-ll- Results The identification of the isotopes in the present samples was confirmed for both the chemical and ion-exchange resin column methods by the use of radioactive spikes. In the latter technique the spikes were used to determine accurately the elution pattern under the conditions of the present work. Regard- less of the number of Lsotopes used in an experiment, the elution pattern remained essentially the same; the isotopes were always eluted in the same fraction as shown in Table 2, Table 2. Summary of the tsotopes eluted from Dowex 50 cationexchange resin Praction Isotopes present Anions Rut? _ppyt 0.5% Oxalic Zr??-Nb?? gr? -Nb?? Acid 0.15 N NH,Cl+ 0.1 N HCl Fe? @r99-Nb9? cst3? 5% Ammonium Citrate 137 cel44 _pp144 gn d-e f-J an 65 690 mnd4 pH 4.1 a-e Min>4 pH 4.6 Sr f-h sr99 90

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