-6concentrated nitric acid. dried and diluted with water, then plated on one and one-half-inch stainless steel planchets. One-ml aliquots of the oxalate and citrate fractions were plated directly on the planchets and dried. The samples were counted for beta activity in a windowless methane gas-flow chamber. The oxalate plates were counted after drying, after flaming, and with a filter of 4.7 mg per cm@ aluminum in order to identify the radiation from Fe>> (16). The remainder of each fraction was dried and analysed with a gamma spectrometer equipped with a two-inch, well-type, sodium iodide crystal. The isotopes were identified by their gamma energies, maximum beta energies, half lives, and elution patterns. Beta and gamma counts were converted to disintegrations per minute (d/m) by the use of correction factors previously described (16). Disintegration rates for the individual radioisotopes were corrected to the date of collection. The fractions eluted from the second column (Dowex 1) were counted in solution for gamma activity and the fractions containing the peaks of radioactivity from Mn54, Co>7»60, op zn©5 were combined into three groups (Mn, Co, Zn), dried, and the disintegration rate of each group determined. Radiochemical separations in duplicate for gr90-y90 POE ARCHIVES made on each of the five samples and their filtrates according to the method outlined in the chemical procedures of the Health and Safety Laboratory (New York Operations Office) (11). et