Neutron Transmission Measurement and Simulation of Ta-181 for Neutron Resonance Thermometry

Tantalum-181 is a typically used nucleus for neutron resonance thermometry. To develop an imaging technique of neutron resonance thermometry, the neutron transmission spectrum for a tantalum foil which was set up in a constant-temperature furnace was measured by the time-of-flight (TOF) method. The thickness of the tantalum sample was 30 or 300 μm. Several temperature conditions were set from 20 to 500°C. A gas electron multiplier (GEM) neutron detector was used. The measurements were performed on the 10th beam line (BL10) of the Material and Life science experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC). To cut-off neutrons below thermal neutron energy, a cadmium filter was inserted on the neutron beam line. The measured neutron transmission spectrum in the eV energy region was compared to the calculated one with the PHITS code. In the calculation, the time distribution of neutron emission from a source was defined as the pulse function of BL10. The distance from the source to a tally was 14.5 m. The evaluated nuclear data of ENDF/B-VIII.0 or JENDL-4.0 were utilized for each calculation with respect to the neutron-induced nuclear reactions of Ta-181. The differences in the calculated neutron transmission spectra due to the evaluated nuclear data are discussed based on the measured spectra.