (e.g., skin cancer), the lack of quantitative doseincidence data precludes derivation of risk estimates. Fur+,hermore, existing observations suggest that the susceptibility of these other tissues to radiation-induction of cancer is low compared with that of the tissues for which risk estimates are given above. It is possible also that the latent

34

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EFFECTS OF RADIATION ON MAN

periods for induction of cancers in these tissues of apparently low susceptibility may extend well beyond the current maximum follow-up period for the major long-term population studies (25 years). The BEIR Committee estimated that the overall excess mortality from cancer in irradiated populations can be accounted for largely by the specific types of cancers for which risk estimates were given above. In the Japanese atomic bomb survivors, this excess a t high doses and dose rates approximates 2.5 deaths per million exposed persons per year per roentgen equivalent, averaged over the period of time in which the excess has been observed. (2) Temporary Sterility or Reduced Fertility. These effects can occur as a result of brief nonfatal whole-body irradiation as a consequence of the exposure of the testes or ovaries, and can persist for many months or even several years, depending upon the size of the dose. For brief exposures, the single doses to the ovaries or testes required to cause permanent sterility in healthy persons of normal fertility are in excess of the total-body dose from which persons have a high probability of dying. (3) Cataract. The incidence of radiation-induced cataract (opacity) of the lens of the eye increases with the dose to the lens. Among the Japanese who survived the atomic bomb radiations, cases of lens opacity that interfered with vision have been rare. Data on radiation effects on the lens of the eye in radiotherapy patients suggest that the brief exposures required to cause lens opacities that impair vision are in excess of 600 R in adults, but as low as 200 R in infants. (4) E'fects on the Embryo and Fetus. The developing organism, embryo and fetus, is particularly vulnerable to radiation injury. Currently available experimental information and fragmentary human data on the general effects of brief radiation exposure a t various general stages of development indicates that: growth retardation, evident a t the end of gestation, can be caused by irradiation a t any time from the implantation stage (when fertilized egg is implanted in the uterus), to the latter part of gestation; prenatal death rate is highest after irradiation in the preimplantation stage and gradually reduces to a low level in the fetal stage (similar to adult in susceptibility to lethal radiation effect); neonatal death rate is highest after irradiation during the period of organ development; the peak incidence of gross congenital malformations is caused by irradiation during the period of organ development (they are rare after irradiation during the preimplantation period, even with exposures of 100-200 R a t time of fertilization) ; and postnatal deatbs and childhood cancers are increased by radiation exposures in the fetal growth period, i.e., in the latter months of pregnancy in the case of the human being. In the case of the Japanese atomic bomb radiation survivors, most of

CLINICAL FEATURES

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35

the pregnant women had a miscarriage shortly after the bombing if radiation exposure was large enough to cause symptoms and signs of acute radiation sickness. Among the few fetuses who survived to term and were delivered successfully there were some developmental defects comparable to those observed in experimental animals irradiated during pregnancy. However, there are not sufficient data on which to base accurate predictions of the outcome of a particular human pregnancy after exposure to a particular dose of radiation. In experimental animals, brief radiation exposures of 50-100 R cause some incidence or degree of effect when administered at any stage of gestation. These effects include some prenatal deaths following irradiation during the preimplantation stage, some offspringwith malformations foIlowing irradiation during the period of organ development, and some cell loss or growth decrement following irradiation during the fetal period. Effects of lesser brief exposure (down to a few R) of embryos have been reported but have been regarded as equivocal or uncertain in significance. Threshold doses, if any, for embryonic effects of irradiation have not been determined. With brief radiation exposures to the developing organism in the uterus, the lowest doses observed to cause effects on development, growth, function or behavior in experimental animals range from a few R to 50 R. A few R kill occasional germ cells at certain stages in early life, with no detectable functional effects. Subtle, but permanent, structural changes in nerve cells are caused by doses of 10-20 R at some stages of development, but no changes in behavior have been detected below about 25 R given at certain sensitive prenatal stages. About 1 R per day over a large part of the gestation period is the lowest level of extended irradiation that has been found to alter development in experimental animals. Data on effects of low radiation levels on development and growth in human beings are very limited. There is anlple evidence to indicate that relatively large radiation doses, such as those which can be received by embryos or fetuses in the uterus incidental to radiation therapy for various gynecological disorders, can cause congenital abnormalities, microcephaly (reduced brain or head sue), mental retardation, and other effects observable after birth, the specific effectsdepending on the stage of gestation at the time of irradiation. Attempts to assess the behavioral effects in Japanese children after exposure in the uterus to the radiations from atomic bombs have been limited by the lack of simple, sensitive tests comparable in simplicity to those which indicated a small but significant deficit in body growth and head size among those survivors closest to the hypocenter of bomb detonation. Mental retardation has had to be severe

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EFFECTS OF RADIATION ON MAN

to be recognized, even with the use of a number of available measures. Mental retardation was rare below 100 R and no excess incidence of it occurred below 25 R. In man, rzbdiation exposure of the embryo during the earlier months of gestation has been observed t o cause decreased body growth, head size, and mental development after as little as 50 R, and some inhibition of body growth possibly after as little as 25 R. As it is recommended that survival from the earlier effects of radiation be the principal determining factor when making decisions during a war emergency, the avoidance of the risks of late somatic effects would be a secondary consideration at such times. 4.4.3 Uses of a Scheme of Injury Classifidion. The discussion of radiation injuries given in the previous section (4.4.2) is comprehensive and consists of most of the clinical entities that have been studied in man. The classification scheme, summarized in Table 3, can be used for two purposes: A. To Estimate the Radiation Dose From Biological Eflec2s. If some or d l of the members of a group exposed under similar conditions develop a combination of the same symptoms and signs that lead to the clinical diagnosis of a type of injury and its level (e.g., acute radiation illness, Level 11), then an estimate of the range and kind of radiation exposures can be made. While the wide variation in human responses makes the range in the exposure estimate large, the group as a whole is expected to react as if all members received the same dose. This use of the classification scheme is important because the dosimetry data furnished by the radiological staff can be scanty and even misleading initially. B. To Predict the Outcome of a Particular Exposure. Any additional exposure that may be required and contemplated for approval by the officialsin charge of the situation can be evaluated in the context of this table t o determine the consequences. Prediction of any individual's outcome is less certain than an estimate of the dosage range based on a competent clinical study of a group of casualties. Nevertheless, in an emergency, many decisions must be made concerning such matters as need for therapy and work assignments, long before the development of the delayed manifestations of radiation injury that may require therapy.

4.5 The Problem of Protracted Exposure

It should be possible, even under massive fallout conditions, to regulate the daily exposure with appropriate guidelines in such a fashion that es-

PROBLEM OF PROTRACTED EXPOSURE

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37

TABLE &Summary of relationships between briej radiation exposure and acute injury

Type of Exposure

Type of Injury

Probable Condition of Ma'ority during hergency

gA%

Comments

Rate dunng Medical Able to Cqe Requ~red Work

Emmency'

-A. Brief. whole-

b0f-b.pmma raysb 12-60 R 60.200 R

Asymptomatic Aoute radiation sicknesa, Level I 200-460 R Acute radiation nickness, Level I1 450-600 R Acute radiation sioknesa, Level 111 More than 800 Aoute radiation sickR ness, Levels IV, V B. Internal D 4 Acute radiation dcknew, with severity posit proportional to internal dose and its location C. Beta i+radik tion of skin Lssathan1.000 Radiation dermatirads tis, Type I 1,MW)-5,000rads Radiation dermatitis, Typea I1 and

No No

Yea Yea

Yes

Noo

Yes

No0

0

Leas than 5 Deaths will wdllr in 60, or percent Less than 60 percent More than 60 percent lW percent

Yea

No

Variea

Varies Low Robability

No

Yes

0

Yea

No

Unoertsin

Ym

No

Uncertain

LII

more, days. Deatha will wcur witbin 30 to 60 days. Deaths will wcur in about one month. Deatha will wcur in two weeka or lesa. No reliable data on relation between internal d m and whole-body brief erternal dm. EC fects may be combined. Associsted with whole body erternal radiation d m of variable a h . Effects may be combined. Mortality possible with extensive skin wrs involved or with added external wbole-body expos'=-'.

