af O mwa. HALLE sew — (>) Cratering events: wive cratering tests conducted as part or the U. S. Atomic Energy Commission Plowshare Prosram for the peaceful application of nucleer explosives took place between 1953 and 1968. Although some radio- activity was devected in the atmosphere following each test, only the Palanquin event of 14 April 1965 resulted in elevated ist levels in the PMN milk (Period 2). is shown in figure 8. ‘The meteorological trajectory for this event Only Helena, Montana, reported detectable levels or zit in milk. | Radioiodine must pass from the atmosphere through crops, cows, dairy transport, storage and pasteurization before its radioactivity is measured in milk in the PHS laboratories. These delays involve only but may, in rare cases, take up to five days for the PMN. 7 a few days . : Further, only one sample per week is routinely collected from cach milkshed. : Thus, the delays and periodic sampling can result in time differences between nuclear cloud arrival and first milk contamination in Table 1 of up to & week anda halt. in period 2. The longest time difference, eleven days, was found : As discussed in the next paragraph, the explanation involves -. another factor, the weather. During the colder haif of the year in northern milksheds, herds are fed . . scored nay so that the cows have’ little opportunity to obtain radioiodine even if fallout were present (10). <A specific instance in which this was observed took place at Helena, Montana, : oh. which according to Weather Bureau : records, was snow-covered on April 16, 1965, the date of fallout deposition from the Palanquin cravering event, until a thaw a few days later. This probable delay in exposure of the cattle to the deposited radioiodine may help to account for the eleven day delay between deposition and Pirst : milk contamination. Tnere were four other cratering tests at the NTS between 1963 and 1968, none of which elevated the PMN milk radioiodine. These tests were : intentionally conducted during the colder half of the year with wind blowing | towards the north to take advantage of the fact that dairy cattle were on dry Seed; the absence of zit in milk does not preclude its deposition. (c) Underground tests: Tre contribution of radioicdine Prom underground nuclear tests at the Nevada Test Site (NTS) in PMN milk since September 1961 has been questioned