Attachment 7 AFSWP - 1100 THE NUCLEAR RADIATION HANDBOOK March 25, 1957 Declassified WITH DELETIONS by DNA Chief, LETS NUCLEAR DEVELOPMENT CORPORATION OF AMERICA White Plains, New York LETTER OF PROMULGATION This handbook is being issued in order to present a compilation of nuclear radiation effects as a reference for those elements of the Armed Forces requiring a treatment in greater detail than is found in "Capabilities of Atomic Weapon." An effort has been made to develop and present in a comprehensive treatment those aspects of nuclear effects which will be of most use. The information reflects weapons effects test data and analysis available early in 1956. It is intended that the material will be periodically revised in order to maintain a current status. A. R. Luedecke Major General, USAF Chief, AFSWP AFSWP - 1100 THE NUCLEAR RADIATION HANDBOOK March 25, 1957 Work Performed under Contract DA 29-044-XZ-442 for the Armed Forces Special Weapons Project NUCLEAR DEVELOPMENT CORPORATION OF AMERICA White Plains, New York PREFACE The status of our knowledge on the penetration of radiation from an atomic weapon through the atmosphere has undergone rapid change, and theoretical and experimental work have made great progress in the past several years. It was therefore felt desirable to take a snapshot of certain phases of this knowledge in order to provide a systematic account of these for military personnel who are required to use them and to assist research personnel by outlining the gaps in the current knowledge. Nuclear Development corporation of America (NDA) was assigned the task of preparing this handbook on nuclear radiation by the Armed Forces Special Weapons Project (AFSWP). It is inevitable in the preparation of a handbook such as this in a field which is progressing so swiftly that all portions are not of equal timeliness. We have made every effort to include information reported formally or available to us up to the 1956 Weapons Tests as well as some limited information arising from those tests. Since this is a handbook, information was gathered from many sources and it is not possible to acknowledge adequately all of them except by formal bibliographical references. We must, however, acknowledge the notable assistance rendered us by the following scientists, who gave their time and ideas freely and graciously when visited by NDA personnel for the purpose of securing advice and information: Dr. V.P. Bond (Brookhaven National Laboratory), Drs. Wendell Biggers, Payne S. Harris and John S. Malik (Los Alamos Scientific Laboratory), Dr. Marguerite Ehrlich (National Bureau of Standards), Dr. Donald K. Willet (Naval Research Laboratory), Dr. Robert Rapp (RAND Corporation), Dr. Richard D. Cadle (Stanford Research Institute) and Dr. Lester Machta (U.S. Weather Bureau). The preparation of this handbook was the work of Messrs. Richard Bakal, Francis Clark, and Drs. Daniel Ekstein, Morton Fuchs, and Robert Liedtke, all of NDA, and Lt. Commander Nathaniel L. Berlin and his colleagues of AFSWP who prepared Chapter II. The quality of this document has been greatly improved as a result of comments and advice received from Major Thomas W. Connolly who acted as the Project Officer for AFSWP for most of the time that the work was being done. J. Ernest Wilkins, Jr. White Plains, N. Y. March 22, 1957 Page iv is blank. iii TABLE OF CONTENTS Page CHAPTER I GENERAL CONSIDERATION 1.1 Introduction 1 1.2 The Fission Reaction 2 1.3 The Fusion Reaction 4 1.4 Weapon Design and Construction 5 1.5 Cloud Dynamics 6 1.6 Flux-Distance Relations 7 1.7 Biological Considerations 9 1.8 Average Air Density 10 1.9 Reference 16 CHAPTER 2 BIOLOGICAL EFFECTS OF RADIATION 2.1 Introduction 17 2.1.1. Sources of Data 17 2.1.2 Types of Hazard 18 2.1.3 Sources of Radiation 19 2.2 External Radiation 19 2.2.1. Introduction 19 2.2.2 Dosimetry 19 2.2.3 Units of Dose 19 2.2.4 Consideration of Depth Dose Curves and Correlation with Biological Effect 19 2.2.5 Dosimetric Methods 21 2.2.6 Significance of Air Dose, Skin Dose, and Mid Line Dose from X-Ray Radiation 24 2.3 Concept of RBE (Relative Biological Effectiveness) 26 2.4 Acute Radiation Sickness 27 2.4.1. Symptomatology 27 2.4.2 Current Therapeutic Concepts 30 2.4.3 Problem of Partial Body Shielding 31 2.4.4 Description of Beta "Burn" 31 2.5 Long Term (Late) Effects 31 2.5.1. Shortening of Life Span 31 2.5.2 Cataracts 33 2.5.3 Fertility 33 2.6 Genetic Effects 34 2.7 Effect of Protraction and Fractionation 34 2.8 Internal Contamination 37 2.8.1 Source 37 2.8.2 Route of Entry into Man 38 2.8.3 Metabolic Fate 38 2.8.4 Biological Effects 39 2.8.5 Therapeutic Aspects 39 2.9 Combined Injuries 39 CONTENTS 2.10 Maximum Permissible Levels of Radiation 40 2.10.1 External Radiation 40 2.10.2 Internal Radiation 40 2.11 Reference 40 CHAPTER 3 INITIAL GAMMA RADIATION 3.1 Introduction 43 3.2 Dose-Distance Relations for Surface Bursts 45 3.2.1 Theoretical Consideration 45 3.2.2 Low and Intermediate Yield Weapon 53 3.2.3 High Yield Weapon 63 3.3 Dose-Distance Relations for Air Bursts 76 3.3.1 Low and Intermediate Yield Weapons 76 3.3.2 High Yield Weapons 77 3.4 Dose-Distance Relations for Underground Bursts 78 3.4.1 Low Yield Weapons 78 3.4.2 Intermediate and High Yield Weapons 81 3.5 Delivery Rate 81 3.6 Initial Gamma Ray Spectrum 84 3.6.1 Initial Gamma Ray Spectrum at the Source 85 3.6.2 Spectral Variation with Distance 87 3.7 Military Shielding 93 3.8 References 106 CHAPTER 4 NEUTRON RADIATION 4.1 Introduction 107 4.2 Theory of Neutron Generation 107 4.2.1 Influence of Weapon Design 107 4.2.2 Fission Weapons 108 4.2.3 Boosted Fission Weapons 109 4.2.4 Thermonuclear Weapons 109 4.3 Experimental Methods and Results 109 4.3.1 Physical Experimental Methods 109 4.3.2 Biological Experimental Methods 114 4.3.3 Experimental Results 115 4.4 Flux-Distance Relations 118 4.4.1 Non-Thermal Neutrons from Fission and Boosted Fission Weapons 119 4.4.2 Non-Thermal Neutrons from Fusion Weapons 120 4.4.3 Thermal Neutrons from Fission and Boosted Fission Weapons 121 4.4.4 Effect of Variations in Atmospheric Density and Humidity 122 4.4.5 Scaling Relations for Variation of Average Quiescent Air Density and Weapon Yield 123 4.4.6 Major Deficiencies in Flux- Distance Relations 125 4.5 Dose-Distance Relations 125 4.5.1 Calculation of Total Neutron Dose 125 4.5.2 Discussion of Dose-Distance Relations 133 4.6 Relative Importance of Neutron Radiation 135 4.7 Neutron Energy Spectrum 137 4.8 Delivery Rates and the Hydrodynamic Effect 137 4.8.1 Prompt Neutrons 138 4.8.2 Delayed Neutrons 138 4.8.3 Experimental Results 139 CONTENTS 4.9 Military Shielding 141 4.10 Reference 143 CHAPTER 5 RESIDUAL GAMMA RADIATION 5.1 Introduction 145 5.2 Mechanism of Fallout 145 5.3 Computation Models 146 5.4 Decay of Activities 150 5.5 Isodose Rate Contours 156 5.6 Determination of Effective Wind Vectors, the Area of Fallout and the Time of Arrival 158 5.6.1 Determination of the Effective Wind Vector 160 5.6.2 Determination of the Fallout Area 164 5.6.3 Determination of Fallout Time Period 170 5.7 Delivery Rates 172 5.8 Scaling with Yield and Effective Wind Velocity 173 5.9 Scaling with Height of Burst 178 5.10 Energy Spectra of Fallout Gamma Radiation 179 5.11 Shielding from Residual Gamma Radiation 182 5.12 Variations Due to Environment 185 5.13 Neutron-Induced Activities 187 5.14 References 188 CHAPTER 6 RESIDUAL BETA RADIATION 6.1 Introduction 189 6.2 Radiation Source Characteristics 191 6.3 Beta-Gamma Dose Ratio at the Source 193 6.4 Beta Depth Dose Behavior 196 6.5 Beta-Gamma Biological Hazard 202 6.6 Miscellaneous Internal Effects 202 6.7 References 203 CHAPTER 7 THE ATOMIC CLOUD 7.1 Introduction 205 7.2 Cloud Dynamics 205 7.3 Cloud Heights and Dimensions 207 7.4 Cloud Characteristics for Calculation of Fallout and Initial Radiation 212 7.5 Cloud Characteristics for Calculation of Aircraft Penetration Dose 213 7.6 References 218 Chapter I GENERAL CONSIDERATION 1.1 INTRODUCTION In this manual an attempt will be made to summarize and correlate the quantitative information at present available on nuclear radiation produced by nuclear weapons. Specifically, it is desired to present methods of determining the values of dose from each of the several important kinds of bomb radiation as a function of distance (and in some cases direction) from the point of burst. R is also desired to know the energy distribution of the radiation making up the dose and the way in which the dose varies with time after burst. Ideally, these methods should be applicable to a wide variety of conditions, among others, bomb yields varying from 0.1 KIT to 100 MT, burst heights varying from -100 to 200,000 ft, air densities varying correspondingly, weapon types including pure fission, boosted, and thermonuclear, and bursts occurring over both earth and water and in the midst of a wide variety of meteorological conditions. In practice and with the present state of knowledge, it is possible to provide quantitative statements for only limited areas of these parameters. In other areas only qualitative statements can be made and sometimes even this is inadvisable. Under these circumstances reliance must be placed on both experimental results and theoretical analyses. Measurements provide the most direct answers when available. Theoretical analyses are used to afford some understanding of the mechanisms involved, so that results can be predicted in areas where experiments are lacking, and so that experimental results can be applied to a variety of conditions. It should be noted that measurements bearing on important problems are often lacking; in addition, when they are available they are often in conflict. Similarly, the theoretical analyses are not always available; when they are available, they are, necessary, based on simple models. Thus, the methods and results which follow are often subject to large and unknown errors. Where possible, an estimate of the magnitude of these errors accompanies the individual section or chapter. Auxiliary to the discussion of the radiation doses themselves, information is presented on several related subjects such as the biological aspects of dose, shielding against the several types of radiation, and the dynamics of the atomic cloud. The subject matter is divided into seven chapters, each of which is briefly outlined below. Chapter I (General Considerations) introduces the problems of nuclear radiation and covers those general areas which are necessary to a more detailed understanding of the subject. Since it is desirable and helpful to have a general knowledge of the nature and functional concepts of nuclear weapons, discussions of the fission and fusion reactions and of weapons design and construction are presented in Sections 1.2 through 1.4. Following these sections are introductory treatments of cloud dynamics (Section 1.5), the relationship between radiation flux and distance from the source point (Section 1.6), and terminology of biological dosage (Section 1.7). Finally, the calculation of the average air density, which applies to each of the later chapters, is covered in Section 1.8. 1 Chapter 2 presents a more detailed treatment of the biological effects of nuclear radiation. If reviews the sources of biological data, the pertinent units and definitions, and several of the measuring techniques. Radiation effects are considered, first due to sources external to the body and then due to internal sources. Both the immediate reactions (which may include nausea, diarrhea, weight loss, fever, changes in blood count, death) and the longer-term effects (which may include reduction of life span, cataract formation, impairment of fertility, and genetic effects) are described. The dependence of these effects on the total dose and on its distribution in time is covered as thoroughly as our present understanding permits. Current values of tolerance levels for external and internal radiation are presented. Chapters 3 through 6 discuss the four general categories of nuclear radiation which result from the explosion of a nuclear weapon. Initial gamma radiation (Chapter 3) is a radiation of electromagnetic waves similar to X-radiation except that the associated particles or photons possess much greater energy. (Photons, or gamma rays, are not particles in the technical sense that they do not possess a non-vanishing rest mass such as is possessed by electrons, protons, neutrons, etc. Nevertheless, they do possess other important properties of particles and it is more useful to think of them as particles for the purpose of the present work.) Initial gamma radiation is emitted during about the first 60 seconds after the time of burst. This time limit is somewhat arbitrary, being chosen for purely practical reasons. Actually, by far the greatest portion of this radiation is emitted during the first few seconds after burst. The source of the radiation is the material in the fireball which later becomes the atomic cloud. Initial gamma radiation usually refers to radiation effects at points external to the cloud. Neutron radiation (Chapter 4) is also emitted during this same time interval. A neutron is an electrically uncharged particle whose mass is nearly the same as that of the nucleus of the hydrogen atom. These is reason to believe that most of the neutron radiation of biological importance is emitted nearly instantaneously at the time of burst. The sources of neutron radiation are also contained in the fireball, and neutron radiation also usually refers to radiation effects a points external to the cloud. Residual gamma radiation (Chapter 5) is of importance at later times. It occurs when radioactive debris from the fission process is scavenged out of the atomic cloud, by large particles of earth for instance, and sifts back down to the ground under the influence of gravity and the local atmospheric conditions. The sources of residual gamma radiation, commonly called fallout, are then distributed upon the surface of the earth and irradiate the whole general environment. Residual beta radiation (Chapter 6) also occurs as a consequence of fallout. The sources of residual beta radiation are, in the main, identical to the sources of initial gamma radiation. Beta particles are the smallest electrically charged particles known. Negatively charged beta particles are called electrons and positively charged beta particles are positrons. Under most circumstances residual beta radiation is of less importance than residual gamma radiation because the penetrating power of beta particles is much less than that of gamma rays. Beta radiation usually affects only the skin of an irradiated animal. The most important properties of the several particles of concern in radiation process, including protons and alpha particles in addition to the particles described above, are given in Table 1.1:1. Chapter 7 presents a discussion of the atomic fireball and cloud. Attention is devoted to the dynamics of cloud formation and growth and to three of the problems upon which these dynamics have a strong influence: the cloud as source of most of the initial gamma and neutron radiation, as the generally accepted origin of the material carrying the residual radiation (fallout), and as a radioactive region of space which may be penetrated by aircraft. 