Gamma spectrometric measurement of uranium isotopic composition and mass in sintered UO₂ pellets using the efficiency transfer method

Gamma spectrometric measurements to determine the isotopic composition and total uranium mass in UO₂ pellets (D = 7.5 mm; H = 3.5 mm, ρ = 10 g/cm³) were carried out. The required efficiency curve was obtained by applying the efficiency transfer method from a calibration standard (D = 65 mm; H = 20 mm) of a slightly acidified water solution. The average isotopic composition of ten UO₂ pellets was consistent with values of natural uranium given by IUPAC. The average relative bias for the ²³⁵U/²³⁸U amount ratio was -0.73% using the 1001 keV gamma line for ²³⁸U and 0.50% using the 63 keV gamma line (186 keV was always used for ²³⁵U). For the total uranium mass, the mean deviation as compared to mass determinations using a balance was 5.5% using the 1001 keV gamma line for ²³⁸U and 4.3% using the 63 keV gamma line.