More than 6,000 Ftadintion dermatitia,TypeIV rads

Mortality p c d b l e with extensive skin wrs involved or with added exh a 1 whole-Wy exposure.

This refers to acute mortality: death during firat 60 days after onset of exposure. For eleotrornagnetio radiations (such as gamma radiation) the exposun, units CB for roenWn) can

be converted s p p m r h a t e l y to absorbed Qee unitn (rad), a t the midline of the body, by multiplying the number of R units by M. O

Except during lllnss-fee latent period.

tablished upper limits can be avoided. The daily exposure can be controlled most practically by regulating the length of time particular persons are authorized to work in radiation fields of known strength. Such exposures would be controlled optimally by use of reliable personnel dosimeters and evaluations by trained radiation safety teams. Since even a relatively small amount of shieldmg of the trunk of the body from radiation can make an appreciable reduction in dose received and in degree of effect, it is important to consider research and develop-

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EFFECTS OF RADIATION ON MAN

ment of feasible portable or wearable shielding for persons carrying out emergency missions involving increased radiation exposure.

4.6

System for Predicting Outcome of Human Exposure

The classification of radiation injuries set out in Table 3 affords a system for predicting outcome that is suitable for planning and training exercises, but it is too cumbersome for operational use in an emergency. The five categories of radiation illness, the four categories of s k i injury, and various possible patterns of brief exposure, protracted exposure, and internal deposition of radioisotopes, added to all the other circumstances of war, provide too many combinations of information and options for action for uniform decision-making. A simpler system based on clinical effects of gamma irradiation is shonm in Table 4, the "Penalty" Table, which indicates the consequences (in terms of death and need for medical care) of various amounts of radiation exposure accumulated within various periods of time. The use of Table 4 is described in detail in Appendix B. Most authorities agree that a single brief whole-body exposure of 200 R will not affect the average adult t o the extent that he is incapable of performing his ordinary activities. I n fact, whole-body exposures of 20& 300 R have been used to treat many patients with advanced cancer without causing any manifest acute clinical effect on their physical condition other than brief periods of nausea and vomiting. Changes in the blood cell counts occurred, as was expected, but usually these were not sufiicient to require medical treatments. Those Marshall Islanders who had the largest exposure to fallout received about 175 R over a peroid of 36 hours. I n this group, which included people of all ages, the only evidence of acute radia.tion sickness was vomiting on the day fallout occurred (about 10 percent reported this symptom) and changes in the white blood cell count and platelet count as early as several weeks later. No treatTABLE &Recommended system j o t predicting outcome of gamma radiation exposure (the "Penally" Table) Medical care will be needed by

ures (R)in Accumluated radiation e any period o T

One Week

NONE SOME (5 percent may die) MOST (50 percent may die)

150

250 450

One Month

200 350 600

Four Months

300 500

-

WORK CAPACITY

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39

ments were needed. For these reasons, a brief exposure of 200 R is regarded as the dividing lime between doses that will and will not cause sickness that requires medical care.

4.7

Prediction of Number of Persons Requiring Hospitalization.

Military medical groups have studied the logistics of handling wartime casualties not only from "conventional" (low-yield) fission bombs b u t also from high-yield thermonuclear weapons. Using the same sources of information that are available to the NCRP, detailed schedules have been prepared t o predict the following: (1) Casualty rate versus exposure. (2) Hospitalization rate versus exposure. (3) Time after bombing a t which hospitalization will be required versus exposure. (4) Duration of hospital stay versus exposure. (5) hquirement for medical supplies versus exposure. (6) Death rate for hospitalized casualties versus exposure. Some of these estimates have been published and used t o develop computer solutions for military and civil defense training exercises. As useful as these procedures are for planning and training purposes, more simplified approaches are presented here for civil defense operational use and local decision-making during an emergency.

4.8 Work Capacity

It is a well known fact that a sick or injured man cannot do as much work as a healthy one, and that starvation and thirst interfere with work capacity. There are countless records of refugee trains, transportation of prisoners, death marches, and the like in which the sick and wounded died when subjected to exertion and deprivation that were tolerated by healthy people. I n spite of familiarity with the problem, no one knows how to quantify this common observation. It would be helpful to be able to predict the reduction in physical effectiveness due to a variety of common toxic agents, but this has not yet been achieved. Therefore, physicians cannot estimate the percent reduction in work capacity that will result from exposure to any given amount of radiation other than that which is expected to cause a clinically evident form of radiation sickness or skin injury severe enough to require medical care. The NCRP con-

40

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FRFECTS OF RADUTION ON MAN

dudes that it ,is not poasible to predict the potential reduction in work capacity prior $0 the onset of obvious illness following exposure to radiation. In the simplest t e r m , a person's work capacity can be expected to decline when he becomes sick or when complications develop from superficial wounds. Until some evident illness occurs, a decision-maker has no alternative but to consider all individuals fit for duty. However, radiation-induced fatigability is a real symptom of the acute radiation syndrome. Unfortunately, there is as yet no objective measure of the degree of physical performance decrement. Clinically, this effect is known to be present during the first 60 days of the acute radiation syndrome m d to persist for several months afterwards. On the basis of radiobiolo'gic observations in irradiated patients, exposures of 230-310 R are thought to be required to produce such an effect in 50 percent of the individuals exposed. However, the dose for a 10 percent level of probability for fatigue i s considered to range from 25 to 65 R,16a dose-response relation which could create problems for shelter directors dealing with a psychologically depressed population. Fatigue as a symptom of anxiety is well known and could be dif3cult to distinguish from fatigue as an effectof radiation on tissues.

. .

4.9

Infection

~ r o ~ o s ato l s consider the rjsk of infection as one of the factors that could influence decision-making in an emergnecy have been examined. Available clinical evidence indicates that persons sick as a result of radiation injury are usually more susceptible to infection. However, no clinical data could be found t o support the concept that asymptomatic radiation injury affected resistance to infection or immunity. Studies on experimental animals 'have also been reviewed and do not support this concept of hypersuscept;ibility, particularly after low doses, and especially when the doses are accumulated a t low exposure rates. '6 Table 10, page 82, in Radiobiological Factors i n Manned Space Plight, Edited by W. Langham, National Academy of Sciences Publication 1487 (National Academy of Sciences-National Research Council, Washington, 1967).

5. The Process of DecisionMaking 5.1 The Relation of Exposure to Effect

In a radiation emergency, the hazard of additional exposure should be graded on a scale ranging from more to less severe outcome as follows: (1) Death from immediate effects of radiation. (2) Immediate radiation sickness or skin injury severe enough to require medical attention and prevent the person from working. (3) No early radiation effects, but high risk of late somatic effects and genetic injury. (4) No early injury and low risk of genetic injury and late somatic effects.