1.2 THE FISSION REACTION Nuclei of the elements uranium-235 (U235),uranium-238 (U238), and plutonium-239 (Pu239) may, under favorable circumstances, break up into two parts when struck by a neutron of appropriate energy. (The symbols inside the brackets give the abbreviation for the element. The superscript on the right gives the mass number, which is the total number of protons and neutrons in the nucleus, for the element and isotope in question. Often the atomic number, which is the total number of elementary positively charged heavy particles or protons in the nucleus, is also given as a subscript to the left of the symbol.) 2 This fission reaction is accompanied by the release of an energy of energy of approximately 200 Mev (1 Mev = 1 million electron volts = 1.603 x 10-2 ergs), which is the reason for the enormous destructive power of nuclear weapons. The fission products, i.e., the large two residual fragments, are not always of exactly the same size, or equivalently, of the same atomic mass and number. There are, in fact more than 50 different nuclides which may arise as a consequence of fission. These fission products are usually formed in highly excited states and must release additional energy before they become stable. This energy is released in the form of beta, gamma, and a very small amount of neutron, radiation. It accounts for a large portion of the radiation effects in which we are interested. The fission process is accompanied by the emission of neutrons. There are an average of v neutrons emitted per fission. The value of v is between 2.5 and 4, depending on the type of material undergoing fission and the energy of the neutron causing the fission. A small fraction, approximately 0.73 percent for U235, of these neutrons is somewhat delayed in time of emission1 since it is emitted from the fission products, but the remainder of the neutrons accompany the fission process itself and are therefore emitted instantaneously. The delayed neutrons observed experimentally have not exceeded 0.7 Mev in energy. TABLE 1.1:1 Charge and Mass of Nuclear Particles Particle Electric charge, coulombs Rest Mass, gm Comments Electron -1.6 x 10 -19 9.1 x 10 -23 Beta particle Positron 1.6 x 10 -19 9.1 x 10 -23 Beta particle Neutron None 1.67 x 10 -24 Proton 1.6 x 10 -19 1.67 x 10 -24 Nucleus of the hydrogen atom Alpha 3.2 x 10 -19 6.64 x 10 -24 Nucleus of the helium atom Photon None None Gamma radiation The reactions involved can be written as follows for fission in U235, where 9n1 is the symbol for a neutron. (Those for Pu238 and U238 are similar except that the neutron which causes fission in U238 must be greater than about 1.5 Mev in energy. Thermal neutrons, on the other hand, will induce fission in U236 and Pu238.) 9n1 (1hermal energy) + U235 - 0.9927 v 9n1 + excited fission fragments + gamma radiation - kinetic energy excited fission fragments - 0.0073 v 9n1 + stable fission fragments + beta and gamma radiation U235 is present in only small amounts in natural uranium, and must be concentrated and purified for use in nuclear weapons. Capture of a neutron by uranium does not always lead to fission. Instead, a heavier uranium isotope, which does not break up this way, may be formed. 3 The energy release of nuclear weapons may be compared with the corresponding energy release from chemical explosives such as TNT. The energy released by the complete combustion of one thousand tons, or one kiloton, of TNT is 4.2x1019 ergs, 1.0x1012 calories, 3.1x1012 foot-pounds, or ILLEGIBLE X1025 Mev. It can be seen, therefore, that insofar as energy release is concerned, about 1.3x1023 ILLEGIBLE are equivalent to one kiloton of TNT, assuming 200 Mev per fission. The number of neutrons per kiloton of energy release is also of interest. Let or be the ration of non-fission to fission neutron to fission neutron captures in the weapon, including non- fission captures in the fissionable material. Then for each fission there will be a net of (v-1-a neutrons produced, since one neutron must be used to maintain the chain reaction. There will be then (v-1-a_ 1.3 x 1023-neutrons produced per equivalent kiloton of TNT. The value of (v-1-a) will usually be about 1.3, but may range from as low as 0.5 to as high as 2.0. Since the initial energy spectrum of fission neutrons is well known, it can be predicted that about 22 percent of these neutrons will initially be greater than 3 Mev in energy. The percentage emerging outside the weapon will, of course, be smaller because of energy degradation in penetrating the weapon casing. The energy release of nuclear weapons, commonly called the yield, is usually measured in terms of kilotons (KT) or megatons (MT) meaning the equivalent number of thousand or million tons of TNT which, when completely burned, give the same energy release. 1.3 THE FUSION REACTION As is now well known, the fission process if not the only way in which large amounts of energy can be released by nuclear reactions. Also of great importance is the fusion reaction utilized in thermo-nuclear weapons. In this reaction, several deuterium nuclei fuse together to form helium, tritium, and hydrogen nuclei with the release of a large amount of energy. A very high threshold energy is needed for this reaction to occur, however, so it is practical only at the high temperature usually attained in fission weapons and a fission bomb is used, for this reason, to initiate the fusion reaction. The fusion reaction is as follows, where 1D2 stands for the deuterium nucleus, 1H1 for the hydro-nucleus, and 1T3 for the tritium nucleus. 1D2 + 1D2 - 1T3 + 1H1 + Me 1D2 + 1D2 - 2He3 + 9n1 + 3.2 Mev These two reactions are about equally likely to occur. The following reaction is about 50 times more probable and will usually go nearly to completion: 1D2 + 1T3 - 2He4 + 9n1 + 17.6 Mev. The total effect of these three reactions is then obtained by summing, which gives 5 1D2 - 2He4 + 2He3 + 1H1 + 2 9n1 + 24.8 Mev. This is the fusion reaction for what is called partial burn. The following reaction is less probable, but may occur under favorable circumstances: 1D2 + 1He2 - 2He4 + 1H1 + 18.4 Mev Adding the last two reactions, we arrive at the reaction for what is called complete burn: 6 1D2 - 2 2He4 + 2 1H1 + 2 9n1 + 43.2 Mev 4 Neutrons are generated in equal numbers by the DD and the DT reactions, as can be seen above. Neutrons from the former reaction are crudely comparable to fission neutrons in energy, but those from the latter are much more energetic -- possessing an energy of 14 Mev in fact. (The rest of the 17.6 Mev is taken up by the recoil of the 2He4 nucleus.) From the above reactions it is seen that there are emitted 1.05 x 1024 high energy (14 Mev) neutrons per kilotron fusion yield in the partial burn case, and an equal number of lower energy neutrons. There is also an average total of 15.1 neutrons emitted per 200 Mev, which may be compared with (v-1-a) = 1.3 neutrons per fission characteristic of fission weapons. Thus, thermo-nuclear weapons generate many more neutrons for any given yield than fission weapons. Corresponding figures for the complete burn case are 0.605 x 1024 high energy neutrons per kiloton, and an equal number of lower energy neutrons. Similarly, there is a total of 9.24 neutrons per 200 Mev. In actual weapons, the true burn is intermediate between the partial and the complete burn bases, usually closes to the partial than the complete. The total energy released in the explosion of a thermonuclear weapon is comprised of the energy yield from the fusion reaction plus a large yield from an associated fission reaction, which is not only that due to the initiating bomb. The 14 Mev neutrons generated in the fusion reaction are utilized to initiate additional fission in both U235 and U238. (In this respect fusion neutrons differ from those produced in fission, which are not sufficiently energetic to fission U238 to any appreciable extent.) Boosted weapons are modified fission weapons to which a small amount of deuterium has been added. The fusion neutrons are utilized to augment the fission reaction in the uranium, thus giving an appreciably increased fission yield compared to that which would occur in the absence of the deuterium. The augmented fission yield is much greater than the direct fussion yield. 1.4 WEAPON DESIGN AND CONSTRUCTION The characteristics of weapon radiation, particularly neutron radiation, are sensitive to the details of weapon design and construction.2 The following discussion is confirmed to fission weapons. Thermo-nuclear weapons, for reasons of security classification in design, are beyond the scope of the present treatment. Weapons are stockpiled with their fissionable materials in a subcritical state, signifying a configuration such that no nuclear reaction can occur. Criticality is reached when the configuration is altered in such a way that the nuclear reaction can just barely start. Further alterations of the same type result in supercriticality, which means that the nuclear reaction, when started, will proceed faster and much more vigorously. It is important that there be no stray neutrons present while the system is going supercritical. If such neutrons are present, predetonation may occur. Predetonation occurs when the nuclear reaction commences before a condition of maximum supercriticality is reached. The result may be a fizzle, signifying the release of a much smaller amount of nuclear energy in the explosion than under optimum conditions. Under normal circumstances (no predetonation), at the precise moment that maximum supercriticality is reached, an artificial neutron source is activated, the fission reaction commences, and the explosion ensures. Criticality is achieved from the initial subcritical condition in a number of ways. The most common is the spherical implosion system. A spherical high explosive shell surrounds the fissionable material. This is exploded at the proper time by detonators symmetrically placed on the outer surface. A spherical implosion shock wave progresses toward the center of the system, compressing the fissionable material abruptly into a highly supercritical state. At the last moment, the shock wave 6 hits the center of the weapon where it activates an artificial neutron sources; the weapon then explodes. This type of weapon is spherically symmetric. The neutron radiation is most strongly influenced by the thickness of the high explosive shell. The high explosive contains hydrogen, which is very efficient in degrading the energy of neutrons by the process of elastic collision. Recent design has tended in the direction of making the high explosive shell thinner and thinner, resulting in less and less attenuation of the neutron dose by this hydrogenous material. Achieving criticality does not depend on compression of the fissionable material instead the fissionable material is divided into two parts which are subcritical when separated. The function of the high explosive at the ends of the apparatus in this case is merely to assemble the two parts quickly. Such weapons are called gun-type weapons. They are now used as artillery shells but are no longer popular as air-dropped weapons except when penetration of the ground surface is desired. Stockpiles weapon types are usually identified by a Mark number, which is abbreviated Mk-. When the models are still experimental, they are identified instead by a TX-number (i.e., MK-35 or Tx-35). Weapons are boosted, when desired, by making minor modifications of the basic unboosted weapons. Boosted weapons fall into the same general classifications outlined above. As previously noted, the weapon strength is called the yield and is given in term of equivalent ILLEGIBLE of TNT in kilotons (KT) or megatons (MT) The yield is controlled by the actual physical size of the weapon and by its detailed design characteristics. A change in physical size results, primarily, in a simple multiplication of the source strength of the radiation produced. A change in weapon design characteristics has much more complicated effects on the radiation. All weapons tested to date of up to about 100 KT yield have been pure fission weapons. In the range of 100 KT to about 1 MT the weapons are either pure fission or boosted fission weapons. In the boosted weapons, however, the yield is essentially all due to the fission reaction and the fusion contribution may be neglected. Above 1 MT the weapons are fusion. 