Probing proton cross-shell excitations through the two-neutron removal from 38Ca

Beck, T.; Gade, A.; Brown, B. A.; Tostevin, J. A.; Weisshaar, D.; Bazin, D.; Brown, K. W.; Charity, R. J.; Farris, P. J.; Gillespie, S. A.; Hill, A. M.; Li, J.; Longfellow, B.; Reviol, W.; Rhodes, D.

doi:10.1103/physrevc.108.l061301

Title: Probing proton cross-shell excitations through the two-neutron removal from ³⁸Ca

Journal Article · 18 December 2023 · Physical Review. C

DOI: https://doi.org/10.1103/physrevc.108.l061301 · OSTI ID:2248079

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^[2]; Brown, K. W. ^[2];

^[4]; Farris, P. J. ^[2];

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^[2]; Li, J. ^[2]; Longfellow, B. ^[5];

^[6]; Rhodes, D. ^[7]

Michigan State University, East Lansing, MI (United States); Michigan State University
Michigan State University, East Lansing, MI (United States)
University of Surrey (United Kingdom)
Washington University, St. Louis, MO (United States)
Michigan State University, East Lansing, MI (United States); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Argonne National Laboratory (ANL), Argonne, IL (United States)
Michigan State University, East Lansing, MI (United States); TRIUMF, Vancouver, BC (Canada)

Bound states of the neutron-deficient, near-dripline nucleus ³⁶Ca were populated in two-neutron removal from the ground state of ³⁸Ca, a direct reaction sensitive to the single-particle configurations and couplings of the removed neutrons in the projectile wave function. Final-state exclusive cross sections for the formation of ³⁶Ca and the corresponding longitudinal momentum distributions, both determined through the combination of particle and γ-ray spectroscopy, are compared to predictions combining eikonal reaction theory and shell-model two-nucleon amplitudes from the USDB, USDC, and ZBM2 effective interactions. The final-state cross-section ratio σ($$2$$$^{+}_{1}$$) / σ (0⁺) shows particular sensitivity and is approximately reproduced only with the two-nucleon amplitudes from the ZBM2 effective interaction that includes proton cross-shell excitations into the pf shell. Characterizing the proton pf-shell occupancy locally and schematically, an increase of the sd – pf shell gap by 250 keV yields an improved description of this cross-section ratio and simultaneously enables a reproduction of the B(E2;$$0$$$^{+}_{1}$$ → $$2$$$^{+}_{1}$$) excitation strength of ³⁶Ca. Furthermore, this highlights an important aspect if a new shell-model effective interaction for the region was to be developed on the quest to model the neutron-deficient Ca isotopes and surrounding nuclei whose structure is impacted by proton cross-shell excitations.

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Research Organization:: Michigan State University, East Lansing, MI (United States)

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Nuclear Physics (NP); National Science Foundation (NSF)

Grant/Contract Number:: SC0023633; SC0020451; SC0019034; FG02-87ER40316; AC02-06CH11357; NA0003180

OSTI ID:: 2248079

Alternate ID(s):: OSTI ID: 2345189

Journal Information:: Physical Review. C, Journal Name: Physical Review. C Journal Issue: 6 Vol. 108; ISSN 2469-9985

Publisher:: American Physical Society (APS)Copyright Statement

Country of Publication:: United States

Language:: English

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Title: Probing proton cross-shell excitations through the two-neutron removal from ³⁸Ca