Determination of 234U isotope in uranium-bearing materials by high-resolution gamma-spectrometry

Abstract

The paper presents research of the existing methods of non-destructive quantitative determination of 234U isotope content in uranium bearingmaterials. Also alternative method is proposed, which is based on the approach of detector calibration on “intrinsic” efficiency. The method is based on finding the ratio of the 234U and 235U isotopes activities using their most intense gamma lines in the energy range of 120...210 keV and as a consequence does not require an estimate of the absolute efficiency of registration of the gamma detector. Certified reference standard samples of uranium-bearing materials CRM 969 and CRM 146 were used as research samples (interval of investigated enrichments on 235U 0,3…93 %), measurements were performed by means of broad-energy detector based on high-purity germanium BeGe 3830 (Canberra, USA) with area 36 cm2 and thickness 3 cm. It was shown that using of the up-to-date software products for isotopic analyses of uranium (MGAU, FRAM) it is difficult to perform of reliable estimation of 234U isotope content in depleted and natural samples due to significant measurement error (from 35 % to 100 %). In case of analyses of enriched uranium the software code MGAU systematically underestimates the content of 234U on 20…30 %. Use of alternative approach for calibration of detector on “intrinsic” efficiency for analyses of 234U results in decrease of measurement error up to 7,5 % in the whole range of enrichment on 235U (0,3…93 %) and investigated concentrations of 234U (20…9800 μg/g). The proposed method does not demand standard samples for equipment calibration and not depend on physical (chemical) form of investigated material and geometry of measurements.