10 1.3 EFFECTS OF IONIZING RADIATION Superficial Doses of Radiation From Beta and Soft Gamma Radiation Tuere Can Be no doubt that the doses of radiation to the surface and thefirst few millimeters of the body were substantially higher than the mid-line dose of gammaradiation as a result of physical considerations of gamma energy and depth dose. In addition, the clinical observations of the skin lesions (see Chap. III) forcefully demonstrated that the dose to the skin varied considerably between individuals and over the surface of any given individual. As will becomeevident in the following discussions of surface dose, it is obvious that any numbers presented are at best only estimates and represent an approximation of some minimal value. In areas where lesions were severe the doses must have been significantly higher than in nondamaged areas. To arrive at some physical estimate of the skin dose, an attempt must be made to add up the contributions of the high energy gamma, the very soft gamma,and the higher energy beta - radiation from the large planar source in which the individuals were of necessity existing. However, as alluded to above and emphasized in Chapter ITI, the largest component of skin irradiation resulted from the spotty local deposits of fallout material on exposed surfaces of the body. The dose from deposited material is impossible to estimate; however, that from the large planar source may be roughly estimated as follows: The beta dose rate in air 3 feet above the surface of an infinite plane contaminated with mixed 24 hourold fission products is estimated to be about three times thetotal air gammadose. The mid-line gammadose is approximately 60 percent of the air dose remaining after excluding that portion of the dose below 80 KV. . This portion in turn is estimated to be 40 percent of the gamma dose measured in air by the instrument. Thus the dose at the surface of a phantom exposed to mixed fission product radiation from an external plane source might be expected to be 3/(0.6) (0.6) or about the mid-line dose, if both are taken at 3 the ground. Such a depth dose meast has in fact been made experimentally at. ous test, using a phantom man exposed the initial and residual radiation (5) depth doses for each situation are sh Figure 1.5, with all data as percentof the meter dose. With the diverging initia tion from the point of explosion, thee: was seen to be 63 percent of the 3 cm. d with the diffuse residual field of fission p providing a semi-infinite planar. source face dose some 8 times greater than the 3. deeper dose from the harder gamma com was observed. This is seen to be of t! order of magnitude as that estimated At heights above and below the 3 footle surface dose would become lower and respectively, but since it is due to soft re of short range, it probably would notex times the 3 foot air gamma dose or 80ti midline dose, even in contact with the An estimate of skin dose due to ground ¢ nation for the Rongelap case would res example, in a figure of about 2,000 rey level of the dorsum ofthe foot, 600 rep at level and 300 rep at the head if contin, posure with no shielding occurred. variation in dose undoubtedly resulte shielding and movement. It thus seem able that the external beta dose from locs skin contamination far outweighed thi the ground in importance, since thelat not high enoughto produce the observed Clothing probably reduced the beta do: the ground by 10 to 20 percent. 1.4 Summary Rapration Doses from gamma. raysorig externally were calculated for the 267 in als who were accidentally exposed to following the nuclear detonation at the Proving Ground in the Spring of 195 dose estimations were made using infot resulting from radiological safety sur