Measurement of Neutron Capture Cross Section of ²³⁷Np by Linac Time-of-Flight Method and with Linac-driven Lead Slowing-down Spectrometer

Abstract

The neutron capture cross section of ²³⁷Np has been measured relative to the ¹⁰b(n, α) standard cross section by the neutron time-of-flight (TOF) method in the energy range of 0.005 eV to 10keV using a 46MeV electron linear accelerator (linac) at the Research Reactor Institute, Kyoto University (KURRi). In order to experimentally prove the result obtained, the supplementary cross section measurement has been made from 0.15 eV to 1 keV using the Kyoto University Lead slowing-down Spectrometer (KULS) coupling to the linac. The relative measurement by the TOF method has been normalized to the reference value (181 b) at 0.0253 eV and the KULS measurement to that by the TOF method.

The existing experimental data and the evaluated capture cross sections in ENDF/b-Vi and JENDL-3.2 have been compared with the current measurements by the linac TOF and the KULS experiments. The energy dependency of the KULS data is close to that of the TOF data which are energy-broadened by the resolution function of the KULS.

It has been found that the data measured by Weston and Todd and evaluated in ENDF/b-Vi and JENDL-3.2 are in general agreement with each current measurement, although those data are systematically lower by about 15% above about 0.2 eV. However, the data by Hoffman et al. are low obviously in the relevant energy region.

KEYWORDS:

• neptunium 237
• neutron capture cross section
• measurement
• 0.005 eV to 10 keV energy range
• time-of-flight method
• neutron reactions
• ¹⁰B(n, α) cross section
• lead slowing-down spectrometer
• C₆D₆ liquid scintillators
• argon-gas counter