Measurement of the production branching ratios following nuclear muon capture for palladium isotopes using the in-beam activation method

Background: The energy distribution of excited states populated by the nuclear muon capture reaction can facilitate an understanding of the reaction mechanism; however, experimental data are fairly sparse. Purpose: We developed a new methodology, called the in-beam activation method, to measure the production probability of residual nuclei by muon capture. For the first application of the new method, we have measured muon-induced activation of five isotopically-enriched palladium targets. Methods: The experiment was conducted at the RIKEN-RAL muon facility of the Rutherford Appleton Facility in the UK. The pulsed muon beam impinged on the palladium targets and gamma rays from the beta and isomeric decays from the reaction residues were measured using high-purity germanium detectors in both the in-beam and offline setups. Results: The production branching ratios of the residual nuclei of muon capture for five palladium isotopes with mass numbers A = 104, 105, 106, 108, and 110 were obtained. The results were compared with a model calculation using the particle and heavy ion transport system (PHITS) code. The model calculation well reproduces the experimental data. Conclusion: For the first time, this study provides experimental data on the distribution of production branching ratios without any theoretical estimation or assumptions in the interpretation of the data analysis