Thermal-neutron capture cross-section measurement of Tantalum-181 using graphite thermal column at KUR

Using an activation method with a well-thermalized neutron field, it is principally possible to drive a thermal-neutron capture cross-section without considering an epithermal neutron component. We demonstrated neutron capture cross-section measurements using the graphite thermal column (TC-Pn) of the Kyoto University Research Reactor. First, in order to confirm that the graphite thermal column was a well-thermalized neutron field, neutron irradiation was performed with neutron flux monitors: 197 Au, 59 Co, 45 Sc, 63 Cu, and 98 Mo. The TC-Pn was confirmed to be extremely thermalized on the basis of Westcott's convention, because the thermal-neutron flux component took a constant value regardless of the sensitivity of each flux monitor to epithermal neutrons. Next, as a demonstration, the thermal-neutron capture cross-section of 181 Ta(n,γ) 182m+g Ta reaction was measured using the graphite thermal column, and then derived to be 20.5 ± 0.4 barn, which supported the evaluated value of 20.4 ± 0.3 barn. The 181 Ta nuclide could be useful as a flux monitor that complements the sensitivity between 197 Au and 98 Mo monitors.