formation has approximately eight times the number of disintegrations v oe per minuteas iodine-131. They are produced by decay of tellurtum135". ar and tellurive-i3i, ‘Tespectively, in the approximately equal amounts of(rtneteleh one gram each per kiloton of fission yield. . tion. Iodine is found to become quickly available for human deposi- Its metabolic pathway in the human will lead to approximately 20% of the amount received being deposited in the thyroid gland. remaining 80% is excreted in a matter of several days. The The action of this beta emitter upon thyroid tissue is in the nature of temporary to permanent celluler damage and is an effect which is sensitive to dose rate in addition to total dose, and hence to the high decay rate of | dodine-131 and to the still higher rate of iodine-133 and other members of the iodine decay series. ; The rapidity with which iodine appeared in the urine following a test detonation, coupled with the similar amounts present in animals of different eating habits, suggested that inhalation rather than ingestion was the probable route of entry. Further substantiation was later established when masked personnel showed urine free of iodine while ummasked personnel showed urinary radio-iodine prior to eating U/ Thus, it appears that leastinitially inhalationiodinedirectly from the ambientairis the chief factor to consider. ~ As previously mentioned,excretion of the non-thyroid deposited fraction takes several days. Thus, personnel briefly exposed to lodine-131 would be expected to have a corresponding excretion curve. That this is not the case has been demonstrated recently. Many curves reveal an 8-day half value time, which is the half-life of iodine-131. One conclusion appears to be that iodine-131, once having fallen out, remains for many days in the immediate environment. That it would remain hovering over an area for weeks in a stable atmosphere is deemed unlikely. Either of two alternatives is more acceptable: 47/ Trum, B.F., Lt. Col., V.C., Oak Ridge Institute of Nuclear Studies, Personal communication. - 123