10 1.3 EFFECTS OF IONIZING Superficial Doses of Radiation From Beta and Soft Gamma Radiation Trrere Can Br no doubt that the doses of radintion to the surface and the first few millimeters of the body were substantially higher than the nud-line dose of gammaradiation asa result of physical considerations of gamma energy and depth dose. In addition, the clinical observations of the skin lesions (see Chap. IIT) force- tuliy demonstrated that the dose to the skin varied considerably between individuals and over the surface of any given individual. As will become evident in the following discussions of surface dose, it is obvious that any numbers presented are at best only estimates and repre- sent 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 gcamma,andthe higher energybeta radiation from the lavge planar source in which the individuals were of necessity existing. Flawever, as alluded to above and emphasized in Chapter TIT, the largest component of skin Irradiation resulted froin the spotty local de- ‘posits 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 mav be roughly estimated as follows: The beta dose rate in nir 3 feet above the surface of an infinite plane contaminated with mixed 24 hourold fission products is estimated to be about three times the total air gamma dose. The mid-line gamma dose is approximately 60 percent of the air dose remuining after excludIng that portion of the dose below 60 KY. This port.on in turn is estimated to be 40 per- cent of the ganima dose measured im air hythe Mistrument. Thus the dose at the surface of 2 phantom exposed to mixed fission product radiation from an external plane source night 500218 RADIATION be expected to be 3/(0.6) (0.6) or about 8 times the the hus ous the mid-line dose, if both are taken at 3 feet off ground. Such a depth dose measurement in fact been made experimentallyat a previtest, using a phantom man exposed to both initial and residual radiation (5). The depth doses for each situation are shown in Figure 1.5, with all data as percent meter dose. With the diverging tion from the point of explosion, Was seen to be 63 percent of the 3 of the 3 centiinitial radiathe exit dose cm. dose, but with the diffuse residual field of fission products providing a semi-infinite planar source, a surface dose some 8 times greater than the 3cm. and deeper dose from the harder gamma components was observed. This is seen to be of the same order of magnitude as that estimated above. At heights above and below the 3 foot level this surface dose would become lower and higher respectively, but since it is due to soft radiation of short range, it probably would not exceed 50 times the 3 foot air gamma dose or 80 times the midline dose, even in contact with the ground. An estimate of skin dose due to ground contamination for the Rongelap case would result, for exninple, in a figure of about 2,000 rep at the level of the dorsum of the foot, 600 rep at the lip level and 300 rep at the head 77 continuous ez- posure with no shielding occurred. Unknown variation in dose undoubtedly resulted from shielding and movement. It thus seems probable that the external beta dose from loca} direct skin contamination far outweighed that from the ground in importance, since the latter was not high enough to produce the observedlesions. Clothing probably reduced the beta dose from the ground by 10 to 20 percent. 1.4 Summary Rapiation Doses from gamma rays originating externally were calculated for the 267 individuals who were accidentally exposed to fallouc following the nuclert detonation at the Pacitie Proving Ground in the Spring of 1954. The dose estimations were made using information resulting from radiological safety surveys on