1.5 CLOUD DYNAMICS For purposes of discussing initial and residual radiation, some knowledge of cloud dynamics is required. Only the necessary definitions and a very crude description of the phenomena involved are presented here. A more detailed discussion will be found in Chapter 7. 6 Just after the time of burst, the weapon components are extremely hot. They expand rapidly, ILLEGIBLE air from the atmosphere as they do so. In these early stages of expansion, we speak of this ILLEGIBLE the fireball. As the fireball continues to expand, it also rises because of the low density of the material in it interior. Further expansion and rising is accompanied by cooling, and the edges of the fireball become somewhat less sharply defined. We then speak of the atomic cloud or just of the cloud. The cloud, except for very minor differences, is just the fireball at a later stage of development. The cloud rise is allowed and, for sufficiently low-yield weapons, it is stopped at the the elevation of the tropopause. The tropopause is the boundary between the troposphere and the stratosphere. The troposphere is the lower layer of the stmosphere in which nearly all vertical convection and turbulence occur. It is characterized by a general linear decrease of temperature with altitude, although localized temperature inversions at low altitudes occur frequently in some parts of the world. The atratosphere is that portion of the atmosphere above the troposphere and is characterized by a constant or alightly increasing temperature with altitude. As a consequence, the air in the atratosphere is quite stable with respect to vertical motion and is therefore stratified into layers. The elevation of the tropopause depends mainly on the lattude and season of the year, although local weather disturbances may cause marked variations from the normal. The height of the tropopause in general varies from about 55,000 ft at the equator to about 30,000 ft at the poles. In middle lattudes, it varies from about 40,000 ft in summer to 33,000 ft in winter. Cloud dynamics, in turn, are markedly affected by the height of the tropopause. Strong local inversions at lower levels, likewise,can exert a damping effect on the cloud rise. 1.6 FLUX-DISTANCE RELATIONS This section consists of a discussion of teh relations between the flux of initial gamma or neutron radiation at points exterior to the fireball and the associated distance from the point of burst. The flux of any type of radiation is the total number of particles (gamma ray photons, neutrons, electrons, positrons, etc.) per unit area and per unit time arriving at a particular point from all directions and at all energies. The unscattered flux is that portion of the total flux which arrives directly at the point in question from the source, without having suffered any previous collisions. The unscattered flux is monodirectional if the source of radiation is a point. For the sake of conciseness, the time integral of the aboveis also often called the flux. We are often interested in the flux due to particles (especially neutrons) within a prescribed range of energy GRAPHIC E, because the biological effect of the radiation is related in a complicated way to the particle energy. The unscattered flux GRAPHIC , at a point source of radiation of intensity S (total number of particles, or particles per unit time) in a uniform homogenous medium is given by 0 u = 5 e - t R ----- 4nR2 t = 1 = pu = p --- --- y t to y to The symbol____ is the total linear attenuation coefficient and ___ is the total mean free path. The symbol p. is the density of the medium measured in units of standard density. Quantities measured at the standard density are so designated by means of a zero subscript. Thus, __ and ___ are the total attenuation coefficient and mean free path at the standard density. These equations show that __ and ___ are proportional to the air density p. 7 The total flux ___,however, also includes radiation which arrives at the point after scattering (and at a lower energy). We define the flux buildup factor B(__R) such that ` EQUATION 0 = 0 u B(mtR). (1.6:2) B(mtR) itself is often crudely exponential in form B(mtR) = e K1mtR (1.6:3) where Kt is constant. Thus, 0 is also still roughly exponential. EQUATION 0 = S e -mt (1-kt)r = S e -mR ---- --- 4nR2 4nR2 (1.6:4) m = 1 = pm = P = mt (1-k1) ---- ----- y y2 where we call (symbol) the apparent linear attenuation coefficient ] and___ the apparent free path. Most experiments have measured _ and ___ rather than ___ and ____. The biological effect of radiation is more closely related to __ than to ___. The buildup factor concept can easily be generalized. One may define, for instance, buildup factors for flux due to radiation in a specific energy range, buildup factors for the energy transported rather than the number of particles, buildup factors for biological dose, etc. Experimentally, it has usually been found that Eq. 1.6:4 remains a fair, although inexact, approximation even if the source of radiation is spread out over a broad band of energies. It also holds reasonably well for non-uniform media such as the atmosphere, whose density varies with elevation. In this case, however, it is necessary to calculate an average air density p. Methods for doing this are described in Section 1.8. Serious modification is required, however, because of perturbation of the medium by the blast. Eq. 16:4, even after defining the average air density p, is still properly true only for an infinite homogeneous medium. At the time of the explosion, a blast wave spreads out from the point of burst. This blast wave is bounded at its outermost radius by a sharp discontinuity known as the shock front which separates the quiescent medium from the disturbed medium. Compression of the medium is maximum at the shock front. At sufficiently late times behind the shock front, there comes to exist a region of rarefield, low density hot air known as the rarefaction phase of the blast wave. Because of this rarefaction phase, the exponential term in Eq 1.6:4 at times shortly after the time of burst can be much more than e_____R. This enhancement of the radiation shortly after the burst by the shock wave has been called the hydrodynamic effect by its discoverer, J. Malik.3 The term time of arrival refers to the elapsed time required after the burst for an effect under discussion to arrive at a specified point. (The effect may be arrival of the shock front, contaminated material, etc.) Several other terms which occur repeatedly in the literature should be understood. Ground zero, or GZ is the vertical projection on the earth's surface of the burst point. Burst height refers to the elevation of the point of burst, either above the ground surface -- or sometimes, above mean sea level. 8 Slant range R is the distance from the point of burst to that point at which the value of flux or dose is desired. If such a point is on the ground surface, R obviously satisfies the relation R2 = (distance from ground zero to receiver)2 + (height of burst above the ground at the receiver)2 We should understand, however, that neutron radiation and gamma radiation from the fission products emanate from a source which, to with a good approximation, is a point source of radiation at the center of the fireball. When the neutrons have been allowed down to thermal energy by successive collisions in the air, they are captured by nitrogen nuclei. About 6 percent of these excited nuclei then emit nitrogen capture gamma radiation, which is of quite high energy (an average of about 6 Mev). This radiation is part of the initial gamma radiation, but obviously its source is distributed over a much larger volume than the gamma radiation from fission products, and the point a source treatment is a much poorer approximation. This is especially true at high altitudes. 1.7 BIOLOGICAL CONSIDERATIONS The relation between radiation flux and biological damage is very complicated. It will be discussed in Chapters 2 and 4. In the present paragraphs only such definitions are included as are necessary to understand the terminology. Dose is a general term used to signify some measure of the radiation absorbed by an organism. Dose is measure in several different kinds of units which are described below. One roentgen or r represents that amount of gamma radiation which, when absorbed in one cubit centimeter of pure dry air at one atmosphere pressure and 0oC, will generate one e.s.u. of charge of either sign, that is 2.08 x 108 ion-pairs. (An ion- pair is the combination of a free electron plus a positively charged atom which is mission an electron.) Since on ion-pair requires the expenditure of an energy of 32.5 ev to form, this is equivalent to 0.1082 erg-cm-3 or 83.5 erg-gm-1 of air. One roentgen equivalent physical or rep is defined as that amount of radiation of any type which, when absorbed in one gram of organic tissue, will deposit 93 ergs of energy. (This unit has also been defined in the literature as 84 erg-gm-1 of tissue, which as led to some confusion. The latter definition will not be used in the present work.) One rad is defined as that amount of radiation of any type which, when absorbed in any material (not necessarily tissue), will deposit an energy of 100 ergy-gm-1. One roentgen equivalent man (or mammal) or rem is defined as that amount of radiation which, when absorbed in mammalian tissue, will ill cause the same biological damage -- according to any definite but arbitrarily defined criterion -- as the absorption of one rep of 400 kev (1 kev = 1 thousand electron volts) gamma radiation. Neutron radiation dosages can be measured in rem, rad, or rep. It cannot be measured in roentgens. Gamma radiation, on the other hand, is most commonly measure in roentgens. This is identical to the dose in rep or rem for photons above 400 kev in energy. The LD__ or 50 percent lethal dose is that dose of any type of radiation which will cause the death, within a certain period of time (usually 30 days), of 50 percent of the population of organisms irradiated. Important simplifications in the relations between radiation flux and dose occur when 1. The shape of the flux energy spectrum is constant from point to point within a satisfactory degree of approximation. In this case, the dose in both rep and rem is simply proportional to the total flux in any specified energy range. 9 2. The RBE is constant with energy so that the doses in rem and rep are either identical or directly proportional to each other. 8 AVERAGE AIR DENSITY The exponential term in Eq. 1.6:4 for the total (scattered and unscattered) radiation from a point source in a homogeneous medium is given as e-_R or e-p__R. For a non-homogeneous atmosphere, however, this exponential requires generalization. An approximation due to Weidler and Ward, 4 which is satisfactory for most application, although not exact, replaces these terms as follows: EQUATION (1.8:1) where = average apparent linear attenuation coefficient between point of burst and receiver p = average air density between point of burst and receiver, expressed in units of d. do - density of pure dry air at 0oC and one atmosphere pressure, 1.293 x 10 -3 gm-cm -3 m = apparent linear attenuation coefficient for air at density d o Since the exponential term will normally be expressed in terms of the apparent linear attenuation coefficient at standard conditions __, it is therefore equal to e -pH0R for homogeneous atmospheres and e -pH0R for non homogeneous atmospheres. the required values of p or p are calculated as outlined below. It the pressure and temperature of the atmosphere are uniform between the burst point and the receiver, the air density p may be calculated from the ideal gas laws and a knowledge of the air pressure and temperature. p x 1 A a p = 0.269 p (1.8:2) --- --- --- -- d 0 G T T where p = air density between burst point and receiver, expressed in units of d o Aa = average molecular weight of air G = gas constant p = atmospheric pressure, milibars T = atmospheric temperature, 0K. Eq. 1.8:2 is presented graphically in Gig. 1.8:1 If the pressure and temperature differences of the atmosphere between the burst point and the receiver are small, the average air density may be satisfactorily found by taking the average between 10 FOR REFERENCE SEE (8bb03.gif) 11 FOR REFERENCE SEE (8bb04.gif) 12 FOR REFERENCE SEE (8bb05.gif) 13 1. We must convert the temperature to oK. Thus, T = 273 + 20 = 293oK/ 2. The air density p is given by p = 0.296 p = 0.269 950 = 0.87, -- --- T 293 which can also be read from Fig. 1.8:1 for p of 950 millibars and T equal to 20 oC. PROBLEM 2 The pressure and temperature at both the point of burst and an external point are given. the pressure, temperature and difference in elevation between the two points are not greatly different. It is required to find the average air density between the two points in units of 1.293 x 10-3 gram-cm-3. Solution 1. Convert the units of pressure to millibars and temperature to oK if the information has not been supplied in three units. 