CheongSoo Lee
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Research Subjects
CheongSoo Lee has a total of 155 co-authors. Here are the top co-authors by number of shared publications:
- Atsushi Tamii
Research Center for Nuclear Physics, The University of Osaka , 10-1 Mihogaoka, Ibaraki, Osaka 567-0047
3 shared publications - Azusa Inoue
Research Center for Nuclear Physics, The University of Osaka , 10-1 Mihogaoka, Ibaraki, Osaka 567-0047
3 shared publications - Byungsik Hong
Korea University
3 shared publications - Cheolmin Ham
Institute for Rare Isotope Science, Institute for Basic Science, Daejeon 34000
3 shared publications - Deuk Soon Ahn
Center for Exotic Nuclear Studies, Institute for Basic Science , 55 Expo-ro, Yuseong-gu, Daejeon 34126
3 shared publications - Dong Geon Kim
Institute for Rare Isotope Science, Institute for Basic Science, Daejeon 34000
3 shared publications
Latest Publications
- Open Access
- 28 July 2026
- Published by Oxford University Press (OUP) in Progress of Theoretical and Experimental Physics
- Vol. 2026 (9)
Performance and Characterization of Large-Area (400 × 200 mm2) PPACs Using 40Ar Beams at the KoBRA Spectrometer
The performance of a large-area $400 \times 200$ mm$^2$ parallel-plate avalanche counter (PPAC) developed for the focal plane of the KoBRA (KOrea Broad acceptance Recoil spectrometer and Apparatus) facility is reported. To maintain high resolution over the extended width, a triple-segmented delay-line readout was implemented for the x-axis. Detection efficiency, position resolution, and timing resolution were measured using $^{40}$Ar beams at 8, 12, and 16 MeV/u as a function of isobutane gas pressure (2–8 Torr) and anode high voltage (400–670 V). Position calibration was carried out using a hole mask with known hole positions and validated across multiple beam energies. Detection efficiencies of $\gt$99% were achieved for both the x- and the y-axis at all beam energies. The intrinsic position resolution at the detector center, after deconvolving the geometric contribution of the calibration hole aperture, was approximately $460\,\mu$m ($\sigma$) with a time-to-digital converter and improved to $320\,\mu$m ($\sigma$) with a waveform digitizer. The single-anode timing resolution was $165 \,{\rm ps}$ ($\sigma$). These results validate the large-area PPAC for heavy-ion beam tracking at KoBRA and establish a performance baseline for future experiments with secondary beams.- 28 July 2026
- Published by Oxford University Press (OUP) in Progress of Theoretical and Experimental Physics
- Vol. 2026 (9)
Open AccessPerformance and Characterization of Large-Area (400 × 200 mm2) PPACs Using 40Ar Beams at the KoBRA Spectrometer
The performance of a large-area $400 \times 200$ mm$^2$ parallel-plate avalanche counter (PPAC) developed for the focal plane of the KoBRA (KOrea Broad acceptance Recoil spectrometer and Apparatus) facility is reported. To maintain high resolution over the extended width, a triple-segmented delay-line readout was implemented for the x-axis. Detection efficiency, position resolution, and timing resolution were measured using $^{40}$Ar beams at 8, 12, and 16 MeV/u as a function of isobutane gas pressure (2–8 Torr) and anode high voltage (400–670 V). Position calibration was carried out using a hole mask with known hole positions and validated across multiple beam energies. Detection efficiencies of $\gt$99% were achieved for both the x- and the y-axis at all beam energies. The intrinsic position resolution at the detector center, after deconvolving the geometric contribution of the calibration hole aperture, was approximately $460\,\mu$m ($\sigma$) with a time-to-digital converter and improved to $320\,\mu$m ($\sigma$) with a waveform digitizer. The single-anode timing resolution was $165 \,{\rm ps}$ ($\sigma$). These results validate the large-area PPAC for heavy-ion beam tracking at KoBRA and establish a performance baseline for future experiments with secondary beams. - Open Access
- 1 June 2026
- Published by Oxford University Press (OUP) in Progress of Theoretical and Experimental Physics
- Vol. 2026 (7)
First Observation of Mirror t and 3He Clusters in Stable Ca Isotopes via Quasi-free ( p , pt ) and ( p , p 3He) Reactions
