— a 26563 ASH OF BIKINI AND ITS EFFECTS ON HUMAN BODY wat We by ceg US ATOGRIC bawatGy H. Kakehi MISSION - Introduction (omitted). Physical Properties of the Ashes: DBMFiles. - . B67 | | MRxA-PacificProvingGromnds- | According to the report of the 'eTenerideotFakaryr Maru, theash began to come down about 3 hours after the hydrogen bomb explosion. It continued to fall about 5 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 mm in diameter. Microscopic examination shows that they are amorphous and porous. stance.(Fig. 1) It might be the fragment of the coralline sub- Its radioactivity was surprisingly strong and even a few grains of ash showed ten-thousands counts per minute on March 16. The thickness of the absorber to reduce the intensity of radiation to a half (or the inverse of the absorption coefficient) is h7mg/cm@Ait0.2mmAl for the @- ray and 5,5miPb for theY¥ - ray (March 17). of thef-ray from the ash is shown in Fig. 2. The radioautograph The half~life was about 8 das at first, but it is in these days (about April 5) of the order of 18 das. Extrapolating the damping curve of radioactivity observed after March 17, the intensity of the @- ray on the next day of the explosion (March 2) is estimated to be about 50 times larger than that of March 17. result may be obtained for the Y- ray too. . Similar The chemical analysis of the ash has been performed at Kimra lab- oratory (Department of Chemistry, Tokyo University). The result pub- lished so far is shown in Table 1. There are several definitions of the half-life according to the purpose as is shown below. The half-life given in Table 1 is the physical half-life defined as the period of time during which the amount of a particular radioactive isotope is reduced to half its initial value. The biological half-life is the time during which the amount of elements deposited in some part of the body decreases to half as a result of assimilation, dissimilation, alteration, excretion, etc. The effective half-life is the time during which the radioactivity of the deposited radioisotope is reduced to half as a result of combination of the two effects mentioned above. This is the quantity which mst be taken account of in discussing the injury produced by the radioactive " glements deposited in the human body. “printed in Journal of Japan Physicians Society, Vol. 31, No. 9 (May 1, 195) (Translated by Toichiro Kinoshita) STATUS VERIFIED C/A/CL_ BY Yece tygn pate 9/8/ _NON-CCRP _ 3