2. compute the average air density directly from the formula. p x 1 (p x p ) = 0.269 (PB + PZ) -- B Z ------ -- -- 2 2 T T B Z Example At the point of burst the pressure is 950 millibars and the temperature 25oC. At the external point the corresponding fitures are 900 millibars and 15oC. The difference in evaluation is 1500 ft. It is required to find the average air density between the two points in units of 1.293 x 10-3 gram-cum-3. 1. We must convert the temperatures to oK T = 273 + 25 = 298 oK B T = 273 + 15 = 288 oK Z 2. The average air density p is given by p = 0.269 (950 + 900) = 0.85 ----- (--- ---) 2 (298 288) PROBLEM 3 The pressure at both the point of burst and an external point are given. the difference in evaluation is also given, and this may be large (more than 2500 ft). It is required to find the average air density between the two points in units of 1.293 x 10-3 gram-cm-3. Solution 1. Convert the units of pressure to millibars and difference of evaluation to feet if the information was not supplied in these units. 14 2. Either compute the average air density p directly from the formula p = 25.8 /Ap/ = 25.8 1000-700 = 0.77, /Ay/ -------- 10,000 which can also be read directly from Fig. 1.8:2 Ap of 300 millibars and At if 10,000 ft, CONVERSION FACTORS For convenience we include here some formulae and conversion factors for use when input data, are supplied in units differet from those illustrated. Units of Pressure 1 standard atmosphere = 29.92 in. of mercury at 0oC = 76 cm of mercury at 0oC = 33.9 ft. of warter at 4oC = 1013.25 millibars = 14.7 lb-in.-2 = 2117 LB-FT-2 1 MILLIBAR = 1000 dyne-cm-2 Units of Temperature F = temperature in degrees Fahrenheit C = temperature in degrees Centigrade K = temperature in degrees Kelvin C = 5/9 (F-32) K = C + 273 15 Units of Length 1 meter = 3.281 ft = 1.094 yd = 6.214 x 10-4 miles 1 in. = 2.54 cm 1.9 REFERENCES 1. S. Glasstone and M. Edlund. Elements of Nuclear Reactor Theory. D. Van Nostrand Co. Inc. Nov., 1952. (Unclassified) 2. S. Glasstone. LA-1632. Jan. 1954. (Secret) 3. J. Malik. LA-1620. Jan. 1954. (Secret) 4. R. C. Weidler and E.N. Ward. SWR 54-5. May 1954. (Secret) 16 Chapter 2. BIOLOGICAL EFFECTS OF RADIATION 2.1 INTRODUCTION This chapter has been prepared to provide a review of the broad field of radiobiology as it applies to military problems. There are some data available for man which are not particularly satisfactory. There is a large volume of data obtained from laboratory and weapons test studies in experimental animals. It is manifestly not possible to cover within the scope of this document the entire field of radiobiology. This chapter attempts to review the problems and to point out and evaluate areas of controversy. For details, it is suggested that the reader consult the general and specific references. In many respects the data presented in other sections of this handbook have been collected for the purpose of evaluating the hazard of ionizing radiation to personnel. Except at very high dosages (10,000 r and greater), ionizing radiation is without effect on ordinary material other than radiation dosimeters and photographic film. The basic purpose of this chapter is to provide some guidance in the use of physical data for the estimation of personnel hazard. There will be some repetition of physical data detailed elsewhere in this handbook to provide continuity. In many, if not most, instances the needed correlation between exposure dose and clinical findings is lacking because of insufficient data. 2.1.1 SOURCES OF DATA The primary sources of pertinent medical radiobiological information are: 1. the evaluation of the results of the Hiroshima and Nagasaki experience by the Atomic Bomb Casualty Commission (ABCC)1, 2. the evaluation of the results of the accidental exposure of the Marshallese during Operation Castle2, 3. accidents in atomic energy laboratories3,4, and 4. clinical radio-therapeutic experience. In addition, there is a large volume of experimental animal data from which certain inferences regarding man may be drawn, but which cannot be directly applied.5,6,7 In general, animal experiments indicate the pattern of response that may be anticipated in man, but are not an ideal source of information. Significant differences in details, particularly quantitative, preclude direct extrapolation to man. In fact, all sources lack certain pertinent critical information. As an example, review of the problems associated with the calculation of radiation dosage at Hiroshima and Nagrasaki results in the conclusion that at Hiroshima neutron effects might predominate while at Nagasaki, "nearly all the dosage is due to gamma rays." Aside from the difficulties associated with estimating the flux and energy spectrum of neutrons and the gamma ray dose, Figure 2.1:1 illustrates the difficulty in assigning to a given location a number for dose because of the rapid decrease of the dose with ground distance, both for neutron and gamma rays.8 This is without consideration of an estimate of shielding factors. As will be discussed later, the biological effectiveness of neutrons may be greater than gamma rays. Comparison of the results obtained at Hiroshima with those at Nagasaki should make some provision for this difference. But, in addition, the flux and spectrum for a given location are so poorly known that, in all probability, quantitative data purporting to relate lethality to dose are of dubious value. The dosimetry problems associated with the exposure of the Marshellese make it difficult to determine precisely the gamma ray dose. The data were insufficient to permit even an attempt to be made to estimate the skin dose resulting from soft X-rays and beta radiation.9 The many problems and uncertainties involved in the dosimetry of accidents in atomic energy laboratories are pointed out in a description of an accident at the Argonne National Laboratory.4 17 FOR REFERENCE SEE (8bb06.gif) 18 Figure 2.1:1 Neutron and Gamma Radiation as a Function of Distance Estimated for Bursts at Hiroshima and Nagasaki.8 The gamma ray dosage in roentgens is plotted as a function of the distance along the ground from the point just below the bomb explosion. The number of neutrons-cm-2 is indicated in the scale at the right of each drawing. This scale applies for slow neutrons, namely those below 1 ev, and for fast neutrons as indicated. The fast neutron curve represents a really wild guess. 2.1.2. TYPES OF HAZARD The personnel hazard may be divided into immediate and late considerations. The immediate hazard is that involved in the production of acute effects, principally lethality, acute radiation illness or skin lesions. The long term problem is that of the late effects, this involves both the individuals concerned and, through the genetic changes produced by radiation, their progeny for many generations. 2.1.3 SOURCES OF RADIATION There are two separate sources of ionizing radiation to be considered. These are: 1. External gamma, beta and neutron radiation. For residual radiation this is a combined beta and gamma radiation; for initial radiation, neutrons are an additional source of ionizing radiation. 2. Internally deposited radioactive materials. For military considerations, this is a problem associated with fallout. 2.2 EXTERNAL RADIATION 2.2.1 INTRODUCTION External radiation constitutes a potential hazard to personnel form the moment of detonation of an atomic weapon. The initial radiation consists of gamma and neutron radiation, propagated for large distances in air. In addition, within the cloud there is beta radiation, but it is difficult to conceive of a situation where beta radiation will constitute a personnel hazard before fallout occurs. While falling and after completion of fallout, the external radiation consists of both beta and gamma radiation. 2.2.2 DOSIMETRY From the standpoint of estimation of personnel hazard from external radiation, the basic necessary physical data are: 1. the type of radiation, whether it be gamma, beta, neutron, or some combination of these; 2. knowledge of the energy spectrum and flux and 3. source geometry. 2.2.3 UNITS OF DOSE There are several units or radiation dose currently employed.10 1. Roentgen - that quantity of X or gamma radiation which produces, in 1 cm3 of pure dry air at STP conditions, 1 e.s.u. of charge or either sign, that is 2.08 X 109 ion-pairs. Since on ion-pair requires the expenditure of 32.5 ev to form, this is equivalent to 0.1082 ergs-cm-3or 83.5 ergs-gm-1 of air. 2. Rep (roentgen equivalent physical) - that quantity of ionizing radiation which results in an absorbed doses in any material at the site of interest that is equivalent to that obtained form 1 r of gamma rays; this quantity is usually taken as 83.5 ergs for 1 gm of air' for soft tissue this is 93 ergs-gm- 1 tissue. This unit is independent of the type of energy of the ionizing radiation. 3. Rad - that quantity of ionizing radiation which results in the transfer of 100 ergs-gm-1 to any material. This is a recently adopted unit. It can be seem that for soft tissue it is almost equivalent to the rep. 4. Rem - roentgen equivalent mammal (man) to be defined later (see Section 2.3). From these definitions it is seen that the roentgen is a unit applicable only to X or gamma radiation, while the rep and rad are independent of the source type and energy. 19 2.2.4 CONSIDERATION OF DEPTH DOSE CURVES AND CORRELATION WITH BIOLOGICAL EFFECT The effect of ionizing radiation is primarily dependent upon the dose absorbed in tissue, not the dose measured in air. The basic problem is a determination or a calculation or the absorbed tissue. This is probably best approached through the use of a depth dose curve. A depth dose curve is a graph of the relative amount of ionization produced at various depths in the body or some other absorber. Depth dose curves have had extensive application in radiation therapy and in radiobiological research. It is this experience which makes possible the quantitative prediction of biological effect (Illegible) a depth dose curve.11 For the range of beta particle energies encountered in fission products maximum penetration into tissue is of the order of millimeters, while for X and gamma rays and neutrons the degree of penetration can vary from a few millimeters to those which traverse the entire body. As a consequence of the change in absorption coefficient with X-ray energy, penetration into the body varies with the energy. For example, at 50 KVP the dose delivered to tissues deeper than 2 cm is a very small compared to that at the skin surface. The skin surface dose to produce in LD56 (lethal dose for 50 percent of the irradiated population) might reasonably be expected to be greater for 50-KVP X-rays than for 250-KVP X-rays since the 50-KVP X-rays may be considered to produce a skin "burn," while with 250-KVP X-rays a relatively uniform dose throughout the body is produced. Fig. 2.2.:1 shows the variation in [FOR REFERENCE SEE (8bb07.gif] Figure 2.2:1 The LD14 for Dogs for Bilateral Radiation as a Function of Energy.12 LD14 for dogs for bilateral radiation as a function of energy.12 (In this instance half of the total dose was delivered to each side of the animal). This figure demonstrates that below 175 KVP the air exposure dose LD14 increases rapidly to 6000 r at 50 KVP. With the weaker X-rays, only the skin and subcutaneous tissues are irradiated. The dose to produce lethality increases with decreasing X-ray energy, since the deeper tissues are not irradiated. At 50 KVP the distribution of the dose in the tissue is comparable to that produced by external beta radiation in the range 2 to 3 Mev. This makes this energy (50 KVP) comparable to external beta radiation, and it would be anticipated that the dose to produce 50 percent lethality would be comparable to that required for external beta radiation. 20 The beta particles arising from fission products constitute a source of radiation only for the skin and, in sufficient quantity, produce a condition known as a "beta burn" which can be lethal. The two principal considerations in the evaluation of the hazard of beta radiation to the body are: 1. dose to skin, and 2. area of skin involved. For example, it has been determined that the LD3050 (lethal dose for 50 percent of the irradiated population in 30 days) for beta radiation to the entire body varies from 2200 rep (baby rat) to 17,000 rep (rabbit);13while the same dose range delivered to a small area of skin, e.g., 1 cm2 will not result in death, but will only local changes in the skin. The relatively low LD50 for beta radiation for the baby rat is probably due to the fact that for such small animals there is significant ionization beneath the skin, and while this is not uniform total body irradiation, a considerably greater percentage of the tissues are irradiated than in larger animals. The lethal dose for beta radiation of man is not known.14 Animal studies indicate that the total integrated dose to produce 50 percent lethality may be directly proportional to the body mass. Extrapolation to man yields an LD50 for beta radiation of approximately 40,000 rep which is not in keeping with other data and should not be used for any personnel hazard calculations. On the other hand, from another line of approach, the beta radiation LD50 dose is calculated to be approximately 5000 rep. The latter appears to be a more acceptable value and is comparable to the LD50 for dogs for 50-KVP X-rays, but it is unestablished and must be considered only as an estimate of questionable value arrived at by extrapolation from animal data. X-rays and neutrons of sufficient energy produce ionization throughout the body resulting, when applied in sufficient quantities, in a cute radiation illness. 