w ered ASH OF BIKINI AND ITS EFFeCTS ON HUMAN BODY wee by H. Kakehi Introduction (omitted). Physical Properties of the Ashes: According to the report of the fishermen of Fukuryu Maru, the ash began to come down about 3 hours after the hydrogen bomb explosion. It continued to fall about S hours at varying rates and covered the boat like the light snow that footprints were left on the deck as they walked around. The ash consists of light and white grains of various size less than 1 rain diemeter, Wicroscopic exemination shows that they are amorphous and porous. It might be the fragment of the coraelline substence. (Fig. 1) Its radioactivity was surprisingly strong and even a few grains of esh showed ten-thousands counts per minute on March 16. The thickness of the absorber to reduce the intensity of rediation to a half (or the inverse of the absorption coefficient) is h7mg/cm@Ais0.em7Al for the @- ray and 5.5roPb for the¥ - ray (Merch 17). The radioeutograph of the#ray from the esh is shown in Fig, 2. The half-life was etout 8 das at first, but it is in these days (about April 5) of the order of 18 days. Extracolating the dexping curve of redioactivity observed efter Merch 17, the intensity of the @- ray on the next day of the explosion (“arch 2) is estimated to be ebout 50 tines larger than thet of March.17, wy .:Sisibsr result ray be obtained for the ¥- ray too. woes :Depa: wetpatamte OFC N plisiarenhs sr’ f, o ess labd; hes been performed at+#atmre ; ; of the nem T The chemical enalysis esh oratory (Department cf Chemistry, Tokvo University). The result published so fer is shcwn in Table 1. Tnere are several definitions cf the half-life according to the purpose 2s is shown below, Tne half-life given in Tatle 1 is the pnvsicel neif-—life aefined <s the period of time curine 2. yrich the amount of @ perticuiar redioaciive isotope is recuce =ve wee Met s initial value. Tne bpiolcgic2i nel*~life is the time Guring wrich the t body decreas3s tc neif amount cf elements deposited in some part of th és a result of assimilation, dissimilaticn, alteration, excretion, etc. The effecvive helf-life is the time during which the recicactivit; of the depcsited radioisotope is reduced to half 4s a result of 1 of the iwo effects mentioned ebove. This is the quantity which o.sv be Cc taken account of in discuSsing the injury produced cy the relioeciive d