3.5 FACTORS INFLUENCING THE SEVERITY OF SKIN LESIONS 3.5.1 The Characteristics of the Fallout Material The fallout material was composed niuunty of caletum oxide front coral, with adherent ftssion products, The skin lesions observed were undoubledly (he result primarity of beta radia tion from fallout material deposited on the skin, with minimal or no contribution from chemical irritation, The garima dose to the skin was small compared to the beta dose, and (hus wats relatively unimportant in producing the lesions. 3.5.2 Energy of Beta Purticles From available data on the fallout material it has been calculated that 50 to 80 per cent of the beta rays during the exposure period were soft with an average energy of about 100 kev. Since 80 microns of tissue produces 50 per cent attenuation of such radiation,' the greater portion of energy was dissipated in the epithelium which is roughly 40 to 70 microns in (hick- ness. The remaining 20 to 50 per cent of the beta rays were of higher energy, with an average of approximately 600 kev. The latter would penetrate weil into the dermasince it takes 800 microns of tissue tu produce 50 per cent attenuation.’ In addition, a wide spectrum of gamma energies irradiated the skin. Approximately 10 per cent of the total gamma spectrum was be- low 80 kev which would be absorbed largely in the superficial layers of the skin. The remainder of the gamma spectrum is distributed between 100 and 1600 kev with a large proportion be- tween 600 and 800 kev. 3.5.3 Physical Dose to the Skin There is no practical] way to estimate the physical dose to the areas of skin where lesions were found. The entire surface of the body of the Rongelap group received approximately 175 r from gamma irradiation derived from fission products distributed on the ground, trees, and buildings. To this 175 r would have to be added the beta component. In view of the high beta to gammaratio in fission products, one might expect the total beta surfacedose to the skin to be large. The maximal skin doses from the plane field of radiation are estimated in chapter 1. To these doses must be added the contribution of the material deposited on the skin. The latter can not be calculated, or estimated biologically with any degree of accuracy. A rough approximation of dose received at the hair follicles can be madeas follows: The hair follicles must have received a dose comparabie to the known minimal epilating dose of about 400 r for 200 kvp X-rays. Since regrowth of hair occurred, the upper limit of dose at the depth of the hair follicle must not have exceeded the permanent epilating dose of around 700 r of 200 kvp X-ray. The individuals who remained indoors or under the trees showed some protection ag compared to those who were in the open during the period of the fallout. Those who went swimming or bathed were also protected to varying degrees. Small children who went wading developed fewer foot lesions. Clothing, even a single layer of cotton material, offered almost complete protection, as was demonstrated by the fact that lesions developed almost entirely on the exposed parts of the body. Since the lesions predominate in areas where perspiration is abundant such as folds of the neck. axillae, and antecubital fossae, it seems likely that the abundant perspiration produced by a hot, humid climate tended to cause the material to concentrate and adhere tu these areas. In addition, the coconut oil hair dressing used by the Marshallese acted as an effective collecting agent for the radioactive material. This was proved since the hair was the most highly contaminated part of the body. The concentration of radioactive material on the hair may have been responsible for the large number of scalp lesions, epilation and the large number and severity of neck lesions in women.