We report systematic data on the quasi-free $(p,pt)$ and $(p,p{^{3}{\rm He}})$ reactions of $\mathrm{^{40\text{-}48}Ca}$ isotopes at an incident proton energy of 226 MeV under recoil-less conditions, with the aim of investigating t and ${^{3}{\rm He}}$ cluster correlations in medium-mass nuclei. In addition, data on $\mathrm{^{12}C}$ and $\mathrm{^{16}O}$ were taken to estimate the contribution of $\mathrm{^{16}O}$ impurities originating from surface oxidation of the Ca targets and to provide benchmark data for light $N=Z$ systems. From the experimental data, state-resolved triple differential cross-sections were extracted, together with separation-energy-integrated triple differential cross-sections as a complementary observable. The state-resolved triple differential cross-sections were analyzed within a distorted wave impulse approximation (DWIA) framework, and experimental spectroscopic factors were deduced using Woods–Saxon wave functions. In addition, theoretical triple differential cross-sections were obtained from DWIA calculations employing cluster wave functions derived from generalized relativistic density functional theory (grDFT) and were compared with the experimental results. For the Ca isotopes, pronounced low-lying S-wave peaks are observed in the separation-energy spectra for both the $(p,pt)$ and $(p,p{^{3}{\rm He}})$ channels. The corresponding low-lying S-wave triple differential cross-sections and experimental spectroscopic factors decrease systematically with increasing neutron number for both the t and ${^{3}{\rm He}}$ clusters. Comparisons with grDFT-based DWIA calculations show that the calculated triple differential cross-sections are of the same order of magnitude as the experimental low-lying S-wave triple differential cross-sections and capture their global decreasing trend toward neutron-rich Ca isotopes. The separation-energy-integrated triple differential cross-sections exhibit a clear channel-dependent behavior: the integrated strength decreases for the $(p,p{^{3}{\rm He}})$ channel, whereas it remains nearly constant for the $(p,pt)$ channel. Overall, the present results demonstrate that quasi-free $(p,pX)$ reactions provide a sensitive and versatile probe of cluster correlations in finite nuclei, and strongly motivate further experimental and theoretical studies of t and ${^{3}{\rm He}}$ cluster formation across a wide range of nuclei.- 1 June 2026
- Published by Oxford University Press (OUP) in Progress of Theoretical and Experimental Physics
- Vol. 2026 (7)
Open AccessFirst Observation of Mirror t and 3He Clusters in Stable Ca Isotopes via Quasi-free ( p , pt ) and ( p , p 3He) Reactions
We report systematic data on the quasi-free $(p,pt)$ and $(p,p{^{3}{\rm He}})$ reactions of $\mathrm{^{40\text{-}48}Ca}$ isotopes at an incident proton energy of 226 MeV under recoil-less conditions, with the aim of investigating t and ${^{3}{\rm He}}$ cluster correlations in medium-mass nuclei. In addition, data on $\mathrm{^{12}C}$ and $\mathrm{^{16}O}$ were taken to estimate the contribution of $\mathrm{^{16}O}$ impurities originating from surface oxidation of the Ca targets and to provide benchmark data for light $N=Z$ systems. From the experimental data, state-resolved triple differential cross-sections were extracted, together with separation-energy-integrated triple differential cross-sections as a complementary observable. The state-resolved triple differential cross-sections were analyzed within a distorted wave impulse approximation (DWIA) framework, and experimental spectroscopic factors were deduced using Woods–Saxon wave functions. In addition, theoretical triple differential cross-sections were obtained from DWIA calculations employing cluster wave functions derived from generalized relativistic density functional theory (grDFT) and were compared with the experimental results. For the Ca isotopes, pronounced low-lying S-wave peaks are observed in the separation-energy spectra for both the $(p,pt)$ and $(p,p{^{3}{\rm He}})$ channels. The corresponding low-lying S-wave triple differential cross-sections and experimental spectroscopic factors decrease systematically with increasing neutron number for both the t and ${^{3}{\rm He}}$ clusters. Comparisons with grDFT-based DWIA calculations show that the calculated triple differential cross-sections are of the same order of magnitude as the experimental low-lying S-wave triple differential cross-sections and capture their global decreasing trend toward neutron-rich Ca isotopes. The separation-energy-integrated triple differential cross-sections exhibit a clear channel-dependent behavior: the integrated strength decreases for the $(p,p{^{3}{\rm He}})$ channel, whereas it remains nearly constant for the $(p,pt)$ channel. Overall, the present results demonstrate that quasi-free $(p,pX)$ reactions provide a sensitive and versatile probe of cluster correlations in finite nuclei, and strongly motivate further experimental and theoretical studies of t and ${^{3}{\rm He}}$ cluster formation across a wide range of nuclei. - Open Access
