Study of neutron emission properties after muon capture on palladium isotopes

The nuclear muon capture reaction is an analogue process of electron capture decay. Contrary to the electron capture, the daughter nucleus of the muon capture can be excited up to around 50 MeV owing to the muon rest mass of 106 MeV/c², and thus decays by emitting neutrons and γ rays. The properties of excited states created by the muon capture, such as excitation energies and neutron emission probabilities, have not been well understood. In this study, we measured the neutron energy distribution and multiplicity after muon capture reactions on palladium isotopes. A liquid scintillator array named SEAMINE was newly designed and constructed. SEAMINE consists of 21 liquid scintillators and seven BaF₂ scintillators in order to measure the neutron time-of-flight. A digital data acquisition system enabled the n – γ discrimination by the pulse shape of the liquid scintillators. The experiments on five isotopically enriched palladium targets (A = 104, 105, 106, 108 and 110) were conducted on February 2017 and January 2018 at the MuSIC beamline, RCNP, Osaka University. We will report on the experiments and show preliminary results.