om vegetation is unkmown. it roins or snows. Precipitacion ccevenging is effective whenever It is believed tnat tnis removal process was particularly effective Tor the Palenouin cloud which was snowed out while moving over Tdaho and Momtana. Finally, the ry miixsheds cover only small areas of the United States. Could a cloud of radioiodine have passed through the country missing every PMN milxshed? nishly unlikely. Such a passage is possible but is Eowever, the first PMY milkshed that the debris will se! ass through outside the State of Nevada lies from 300 to 600 miles from ct he NUS, depending on direction o> cloud travel. Tae answer to the 52 fo esvion neading this paragraph therefore is that the concentration of radioiodine in most cases is probesiy too low to cause an elevated milk concentration by the time the radioiodine cloud reaches the PMN. summery and Conclusion PMN milk in the United States from April 1963 to December 1968. wee ee oe Six atmospheric tests conducted in Western China provided the source of gene ae . Ss a . 131 radioiodine for the majority of cases of elevated concentrations of I 3 in Atmospheric tests in the South Pacific probably acccunted for only one elevated value, in the Canal Zone. During periods without zist fallout from atmospheric tests, 132 contained ~~ undexzround and 5 crate ering tests were reported in the U. S. almost all at the NES. In addition, underground tests were reported to have vented. During the same period no PMN miik samples contained zist greater than 30 pei/1 except Por the period following the Palanquin cratering event and the unexplained episode in the southeastern U. S. The evidence since 1963 scronzly suggests that nuclear cratering events conducted in the cold season with wind biowing toward the north did not contribute significantly to elevated radioiodine in the PMY milk. The limited data from state networks conTirm the presence or absence or qtst measuring radioiodine in milk in PMY milk with minor exceptions. However, a local Public Health Service network surrounding the NTIS showed radiotodine in|milk following 13 of 25 rocket tests, four of five cratering our SYpto— tests, and Sour of “trtcen unscheduled ventings from underground tests. Only after one cratering test, Palencuin, did the PMN also contain zisi in milx. it is suggested that avmosphneric mixing and removal processes diluve the radioactive clouds. Teese as well as non-meteorological factors account for the absence of PMY contexnination when the local PES network reveaiec elevated radioiodine. —.