- 9 March 2026
- Published by Oxford University Press (OUP) in Progress of Theoretical and Experimental Physics
- Vol. 2026 (5)
Proton-Induced Deuteron Knockout ( p,pd ) on 12C and 16O at 226 MeV
The proton-induced deuteron knockout reaction (p, pd) provides a unique opportunity to exploit proton-neutron correlations and the deuteron cluster structure of nuclei. Direct deuteron knockout experiments on 12C and 16O under quasi-free scattering conditions have been carried out under the ONOKORO project using a 226 MeV proton beam at RCNP, Osaka, Japan. Deuterons from the knockout reaction, acting as clusters, were unambiguously detected at the focal plane of the Large Acceptance Spectrometer. Outgoing protons, following the knockout of clusters, were detected at the focal plane of the Grand Raiden spectrometer to correctly reconstruct the expected events. (p, pd) reactions are established successfully, and excitation energy spectra for the residual nuclei 10B and 14N are obtained. Results showed that a large difference in transition strength toward the low-lying energy level of residual nuclei, including the ground state, was found in comparison to other studies. Theoretical calculations using the PIKOE package based on the distorted-wave impulse approximation are conducted to deduce the triple differential cross section of (p, pd) reaction, and experimental spectroscopic factors of the deuteron cluster are obtained by normalizing the experimental cross section to the theoretical computation. Consistent spectroscopic factors in comparison to shell-model expectations are obtained for transitions involving the orbital angular momentum L = 0 of the cluster. The present work demonstrates that the (p, pd) reactions at 226 MeV as a spectroscopic tool have an advantage in examining spectroscopic aspects of deuteron clustering and the mechanism to form a proton-neutron pair in the spin triplet state with a negligible interference of final state interactions and refraction effects.
- 9 March 2026
- Published by Oxford University Press (OUP) in Progress of Theoretical and Experimental Physics
- Vol. 2026 (5)
Open AccessProton-Induced Deuteron Knockout ( p,pd ) on 12C and 16O at 226 MeV
The proton-induced deuteron knockout reaction (p, pd) provides a unique opportunity to exploit proton-neutron correlations and the deuteron cluster structure of nuclei. Direct deuteron knockout experiments on 12C and 16O under quasi-free scattering conditions have been carried out under the ONOKORO project using a 226 MeV proton beam at RCNP, Osaka, Japan. Deuterons from the knockout reaction, acting as clusters, were unambiguously detected at the focal plane of the Large Acceptance Spectrometer. Outgoing protons, following the knockout of clusters, were detected at the focal plane of the Grand Raiden spectrometer to correctly reconstruct the expected events. (p, pd) reactions are established successfully, and excitation energy spectra for the residual nuclei 10B and 14N are obtained. Results showed that a large difference in transition strength toward the low-lying energy level of residual nuclei, including the ground state, was found in comparison to other studies. Theoretical calculations using the PIKOE package based on the distorted-wave impulse approximation are conducted to deduce the triple differential cross section of (p, pd) reaction, and experimental spectroscopic factors of the deuteron cluster are obtained by normalizing the experimental cross section to the theoretical computation. Consistent spectroscopic factors in comparison to shell-model expectations are obtained for transitions involving the orbital angular momentum L = 0 of the cluster. The present work demonstrates that the (p, pd) reactions at 226 MeV as a spectroscopic tool have an advantage in examining spectroscopic aspects of deuteron clustering and the mechanism to form a proton-neutron pair in the spin triplet state with a negligible interference of final state interactions and refraction effects.