5.2 Predicting the Outcome The major question to be answered, whenever a decision must be made to expose an individual to additional radiation, is how much radiation injury will be caused by particular total exposures accumulated in particular time intervals. The answer to this question, for purposes of operational decision-making, can be obtained from the information provided in Section 4, particularly Table 4 (the "Penalty" Table), which is recommended for use in predicting the outcome of exposure. The use of this table is discussed in Appendix B. The table was constructed to also answer the converse question, "What total exposures accumulated in what periods of time are required to make certain effects likely?" The "Penalty" Table gives these exposures as functions of the periods of time over which the exposures occurred. Separate exposures received a t different rates of accumulation must be added to determine the total exposure because a t present there is no better way to relate effect to exposure. Data of this nature from experiments on animals are insufficient for constructing a more accurate model owing to the infinite combinations of doses and exposure times required. The influence of exposure period upon the radii-

42

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PROCESS OF DECISION-IvlAICING

tion dose necessary to cause a particular effect is considered in detail in Section 4.

5.3 The Population at Risk The effect of a given dose of radiation will vary somewhat among individuals, partly due to age, sex, race, and general health. The sick, aged and very young are the most susceptible. Nevertheless, it is generally advisable for the decision-maker to consider the entire population equally susceptible to the effects of radiation, with the exception that children and pregnant womenshould be treated as being more susceptible. Genetic considerations dictate that, when feasible, special protection should go to people of prereproductive ages.

5.4

Distinction Between Causes of Injuries

When the number of people involved in an emergency is very la.rge-as in the case of an attack with nuclear weapons-it may be difficult to make special provisions for the more vulnerable individuals, however desirable such a policy may be. Furthermore, i t is advisable during the period of intense emergency to make no administrative distinctions between injury due to radiation and that due to other causes.

5.5 The Probable Outcome The term "clinical radiation injury" is comprised of at least five graded categories of sickness due to exposure of the whole body (or most of it) to external or internal gamma radiation; a t least four graded categories of skin damage due to beta radiation; and several different types of internal injury due to selective (local) deposition of radioisotopes. In every instance it is possible to anticipate a particular effect a t an approximate accumulated dose and exposure duration. As mentioned earlier, these predictions are based on limited experience with man, and made primarily from judgmental extrapolation of results from experiments with animals. To facilitate decision-making in time of emergency, i t is recommended that the anticipated outcome of an exposure to radiation be fitted into one of the following categories:

SUMMARY

/

43

1. Medical care not required during the emergency period. (Late somatic and genetic effects in this group.) 2. Medical care required during the emergency period. (a) During the early period. (Symptoms will be primarily gastrointestinal, with incapacity usually brief.) (b) During a subsequent period, beginning after about three weeks. (Symptoms will be infection and hemorrhage, with incapacity usually prolonged over several weelcs. Treatment may be complex.) 3. Death. (a) Early, occurring within ten days, usually with neurological, cardiovascular, or severe gastrointestinal symptoms. (b) Delayed, occurring usually in the second to fourth week (sometimes during the second month) after a nuclear attack, from infection or hemorrhage, or both, usually in individuals who had severe though transient early gastrointestinal symptoms. (Some of these will represent treatment failures from 2(b).)

5.6 Summary

As discussed above (Section 5.4), it is advisable in the period of intense emergency to make no distinction between the injuries due to irradiation and those due to other causes. At any time when a decision is required regarding additional exposure to radiation (usually to only a small fraction of the total population being considered)-four questions must be answered before a proper determination can be made: (1) How large is the accumulated exposure up to that time, and over what period(s) of time was it received? (2) Is the physical condition of the individual(s) consistent with the predicted effect of such an exposure received in that period of time? (3) How large is the proposed additional exposure and the duration of this exposure? (4) What is the physical condition of the individual(s) likely to be after the additional exposure? It will be the function and responsibility of the decision-maker to weigh the probable outcome for individuals against the probable outcome for a (usually) larger group of people if the proposed action (e.g., the obtaining of water, food, medicines) were not carried out. The more severe the latter, the more risk will be warranted for the few. The results

44

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PROCESS OF DECISION-MAKING

of this mental "weighing" process will not be identical among all "decision-makers", but it is to be hoped that the individuals charged with such formidable responsibility are equally well aware of the factors involved and their relative importance for maximum survival of individuals and the population.

APPENDIX A

Glossary The following definitions are given for purposes of clarification of the contents of this report. In some instances they may differ somewhat from common usage. Many of the quantities and units defined below have been the subject of extensive analysis by the International Commission on Radiation Units and Measurements (ICRU). This information has been published as ICRU Report 19'' where precise definitions may be found. absorbed dose: The mean energy imparted by ionizing radiation to the matter

i n a volume element, divided by the mass of the matter in that volume element. The special unit of absorbed dose is the rad. absorbed dose rate: An increment of absorbed dose, divided by a time interval. Special units of absorbed dose rate are rsdsl per second, rads per minute, etc. activity: The number of spontaneous nuclear tranformations which occur in a quantity of a radioactive nuclide, divided by the time interval during which those transformations occur. The special unit of activity is the curie. acute: An adjective indicating a short and relatively severe course, for example, acute radiation effects. This adjective has also been used sometimes to indicate brief irradiation a t high dose rate as distinguished from irradiation over long periods of time a t low dose rate. (See chronic.) acute radiation syndrome: The set of symptoms and signs of the acute illness caused by brief whole-body irradiation. air burst: A nuclear detonation a t an altitude a t which the fireball at maximum diameter does not touch the surface of the earth. alpha particle: A helium4 nucleus emitted by an atomic nucleus during a nuclear transformation. anorexia: The lack or loss of the appetite for food. beta burn: A skin burn caused by exposure to beta radiation. beta particle: An electron, of either positive or negative charge, emitted by an atomic nucleus or neutron during a nuclear transformation. burn (of skin): Grossly visible damage caused by heat (thermal burn) or by ionizing radiation. A first degree burn shows reddening of akin and is mild like that of sunburn without blistering; a second degree burn is characterized by blistering as in severe sunburn; a third degree burn is very severe with destruction of the full thickness of the skin. burst; See air b u n t , surface burst. carcinogenesis: The production of cancer.

'"Radiation Quanlilies and Unils, ICRU Report 19 (International Commission on Radiation Units and Measurements, Washington, 1971).

