MEASUREMENTS OF AIRBORNE RADIONUCLIDES 217 The particulate material collected on membrane filters was chemically fractionated to determine the oxidation states of the asso- ciated “I. This involved addition of I”, I0,, and 10; carriers, leaching with cold water at pH 12, and chemical fractionation. The experimental results are summarized in Table 3; they show that about twoTable 3—CHEMICAL FORM OF !3!1] COLLECTED ON MEMBRANE FILTERS 131] leached from : “ Fractionation of leached 131 ‘I Date filters, % I, + 1°, % 1035, % 107, % Oct. 24, 1962 44 ~ 57 ~ 38 <5 Oct. 25, 1962 42 ~ 66 ~ 29 <5 thirds of the '%'] was in the form of I, or 1°, about one-third was pres- ent as 103, and little or none was present as I0,. At the Hanford Atomic Products Operation at Richland, Wash., small amounts of “Z are released continuously from the exhaust Stacks of the chemical-separations plants. This source of 13ty permits a continuation of studies of the physical and chemical behavior of atmospheric radioiodine. Although the 1317 yeleased from the separations-plant stacks is essentially gaseous, it has been found to be a complex mixture consisting of about one-half I, and HI, with the re- mainder consisting of several different organic iodide compounds.“ The chemical species of these organic iodides are presently being investigated. During a period of above normal 1317 emission from a separationsplant stack, air samples were collected at distances up to 25 miles to determine if rapid changes occurred as the material moved from its point of release. Sampling was performed from an airplane with the use of a vacuum pumpthat pulled air through a membrane filter of 5u pore size followed by a charcoal trap. Samples were collected at 200 to 500 ft by multiple penetrations of the stack plume at 1, 3, 5, 10, and 25 miles from the source. The fraction of ‘*'I in the gaseousstate is shown in Table 4. It is interesting that there was very little change in physical form over the distances measured, The total sample activities collected at 25 miles on Sept. 4, 1963, and 10 miles on Sept. 3, 1963, were low, and the apparent change in physical form may not be significant. The major change occurred within the first mile. SHORT-LIVED COSMIC-RAY-PRODUCED RADIONUCLIDES In a consideration of methods of studying atmospheric phenomena including cloud physics, washout, and rainout, it becomes apparent that