An Improved Procedure for U²³⁵ Isotopic Ratio Analysis in Impure Materials

An improved neutron activation procedure for determining the U²³⁵ content in impure uranium samples is presented. With 95% confidence, a relative precision of ±1% is obtained at the level of 0.7 wt % U²³⁵. An ethyl acetate extraction is used to purify the uranium chemically. Most of the uranium decay products are removed by extraction with 2-thenoyltrifluoroacetone (TTA) in xylene. The purified uranium, which is subsequently activated as U₃O₈, has a consistent gamma background level. Utilization of a i.d. well scintillation crystal has permitted the use of large diameter aluminum planchettes holding 2 gm aliquots of U₃O₈. This system has minimized the problem of varying irradiation geometries caused by differences in U₃O₈ bulk density. Data from a sample recycle program are presented to illustrate the relative precision of ±1%. Comparisons between neutron activation and mass spectrometric results agree within ±1%.