46

46

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APPENDIX A

cataract: An opacity of the crystalline eye lens or of its capsule. chronic: An adjective indicating persistence over a long period of time, for ex-

ample, chronic radiation effects. This adjective has also been used sometimes to indicate continuous or intermittent irradiation over long periods of time a t relatively low dose rate, as contrasted with brief irradiation a t high dose rate. clinical sign : See sign (clinical). collision stopping power: Mean energy lost by directly ionizing particles in atomic collisions per unit length of the particle track. congenital: An adjective referring to conditions existing a t , and usually before birth, e.g., congenital abnormality. contamination: See radioactive contamination. curie (Ci): The special unit of activity: one curie equals 3.7 X low per second. decay: See radioactive decay. decontamination: The removal or reduction of radioactive contamination. dermal: An adjective meaning of, or pertaining to, the skin. dermatitie: Inflammation of the skin. desquamation: I n reference to the skin, is the shedding or sloughing of the epidermis (external covering of the skin) in dry scales or sheets (dry desquamation) or in moist masses (wet desquamation). dose: A general term used in this report to connote absorbed dose or exposure. When used for beta radiation, this term indicates only the absorbed dose to specified tissues. dose rate: An increment of dose, divided by a time interval. dosimeter: An instrument for measuring or evaluating exposure or absorbed dose. doubling dose: The amount of radiation needed to double the natural incidence of a genetic or somatic anomaly. eczema: A chronic inflammatory skin disease characterized by lesions varying greatly in character, with the formation of blisters, scales and crusts. electromagnetic radiation: (1) Propagation of energy by means of electromagnetic waves; (2) Radiation consisting of associated and interacting electric and magnetic waves that travel a t the speed of light, e.g. x rays, gamma rays, radio waves, light. electron: An elementary particle having a negative electric charge of 1.60210 X lCIQ coulomb and a rest mass 1/1837 that of the proton. Electrons surround the positively charged nucleus. element: One of the known chemical substances that cannot be divided into simpler substances by chemical means. emitter: See radiation emitter. enteritis: Inflammation of the intestine. epilation: Loss of hair. erythema: A n m e applied to redness of the skin produced by congestion of the capillaries which may result from a variety of causes, including irradiation of the skin. exposure: A quantitative measure of x or gamma radiation a t s certain place, based on its ability to produce ionization in air. The special unit of exposure is the roentgen. ('%xposure" also is frequently used as a synonym for "irradiation".) exposure rate: An increment of exposure, divided by a time interval. Special units of exposure rate are roentgens per second, roentgens per minute, etc.

APPENDIX A

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47

fallout: Airborne particles containing radioactive material which settle to the surface of the earth following a nuclear explosion; also, the deposition on the surface of the earth of radioactive substances resulting from a nuclear explosion. Early fallout, also called local fallout, is that fallout which settles to the surface of the earth during the first 24 hours after a nuclear explosion; delayed fallout, also called worldwide fallout, is that fallout which settles to the surface of the earth a t some time later than the firat 24 hours after a nuclear explosion. f a l l o u t shelter: An enclosed area or place which can provideuefuge and protection temporarily against fallout radiation by restricting the fallout to distant locations (geometry protection) and by absorbing some of the radiation directed toward the shelter (barrier protection). fission (nuclear fission) : The division of a heavy nucleus into two (or, rarely, more) parts with massee of equal order of magnitude, usually accompanied by the emission of neutrons, gamma radiation, and, rarely, small charged nuclear fragments. fission product: A nuclide produced either by fission or by the subsequent radioactive decay of a nuclide thus formed. fusion (nuclear fusion): The process in which nuclei undergo fusion reactions. fusion reaction (nuclear fusion reaction) : A reaction between two light nuclei resulting in the production of a t least one nuclear species heavier than either initial nucleus. g a m m a radiation: Electromagnetic radiation emitted by an atomic nucleus during a nuclear transformation, or by particles during annihilation. g a m m a ray: See gamma radiation. genetic: An adjective pertaining to biologica.1 reproduction and inheritance, e.g., genetic effects of radiation. gestation: The period of development of the young in the uterus, from the time of fertilization of the ovum to birth. ground zero: The point on the surface of the earth vertically below or above the point a t which a nuclear explosion is initiated. half-life (radioactive half-life): The time in which half the atoms of a particular substance undergo radioactive decay. helium-4: An element with two protons and two neutrons in the nucleus. hemorrhage: Bleeding. h o t spot: A localized surface area of higher-than-average radioactivity. hypothyroidism: Diminished production of thyroid hormone. i n i t i a l nuclear radiation: The nuclear radiation created as a result of a nuclear explosion during the first minute after initiation of that explosion. i n t e r n a l conversion: The emission of an electron in the de-excitation of a nucleus by direct coupling between the excited nucleus and an extranuclear electron. i n t e r n a l radiation: A term referring to radiation emitted from radioactive substances within the body. ion: An atom or molecule that has lost or gained one or more electrons to become electrically charged. ionization: The process of adding one or more electrons to, or removing one or more electrons from, atoms. ionizing radiation: Any radiation consisting of directly or indirectly ionizing particles or a mixture of both. Directly ionizing particles are charged particles (electrons, protons, alpha particles, etc.) having sufficient kinetic energy to

48

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produce ionization by collision. Indirectly ionizing particles are uncharged particles which can liberate directly ionizing particles or can initiate nuclear transformations. irradiation : exposure to radiation. isomeric t r a n s i t i o n : Change of a nucleus from a higher energy state to a lower energy state of the same nuclide accompanied by the emission of a gamma ray. isotope: One of two or more nuclides having the same number of protons, but different numbers of neutrons in the nucleus. k i n e t i c energy: Energy due to motion. Klinefelter's disease: Refers to Klinefelter's syndrome, a condition characterized by the presence of small, degenerative, scarred testes associated with an abnormality of the sex chromosomes. latency o r l a t e n t period: The period of time between exposure t o s damaging agent, e.g., radiation, and the detection of a specified eKect of that agent. lesion: Any pathological or traumatic disorganization or discontinuity of tissue or loss of function of a part. l e t h a l radiation dose: The radiation dose (usually total-body) required to cause death in 100 percent of a large group of people (LDloo) within a specified time period, e.g., LD~oo~so days median l e t h a l radiation dose (MLD or LD,o): The radiation dose (usually total-body) which is expected to be fatrtl to 50 percent of a large group of people within a specified time period, e.g., LDso/ao day.. microcephaly : Reduced brain or head size. m i t o t i c activity: A term referring t o the reproduction of cells by the division process called mitosis. m o n i t o r (radiation m o n i t o r ) : A radiation detector whose purpose is to measure the level of ionizing radiation (or quantity of radioactive material). The term is frequently prefixed with a word indicating the purpose of the monitor, such as: areamonitor, air particle monitor. Radiation monitor is also a descriptive name for the person who uses such a detector. m u t a t i o n : An inheritable change owing to a change in properties of a gene. myeloproliferative diseases: Diseases characterized by abnormally increased production of bone marrow cells in and outside of the normal bone marrow locations. neoplasia: The fonnation of any new and abnormal growth, such as a tumor. n e u t r o n : An elementary particle having no electric charge and a rest mass of 1.67482 X lo-" kilogram. The neutron is a constituent of the nucleus of every atom heavier than ordinary hydrogen. nuclear electron c a p t u r e : A mode of radioactive decay of a nuclide in which an orbital electron is captured by and merges with the nucleus. nuclear fission: See fission. n u c l e a r fusion: See fusion. nuclear radiation: Radiation emitted as a result of nuclear transformation. n u c l e a r t r a n s f o r m a t i o n : A change of nuclide or an isomeric transition. nuclear weapon: Any weapon based on fission or fusion of atomic nuclei. nucleus: The positively charged central portion of an atom, with which is aasociated almost the whole mass of the atom, but only a minute part of its volume. nuclide: A species of atom having specified numbers of neutrons and protons in its nucleue. photon: A packet of electromagnetic energy. p o s t n a t a l : Occurrence after birth.

