of exposure. Later, the appearance of fever, infections, and bleeding from the gumsor other parts of the body will also serve as indications of severity of exposure (see Figure 1). of growth and development in some exposed male children; a slight increase in miscarriages and stillbirths in exposed women duringthe first five years after exposure; and an increase in pigmented moles in areas of beta burns. During the past three Importance of bone marrow dose. It is clear that years, six cases of nodules of the thyroid glands fallout, and emphasize the importance of radio- the degree of destruction of blood-forming cells is the critical factor in the "survival possible” dose range of radiation. The dose to the bone marrow, where blood cells are formed, thus becomes the all-important consideration. Blood-forming marrow is encased in bone that varies considerably in depth iodines in early fallout situations. in various parts of the body (from a few cm to 11 cm among the exposed people have occurred. Five of these were not malignant and appearedin children, and one was a cancerous nodule in an adult woman. These are undoubtedly related to exposure of the thyroid gland to radiociodines absorbed from the or more, with an average depth of 5 cm).(4) There- These studies have helped place the hazards of fallout in proper prospective. It is clear that penetrating gamma radiation is by far the most fore, the critical dose could be considered roughly at the 5-cm body depth. Attenuation of the gamma radiation through the shielding structures will result in considerable degradation and scattering of the incident radiation so that a good portion of the measured radiation may be too soft to reach much serious hazard. The Role of Protective Structures in Fallout Situations of the critical organ system (the bone marrow). Furthermore, bone covering the marrow may further Let us examine the importance of protective struc- attenuate radiation. It is not believed likely that the photoelectric effect produced in bone will seriously alter the dose to the bone marrow.(9,6) If one can insure a dose to the bone marrow of not over 200 rads in 24 hours in an uncomplicated case, survival tures as related to each of the hazards of fallout. Gamma hazard. Attenuation of the gamma radiation is the most important role of protective structures in regard to fallout. In order to understand the should be probable. It would be ideal to have radia- importance of this fact, let us examine the possible tion-detection instruments in protective structures, effects of such radiation on man when delivered to the whole body in a relatively short period of time, Several categories of effects can be based on the prognosis related to radiation dose. 3) With very large doses, greater than 600 rads, survival is improbable. With doses greater than 600-700 rads, which would measurethe total absorbed dose at 5 cm body depth. The dose rate is another important factor to be considered. Protraction of radiation is known to reduce the effect. Thus, further radiation at more protracted dose rates over the ensuing days after and in the thousands of rads, brain damage and gas- fallout could be tolerated, perhaps 100 rads the second day and lesser amounts thereafter. This dose schedule would allow for more free movement of personnel after the first day or so trointestinal damage would be so severe that death would occur within the first 4-5 days and no treatment would be capable of life-saving. With doses between 200-600 rads survival is possible. With this L717 - OS degree of exposure, blood-cell destruction is the predominant effect, and may result in infections, bleeding, and possibly death. Figure 1 shows blood changes and clinical signs in cases where survival qT T F | ,PERIOD OF NAUSEA, VOMITING, DIARRHOEA T T “é, is possible (200-600 rads). With doses below 200 5 100 rads survival is probable, since the blood-cell de- | o uo struction per se will be insufficient to result in death. a = 75 One must remember that other stresses, such as physical trauma, blast injury, thermal burns, sick- x Oo z ness, starvation, and thirst will undoubtedly lower - oO - the dose at which survival is possible. z wi 50 « tl Since reliance on blood counts as an index of the degree of blood cell destruction will not be likely FEVER INFECTIONS BLEEDING POSSIBLE DEATH PLATELETS 4 \ 25 \ under the conditions considered, it should be noted that there are certain signs that will roughly indicate the severity of radiation exposure. The severity of the nausea, vomiting, and diarrhea during the early oO ° L 5 I 10 L ‘= at ‘ “7 ~ — =_-—_— i nana | _t 20 25 30 DAYS AFTER EXPOSURE 35 / on a” t 40 Figure 1. Schematic graph showing major blood changes and clinical signs for radiation doses where survival is possible (200-600 rads). period after exposure and the duration of these symptoms are important indications of the extent 26 5007804 TT 48