2.2.5 DOSIMETRIC METHODS In general, and for most peacetime applications, film badges are the most common dosimeters in current use. Varying sensitivity to various types of ionizing radiations precludes their use for precise dose measurements in mixed radiation fields. In addition, at weapons tests, where mixed radiations make the physical measurement of dose difficult, biological dosimeters have been used. Generally, mice are placed at various distance from the point of detonation in suitable containers to protect against the effects of thermal radiation and blast. Then the effects of the ionizing radiation are measured by one or more biological endpoints. The biological endpoints used are: 1. mortality (30 days) 2. change in weight of the spleen and thymus, 3. depression of red cell formation, as measured by the incorporation of radioactive iron into red cells, 4. change in weight of the gastro-intestinal tract, and 5. survival time (in the supralethal dose range). The results are then compared wit those obtained with X-rays in similar animals under laboratory conditions, The results are expressed not in terms of the mixed bomb ionizing radiation, but that at a particular station, the total effect of the ionizing radiations received is equivalent to a particular dose of X-rays. 15,16 The results may be expressed in rem (see Section 2.3 for definition of rem). Chemical dosimeters have also been developed, but are less widely used than any other type of dosimeter. It is probable that because of their relative simplicity, chemical dosimeters will become more widely used.17 Scintillation glass dosimeters have also been developed for wide distribution in the armed services.18 Gamma radiation is generally best determined by some type of ionization chamber, although if suitably calibrated, photographic film may be used. 21 The measurement of neutrons is more complex. There are several methods; one is the measurement of flux and energy spectrum and calculation from this data of depth dose curve. The flux and energy spectrum of neutrons can be determined through the use of the activation detector methods (see Chapter 4). Calculation of a depth dose curve for neutrons is not a simple matter. For small animals (mice), a first collision tissue dose calculation is adequate. Assuming a tissue equivalent medium, the mean energy absorbed is 19 [FOR REFERENCE SEE (8bb08.gif)] 22 [FOR REFERENCE SEE (8bb09.gif)] 23 (1)These are estimated values. it is suggested that the reader review the source reference21 for a better appreciation of the methods used to calculate these numbers and their validity. it is probable that these numbers may be changed significantly in the future. (2)Based on the values given in the source reference23 for conversion from rep to neutrons of 1.3 and 450 rem, respectively. mately a 94-fold decrease in the calculated flux to produce 50 percent lethality. Fast neutrons are slowed down in tissue by elastic collisions of which 85 to 95 percent occur with hydrogen and result in (Illegible) protons. Because of this and because of the relatively high, compared to X-rays, linear energy transfer of protons, the biological effect produced is greater than would be predicted from a comparable absorbed dose (in erg- gm-1) of X-rays (see Section 2.3). For thermal neutrons, on the other hand, capture reactions predominate. These are the (n,p) reaction with N14), resulting in the emission of a 0.66 Mev proton, and the (n,y) reaction with hydrogen with subsequent emission of a 2.2 Mev gamma ray. It has been calculated that below 10 kev the latter reaction predominates. Recently it has been observed that for five test weapons, within the ground range of interest, the bomb neutron spectrum is relatively constant. For these five weapons, a caculation of dose due to the entire bomb neutron spectrum can be carried out from the measuremenet of the flux of a single energy region. It has not been determined whether this will hold for othre weapon types, although preliminary re-evaluation of previous weapons test biological data indicates that may be so. The dose due to beta radiation is best determined by a suitable thin walled ionization chamber. As will be discussed below, an important consideration is the source and receiver geometry.24 Initial radiation can, to some extent, be considered to be unidirectional gamma and neutron irradiation, the departure from unidirectional being a result of multiple scattering in air, while for fallout radiation, the situation is different. Beta radiation can be considered to arise from two sources: 1. beta particles emitted from fission products upon the surface of the ground, and 2. beta particles emited from fission products that contaminate the skin or clothing. In case one, the individual is in a field of beta radiation, and, aside from consideration of the protection due to clothing and the attenuation of the flux with height from the ground surface, may be considered to be in a field of uniform beta radiation. However, in case two, there is the beta radiation arising from "hot particles" contaminating the skin or clothing and producing a local area of intense irradiation which can result in a localized skin "burn." Directly measured depth dose curves furnish the most satisfactory approach to the prediction of biological effect. The ue of small ionization chambers in a phantom appears to be satisfactory.25,26 This type of measurement consists in the placing of small ionization chambers at various depths in a masonite phantom. After exposure, the readings of the ionization chambers are plotted as a function of the depth from the surface of the phantom. This is a directly determined depth dose curve for the particular source, source geometry and receiver. For neutron irradiation a first collision dose-calculation with an estimate of the attenuation due to depth is a good approximation. Typical field test beta and gamma depth dose curves are shown in Fig. 2.2:4. 2.2.6 SIGNIFICANCE OF AIR DOSE, SKIN DOSE, AND MID- LINE DOSE FROM X-RAY RADIATION 1. Collimated beam source geometry Considerable confusion has arisen from failure to stipulate how the dose was measured.24 This is because from the same narrow collimated X-rays flux in air, the three quantities, air dose, skin dose, and mid-line dose, can and do differ significantly. Air exposure is the dose measured in free air, that is, without backscatter. Skin dose is the dose measured with backscatter, that is, the ionization chamber is placed at the surface of the body. Mid-line dose is the dose either measured in a phantom with size and radiation absorption characteristics similar to the biological object under consideration or calculated from a knowledge of the energy spectrum and absorption constants. The skin dose is higher than the air exposure dose due to backscatter. The increase due to bacscatter varies with the energy and may amount to an increase of as much as 50 percent or more above the air dose.27 The 24 24 mid-line dose is a function of theenergy spectrum and body size and is usually less than the air dose and skin dose. The relationship between air dose and mid-line dose is dependent upon the source and receiver geometry and with low energy X-rayson the absorption coefficient. Since thereis considerable variation with energy in the absorption coefficient, the ratio mid-line dose/air dose can vary considerably. For example, from weak X- rays (below 50 KVP), the mid-line dose may be negligible as compared to the skin dose, in which case the ratio mid-line dose/air will be ver low while in the gamma ray region this ratio may approach one. [FOR REFERENCE SEE (8bb10.gif)] It can be readily seen that failure to stipulate the measurement conditions has led to considerable confusion. 2. Infitinte place source geometry For the case of radiation in a fallout field, i.e., infinite plane source geometry, the relationship between air dose, skin dose, and mid-line dose is different. Direct observation of the hard gamma radiation component of a fallout field in a phantom masonite man indicates that within the error of measurement thee is no appreciable change below 3 cm with depth, that, the gammaradiation depth dose curve is relatively flat, and equal to the free air exposure in roentgens,25, 26 as measured by a thick walled ionization chamber. Which of these three measurements, air, skin or mid- line dose, is the most satisfactory? In all probability, there is no single measurement which will be satisfactory in all cases. For weak X-rays (below 50 KVP) certainly the mid-line dose is unsatisfactory, while the skin dose or air dose may be 25 [FOR REFERENCE SEE (8bb11.gif)] For the fallout field where there is a combination of both beta radiation X-rays, and gamma rays, the use of the phantom masonite man probably defines the problem most satisfactorily since the results permit an evaluation of the (1) dose to skin and (2) the whole body dose. The results may be expressed as a ratio, beta-gamma dose ratio. Experimentally this measurement has been carried out in a limited number of conditions. Values of the beta-gamma dose ratio varying between 2.5 and 28 have been observed at field tests. 26,28 Dale (cited by Kendall28) has worked out on a theoretical basis the variation with time of this ratio up to 400 days. Initially, the ratio surface dose/mid-line dose is high, approximately 15 to 20,, decreasing to a minimum (approximately 2) at 10 to 20 days. (see Fig. 2.2:5). 2.3 CONCEPT OF RBE (RELATIVE BIOLOGICAL EFFECTIVENESS 29,30,31,32 Withe the availability of various types of ionizing radiation, it early became apparent that prediction of the effects of a given physical dose was inaccurate when the biological effects of heavy ionizing particles were compared to those X-rays. This was particularly true for external neutron irradiation. Initially, neutron dosages were measured with a Victoreen ionization chamber and in units of n. One n is the neutron flux to produce a reading equivalent to 1 r in a 100 cm2 Victoreen ionization chamber. Recently it has been confirmed that 1 n = 2 rep. 33 However, the biological effect of 1 rep of neutrons is greater than would be anticipated from 1 rep of gamma radiation. To rationalize this discrepancy, the concept of relative biological effectiveness (RBE) was introduced. When compared to X-rays, and for equivalent biological effect, the dose required of any ionizing radiation is the product of the RBE and the dose delivered in rep. It should not be inferred that RBE is used only in connection 26 with neutrons. The RBE has been determined for alpha particles, protons, beta particles and within the spectrum of X and gamma rays. RBE is not a simple concept, it depends upon: 1. type and energy spectrum of ionizing radiation, 2. biological endpoint meansured, and 3. dose and dose rate.32 It is particularly when different biological endpoints are considered that a large range of values for RBE are encountered. With the development of the concept of RBE, a new unit, the rem (roentgen equivalent mammal (man), came into use. The rem is the product of the absorbed dose (in rep) and the RBE for the particular type of ionizing radiation used and biological endpoint measured. An explanation for the fact that from a given physical dose the magnitude of the biological results varies is probably related to differences in linear energy transfer. Basically, it has been observed that,for the same physical dose, as the linear energy transfer (or the density of ionization per unit path length) increases, the magnitude of the biological effect goes through a maximum. A rigorous discussion of the mechanisms involved is not attempted here. Then, for the heavy charged particles (alpha particles and protons), the biological effect will generally be greater than for gamma rays. Since most of the energy transmitted to tissues from neutrons is through the ionization produced by recc.1 protons, it would be anticipated that for a given physical dose (erg-gm-1) neutrons would produce a greater biological effect than gamma rays. For military medical purposes, an important RBE, but not the only one desired, is the RBE for bomb neutrons for acute lethality, that is for the LD56. This RBE has not been determined directly. An acute response which has been thoroughly studied is the spleen-thymus weight loss. Field tests indicate that this RBE is approximately 1.7 in mice.34 Based on this value the spleen-thymus RBE for man has been estimated to be l.3.35 Until more definitive data become available, these values may be considered to apply for the LD56 RBE. For 60-in. cyclotron fast neutrons with a different spectrum, the LD56 RBE in dogs is approximately one.36 This indicates that the estimate of 1.3 may be high and that the RBE for acute lethality for man for bomb neutrons may be one or less. 2.4 ACUTE RADIATION SICKNESS 2.4.1 SYMPTOMATOLOGY For military medical purposes the acute radiation syndromeshould be considered from the following standpoints: 1. symptomatology and relationship of symptomatology to continued military effectiveness, 2. incidence and duration of symptoms as a function of dose, and 3. incidence of lethality as a function of dose. For man the most useful sources o information are (l1) the evaluation by the ABCC of the Hiroshima and Nagasaki experiences,1 (2) experience derived from clinical radiation therapy, and (3) the evaluation of the Marshallese exposed in 1954.2 Unfortunately, all these sources of information contain basic