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Single-particle strength toward N = 32: Spectroscopy of 51 Ca via the 50 Ca(d, p) reaction

C. Ferrera, K. Wimmer, D. Suzuki, N. Imai, A. Jungclaus, T. Miyagi, Y. Utsuno, D. Das, T. Chillery, S. Hanai, J. W. Hwang, N. Kitamura, R. Kojima, S. Michimasa, R. Yokoyama, Y. Anuar, M. Armstrong, S. Bae, Y. Cho, M. Dozono, F. Endo, S. Escrig, N. Fukuda, T. Haginouchi, S. Hayakawa, Y. Hijikata, G. Ikemizu, S. Ishio, A. Kasagi, K. Kawata, J. Li, S. Masuoka, B. Moon, K. Okawa, S. Ota, H. Qin, T. Saito, A. Sakaue, H. Sakurai, Y. Shimizu, S. Shimoura, Y. Son, T. Sumikama, H. Suzuki, H. Takeda, Y. Togano, J. Vesic, K. Yako, Y. Yamamoto, K. Yoshida, M. Yoshimoto

Abstract

States in the neutron-rich isotope 51 Ca were populated via the 50 Ca(d, p) transfer reaction in inverse kinematics at a beam energy of about 14 AMeV. The experiment was performed using a decelerated radioactive 50 Ca beam from the OEDO facility and the TiNA2 silicon array in combination with the SHARAQ magnetic spectrometer at RIBF/RIKEN. The energies of excited states in 51 Ca were reconstructed via missing mass spectroscopy, and angular distributions of protons were measured to extract differential cross sections. From a comparison with adiabatic distorted wave approximation (ADWA) calculations, spectroscopic factors were deduced for several states, including the ground state and excited states up to 4.2 MeV. These results are compared with shell-model calculations, as well as ab initio valence-space in-medium similarity renormalization group (VS-IMSRG) predictions. The data support the assignment of the 1/2- and 5/2- single-particle states and provide evidence for a candidate 9/2+ state with a structure consistent with neutron excitation into the 0g9/2 orbital. These findings contribute new constraints on the single-particle structure and shell evolution in neutron-rich calcium isotopes.

Single-particle strength toward N = 32: Spectroscopy of 51 Ca via the 50 Ca(d, p) reaction

Abstract

States in the neutron-rich isotope 51 Ca were populated via the 50 Ca(d, p) transfer reaction in inverse kinematics at a beam energy of about 14 AMeV. The experiment was performed using a decelerated radioactive 50 Ca beam from the OEDO facility and the TiNA2 silicon array in combination with the SHARAQ magnetic spectrometer at RIBF/RIKEN. The energies of excited states in 51 Ca were reconstructed via missing mass spectroscopy, and angular distributions of protons were measured to extract differential cross sections. From a comparison with adiabatic distorted wave approximation (ADWA) calculations, spectroscopic factors were deduced for several states, including the ground state and excited states up to 4.2 MeV. These results are compared with shell-model calculations, as well as ab initio valence-space in-medium similarity renormalization group (VS-IMSRG) predictions. The data support the assignment of the 1/2- and 5/2- single-particle states and provide evidence for a candidate 9/2+ state with a structure consistent with neutron excitation into the 0g9/2 orbital. These findings contribute new constraints on the single-particle structure and shell evolution in neutron-rich calcium isotopes.
Paper Structure (14 sections, 9 figures, 2 tables)

This paper contains 14 sections, 9 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Experimental setup
  3. Beam production and transport
  4. TiNA2 charged particle array
  5. Reaction product detection in SHARAQ
  6. Data Analysis
  7. Beam tracking and identification
  8. Recoil detection and missing mass reconstruction
  9. SHARAQ analysis
  10. Results
  11. Missing-mass spectrum
  12. Differential cross sections
  13. Discussion
  14. Conclusion

Figures (9)

  • Figure 1: TiNA2 charged particle detector array in backwards configuration. The double-sided (TTT) and single-sided (YY1) silicon strip detectors are colored in blue and the CsI crystals in gray.
  • Figure 2: Particle identification in BigRIPS through measurement of the time-of-flight from F3 to FE9 and the position in the FE9 dispersive focal plane.
  • Figure 3: Target midpoint kinetic-energy distribution of all $^{50}$Ca beam ions (black line), those ions reaching the CD$_2$ target (blue), and finally only those which were transmitted to the SHARAQ spectrometer (red). The apparent difference in statistics between the two experiments is mainly due to the choice of a larger trigger downscale factor in 2024.
  • Figure 4: (a) Particle identification of the secondary beam in the SHARAQ spectrometer. (b) Mass-to-charge ratio gated on incoming $^{50}$Ca beam particles detected in the SHARAQ spectrometer for 2022 and 2024. Outgoing $^{50}$Ca in different charge states is identified.
  • Figure 5: Excitation energy vs $A/q$, A transition in $A/q$ is observed at the neutron separation energy $S_n = 4.815$ MeV wang21. Data from the forward box detectors from 2024 are shown.
  • ...and 4 more figures