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Title: Two-neutron knockout as a probe of the composition of states in Mg 22 , Al 23 , and Si 24

Abstract

Simpson and Tostevin proposed that the width and shape of exclusive parallel momentum distributions of the A - 2 residue in direct two-nucleon knockout reactions carry a measurable sensitivity to the nucleon single-particle configurations and their couplings within the wave functions of exotic nuclei. We further report here on the first benchmarks and use of this new spectroscopic tool. Exclusive parallel momentum distributions for states in the neutron-deficient nuclei Mg 22 , Al 23 , and Si 24 populated in such direct two-neutron removal reactions were extracted and compared to predictions combining eikonal reaction theory and shell-model calculations. For the well-known Mg 22 and Al 23 nuclei, measurements and calculations were found to agree, supporting the dependence of the parallel momentum distribution width on the angular momentum composition of the shell-model two-neutron amplitudes. In Si 24 , a level at 3439(9) keV, of relevance for the important Al 23 ( p , γ ) Si 24 astrophysical reaction rate, was confirmed to be the 2 2 + state, whereas the 4 1 + state, expected to be strongly populated in two-neutron knockout, was not observed. This puzzle is resolved by theoretical considerations of the Thomas-Ehrman shift, which also indicates that a previously reported 3471-keV state in Si 24 is, in fact, the ( 0 2 + ) level with one of the largest experimental mirror-energy shifts ever observed.

Authors:
ORCiD logo [1]; ORCiD logo [1];  [2];  [3];  [1]; ORCiD logo [1];  [1];  [4];  [5];  [1];  [1];  [1];  [6];  [1];  [7]
  1. Michigan State Univ., East Lansing, MI (United States)
  2. Univ. of Surrey, Guildford (United Kingdom)
  3. Australian National Univ., Canberra, ACT (Australia)
  4. Michigan State Univ., East Lansing, MI (United States); Univ. of Massachusetts, Lowell, MA (United States)
  5. Michigan State Univ., East Lansing, MI (United States); Univ. of the West of Scotland (United Kingdom)
  6. Michigan State Univ., East Lansing, MI (United States); Florida State Univ., Tallahassee, FL (United States)
  7. Michigan State Univ., East Lansing, MI (United States); Science and Technology Facilities Council (STFC), Oxford (United Kingdom). Diamond Light Source, Ltd.
Publication Date:
Research Org.:
Michigan State Univ., East Lansing, MI (United States); Univ. of California, Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP); National Science Foundation (NSF); Science and Technology Facilities Council; USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation
OSTI Identifier:
1604421
Alternate Identifier(s):
OSTI ID: 1604487; OSTI ID: 1604763
Grant/Contract Number:  
SC0020451; PHY-1102511; PHY-1565546; NA0003180; FG02-08ER41556; ST/L005743/1; PHY-1811855
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review C
Additional Journal Information:
Journal Volume: 101; Journal Issue: 3; Journal ID: ISSN 2469-9985
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; gamma-ray spectroscopy; nuclear structure; shell model; direct reactions; radioactive beams; gamma-ray spectroscopy, nuclear structure, shell model, direct reactions, radioactive beams

Citation Formats

Longfellow, B., Gade, Alexandra, Tostevin, J. A., Simpson, E. C., Brown, B. A., Magilligan, A., Bazin, D., Bender, P. C., Bowry, M., Elman, B., Lunderberg, E., Rhodes, D., Spieker, M., Weisshaar, D., and Williams, S. J. Two-neutron knockout as a probe of the composition of states in Mg22,Al23 , and Si24. United States: N. p., 2020. Web. https://doi.org/10.1103/PhysRevC.101.031303.
Longfellow, B., Gade, Alexandra, Tostevin, J. A., Simpson, E. C., Brown, B. A., Magilligan, A., Bazin, D., Bender, P. C., Bowry, M., Elman, B., Lunderberg, E., Rhodes, D., Spieker, M., Weisshaar, D., & Williams, S. J. Two-neutron knockout as a probe of the composition of states in Mg22,Al23 , and Si24. United States. https://doi.org/10.1103/PhysRevC.101.031303
Longfellow, B., Gade, Alexandra, Tostevin, J. A., Simpson, E. C., Brown, B. A., Magilligan, A., Bazin, D., Bender, P. C., Bowry, M., Elman, B., Lunderberg, E., Rhodes, D., Spieker, M., Weisshaar, D., and Williams, S. J. Thu . "Two-neutron knockout as a probe of the composition of states in Mg22,Al23 , and Si24". United States. https://doi.org/10.1103/PhysRevC.101.031303. https://www.osti.gov/servlets/purl/1604421.
@article{osti_1604421,
title = {Two-neutron knockout as a probe of the composition of states in Mg22,Al23 , and Si24},
author = {Longfellow, B. and Gade, Alexandra and Tostevin, J. A. and Simpson, E. C. and Brown, B. A. and Magilligan, A. and Bazin, D. and Bender, P. C. and Bowry, M. and Elman, B. and Lunderberg, E. and Rhodes, D. and Spieker, M. and Weisshaar, D. and Williams, S. J.},
abstractNote = {Simpson and Tostevin proposed that the width and shape of exclusive parallel momentum distributions of the A-2 residue in direct two-nucleon knockout reactions carry a measurable sensitivity to the nucleon single-particle configurations and their couplings within the wave functions of exotic nuclei. We further report here on the first benchmarks and use of this new spectroscopic tool. Exclusive parallel momentum distributions for states in the neutron-deficient nuclei Mg22,Al23, and Si24 populated in such direct two-neutron removal reactions were extracted and compared to predictions combining eikonal reaction theory and shell-model calculations. For the well-known Mg22 and Al23 nuclei, measurements and calculations were found to agree, supporting the dependence of the parallel momentum distribution width on the angular momentum composition of the shell-model two-neutron amplitudes. In Si24, a level at 3439(9) keV, of relevance for the important Al23(p,γ)Si24 astrophysical reaction rate, was confirmed to be the 22+ state, whereas the 41+ state, expected to be strongly populated in two-neutron knockout, was not observed. This puzzle is resolved by theoretical considerations of the Thomas-Ehrman shift, which also indicates that a previously reported 3471-keV state in Si24 is, in fact, the (02+) level with one of the largest experimental mirror-energy shifts ever observed.},
doi = {10.1103/PhysRevC.101.031303},
journal = {Physical Review C},
number = 3,
volume = 101,
place = {United States},
year = {2020},
month = {3}
}

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