arXiv subjects

Taichi Miyagawa

Publications and source records attributed to Taichi Miyagawa.

4 recordsLinked to original sources

arXiv2026

Ion-Optical Tuning of the Large Acceptance Spectrometer for Improved Angular Resolution and Acceptance

The trade-off between angular resolution and acceptance in scattering-angle measurements with a magnetic spectrometer is quantitatively evaluated for the Large Acceptance Spectrometer (LAS). The dependence on the multipole magnet field strength is investigated. Third-order transfer matrices were calculated with GICOSY, and particle transport was simulated with MOCADI. The vertical angular resolution is defined as the standard deviation between reconstructed and true angles, while the acceptance is determined from the transport efficiency within an elliptical gate in target angle space. The resolution improves with increasing field strength, reaching $σ_b \sim 5.5$ mrad at +20\%, consistent with $5.43 \pm 0.20$ mrad. In contrast, stronger fields reduce the vertical acceptance and solid angle. These results demonstrate a trade-off between resolution and acceptance. Enhanced vertical focusing shifts the focal condition away from the nominal focal plane, enabling high-precision reconstruction.

physics.ins-det↗

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↗

arXiv2025

Ion Optics for quasi-free $(p,pα)$ reactions with Grand Raiden Spectrometer

The quasi-free $(p,pα)$ reaction is a powerful tool to probe preformed $α$ clusters in nuclei, but it requires accurate reconstruction of both momentum and scattering angles at the reaction point. In this work, ion-optical analysis for $(p,pα)$ measurements with the Grand Raiden spectrometer is presented. An under-focus optical setting was adopted to preserve sensitivity to the vertical scattering angle while maintaining high momentum resolution. The focal-plane geometry was determined independently as a purely geometrical reference. Momentum calibration was performed using elastic scattering of $^{206}$Pb$(p,p)$ at a fixed spectrometer angle. Scattering angles were reconstructed using ion-optical relations, and residual higher-order effects were corrected by a multidimensional fit. The dominant contributions to the reconstruction were found to arise from terms up to third order within the experimental acceptance. This ion-optical framework enables consistent event-by-event reconstruction of the reaction kinematics and provides a reliable basis for quasi-free $(p,pα)$ analyses.

physics.ins-det↗

arXiv2025

Quantification of Oxygen and Carbon in Calcium Targets for Reliable Ca$(p,pα)$ Measurements

Reliable extraction of Ca$(p,pα)$ cross sections requires accurate correction for oxygen and carbon impurities in calcium targets. In this work, the relative amounts of these light elements in $^{40,42,44,48}$Ca targets are determined using 65-MeV proton elastic scattering, where the Ca/Mylar yield ratios provide a direct measure of the corresponding O and C atomic ratios. These experimentally determined ratios are then applied to the 392-MeV $(p,pα)$ spectra to subtract the O and C contributions in a fully data-driven manner. The method does not rely on assumptions about absolute contamination levels or reaction-model calculations, and enables a consistent and reliable determination of Ca$(p,pα)$ yields across the calcium isotopic chain.

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