Thermal-Neutron capture cross-section measurements of Neptunium-237 with graphite thermal column in KUR

Abstract

ABSTRACT In terms of nuclear transmutation studies of minor actinides in nuclear wastes, the present work selected 237Np among them and aimed to measure the thermal-neutron capture cross-section of 237Np using a well-thermalized neutron field by a neutron activation method because there have been discrepancies among reported cross-section data. A 237Np standard solution was used for irradiation samples. The thermal-neutron flux at an irradiation position was measured with flux monitors: 45Sc, 59Co, 98Mo, 181Ta, and 197Au. The 237Np sample was irradiated together with the flux monitors for 30 minutes in the graphite thermal column equipped in the Kyoto University Research Reactor. The similar irradiation was repeated once more to confirm the reproducibility of the results. After irradiation, the 237Np samples were quantified using 312-keV gamma-ray emitted from 233Pa in radiation equilibrium with 237Np. The reaction rates of 237Np were obtained from the peak net counts of gamma-rays emitted from generated 238Np, and then the thermal-neutron capture cross-section of 237Np was found to be 173.8 ± 4.7 barn by averaging the results obtained by the two irradiations. The present result was in agreement with the reported data given by a time-of-flight method within a limit of uncertainty.