Neutron emission following nuclear muon capture on palladium isotopes

TL;DR

This study measured neutron energy spectra following nuclear muon capture on palladium isotopes, providing new systematic data in the A~100 mass region and insights into the reaction dynamics.

Contribution

First systematic measurement of neutron spectra from muon capture on palladium isotopes in the A~100 region, comparing experimental data with theoretical models.

Findings

Neutron spectra from 1 to 20 MeV were obtained for five isotopes.

Spectral shapes below 4 MeV align with evaporation model predictions.

Indication of small-angle neutron correlation was observed.

Abstract

The energy spectra of the neutrons emitted following nuclear muon capture on palladium isotopes ($A=104$, 105, 106, 108, and 110) were measured using isotopically enriched target. \item[Method] The experiment was performed at the MuSIC-M1 beamline at the Research Center for Nuclear Physics (RCNP), Osaka University. The neutrons and $\gamma$ rays were detected with twenty-one liquid scintillators and BaF$_2$ detectors. The time-of-flight method was used to determine the neutron energy. \item[Results] Neutron energy spectra from 1\,MeV up to 20\,MeV were measured for five palladium isotopes, providing the first systematic data in the $A\sim100$ region. The spectral shapes were compared with the previous measurement for heavy nuclei and theoretical calculations. The neutron-neutron opening angle distribution was also measured and an indication of small angle correlation was found. \item[Conclusions] The spectral shape below 4\,MeV was well explained consistently with the previous measurement by the evaporation model introducing a mass number scaling. The neutron energy spectrum around 10\,MeV plays a key role in understanding the dynamics of the nuclear muon capture reaction because it is the result of the transition from the direct and pre-equilibrium neutron emission onto the evaporation process.