uncertainties precluding good quantiative conclusions. The Hiroshima and Nagasaki data are valuable for a description of disease, but cannot be closely correlated with dose because the dose is not known nor are estimates of the dose good. Clinical radiation therapy experience is complicated because most is partial body radiation, and in addition is complicated seriously by the underlying disease for which the patient is receiving therapy. Furthermore, many patients have imparted to them some degree of awareness of nausea and vomiting as possible complications of radiation therapy, making this symptom difficult to evaluate. The knowledge gained from the study and treatment ofthe Marshallese is also complicated by uncertainty as to the dose received and the effect of a changing dose rate. 27 [FOR REFERENCE SEE (8bb12.gif)] 28 The situation is such that for the acute radiation syndrome, the symptoms encountered can be described. Evaluation in relation to dose, more importantly quantitative evaluation as to incidence particularly in the range from no symptoms to 50 to 60 percent individuals symptomatically affected not available. There is no information available for the case of protracted radiation. The earliest symptoms are nausea and vomiting, generally occurring within 6 hours after a single acute whole body penetrating gamma ray exposure37, 38 (see Figs. 2.4:1 and 2.4:2). Hereafter in the discussion, it is implied that the air dose figure mentioned does not include scattered soft gamma radiation. The incidence of nausea and vomiting as a function of dose is not well known. Probably below 50 to 100 r (air gamma exposure) there are no symptoms, and above 250 to 300 r there is a 100 percent involvement, but between no involvement and 100 percent involvement, the data are meager. The sickness dose for 50 percent of the population exposed is estimated as 250 r.39 In a study of a small group (approximately 20 patients) treated with 200 r (skin dose) unilateral almost whole body radiation exposure, nausea and vomiting was noted in approximately 30 percent.40 Of the Marshallese exposed to 175 r (air dose) over a period of approximately 46 hours, with 75 percent of the dose delivered in 36 hours, nausea was noted in two-thirds and vomiting and diarrhea in one-tenth. At doses below 200 r there are no additional symptoms. When both nausea and vomiting exist, it should be presumed that such individuals are not capable of satisfactorily performing a military task. There is no information on the capability of man to perform work following an exposure to radiation sufficient to induce these symptoms, nor is there adequate information as to the duration of these symptoms. Other clinical states involving nausea, vomiting and diarrhea are generally associated with malaise and lassitude sufficient to prevent the carrying out of useful physical work. In addition, the unevaluated and unknown degree to which individuals are motivated may play an important role. For the present the assumption of inability to perform a task is probably the best that can be made. The time required for recovery from these symptoms to full working or even partial working capability is not known; possibly a few days are sufficient. At higher dose levels additional manifestations of radiation sickness appear, generally after a latent period of a few days. Because of the scarcity of data, it is difficult to describe the precise time course of the onset and extent of involvement, although various tables have been prepared in general having their origin in the Hiroshima and Nagasaki experiences. Following the initial nausea and vomiting, there is a latent period or asymptomatic period varying from approximately 1 to 3 weeks at 200 r to perhaps of the order of 1 week in the mid- lethal range (400-500 r). Following the asymptomatic period, at 2 to 4 weeks after exposure, malaise and loss of hair (epilation) occurs. Small hemorrhages (petechiae) in the skin and mouth appear. Ulcerations in the mouth with symptoms similar to that of a sore throat plus bleeding from the gums occurs.. Similar ulcerations in the bowel result in diarrhea. These complications are associated with alterations in the blood clotting mechanisms and a low white blood count. In the more heavily exposed (within the lethal range), anorexia, weight loss, and fever become the prominent symptoms. The red blood count decreases, and the symptoms become more pronounced, leading to death. Analysis of the Japanese experience indicates that percentage lethality can be correlated with lowest white blood count at particular times (see Fig. 2.4:3).41 In the survivors there is a variable period during which recovery takes place. In the range of moderate to marked symptomatology, recovery to the point of being able to perform usual tasks may be of the order of 3 to 6 months or even longer. At supralethal doses, 1500 r or greater, central nervous system alterations have been observed in monkeys. At very high doses (10,000 r or greater) delivered in less than an hour, death may supervene during the irradiation or within a few hours. In monkeys lethargy,convulsions, and other neurological manifestations occur.42 No data are available for man in this dose range. At present it is not possible to predict for a given air dose for either unilateral exposure or for infinite plane source geometry the percentage lethality. It is recognized that for unprotected exposure in a fallout field there is received a combined beta and gamma radiation. Consideration of the biological effect of this type of mixed radiation is not possible at present. Probably below 200 r air dose there will no lethality, or at most, a few percent, while above 700 r there will be a few survivors. Where in this range the LDx falls is open to question. By convention it has been set at 400 to 450 (with an unspecified source and source geometry), but this is not fixed. Furthermore, the shape of the 29 mortality vs dose curve is not known for man. In experimental animals, the shape of the mortality vs dose curve has been determined in a large number of experiments. A convenient method of expressing as a result is the probit transformation, since this transformation results in a straight line.43 However, it must be pointed out that these studies in, animals, except for a few such as those carried out in (Illegible) dogs, have been conducted with pure bred laboratory animals of the same age. To postulate similar results from a probit transformation in man is not reasonable. In addition, the effect of changing the source geometry is not known for man, although it would be expected that a change from unilateral to bilateral exposure or to infinite plane source geometry would produce a significant decrease in air dose LD56 as it does in the pig.44 The original analyses of the Hiroshima and Nagasaki data and speculation led to the adoption of 450 r as in LD56. The experience gained from the Marshallese suggests a lowering below 450 r. [FOR REFERENCE SEE (8bb13.gif)] Figure 2.4:3 Correlation Between Human Mortality and White Blood Count.41 It should not be thought that these indicate basic differences: the original figures derived from the Japanese data are subject to considerable error with regard to dose and are for unilateral single short duration radiation, while the Marshallese data result from a more protracted radiation, with an infinite plane source geometry plus an unknown quantity and unknown effect of beta radiation to the skin, and from the opinion that the dose received was on the borderline of lethality (50 to 200 r more would produce some mortality). Recent review of the Japanese data in the light of newer weapons test data suggests an increase of the LD56 to approximately 650 r (air dose). Weapon yield, height of burst, air density, and shielding uncertainties for the Hiroshima and Nagasaki bombs are such as to cause this estimate to be questioned seriously. In fact, the error assigned is approximately + 200 r.35 2.4.2 CURRENT THERAPEUTIC CONCEPTS45 As a basis for discussion, it must be presumed that at present there is no specific curative treatment for the acute radiation syndrome in man. For the experimental animal, there are a number of modalities used either before or after irradiation, leading to reduction in acute mortality. These are (1) radiation in the hypoxic state, (2) transfusion of bone marrow or spleen or homogenates of bone marrow or spleen, (3) various chemicals, e.g., cystein, (4) antibiotics, and (5) blood transfusions. Only the last two are, at present, to be considered applicable to man. In clinical radiation therapy amelioration or reduction in the incidence of nausea and vomiting (Illegible) been claimed for a number of diverse agents, e.g. (1) adrenal cortical hormones, (2) adreno(Illegible) hormone, (3) various vitamin preparations, and (4) beta-mercaptoethylamine. All of 30 these are of somewhat dubious value. Lacking a specific therapeutic agent or regime, treatment been symptomatic and supportive. Bed rest, fluids, antibiotics and transfusions have been used indicated. 2.4.3 PROBLEM OF PARTIAL BODY SHIELDING Clinical radiation therapy experience and extensive experimental animal research indicate that shielding part of the body is effective in reducing the magnitude of the actue radiation injury and is associated with an accelerated recovery, particularly of the bone marrow. It is probably this latter fact that accounts for the reduction in mortality. The value of such shielding in military situations is difficult to estimate. The degree to which this permits an individual to raise head and shoulders above ground level while in a foxhole or be exposed through an aperture in some other shielding and avoid the consequences of radiation injury is not known. An additional problem in shielding considerations is the fact that the more desirable types of shielding for neutrons are not the same as for gamma rays. It has been found that for shelters with about 3-l/2 ft. or more overlay of earth, gamma radiation is the most important factor even when the outside neutron flux, as measured with a sulfur threshold detector, was 2.4x1011 neutrons-cm-2or less46, a flux which is approximately four times the LD56 (see Table 2.2:1). 2.4.4 DESCRIPTION OF BETA "BURN" For localized beta radiation the best clinical description available is that of the results in the Marshallese. In these individuals the minimum time for development of skin lesions was 12 to 15 days. The first indication of the development of a skin lesion was an increase in skin pigment in localized areas. This was followed by scaly desquamation in the central portion of the lesion, leaving an area of pink depigmented skin. Gradually the pink area spreads out into the darker-pigmented area, with eventual complete healing. In other areas, presumably where the dose to the skin was greater, blisters developed which opened, leaving a raw, weeping area. This is comparable to a second degree thermal burn. New skin covered these areas in 7 to 10 days, and was followed by pigmentation. Unfortunate the dose to the skin could not be measured and cannot be calculated or estimated. Presumably lesions which developed blisters resulted from a dose to the skin, which if the total body skin were involved, would be lethal. However, if lethality is comparable o that observed in thermal burns, involvement of less than 100 percent of the skin would result in lethality. For example, an untreated 33 percent body surface area second degree thermal burn is in the lethal range. Probably similar results would be obtained with beta radiation. Table 2.4:1 shows the surface dose required to produce recognizable epidermal injury for pigs, sheep, rabbits, rats, and mice for several different isotopes. Except for S35 this dose is from 1500-5000 rep. For S35 it is 20,000-30,000 rep. Higher doses are needed when S35 is used, since only a small fraction of the beta particles will penetrate to the sensitive layer of the skin. For other weak beta emitters similar considerations will apply. Calculation of the dose at the sensitive layer of the skin under these conditions is difficult and not reliable. 