The applicability of MGA method for depleted and natural uranium isotopic analysis in the presence of actinides (Th-232, Np-237, Pa-233 and Am-241)

摘要

The multi-group analysis (MGA) method for the determination of uranium isotopic abundances in depleted uranium (DU) and natural uranium (NU) samples is applied in this study. A set of non-destructive gamma-ray measurements of DU and NU samples were performed using a planar Ge detector. The relative abundances of U-235 and U-238 isotopes were compared with the declared values of the standards. The relative abundance for U-235 obtained by MGA for a "clean" DU or NU sample with a content of uranium > 1 wt% is determined with an accuracy of about +/- 5%. However, when several actinides such as Th-232, Np-237, Pa-233 and Am-241 are present along with uranium isotopes simulating "dirty" DU or NU, it has been observed that MGA method gives erroneous results. The U-235 abundance results for the samples were 6-25 times higher than the declared values in the presence of above-mentioned actinides, since MGA is utilized the X-ray and gamma-ray peaks in the 80-130keV energy region, covering XK alpha and XK beta regions. After the least-squares fitting of the spectra, it is found that the increases in the intensities of the X-ray and gamma-ray peaks of uranium are remarkably larger in the complex 80-130 keV region. On the other hand, it is observed that the interferences of the actinide peaks are relatively less dominant in the higher gamma-ray region of 130-300 keV. The results imply the need for dirty DU and NU samples that the NIGA method should utilize the higher energy gamma-rays (up to 1001 keV of Pa-234m) combined with lower energies of the spectra, which may be collected in a two detector mode (a planar Ge and a high efficient coaxial Ge). (c) 2007 Elsevier Ltd. All rights reserved.