arXiv subjects

Shoichiro Kawase

Publications and source records attributed to Shoichiro Kawase.

6 recordsLinked to original sources

arXiv2026

Energy spectra of light charged particles emitted following muon nuclear capture on $^\mathrm{nat}$Si

Background: Charged-particle emission following muon nuclear capture (muNC) probes the de-excitation dynamics of highly excited nuclei, particularly the interplay between preequilibrium and evaporation processes. While proton emission has been relatively well studied, data on composite charged particles remain limited, especially for low-energy alpha particles. Purpose: This work aims to measure energy spectra for individual charged-particle species following muNC on silicon and constrain theoretical descriptions of preequilibrium, evaporation, and composite-particle emission. Method: An experiment was performed at the RIKEN-RAL Muon Facility. Charged particles were identified using Delta E-E telescopes and digital pulse-shape analysis with nTD-Si detectors. Initial energy spectra were reconstructed by unfolding and compared with the microscopic and evaporation model (MEM) and PHITS calculations incorporating the surface coalescence model and meson-exchange-current extension. Results: Energy spectra of protons, deuterons, tritons, and alpha particles were extracted over a broad energy range, including the first measurement of the low-energy alpha-particle spectrum. MEM more closely reproduces the proton, deuteron, and triton spectral shapes and describes the low-energy alpha-particle spectrum well. PHITS reproduces the overall slope of the alpha-particle spectrum but exhibits particle-dependent discrepancies in absolute yields, including an overestimation of the evaporation component for all four species. Conclusion: The results demonstrate particle-species-dependent differences in charged-particle emission following muNC. These spectra constrain descriptions of preequilibrium and evaporation processes and highlight the need for improved modeling of composite-particle emission.

nucl-ex↗

arXiv2026

Muon Nuclear Data Development Project

Negative muon-induced nuclear reactions play a critical role in a wide range of scientific and technological applications; however, comprehensive nuclear data for these processes remain unavailable. To address this gap, we have launched the Muon Nuclear Data (muND) Development Project in Japan, aiming to construct a dedicated data library for muon capture reactions. The library consists of four sub-libraries: muonic X-ray energies and intensities (XR), lifetimes of muonic atoms and nuclear capture rates (LT), energy spectra of emitted particles (ES), and production branching ratios of residual nuclei (BR). This project integrates experimental measurements, theoretical modeling, and machine learning techniques to compile and evaluate the data. We report the current status and recent progress of each sub-library.

nucl-ex↗

arXiv2026

Chirality in $(\vec{p},2p)$ reactions induced by proton helicity

It is shown that longitudinally polarized protons can be used to induce chirality in the final states of the $(\vec{p},pN)$ reaction at intermediate energies, when there exist three final-state particles with non-coplanar momentum vectors. The analyzing power $A_z$ is proposed as a measure of this effect. Theoretical descriptions to obtain $A_z$ based on an intuitive picture as well as a distorted wave impulse approximation are presented, showing that the helicity of incident protons is coupled to the chirality of the orbital motion of a single-particle wave function, resulting in the chirality of the final states and a large $A_z$ value.

nucl-th↗

arXiv2026

Establishing the $^{40}$Ca$(p,p α)$ reaction at 392 MeV under quasi-free scattering conditions

The $(p,p α)$ reaction offers a direct means to probe preformed $α$-cluster structures in nuclei under quasi-free scattering conditions. Previous studies around 100 MeV provided valuable insights into $α$ clustering, but quantitative comparison with microscopic cluster wave functions remained limited due to strong distortion effects. At higher energies, the reaction mechanism becomes simpler and the distorted-wave impulse approximation (DWIA) provides a more reliable framework for quantitative analysis. In the present work, the $^{40}$Ca$(p,pα)$ reaction was measured at an incident energy of 392 MeV using the high-resolution Grand Raiden and LAS spectrometers at RCNP. Despite the small cross section in this energy region, the achieved resolution allowed clear separation of the ground and excited states of the residual $^{36}$Ar nucleus, and corresponding momentum distributions were extracted. DWIA calculations using a Woods-Saxon $α+ ^{36}$Ar bound-state wave function yielded an experimental spectroscopic factor of $ S_{\mathrm{FAC}}^{\mathrm{WS}} = 0.51 \pm 0.05 $, consistent with the previous result at 101.5 MeV $(0.52 \pm 0.23 )$. This agreement demonstrates that the reaction mechanism is well described across a wide energy range. The present study establishes the feasibility of high-precision $(p,pα)$ measurements at several hundred MeV and highlights their potential as a quantitative probe of $α$ clustering in medium-mass nuclei, forming the basis for systematic studies in both stable and unstable systems.

nucl-ex↗

arXiv2024

Muon Nuclear Data

We plan to develop a new nuclear database for muon-induced nuclear reactions (muon nuclear data). The database will consist of (1) energies and intensities of the muonic X rays, (2) lifetimes of the muonic atom, (3) production branching ratio of the residual nuclei by muon capture, (4) emission probabilities of the particles after muon capture, and (5) energy spectra of the emitted particles after muon capture. In this paper, we review the present status and current investigations for the muon nuclear data.

nucl-ex↗

arXiv2023

Effect of large-angle incidence on particle identification performance for light-charged ($Z \le 2$) particles by pulse shape analysis with a pad-type nTD silicon detector

In recent years, particle discrimination methods based on digital waveform analysis techniques for neutron-transmutation-doped silicon (nTD-Si) detectors have become widely used for the identification of low-energy charged particles. Although the particle discrimination capability of this method has been well demonstrated for small incident angles, the particle discrimination performance may be affected by changes in the detector response when the detector is moved closer to the charged particle source and the incident position distribution and incident angle distribution to the detector become wide. In this study, we performed a beam test for particle discrimination in light-charged ($Z \le 2$) particles using the digital waveform analysis method with a pad-type nTD-Si detector and investigated the dependence of the performance of the particle discrimination on the incident position and incident angle. As the incident angle increased, a decrease in the maximum current was observed, which was sufficient to affect the performance of the particle discrimination. This decrease can be expressed as a function of the penetration depth of the charged particles into the detector, which varies for each nuclide.

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