2.5 LONG TERM (LATE) EFFECTS 2.5.1 SHORTENING OF LIFE SPAN The long term effects of irradiation can best be considered from the standpoint of reduction in life span.47 Animal experimental data clearly indicate that one of the consequences of total body X-radiation is shortening of life span. This reduction in life span is conspicucus in the case of those who develop leukemia, but other tumors may have their origin in radiation. However, in many instances, there is no specific pathological change attributable to X-radiation but a general pattern of premature aging. For this reason, shortening of life span, which represents the end result of all the injury produced, is probably the most sensitive and satisfactory criterion for determination of the long term hazard. There are several different mathematical approaches to the study of this problem. These are the adaptation of the Gompertz formulation to radiation, the Sacher, and the Blair theories.47 31 From the available animal data, the life span shortening for a single acute dose is on the average 3 percent per 100 r. The relationship between reduction in remaining life span and dose is (Illegible) For older animals, theory predicts that the percentage reduction of life span increases approximately threefold. Fig. 2.5:1 shows the predicted results for chronic radiation. What can be said about man? At present, there is only one good potential opportunity for observation and that is the experience at Hiroshima and Nagasaki. It is hoped that in the near future the ABCC will publish their findings in this field. It is possible, but not probable, that some data regarding shortening of life span from a sublethal dose of radiation may become available from the continuing TABLE 2.4:1 Surface Doses (rep) Required to Produce Recognizable Epidermal Injury2 Average Surface Investigator Animal Isotope Energy, Mev Dose rep Renshaw, et al Rats p22 0.5 1500-4000 Raper&Barns Rats p22 0.5 4000 Raper&Barns Mice p22 0.5 1500 Raper&Barns Rabbits p22 0.5 5000 Lushbaugh Sheep Sr30 0.3 2500-5000 Moritz & Henreques Pigs S36 0.05 20,000-30,000 Moritz & Henriques Pigs Co90 0.1 4000-5000 Moritz & Henreques Pigs Cs137 0.2 2000-3000 Moritz & Henriques Pigs Sr90 0.3 1500-2000 Moritz & Henriques Pigs Y05 0.5 1500-2000 Moritz & Henriques Pigs Y00 0.7 1500-2000 study of the Marshallese. However, it has recently been reported that radiologists have an aveage life span of 5.2 years (approximately 12 percent) less than other physicians not exposed to radiation.48 This reduction is compatible with the extrapolatin of the animal results to man and estimates of the exposure of radiologists to radiation. Brues and Sacher have developed two postulates for the extra-polation from species to species. These are: 1. For the single acute dose - the percentage reduction in life span is the same. 2. For chronic irradiation - to produce the same percentage reduction remaining in life span, the dose rate to an individual of species 2 should be EQUATION D2 = D1 n (2.5:1) where n = Life span species 1 -------------------- Life span species 2 D1 = chronic dose rate to species 1 D2 = chronic does rate to species 2 Also, for man, the dose rate to produce the same percentage decrease in life span should be approximately l/18 that observed in the rodent. 32 There are two features of Blair's theory and method of analysis that require further explanation. The Blair theory predicts that the acute does LD56 decreases with age and that this decrease is linear. This has been tested in only a very limited way, and indeed the acute LD56 dose does decrease with age in rats, but the data are not sufficient to determine the rate of decrease of LD56 with age. Because of certain pulmonary complications observed in older rats, extension of this observation to other speciesmay not be warranted. The Gompertz function type of analysis also predicts that the LD56 should decrease with age. Since aging and irradiation injury are additive, older animals will require less additional injury, whatever the source, to produce death if the injury produced is comparable to normal aging. For man, there is no information available on this aspect. FOR REFERENCE SEE (8bb14.gif) Figures 2.5:1 Predicted Shortening of Life Span from Chronic Radiation as a Function of Dose Rate for Rodents, with Extrapolation to Man. Extrapolated results for man are given based on the Blair Theory, the Gompertz Function, and the Sacher and Brues Postulate. The results of the Sacher and Brues Postulate are almost identical to those obtained and plotted from the Gompertz Function. 2.5.2 CATARACTS49 Cataracts ae changes in the lens of the eye which can impair vision. The dose to produce cataracts in man is not known with any degree of certainty. It is probably relatively low for X- rays, in the range of the LD56, and considerably lower (estimated at 50 r or approximately 100 rep) for neutrons. Cataracts are a particularly serious potential complications of neutron radiation. The RBE for cataract formation from neutrons is approximately 10 to 20. 2.5.3 FERTILITY48 Fertility is difficult to evaluate quantitatively. Depending upon the dose, there can be anything from a mild depression of sperm formation up to permanent sterilization. The dose for permanent sterilization is in the range of slightly larger thant the lethal dose. In males a single sublethal dose 33 results in a decrease in sperm count that can be considered as relativesterility. Recovery is a slow process, taking up to one year.4 For the female, doses of 125-150 r produce amenorrhea, and 170 r produces sterility of 12 to 36 months duration. Parenthetically, it is of interest to note that survivors of serious radiation accidents have produced children. 2.6 GENETIC EFFECTS48 That radiation results in genetic changes is unquestioned. While much work has been done on the genetic changes induced in lower organisms, particularly the fruit fly, there is little mammalian experimental data and that almost entirely in the mouse. The great uncertainty for man is the relationship between dose and number of mutations produced and their manner of expression. In general, it is assumed that radiation-induced mutations are deleterious. Genetic changes are a problem for the survival of mankind when the whole population or a large fraction of the population is heavily exposed; radiation of small groups is more a problem in the concern of the individual for the welfare of his progeny than for the survival of mankind but cannot be neglected. With the increasing development and use of various radioactive isotopes for nonmedical purposes and the use of reactors for propulsion and power systems, large numbers of people may be exposed to radiation. Thus, the small groups may become considerably larger in the near future. There are several observations regarding the genetic changes induced by radiation which may be summarized as follows: 1. Radiation induced mutations are deleterious-- if not all, most are. 2. There is no recovery from radiation-induced injury as it concerns genetic changes. 3. The amount of injury produced is directly proportional to the total dose. From experimental observations in fruit flies and mice, it is suggested that a dose of 30-80 of the entire population will double the mutation rate. The consequences of this are difficult to estimate. Particularly so since the manner of expression of many of these genetic changes is not completely understood; in fact, is but little understood. These changes could find expression in terms of various constitutional deficiencies, varying from those which result in a shortening life span to those involving the capacity to perform mental tasks. It is entirely possible that doubling the mutation rate could be a serious burden, economically and medically.39 It has been recommended that the average dose for the reproductive period be kept below 20 r above background. For some individuals, this may be exceeded but should be limited to a total dose of 100 r, of which no more than 50 r should be accumulated before age 30.48 2.7 EFFECT OF PROTRACTION AND FRACTIONATION47 Both animal experimental evidence and clinical radiation therapy experience clearly indicate that protraction of the delivery of the dose for days, weeks or months, or fractionation of the dose over similar periods of time results in a smaller biological effect, generally a lower incidence of lethality that does a single dose of the same magnitude delivered over a period of minutes. This does not include genetic effects. This implies recovery from the injury produced by radiation. The rate of recovery may be measured by administering a sublethal dose, generally 1/2 LD56 and then at various later time intervals determining the additional dose required to produce 50 percent lethality. Such experiments show that the amount of the second dose to produce 50 percent lethality increases with time. If the logarithm of the difference between the single dose LD56 and the second dose to produce 50 percent lethality is plotted as a function of time, a straight line is obtained for short times, implying that recovery is a first order process. (LD54 - Second Dose) = (First Dose) eşt. However, experimental studies show that recovery is not complete; the irreparable component amounts to about 10 to 20 percent of the injury produced. In the mouse the recovery rate is from 20 percent-day-1, in the rat 7 to 20 percent-day-1, in the dog about 4 to 5 percent- day-1, and in the monkey 14 percent-day-1. The recovery rate for 34 man is not known. Studies of the recovery rate for erythema (reddening of the skin) in man indicate much larger recovery rates; however, this is not the recovery rate desired for military medical purposes. Actually, the recovery measured in lethality experiments is not a single physiological process, it represents the net recovery of all the physiological processes necessary for the maintenance of life, and with each weighted according to its significance in the maintenance of life. The effective dose is defined in terms of the results of a single acute dose, and is best illustrated by an example. If the acute dose to produce 50 percent lethality within 30 days is 400 r, then the effective dose of any system of fractionation or protraction that produces 50 percent mortality in 30 day is 400 r, although the physical dose may be much greater than 400 r. From the Blair theory, for the particular case that the animals are young, that each dose is administered within a short period of time, and that death occurs in a few weeks EQUATION D = [ nf + (1 -f (w -n0/\t -1)] (2.7:1) eff [ ------------------] [ (e -0/\t -1) ] where f = fraction of injury, irreparable D = single dose n = number of single doses D 0 = rate of recovery, day -1 /\t = interval between single doses, days. For man it is recommended that 0 = 0.05 day-1 be used rather than the more commonly quoted 0 = 0.29 day-1, which is based on animal data. It is recommended that a value of f between 0.10 and 0.20 be used, although there is no evidence to support this recommendation. Other relationships proposed for calculation of the effective dose are those of Loutit, that in the French EAW, and that of Hoffman and Reinhard Loutit proposes that D = t k2 D(0) eff (2.7:2) where D(0) = constant dose rate, r-day -1 k 2 = constant = 0.64 t = time of irradiation, days. The French EAW proposed that D = D (0) [ 1 - 1 - k3)t] (2.7:3) eff ----- [ ] k 3 where K3 = constant = 0.36. 35 FOR REFERENCE SEE (8bb15.gif) 36 FOR REFERENCE SEE (8bb16.gif) Figure 2.7:2 The Ratio of the Physical Dose and the Effective Dose to H=l Hour Dose Rate for a Fallout Field Using the Blair Equations as Modified for a Changing Dose Rate. Time of entry into fallout field is H+l2 hr. Curve I shows the predicted effective dose for the conditions that f = 0.2 and _ 0.04 day-1. Curve II shows the predicted effective dose for the conditions that f = 0.2 and __ _ 0.24 day-1. 2.8 INTERNAL CONTAMINATION 2.81 SOURCE The radioactive isotopes produced in the process of fissioning of uranium and plutonium in an atomic explosion are widely distributed over the entire world by the winds. There is a slow settling of 37 these particles from the atmosphere, the rate of descent being governed by particle size and shape, and the location of the fallout being dependent upon the rate of descent and wind patterns. There are a number of variables involved, none of which is completely understood.50 The quantity of material in the atmosphere and the rate of movement from the stratosphere to the troposhere have been estimated, the latter having a half-time of approximately 10 years and the former has been estimated as varying upwards from a few percent to over 50 percent for a land burst. 2.8.2 ROUTE OF ENTRY INTO MAN There are three routes of entry: inhalation, ingestion, and open wounds. 1. Inhalation During the period when radioactive particles are falling out, inhalation is a route of entry into the body. After settling on the ground, these particles can become airborne again and thus available for inhalation. The distribution within the respiratory passage of radioactive particles inhaled is strongly dependent upon particle size.51 In general, a. Particles less than 0.1 micron are inhaled and then exhaled. b. Particles 0.1 to 3.0 microns reach the lungs and are deposited in the alveoli. c. From 3.0 to 10 microns particles reach and deposit themselves upon the walls of the trachea, bronchi, and bronchioles, and are worked up to the larynx and ultimately swallowed. d. Above 10 microns particles are filtered out in the nose. Rainfall occurring at the time of passage of the atomic cloud has been shown to result in an increase in the urinary Sr36 and I101 content of man, strongly implicating inhalation as a significant route of entry.52 2. Ingestion Radioactive materials settling upon the ground may be incorporated into or coat the surface of plants which are subsequently eaten by man or by livestock which later are eaten by man. Evaluation of the importance of this route of entry and the hazard involved is complex. Movement of fission products through the soil, uptake by plants, use of plants for animal fodder, and subsequent ingestion by man all are important and not well documented factors. The presence and amount of Sr36 in dairy products is well documented, although the details, particularly quantitative, of the movement of this Sr36 through the biosphere are lacking.53 The relative significance of these two routes of entry is still to be determined. Water does not appear to be a significant route of entry of fission products into man.53 However, this may not be applicable for local fallout. 3. Open wounds Open wounds do not appear to be a significant route of entry into man except in unusual circumstances. 