APPENDIX A

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49

prenatal: Existence or occurrence before birth. prodromal: An adjective referring to early signs or symptoms indicating the approach or subsequent development of a disease or other morbid state. prophylactic: A term referring to an agent or condition which ten& to ward off or prevent a disease or damage. proton: An elementary particle having a positive electric charge of 1.60210 X 10-lg coulomb and a rest mass of 1.6726 X lo-=' kilogram. The proton is a constituent of the nucleus of every atom. quality: See radiation quality. rad: The special unit of absorbed dose; one rad equals 0.01 joule per kilogram. radiation: The propagation of energy through space. radiation b u r n : See burn (of skin). radiation e m i t t e r : Any substance which is radioactive and therefore a source of radiation. radiation injury: The damage caused by interaction of radiation with tissue. radiation (ionizing) : See ionizing radiation. radiation m o n i t o r : See monitor. radiation quality: (1) For electromagnetic radiation, a measure of the penetrability of the radiation. (2) A characterization of directly ionizing radiation in terms of its collision stopping power. radioactive contamination (contamination): A radioactive substance dispersed in materials or places where i t is undesirable. radioactive decay (decay) : A spontaneous nuclear transformation in which a nucleus emits particles or gamma radiation, or a nucleus undergoes spontaneous fission, or an atom emits x radiation or electrons following nuclear electron capture or internal conversion. radioactivity: The property of certain nuclides of spontaneously emitting particles or gamma radiation, or of undergoing spontaneous fission, or of emitting x radiation or electrons following nuclear electron capture. radioiodine: Any radionuclide which has 63 protons in its nucleus and is therefore an isotope of the element iodine. radionecrosis: Radiation-induced cell death. radionuclide: A radioactive nuclide. residual nuclear radiation: The nuclear radiation created as a result of a nuclear explosion during some time later than one minute after initiation of that nuclear explosion. roentgen (R): The special unit of exposure; one roentgen equals 2.58 X lo-' coulombs per kilogram. s h e l t e r : See fallout she1ter. sign (clinical) : Any objective evidence of damage or diseese. somatic: An adjective pertaining to characteristics of or effects on the body, a s distinguished from genetic characteristics or genetic effects in offspring. surface b u r s t : A nuclear detonation a t the surface of the earth, or a t such a height above the earth that the fireball makes contact with the surface. survey meter: An instrument used to measure the exposure rate in roentgens per hour a t the point being metered. symptom: Any functional evidence of disease or of a patient's condition. t h e r m a l radiation (as applied to nuclear weapon effects) :The electromagnetic radiation emitted from a nuclear explosion a s a consequence of very high temperature. thermonuclear reaction: A nuclear reaction in which the participating par-

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50

APPENDIX A

ticles obtain the required kinetic energy from thermal agitation; the term usually applies to the nuclear fusion reaction. .. transepidermal injury: See desquamation (wet). x radiation: Electromagnetic radiation not resulting from nuclear transformam. The t.&m x ray is sometimes used tions and of wavelength smaller than in other publications to include gamma radiation, but this usage is not employed in this report. x rays: See x radiation. -

APPENDIX B

The Use of the "Penalty" Table in Decision-Making (DoseTime Considerations) Introduction

In Section 4.6 a system for predicting the outcome of human exposure is developed. As was pointed out there, the damage to living tissues caused by a given amount of radiation (of the type emanating from fallout) is expected to be less if the exposure period is protracted, i.e., when the exposure rate is decreased with the increase in exposure time. In the "Penalty" Table developed in Section 4.6 and copied below, this doserate effect htw been taken into account. This table of radiation exposure coilstraints provides a simple guide for use by decision-makers. It relates three categories of exposure-rate conditions (columns a, b, c) with three categories of expected consequences (rows A, B, C ) , depending upon total accumulated exposure. Examples of the use of the table are given below. THE "PENALTY" TABLE Accumulatsd radiation exposura, (R)in any period of

Medical care will be needed by

A B C

NONE S O M E (5 percent may die) M O S T (50 percent may die)

a

b

c

One Week

One Month

Four Months

150 250 450

200

300 500

350 600

-

A B C

Examples of Use of tho "Penalty" Table

Example 1. Purpose: To limit exposure to low medical risk. (Refer to row A.) To achieve this purpose, it would be necessary to limit the total radia51

52

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APPENDIX B

tion exposure of individuals to less than 150 R in any one week (column a ) ; 200 R in any one month (column b); and 300 R in any four-month period (column c). For example, if individuals receive the one-week limit of 150 R (column a) within the first week, then the limit for additional exposure during the ensuing three weeks of the first month, to keep within the one-month limit (column b), would be 200 R - 150 R = 50 R. This additional exposure of 50 R could be received in any period of time, ranging from one day to three weeks of the ensuing three weeks of the first month, without exceeding the one-week or one..n~onthlimits in the "Penalty" Table. However, if this additional exposure of 50 R were received, for example, within the second meek, then the individuals would have to be kept free of further exposure during the remainder of the f i s t month to keep within the one-month limit for row A (200 R). Similarly, if the individuals have received the limit of 200 R in the first month, without exceeding 150 R in any one week of that month, the limit of additional exposure for the ensuing three months of the first four months (column c) would be 100 R for a total of 300 R (200 R 100 R)in four months.

+

Example 2. Purpose: Operations a t the intermediate level of significant medical risk (row B), justified by highly critical emergency situations.

In this case, the decision-maker may find it necessary to allow greater exposure than one or another of the limits indicated in row A, but would be constrained whenever possible by other limits in row A, and always by limits in row B of the Penalty Table. For example, if individuals who have received 150 R within the first week are required in some emergency to receive an additional 200 R during the remainder of the first month (for a total of 350 R in the first month), it is desirable, if possible, that the one-week constraint for row A (column a) be observed by allowing no more than 150 R of this additional exposure during any one week within that month, even though the onemonth limit (200 R) and four-month limit (300 R) for row A will have been exceeded and the one-month limit (350 R) for row B will have been reached. If it is not possible to keep within any of the constraints for row A, then the row B constraints have to be applied, in an attempt to keep exposure in any one week as far as possible below 250 R, to limit the exposure during the first month to 350 R. Any additional exposure after this first month must be kept as far as possible below the additional 150 R which would attain the four-month limit of 500 R (row B).

APPENDIX B

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53

As in Example 1, the decision-maker could schedule exposures in a variety of ways within the constraining limits to meet the work required by the problem a t hand.

Example 3. Purpose: Operations a t the high levels of medical risk (row C), justified only by extremely critical emergency situations. In extreme emergencies, situations could arise that might justify operating a t the high risk level (row C). Those activities that could result in saving a significant number of lives may call for the deliberate exposure of some persons a t the highest constraint levels where radiation sickness and a 50 percent probability of death are expected (row C). If such situations arise, the decision-makers would use for guidance row C of the Penalty Table in a manner similar to that discussed for the low or intermediate risk rows (A and B) in Examples 1 and 2 above.

Basis for Selection of Values for the Penalty Table There is no directly applicable disaster or laboratory experience involving humans that supports unequivocally the choice of all of the numbers in the "Penalty" Table. There is also no satisfactory biological model or mathematical formula relating radiation effects (of the type considered here) to exposure rates and durations, that provides a satisfactory basis for deriving the amounts of exposure indicated in the table for time periods greater than one day. The choice of the numbers was based on judgment derived from extensive clinical radiotherapy experience, pathological studies of radiation-accident victims, and laboratory experiences with numerous large and small animals.

