Measurement of the thermal neutron capture-cross section of ¹⁹¹ Ir at ANNRI MLF J-PARC

Thermal neutron capture cross-section for191Ir, σIr(Eth), is a prominent parameter in producing192Ir radionuclide used in high-dose-rate brachytherapy. However, considerable discrepancies exist in past measurements using the activation method and a derived cross-section data calculation from positive resonance parameters of 191Ir, which were measured using the neutron time-of-flight (TOF) method. Therefore, for the first time, we aimed to measure the σIr(Eth) accurately using the neutron TOF method. Experiments were performed using a pulsed neutron beam and a NaI(Tl) detector at the Accurate Neutron–Nucleus Reaction Measurement Instrument of the Materials and Life Science Experimental Facility in the J-PARC. The σIr(Eth) was derived from the capture yield using the pulse height weighting technique. As a result, this study obtained the σIr(Eth) as 949 ± 80 b. The result agrees with some activation data and the evaluated nuclear data libraries, JENDL-5 and ENDF/B-VIII.0, within its uncertainty of 8.4%. This study provides a data reference for the σIr(Eth) measurement using the neutron TOF method.