-2somewhat larger dhe to the short-lived iodine isotopes (1) and the yb from Pacific and Russian tests. yi3t is a Fission product formed in nuclear explosions. It and other products are carried in the air downwind from the point of detanation. When this fallout settles on pastures, contaminated. feed. the exposed forage becomes yi3t appears in the milk of cattle ingesting yi31 in their If wan drinks this radioactive milk, irreadiates his thyroid gland. ting thyroid exposure from I 131 yl concentrates in and These processes suggest 5 ways for estimaThey are listed in decreasing order of valicity in Table 1 and will be discussed separately. Table lL moowr WAYS OF ESTIMATING THYROID EXPOSURE it in thyrcid gland I in milk Gamma activity in pastures Beta activity in air Fission yield and fallout trajectory mHyRoD The most direct way to evaluate I 131 measure its I 131 dose to the thyroid is to contest by »~rey counting. We measured yb! in 24 people during the Utah nm. fartdent of 1962, but unfortunately failed to include sitea se 43) Qrildren 0-2 years old are regarded as most a 'geaiation damage because of “@) the emall size of ach aq ioe presumed greater sensitivity to irradiation and appear. A drawback to thyroid count ing is that specialised equipment is required and only a Limited mmber of people cen be evaluated. p. 2) my wrx Fresh milk is by far the major source of fallout yi for our