-3Materials and Methods The procedures employed in the present investigation. (1) Gamma spectra were made on dried or ashed samples to determine if gamma peaks other than those from expected fission products were present. (2) Selected samples were wet or dry ashed, dissolved in acid solution, and separated by a cation exchange technique on Dowex 50. (3) The various fractions from the resin columns were ex- amined by means of 7 spectrometry, A mass absorption, and ra- dioactive decay determinations. (4) Those fractions containing several isotopes (e.g., rare earths or heavy metals) were separated further by subse- quent cationic exchange or by chloride complexing techniques on anionic exchange resin. (S) The fractions from the second ion exchange treatment (4) were examined by the methods set forth in (3). (€) Chemical separations by precipitation techniques were done on selected fractions from (3) or (4) to further establish the identity of the isotope in question and to rule out the presence of isotopes of other elements with similar 7 characteristics. Control experiments with radioactive spikes were conducted to determine the reliability of the results obtained with the techniques used. The radiochemical technique for the separation of the nuclides in the samples by means of ion-exchange columns was adapted from cay yyye a 4