The NCRP The National Council on Radiation Protection and Measurements is a nonprofit colporation chartered by Congress in 1964 to: 1. Collect, analyze, develop, and disseminate in the public interest information and recommendations about (a) prokction against radiation and (b) radiation measurements, quantities, and units, particularly those concerned with radiation protection; 2. Provide a means by which organizations concerned with the scientific and related aspects of radiation protection and of radiation quantities, units, and measurements may cooperate for effective utilization of their combined resources, and to stimulate the work of such organizations; 3. Develop basic concepts about radiation quantities, units, and measurements, about the application of these concepts, and about radiation protection; 4. Cooperate with the International Commission on Radiological Protection, the International Commission on Radiation Units and Measurements, and other national and international organizations, governmental and private, concerned with radiation quantities, units, and measurements and with radiation protection. The Council is the successor to the unincorporated association of scientists known as the National Committee on Radiation Protection and Measurements and was formed to carry on the work begun by the Committee. The Council is made up of the members and the participants who serve on the fifty-four Scientific Committees of the Council. The Scientific Committees, composed of experts having detailed knowledge and competence in the particular area of the Committee's interest, draft proposed recommendations. These are then submitted to the full membership of the Council for careful review and approval before being published. The following comprise the current officers and membership of the Council : Oficers President Vice President Secrelary and Treasurer Assistant Secretary Assistant Treasurer

LAURISTON S . TAYLOR E. DALETROUT W . ROGER NEY EUGENE R. FIDELL HAROLD 0.WYCKOFF

THE NCRP

SEYMOUR ABRAHAMSON WILLIAMJ. BAIR VIC~OR P. BOND ROBERTL. BRENT A. BERTRANDBRILL F. BROWN REYNOLD WILLIAMW. BURR,JR. LEO K. BUSTAD MELVINW. CARTER GEORGE W. CASARETT RANDALL S. CASWELL H. CHAMBEULAIN RICHARD ARTHURB. CHILTON CYRILL. COMAR JAMESF. CROW MEURILEIBENBUD THOMAS 9. ELY ASHERJ. FINKEL DONALD C. FLECKENSTEIN F. FOSTXR RICHARD HYMERL. FRIEDELL MARVIN GOLDMAN ROBERT0. GORSON ARTHURW. GUY ELLISM. HALL WILLIAMT. HAM,JR. JOHN H. HARLEY ROBERTJ. HASTERLIK JOHN W. IIPALY JOHN M. HESLEP MARYLOU INGRAM SEYMOUE JABLON GEORGEV. LEROY EDWARD H. LEWIS CHARLBS W. MAYS

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ROGER0. MCCLELLAN ROBERTW. MILLER DADEW. MOELLFJR KARLZ. MORGAN RUSSELLH. M O R ~ A N PAULE. MORROW ROBERTD. MOSELEY,JR. JAMES V. NEEL ROBERTJ. NELSEN PETERC. NOWELL HERBERTM. PARKER LESTERROGERS I-IARALD H. Ross1 ROBERTE. ROWLAND WILLIAML. RUSSELL J O H NH. RUST EUGENE L. SAENGER HARRYF. SCEULTE RAYMOND SELTSER WARREN K. SINCLNR WALTERS. SNYDER LEWISV. SPENCER J. NEWELLSTANNARD CHAUNCEY STARR JOHN B. STORER LAWRISTON S. TAYLOR E. DALETROUT ARTHURC. UPTON JOHNC . \'ILLFORTH GEORGEL. VOELI NIEL WALD EDWARD W. WEBBTER GEORGEM. WILKENING HAROLD 0. WYCKOFF

Honorary Members

. .

.

EDGARC. BARNES CARLB. BRAESTRUP AUSTINM. BRUES L. DUNHAM CHARLES PAULC. HODQES EDITHH. QUIMBY SHIELDS WARREN

Currently, the following Scientific Committees are actively engaged in formulating recommendations: SC-1: Basic Radiation Protection Criteria SC-7: Monitoring Methods and Instruments

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THE NCRP

SC-9: Medical X- and Gamma-Ray Protection up to 10 MeV (Structural Shielding Design) SC-11: Incineration of Radioactive Waste SC-18: Standards and Measurements of Radioactivity for Radiological Use SC-22: Radiation Shielding for Particle Accelerators SC-23: Radiation Hazards Resulting from the Release of Radionuclides into the Environment SC-24: Radionuclides and Labeled Organic Compounds Incorporated in Genetic Material SC-25: Radiation Protection in the Use of Small Neutron Generators SC-26: High Energy X-Ray Dosimetry SC-28: Radiation Exposure from Consumer Products 8C-30: Physical and Biological Properties of Rdionuclides SC-31: Selected Occupational Exposure Problems Arising from Internal Emitters SC-32: Administered Radioactivity SC-33: Dose Calculations SC-34: Maximum Permissible Concentrations for Occupational and NonOccupational Exposures SC-35: Environmental Radiation Measurements SC-36: Tritium Measurement Techniques for Laboratory and Environmental Use PC-37: Procedures for the Management of Contaminated Persons SC-38: Waste Disposal SC-39: Microwaves SC-40: Biological Aspects of Radiation Protection Criteria SC-41: Radiation Resulting from Nuclear Power Generation SC-42: Industrial Applications of X Rays and Sealed Sources SC43: Natural Background Radiation SC-44: Radiation Associated with Medical Examinations SC-45: Radiation Received by Radiation Employees SC-46: Operational Radiation Safety SC47: Instrumentation for the Determination of Dose Equivalent SC48: Apportionment of Radiation Exposure SC-49: Radiation Protection Guidance for Paranledical Personnel 8C-60: Surface Contamination SC-61: Radiation Protection in Pediatric Radiology and Nuclear Medicine Applied to Children SC-52: Conceptual Basis of Calculations of Dose Distributions SC-53: Biological Effects and Exposure Criteria for Radiofrequency Electromagnetic Radiation SC-54: Bioassay for Assessment of Control of Intake of Radionuclides

In recognition of its responsibility t o facilitate and stimulate cooperation among organizations concerned with the scientific and related aspects of radiation protection and measurement, the Council has created a category of NCRP Collaborating Organizations. Organizations or groups of organizations which are national or international in scope and are concerned with scientific problems involving radiation quantities,

THE NCRP

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units, measurements and effects, or radiation protection may be admitted to collaborating status by the Council. The present Collaborating Organizations with which the NCRP maintains liaison are as follows: American Academy of Dermatology American Association of Physicists in Medicine American College of ~ a d i o l & ~ American Dental Assooiation American Industrial Hygiene Association American Insurance Association American Medical Association American Nuclear Society American Occupational Medical Assooiation American Podiatry Association American Public Health Association American Radium Society American Roentgen Ray Society American Society of Radiologic Technologists American Veterinary Medical Association Association of University Radiologists Atomic Industrial Forum Defense Civil Preparedness Agency Genetics Society of America Health Physics Society National Bureau of Standards National Electrical Manufacturers Assooiation Radiation &search Society Radiological Society of North America Society of Nuclear Medicine United States Air Force United States Army United Statea Atomic Energy Commission United States Navy United States Public Health Service

The NCRS has found its relationships with these organizations to be extremely valuable to continued progress in its program.