- Open Access
- 18 February 2026
- Published by Oxford University Press (OUP) in Progress of Theoretical and Experimental Physics
- Vol. 2026 (4)
Establishing the 40Ca(p,p α ) Reaction at 392 MeV under Quasi-Free Scattering Conditions
The $(p,p\alpha )$ reaction offers a direct means to probe preformed $\alpha$-cluster structures in nuclei under quasi-free scattering conditions. Previous studies around 100 MeV provided valuable insights into $\alpha$ 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$(p,p\alpha )$ reaction was measured at an incident energy of 392 MeV using the high-resolution Grand Raiden and Large Acceptance Spectrometer 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 $\alpha + {}^{36}$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 ($0.52 \pm 0.11$). This agreement demonstrates that the reaction mechanism is well described across a wide energy range. The present study establishes the feasibility of high-precision $(p,p\alpha )$ measurements at several hundred MeV and highlights their potential as a quantitative probe of $\alpha$ clustering in medium-mass nuclei, forming the basis for systematic studies in both stable and unstable systems.- 18 February 2026
- Published by Oxford University Press (OUP) in Progress of Theoretical and Experimental Physics
- Vol. 2026 (4)
Open AccessEstablishing the 40Ca(p,p α ) Reaction at 392 MeV under Quasi-Free Scattering Conditions
The $(p,p\alpha )$ reaction offers a direct means to probe preformed $\alpha$-cluster structures in nuclei under quasi-free scattering conditions. Previous studies around 100 MeV provided valuable insights into $\alpha$ 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$(p,p\alpha )$ reaction was measured at an incident energy of 392 MeV using the high-resolution Grand Raiden and Large Acceptance Spectrometer 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 $\alpha + {}^{36}$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 ($0.52 \pm 0.11$). This agreement demonstrates that the reaction mechanism is well described across a wide energy range. The present study establishes the feasibility of high-precision $(p,p\alpha )$ measurements at several hundred MeV and highlights their potential as a quantitative probe of $\alpha$ clustering in medium-mass nuclei, forming the basis for systematic studies in both stable and unstable systems. - Open Access
- 9 July 2025
- Published by Oxford University Press (OUP) in Progress of Theoretical and Experimental Physics
- Vol. 2025 (7)
Nondestructive Bunch Shape Monitoring Method for Nonrelativistic Ion Beams Based on Capacitive Pick-up Type Bunch Shape Monitor
Detailed information on the longitudinal shape of beam bunches is crucial in ion beam accelerator facilities for understanding beam dynamics and analyzing experimental data. Particularly for the low-energy ion beams, nondestructive bunch shape monitoring through capacitive pick-up monitors remains a challenge due to the longitudinal electric field spread of nonrelativistic bunches. This study presents the development and optimization of a capacitive pick-up type bunch shape monitor (CPU-BSM) designed to nondestructively measure nanosecond-scale bunch shapes of nonrelativistic ion beams. An algorithm for reconstructing the longitudinal bunch shape from integrated signals of the CPU-BSM was developed, and bench tests were employed to verify the manufactured system before its practical application with real beams. Subsequently, proof-of-principle experimental validations were performed using nonrelativistic proton beam bunches. The results confirmed the CPU-BSM’s capability to measure nanosecond-scale bunch shapes sufficiently, even with non-Gaussian distributions. The bunch shape measurement method proposed in this study involves minimal interaction with the beam, allowing it to be used online during user experiments at various ion beam facilities.
- 9 July 2025
- Published by Oxford University Press (OUP) in Progress of Theoretical and Experimental Physics
- Vol. 2025 (7)
Open AccessNondestructive Bunch Shape Monitoring Method for Nonrelativistic Ion Beams Based on Capacitive Pick-up Type Bunch Shape Monitor
Detailed information on the longitudinal shape of beam bunches is crucial in ion beam accelerator facilities for understanding beam dynamics and analyzing experimental data. Particularly for the low-energy ion beams, nondestructive bunch shape monitoring through capacitive pick-up monitors remains a challenge due to the longitudinal electric field spread of nonrelativistic bunches. This study presents the development and optimization of a capacitive pick-up type bunch shape monitor (CPU-BSM) designed to nondestructively measure nanosecond-scale bunch shapes of nonrelativistic ion beams. An algorithm for reconstructing the longitudinal bunch shape from integrated signals of the CPU-BSM was developed, and bench tests were employed to verify the manufactured system before its practical application with real beams. Subsequently, proof-of-principle experimental validations were performed using nonrelativistic proton beam bunches. The results confirmed the CPU-BSM’s capability to measure nanosecond-scale bunch shapes sufficiently, even with non-Gaussian distributions. The bunch shape measurement method proposed in this study involves minimal interaction with the beam, allowing it to be used online during user experiments at various ion beam facilities.