26e 
concentrated 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 , CodT, 60, or 
zn©5 were combined into three groups (Mn, Co, Zn), dried, and 
the disintegration rate of each group determined. 
Radiochemical separations in duplicate for 8r90-y99 were 
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). 