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THE NCRP

The Council's activities are made possible by the voluntary contribution of the time and effort of its members and participants and the generous support of the following organizations: Alfred P. Sloan Foundation American Academy of Dental Radiology American Academy of Dermatology American Association of Physicists in Medicine American College of Radiology American College of Radiology Foundation American Dental Association American Industrial Hygiene lissouiation American Insurance Association American Medical Association American Mutual Insurance Alliance American Nuclear Society American Occupational Medical Association American Osteopathic College of Radiology American Podiatry Association American Public Health Association American Radium Society American Roentgen Ray Society American Society of Radiologic Technologists American Veterinary Medical Association American Veterinary Radiology Society Association of University Radiologists Atomic Industrial Forum Battelle Memorial Institute College of American Pathologists Defense Civil Preparedness Agency Edward Mallinckrodt, Jr. Foundation Environmental Protection Agency Genetics Society of America Health Physics Society James Picker Foundation National Bureau of Standards National Electrical Manufacturers Association Radiation Research Society Radiological Society of North America Society of Nuclear Medicine United States Atomic Energy Commission United States Public Health Service

To all of these organizations the Council expresses its profound appreciation for their support. Initial funds for publication of NCRP reports were provided by a grant

THE NCRP

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from the James Picker Foundation and for this the Council wishes to express its deep appreciation. The NCRP seeks to promulgate information and recommendations based on leading scientific judgment on matters of radiation protection and measurement and t o foster cooperation among organizations concerned with these matters. These efforts are intended to serve the public interest and the Council welcomes co~nnlentsand suggestions on it,s reports or activities from those interested in its work.

NCRP Reports NCRP Reports are distributed by the NCRP Publications' office. Information on prices and how to order may be obtained by directing an inquiry to : NCRP Publications P.O. Box 30175 Washington, D.C. 20014 The extant NCRP Reports are listed below. NCRP Report No. 8 9 10 12 14 16 22

Title Control and R e m a l of Radioactive Contamination i n Laboratories (1951) Recommen$atim for Waste Disposal of Phoaosphorus-3B and Iodine-131 for Medical Users (1951) Radiological Motdoring Methods and I.pzstruments (1952) Recommendations for the Disposal of Carbon-14 Wastes (1953) Protection Against Betairon-Synchrotron Rdiations Up To 100 Million Electron Volts (1954) Radioactive Waste Disposal i n the Ocean (1954) Maximum Permissible Body Burdens and Maximum Permissible Concentrations of Radionuclides i n Air and i n Water for Occupatimud Exposure (1959) [Includes Addendum 1 issued in August 19631 Measurement of Neutron Flux and Spectra jor Physical and Biological. Applications (1960) Measurement of Absorbed Dose o f Neulrons and of Miztures of Neutrons and Gamma Rays (1961) Stopping Powers for Use with Caoity Chambers (1961) A Manual of Radioactivity Procedures (1961) Safe Handling of Radioactwe Malerials (1964) Shielding for High-Energy Electron Acceler& Installations (1964) Radiation Protection i n Educational Institutions (1966) Medical X-Ray and Gamma-Ray Protection for Energies Up lo 10 MeV-Equipmenl Design and Use (1968) Medical X-Ray and Gamma-Ray Protection for Energies U p to 10 MeV-Structural Shielding Design and Evaluation (1970) 60

NCRPREPORTS

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Dental X-Ray Protection (1970) Radiation Protection in Veleriwy Medicine (1970) Precadions i n the Management of Patients Who Have Reeeived T h e r a w i c Amounts of Radionuclides (1970) Protection Against Neutron Radidion (1971) Basic Radiation Prdeelion Ciiteria (1971) Proteetion Against Radialion From Brachytherapy Sources (1972) Speeijication of Gamma-Ray Brachytherapy Sources (1974) Radiologicat Factors Afleding Decision-Making in a Nuclear Attack (1974)

Binders for NCRP Reports are available. Two sizes make it possible to collect into small binders the "old series" of reports (NCRP Reports Nos. 8-31) and into large binders the more recent publications (NCRS Reports Nos. 32-42). Each binder will accommodate from five to seven reports. The binders carry the identification "NCRP Reports" and come with label holders which permit the user to attach labels showing the reports contained in each binder. The following bound sets of NCRP Reports are also available: Volume I. NCRP Reports Nos. 8, 9, 10, 12, 14, 16, 22 Volume 11. NCRP Reports Nos. 23, 25, 27, 28, 29, 30, 31 Volume 111. NCRP Reports Nos. 32, 33, 34, 35, 36, 37 Volume IV. NCRP Reports Nos. 38,39,40,41 (Titles of the individual reports contained in each volume are given above.) The following NCRP reports are now superseded and/or out of print: NCRP Report No. 1 2

3 4 5

Title X-Ray Protection (1931). [Superseded by NCRP Report No. 31 Radium Proteelion (1934). [Superseded by NCRP Report No. 41 X-Ray Protection (1936). [Superseded by NCRP Report No. 61 Radium Prokction (1938). [Superseded by NCRP Report No. 131 Safe Handling of Radioactive Luminous Compounds (1941). -

-

[Out of print]

6 7 11

Medical X-llay Protection up to Two MiUion Volls (1949). [Superseded by NCRP Report No. 181 Safe Handling oj Radioactive Isotopes (1949). [Superseded by NCRP Report No. 301 Maximum Pemissible Amounts of Radioisolopes i n the Hu-

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13 15

17

18 19 20

21 24

26

29

man Bodu and Maximum Permissible Concentralions i n Air and iba2er (1953). [Superseded by NCRP Report No. 221 Prolectwn Against Radiatirms f r m Radium, Cobalt-60 and Cegum-137 (1954).[Superseded by NCRP Report No. 241 Safe Handling oj C a d w s Containing Radioactive Isotopes (1953).[Superseded by NCRP Report No. 211 Permissible Dose from Exlemzal Sources of Ionizing Radiation (1954)including Maximum Permissible Exposure lo Man, Addendum to National Bureau oj Standards Handbook 69 (1958). [Superseded by NCRP Report No. 391 X-Ray Protection (1055).[Superseded by NCRP Report No. 261 Regulalion of Radialiun Exposure by Legislative Means (1955). [Out of print] Protection Against Neutron Radiation U p lo 30 Million Electron Volts (1957).[Superseded by NCRP Report No. 381 Saje Handling of Bodies Conhiniizg Radioactive Isotopes (1958). [Superseded by NCRP Report No. 371 Proleetion Against Radiations jrom Sealed Gamma Sources (1960).[Superseded by NCRP Reports Nos. 33, 34 and 401 Medical X-Ray Protection Up to Three Million VoUs (1961). [Superseded b y NCHS Reports Nos. 33, 34,35 and 361 Exposure to Radiation in an Emergency (1962)[Superseded by NCRP Report No. 421

The following statements of the N C R P were published outside of the

NCRP Report series: "Blood Counts, Statement of the National Committee on Radiation Protection," Radiology 63,428 (1954) "Statements on Maximum Permissible Dose from Television Receivers and Msximum Permissible Dose to the Skin of the Whole Body," Am. Jr. of Roentgenol., Radium Therapy and Nucl. Med. 8 4 152 (1960)and Radiology 75,122 (1960) X-Ray Protection Standards for Home Television Receivers, Intm'm Stdement of the National Council on Radiation Protection and Measurements (National Council on Radiation Protection and Measurements, Washington, 1968) Specification of Units jor Natural Uranium and Ndural Thorium, (National Council on Radiation Protection and Measurements, Washington, 1973) Copies of t h e statements published in journals m a y be consulted in libraries. A limited number of copies of t h e last two statements listed above are available for distribution b y NCRP Publications.

