Studies on radioiodine concentrations in air, precipitation, grass, cows' and goats' milk after the Chinese nuclear bomb test on September 26th, 1976

Following the nuclear-bomb test, actual values for I131 in air, precipitation, on vegetation as well as in cows- and goats milk were measured over a period of six weeks. The applied analytical methods with an achieved detection sensitivity in the range of some per cent of the measured concentrations are described in detail. The following I131 concentrations were found in the different media: Air: max 191 fCi/m3, average value: 42,5 fCi/m3; precipitation: max 6,3 pCi/1, average v.: 3,0 pCi/1; grass: max 164 pCi/m2, average v.: 105 pCi/m2; cow milk: max 18,5 pCi/1, average v.: 9,0 pCi/1; goats milk: max 26,9 pCi/1, average v.: 14,9 pCi/1. With the additional assumption on a rentention factor on grass for washout (20%) and an effective half-life of I131 on grass (3,9 d and 5 d) from these data the deposition velocity of I131 on pasture and the transfer coeficients (3.9 d eff. hl) air - grass and grass - milk as well as air - milk have been calculated. The concentration of I131 in goats milk showed a higher value as in cows milk by a factor of 2 to 3. For the period of these six weeks, the radiation exposure to the thyroid was calculated: for an infant: 4 mrem, for an adult: 0,3 mrem, whereby the main contribution is due to the ingestion of fresh milk. (orig./HP)