2.8.3 METABOLIC FATE The metabolic fate of the fission products is dependent upon a number of factors. For each element it is different, and for each element and chemical species of a given element it may be different. For example, particles inhaled and reaching the alveoli, if they are soluble in body fluids, are absorbed, reaching the blood stream, and are subsequently distributed throughout the body in accordance ___ the manner in which the body treats that particular compound, while if insoluble, the particles may concentrated in the lymphatic system of the lung and remain within the lungs and lymph nodes draining the lungs for that individual's lifetime, constituting local areas of intense radiation. The considerations of particle size and chemistry must be applied to all of the fission products. 38 Within the gastro-intestinal tract, similar considerations apply. For materials that absorbed, the distribution in the body varies. For example, iodine, as iodide, is taken up by the thyroid gland and subsequently released to the blood stream as originally bound iodine. Probably most important is the fact that many of the fission products that reach the blood stream are taken up and retained for long periods of time by bone. Animal experimentation and the history of the radium dial workers indicate that this is a serious problem leading to serious complications, such as malignant bone tumors, although other less serious pathology can does occur. In fact, in animal experiments it can be shown that such bone deposition can lead to shortening of life span in the absence of specific pathological changes in the bone.54 2.8.4 BIOLOGICAL EFFECTS The quantities of most materials that can gain entry into the body are such that if they are not normal metabolites, the quantity present is not sufficient to be toxic merely by virtue of their chemistry; the injury produced is that of irradiation of the tissues. Depending upon the tissue involved, time factors, and the dose and dose rate, a wide range of pathological changes may occur. These will vary from no discernible anatomical change, but with subtle physiological changes for low doses, to the production of malignant tumors at higher doses. The latent period for these changes may, as in the case of radium dial workers, be up to 10 to 20 years or more. 2.8.5. THERAPEUTIC ASPECTS The therapeutic problem is largely concerned with a particular class of isotopes, namely, those associated with deposition in the bone and commonly called "bone seekers." Unfortunately, therapeutic measures now under investigation, principally removal by chemical agents, are not particularly promising.55 Therapy of the radiation injury produced by internally deposited radioactive isotopes is as unsatisfactory as for external radiation; there is no good means of treatment. Analysis of the biological properties of the fission products has indicated that the long-lived isotope of strontium, Sr36, is the greatest hazard, although it is not the only long- lived isotope that may be hazardous. Project Sunshine has reviewed the biological properties of strontium, the worldwide distribution, in particular in food and water, and the present levels of body burden of Sr36 53. The fact is that Sr36 is now present in human bone and is thought to be derived from food, principally dairy products. At present the quantity of Sr36 present in man is low compared to the estimated toxic levels. However, the change in bone Sr36 content with time is not known; a good evaluation of the tolerance level is lacking and recent work implicates an inhalation route of entry as at least partially responsible for the present body burden. While considerable attention has been directed towards Sr36, other fission products can and do gain entrance to the body.52, 56 It is the bone deposition of Sr36 that gives rise to concern; the majority of the other fission products are either products are either produced in small quantities compared to strontium, are relatively rapidly excreted or have short physical half-lives. In the latter class fall the iodine isotopes. Nevertheless, they will contribute to the injury produced and should not be ignored. 2.9 COMBINED INJURIES57, 58, 59 Experiments in swine, dogs, and in rats indicate that the lethality of combined nuclear radiation damage and thermal injury is greater than would be expected. These studies have been carried out by determining the lethality produced by thermal injury alone, by radiation injury alone, and by combined injuries. For example, thermal burns and radiation exposures that, by themselves, would result in no mortality give rise to significant mortality when combined. Also thermal burns or radiation injury at levels that result in low mortality when combined lead to considerably greater lethality than expected. Quantitative translation of this data to man is not possible at this time. Nevertheless, it should be anticipated that in man the same findings will occur; namely, that these effects are not simply additive. It is also probable that similar results will be obtained when radiation is combined with other forms of traumatic injury. A calculation of the magnitude of this effect is not possible. The variety of types traumatic injury is such that any calculation would be of little value. 39 2.10 MAXIMUM PERMISSIBLE LEVELS OF RADIATION As a fundamental premise it must be considered that all radiation is deleterious. However, radiation and certain radioisotopes have come to play important roles. For example, great strides have been made in medicine since the introduction of X-rays for diagnostic purposes; radioactive isotopes have proven to be a potent tool in medical research, and to have therapeutic value in certain diseases; the industrial uses of X- rays and radioactive isotopes are increasing rapidly; and finally, reactors are being used for the production of power. With all these beneficial uses, there comes the hazard involved. 2.10.1 EXTERNAL RADIATION Since the introduction of X-rays, as more data on the late effects of irradiation became available, there has been a progressive reduction in what has been considered to be a "safe" maximum level of exposure. Handbook No. 59 (National Burea of Standards) reviews the present "tolerance" levels. In general, it is recommended that for continuous total body X or gamma radiation, the maximum permissible exposure be 0.3r-week-1. However, it should be mentioned that this number is being reviewed, and that probably some reduction will be made.(1) 2.10.2 INTERNAL RADIATION The maximum allowable concentration of radioactive isotopes in the body is largely based upon the assumption that the dose rate to the critical organ be no greater than 0.3r-week- 1. Because of varying biological properties, the critical organs vary with different isotopes. In general, bone and bone marrow are the critical organs, although not for all isotopes. Handbook No. 52 (National Bureau of Standards) lists values of the maximum permissible amount for a number of isotopes. Calculation of these quantities is complex, and depends upon the distribution within the body, the radiations emitted, the biological turnover time, and for alpha emitters an estimate of RBE or comparison with radium. There are many uncertainties involved, and like the limits set for external radiation, they are being reviewed. 2.11 REFERENCES 1. A. W. Oughterson et al USAEC NP-3036 through 3041. 1951. (Unclassified) 2. E. P. Cronkite et al. WT-923. Oct. 1954 (Confidential) 3. L. H. Hemplemann et al. Ann. Inst. Med. 36. 279. 1952. (Unclassified) 4. R. J. Hasterlik and E. D. Marinelli. Proc. Int. Conference on the Peaceful Uses of Atomic Energy. Vol. XI. 1956. (Unclassified) 5. A. Hollaender. Radiation Biology. McGraw-Hill Book Co. 1954-55. (Unclassified) 6. Z. M. Bacq and P. Alexander. Fundamentals of Radiobiology. Academic Press. 1955 (Unclassified) 7. D. E. Lea. Action of Radiations of Living Cells. 2nd ed. Macmillan Co. 1954. (Unclassified) 8. R. W. Wilson. Radiation Research 4. 349. 1956 (Unclassified) 9. C. A. Sondhaus and V. P. Bond. WT-939. Dec. 1955. (Secret) (1) The results of this review were unofficially announced at the time of publication of this handbook. The revised value of the maximum permissible exposure for external and continuous total body X or gamma radiation is 5 r-yr-1. Somewhat higher dose rates are allowed for shorter time periods. 40 10. Permissible Dose From External Sources of Radiation. NBS Handbook 59. Sept. 1954. (Unclassified) 11. O. Glasser et al. Physical Foundation of Radiology. 2nd ed. P. B. Hoeber, Inc. 1952. (Unclassified) 12. E. L. Alpen and V. P. Bond. USNRDL. Private Communication. 13. J. R. Raper et al. Comparative Lethal Effects of External Beta Radiation; from R. E. Zirkle. Effects of External Beta Radiation. NNES. Div. IV Vol. 22E. McGraw-Hill Book Co. 1951. (Unclassified) 14. A. Broido and J.D. Teresi. USNRDL. Tech. Memo. No. 4. 1954 (Unclassified) 15. Scientific Director's Report of Atomic Weapons Tests at Eniwetok. Wt-18. 1951. (Secret) 16. Scientific Director's Report of Atomic Weapons Tests at Eniwetok. Wt-43. 1951. (Secret) 17. G. V. Taplen. Chemical and Colorimetric Indicators; from G.J. Hine and G.L. Brownell. Radiation Dosimetry. Academic Press. 1956. (Unclassified) 18. J.H. Schulman et al. Nucleonics 11. 10. 1953. (Unclassified) 19. E. Tochilin et al. Radiation Research 4. 158. 1956. (Unclassified) 20. H.H. Rossi. Neutron and Mixed Radiation; from G. H. Hine and G.L. Brownell. Radiation Dosimetry. Academic Press. 1956. (Unclassified) 21. L. Cave. FWE-16. Dec. 1951. (Confidential) 22. V.P. Bond. USNRDL. Private Communication. Aug. 1956. 23. J.S. Cheka. Nucleonics 12. 6. 1954. (Unclassified) 24. V.P. Bond et al. BNL and NMRI. The Effect of Exposure Geometry and Beam Spectrum on the Lethal Dose of Penetrating Ionizing Radiation for Large Mammals and Man. To be published. (Unclassified) 25. F. W. Chambers et al. WT-719. Dec. 1955 (Secret) 26. G.W. Imiri, Jr. and R. Sharp. ITR-1120. May 1955. (Confidential) 27. H.E. Johns. X-Rays and Telisotope Gamma Rays; from G. J. Hine and G. L. Brownell. Radiation Dosimetry. Academic Press. 1956. (Unclassified) 28. R.A. Kendall. FWE-74. May 1956. (Confidential) 29. J. W. Boag. NBS-2946. Dec. 1956. (Unclassified) 30. J. Furchner. LA-1849. March 1954. (Unclassified) 31. R.E. Zirkle. The Radiobiological Importance of Linear Energy Transfer; from A. Hollaender. Radiation Biology. Vol. 1. McGraw-Hill Book Co. 1954. (Unclassified) 32. J.B. Storer et al. Biological Effectiveness of Varying Radiations in Mammalian Systems. To be published in Radiation Research. 1956. (Unclassified) 33. H.H. Rossi. Radiology 61. 93. 1953. (Unclassified) 34. P.S. Harris et al. ITR-1167. May 1955. (Secret) 35. P.S. Harris. Proc. Tripartite Conference on Weapons Effects. Nov. 1955. (Secret) 36. V.P. Bond et al. Radiation Research 4. 139. 1956. (Unclassified) 37. W.M. Court-Brown. British Med. J. April 1953. (Unclassified) 38. R.A. Conrad. Radiation Research 5. 167. 1956. (Unclassified) 39. United Kingdom Medical Research Council. The Hazards to Man of Nuclear and Allied Radiations. Her Majesty's Stationery Office. June 1956. (Unclassified) 40. V.P. Collins et al. AFSWP-809. Jan. 1956. (Unclassified) 41 41. E.P. Cronkite et al. NMRL. Private Communication. 42. J.E. Pickering et al. School of Aviation Medicine. Report No. 55-77. March 1956 (Secret) 43. D. J. Finney. Probit Analysis. 2nd ed. Cambridge Univ. Press. 1952. (Unclassified) 44. J. L. Tullis et al. Amer. J. of Roentgenology 67. 620. 1952. (Unclassified) 45. E. P. Cronkite. Military Medicine 118. 328. 1956. (Unclassified) 46. V.P. Bond. WT-793. Sept. 1953. (Secret) 47. N.L. Berlin and F.L. Dimaggio. AFSWP.608. June 1956. (Unclassified) 48. National Research Council. The Biological Effects of Atomic Radiation, Summary Reports. 1956. (Unclassified) 49. W.T. Hamm, Jr. Arch. Opthal. 50. 618. 1953 (Unclassified) 50. R.D. Maxwell et al. AFSWP-978. Sept. 1956. (Secret) 51. J.H. Brown et al. Amer. J. Pub. Health 40. 450. 1950. (Unclassified) 52. J.B. Hartgering et al. AFSWP-89. Nov. 1955. (Secret) 53. W.F. Libby. WASH-406. July 1956. (Secret) 54. H.A. Blair. UR-274. Sept. 1953. (Unclassified) 55. H. Foreman. J. Amer. Pharm. Assoc. 42. 629. 1953. (Unclassified) 56. C.E. Miller and L.D. Martinelli. Amer. Assn. for the Advancement of Science. Vol. 124. No. 3212. June 1956. (Unclassified) 57. H. Baxter et al. Ann. Surg. 137. 450. 1953. ( (Unclassified) 58. J. W. Brooks et al. Ann. Surg. 136. 533. 1952. (Unclassified) 59. E.L. Alpen and G.E. Sheline. USNRDL-402. May 1953. (Unclassified) GENERAL REFERENCES a. A. Hollaender. Radiation Biology. McGraw-Hill Book Co. 1954-55. (Unclassified) b. Z.M. Bacq and P. Alexander. Fundamentals of Radiobiology. Academic Press. 1955 (Unclassified) c. A. Haddow. Biological Hazards of Atomic Energy. Oxford Univ. Press. 1952. (Unclassified) d. D.E. Lea. Action of Radiation on Living Cells. 2nd ed. MacMillan Co. 1954. (Unclassified) e. O. Glasser et al. Physical Foundation of Radiology. 2 d ed. P.B. Hoeber, Inc. 1952 (Unclassified) f. E.P. Cronkite and V.P. Bond. Effects of Radiation on Mammals. Annual Review of Physiology 18, 483. 1956. (Unclassified) g. G.J. Hine and G.L. Brownell. Radiation Dosimetry. Academic Press. 1956. (Unclassified) h. National Research Council. Pathologic Effects of Atomic Radiation. Publication 452. (Unclassified) i. United Kingdom Medical Research Council. The Hazards to Man of Nuclear and Allied Radiations. Her Majesty's Stationery Office. June 1956. (Unclassified) j. E. Tochilin et al. Cyclotron Neutron and Gamma Ray Dosimetry for Animal Irradiation Studies. Radiation Research 4. 158. 1956. (Unclassified) k. A. Oughterson and S. Warren. Medical Effects of the Atomic Bomb in Japan. NNES. Div. VIII. Vol. 8 McGraw-Hill Book Co. 1956. (Unclassified) 42