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

ABSTRACT

Thermal neutron capture cross-section for¹⁹¹Ir, ${\mathit{\sigma }}_{\mathrm{Ir}}$(E_th), 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 ${\mathit{\sigma }}_{\mathrm{Ir}}$(E_th) 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 ${\mathit{\sigma }}_{\mathrm{Ir}}$(E_th) was derived from the capture yield using the pulse height weighting technique. As a result, this study obtained the ${\mathit{\sigma }}_{\mathrm{Ir}}$(E_th) 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 ${\mathit{\sigma }}_{\mathrm{Ir}}$(E_th) measurement using the neutron TOF method.

KEYWORDS:

• ¹⁹²Ir radionuclide
• high-dose-rate brachytherapy
• ¹⁹¹Ir$\left(\mathrm{n},\mathit{\gamma }\right)$¹⁹²Ir reaction
• neutron time-of-flight method
• pulse height weighting technique
• ANNRI
• MLF
• J-PARC
• thermal neutron capture cross section

Acknowledgments

The authors would like to thank the staff for their efforts in operating the accelerators and the neutron production target of the J-PARC/MLF. We are grateful to Mr Masayuki Tsuneyama, Nihon Advanced Technology, Co. Ltd., for his useful support in preparing the experimental samples. This research was conducted with the supercomputer HPE SGI8600 in the Japan Atomic Energy Agency for the numerical simulations.

Disclosure statement

No potential conflict of interest was reported by the author(s).