Investigation into the Occurrence of Radioiodine in Air, Precipitation, Grass, Cow- and Goat-Milk Following the Chinese Atomic Bomb Test of September 26, 1976

摘要

Following the Chinese nuclear bomb test (September 26, 1976), actual values for iodine-131 in air and precipitation, on vegetation as well as in cows- and goats-milk were measured over a period of six weeks. The measurement techniques with an achieved detection sensitivity in the range of a few percent of the measured concentrations are described in detail. The following I-131 concentrations were found in the different media: Air : max 191 fCi/m exp 3 , average value : 42.5 fCi/m exp 3 ; Precipitation : max 6.3 pCi/l, average value : 3.0 pCi/l; Grass : max 164 pCi/m exp 2 , average value : 105 pCi/m exp 2 ; Cow's Milk : max 18.5 pCi/l, average value : 9.0 pCi/l; and Goat's Milk : max 26.9 pCi/l, average value : 14.9 pCi/l. With the additional assumption on a retention factor for washout of grass (20 percent) and an effective half-life of I-131 on grass (3.9 d and 5 d), the attempt was made to calculate from these data the deposition velocity of radioiodine on pasture and the transfer coefficients from air to grass and from grass to milk as well as from air to milk. On the basis of an effective half-life of 3.9 d, the following values for these parameters have been calculated: Deposition velocity: 0.15 to 1.4 cm/s, average value: 0.74 cm/s; Air-Grass: 1.6 x 10 exp 3 - 8.3 x 10 exp 3 Ci/m exp 2 : Ci/m exp 3 , average value: 4.8 x 10 exp 3 Ci/m exp 2 : Ci/m exp 3 ; Grass-Milk: 0.64 x 10 exp -1 to 1.36 x 10 exp -1 Ci/l : Ci/m exp 3 , average value: 0.84 x 10 exp -1 Ci/l : Ci/m exp 3 average value: 0.84 x 10 exp -1 Ci/l : Ci/m exp 3 ; Air-Milk Transfer Factor (wet deposition): 53 to 804 Ci/l : Ci/m exp 3 , average value: 544 Ci/l : Ci/m exp 3 . The concentration of I-131 in goats milk showed a higher value than 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. (ERA citation 03:045318)