Index Accumulated exposure, 16 Acute radiation injury, biological features of, 18 Acute radiation syndrome, 24,25 Clinical levels of severity of acute radiation effects,25 Systemic radiation damage, 25 Toxic symptoms, 25 Assumptions, 2 NucIear disasters, 2

Decay of radioactivity, 12 Decision-making (use of the penalty table), 51 Examples of use of the penalty table, 51 Decision-making process, 41,42,43 Distinction between causes of injuries, 42 Population at risk, 42 Predicting the outcome, 41 Probable outcome, 42 Relation of exposure to effect, 41 Summary, 43 Distinction between causes of injuries, 42 Dose-time considerations (use of the penalty table in decision-making), 51 Basis for selection of values for the penalty table, 53 Examples of use of the penalty table, 51 Dose units, 4,5 Absorbed radiation dose, 4 Beta-radiation dose, 6 Gamma-radiation exposure, 4 Rad, 5 Roentgen (R), 4

Biological features of acute radiation injury, 18,19 Acute radiation syndrome, 19 Acute symptoms, 19 Biological repair processes, 19 Fractionated exposure, 19 Protracted exposure, 19 Chronic radiation illness, 27 Clinical features of radiation injury, 24, 27,29,30,31,36 Acute radiation syndrome, 24 Asymptomatic radia.tion injury, 24 Chronic radiation illness, 27 Classification of radiation injury, 24 Estimation of the radiation dose from biological effects, 36 Gastrointestinal distress, 24 Genetic effects of radiation, 30 Late somatic effects of radiation, 31 Prediction of the outcome of a particular exposure, 36 Radiation injury from internallydeposited radioisotopes, 29 Radiation injury to the skin, 27 Signs, 24 Symptoms, 24 System of prediction, 24 Uses of a scheme of injury classification, 36

Effects of radiation on man, 18,20,24,36, 38,39,40 Biological features of acute radiation injury, 18 Clinical features of radiation injury, 24 Genetic effects, 18 Infection, 40 Prediction of number of persons requiring hospitalization, 39 Protracted exposure, 36 Radiation injury, 18 Somatic effects, 18 Statistical features of radiation injury, 20

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64

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INDEX

System for predicting outcome of human exposure, 38 Work capacity, 39 Expoaure and expoawe rate calculations, 12,13,14,16 Accumulated exposure, 16 Approximate rate of decay of radioactivity from fallout, 13 Decay of radioactivity, 12 Dose rate prediction, 12 Exposure rate, 12 Formulas, 12 Half-life, 12 Rate of decay, 12 Seven-ten rule, 16 Total exposure, 15 Values for use in exposure rate formulas, 14

Exposure, protracted, 36,37 Fallout, 9, 10, 11 Atomic cloud, 10 Cool spots, 10 Delayed fallout, 10 Distribution of early fallout, 10 Early fallout, 9 Fallout patterne, 11 Fission fragments, 9 Formation of, 9 Hot spots, 10 Fission reaction, 7 Fusion reaction, 7 Gamma radiation, measurement of, 11 Genetic effects of radiation, 30,31 Doubling dose, 31 Genetic injury, 30 Mutations, 30 Glossary, 45 Infection, 40 Instruments, radiation monitoring, 16 LDm, 20,22 Limitations of the report, 3 Delayed neutrons, 3 Neutron dose, 3 Prompt neutrons, 3

Measurement of gamma radiation, 11, la Beta radiation dose, 11 Dose, 11 Exposure, 11,lZ Gamma radiation exposure, 11 Gamma radiation exposure rate, 12 One-hour rate, 12

Rad, 11 Reference location, 12 Reference time, 12 Roentgen, 11 Median lethal dose, 2 0 , B Monitoring instruments, 17 Maintenance and calibration facilities, 17 Radiological monitors, 17 National Academy of Sciences Advisory Committee on the Biological Effects of Ionizing Radiations, 32,33 Assumption of linear dose-effect relationship, 32 Neutron dose, 3 Nuclear explosions, types of, 6 Air bursts, 6 Fireball, 6 Nuclear detonation, 6 Radioactive fallout, 6 Surface bursts, 6 Thermal radiation, 6 Nuclear radiation (residual, fission products), 8 Nuclear reactions (fission and fusion), 7 Fission fragments, 7 Fission reaction, 7 Fusion reactions, 7 Thermonuclear reactions, 7 Nuclear weapons, general aspects, 7 Nuclear reactions (fission and fusion), 7 Pendty table, 38 Penalty table, use of in decision-making (dose-time considerations), 51 Examples of use of the penalty table, 61 Population a t risk, 42 Predicting the outcome, 41 Penalty table, 38,41

INDEX Prediction of number of persons requiring hospitalization, 39 Probable outcome, 42 Clinical radiation injury, 42 Protracted exposure, 36,37 Probable condition of majority during emergency, 37 Probable mortality rate during emergency, 37 Summary of relationships between brief radiation exposure and acute injury, 37 Type of exposure, 37 e p e of injury, 37 Radiation injury, classifxation of, 24 Radiation injury from internallydeposited radioisotopes, 29,30 Contaminated milk, 30 Exposed children, 29 Hypothyroidism, 29 Prophylactic, 30 Radioiodines, 29 Strontium, 29 Thyroid cancer, 29 Thyroid gland, 29 Thyroid neoplasia, 30 Radiation injury to the skin, 27,28 Chronic radiation dermatitis, 28 Dermal radionecrosis, 28 Desquamation, 28 Epilation, 27 Erythema, 28 Radiation dermatitis, 27 Thermal burn, 28 Transepidermal injury, 28 Radiation monitoring instruments, 16 Availability of civil defense radiological equipment, 16 Dosimeters, 16 Survey meters, 16 Radioactivity, 8 Radioactivity, decay of, 12 Relation of exposure to effect, 41 Residual nuclear radiation, 9 Residual nuclear radiation and fallout, 8 Alpha radiation, 8 Beta-particle radiation, 8 Gamma rays, 8

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Residual nuclear radiation from fission products, 8 , 9 Alpha particles, 9 Beta particles, 8,9 Daughter product, 8 Decay products, 8 Fallout, 8 Fiesion fragments, 8 Gamma radiation, 8 Gamma rays, 9 Half-life, 8 Radiation burns, 9 Radioactive nuclides, 8 Radioactivity, 8 Radioiodines, 9 Radionuclide, 8 Somatic effects of radiation, 31, 32, 33, 34, 35 Assumption of linear dose-effect relationship, 32 BEIR Committee, 32 Cancer production, 32 Cataract, 34 Effects on the embryo and fetus, 34,35 Late effects, 31 Linear dose-effect relationship, 33 National Academy of Sciences Advisory Committee on the Biological Effects of Ionizing Radiations, 32 Ninety-five percent lethal dose ( L D d , 21 Radiation carcinogenesis, 32 Risks of radiation-induction of various cancers, 33 Sterility, 34 Risk of genetic injury, 23 Statistical features of radiation injury, 20,21,22,23 Acute hematopoietic death, 20 Anorexia, 21 Chromosome abnormalities, 23 Diarrhea, 21 Dose-response relationship, 20 Effects of radiation exposure, 21, 22, 23 Fatigue, 21 Fifty percent lethal dose, 20 Five percent lethal dose, 20 Klinefelter's disease, 23

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INDEX

Level of radiation sickness, 21 Median lethal dose (MLD), 20 Nausea, 21 Non-lethal physiologic effects, 21 Prodromal gastrointestinal distress, 21 Prodromal responses, 21 Risk of late somatic effects, 23 Twenty-five percent lethal dose, 20 Vomiting, 21

System for predicting outcome of human exposure, 38 Penalty table, 38 Weapons, general aspects of, 6 Nuclear explosions, types of, 6 Work capacity, 39 Acute radiation syndrome, 40 Radiation-induced fatigability, 40