Two-neutron knockout as a probe of the composition of states in Mg22,Al23 , and Si24

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.

doi:10.1103/PhysRevC.101.031303

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

Journal Article · 12 March 2020 · Physical Review C

DOI: https://doi.org/10.1103/PhysRevC.101.031303 · OSTI ID:1604421

^[1];

^[2]; Tostevin, J. A. ^[3]; Simpson, E. C. ^[4]; Brown, B. A. ^[2];

^[2]; Bazin, D. ^[2]; Bender, P. C. ^[5]; Bowry, M. ^[6]; Elman, B. ^[2]; Lunderberg, E. ^[2]; Rhodes, D. ^[2]; Spieker, M. ^[7]; Weisshaar, D. ^[2]; Williams, S. J. ^[8]

Michigan State Univ., East Lansing, MI (United States); Michigan State University
Michigan State Univ., East Lansing, MI (United States)
Univ. of Surrey, Guildford (United Kingdom)
Australian National Univ., Canberra, ACT (Australia)
Michigan State Univ., East Lansing, MI (United States); Univ. of Massachusetts, Lowell, MA (United States)
Michigan State Univ., East Lansing, MI (United States); Univ. of the West of Scotland (United Kingdom)
Michigan State Univ., East Lansing, MI (United States); Florida State Univ., Tallahassee, FL (United States)
Michigan State Univ., East Lansing, MI (United States); Science and Technology Facilities Council (STFC), Oxford (United Kingdom). Diamond Light Source, Ltd.

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 ${}_{22}{Mg}, {}_{23}{Al}$ , and ${}_{24}{Si}$ 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 ${}_{22}{Mg}$ and ${}_{23}{Al}$ 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 ${}_{24}{Si}$ , a level at 3439(9) keV, of relevance for the important ${}_{23}{Al} (p, γ) {}_{24}{Si}$ 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 ${}_{24}{Si}$ is, in fact, the ( $0_{2}^{+}$ ) level with one of the largest experimental mirror-energy shifts ever observed.

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

Sponsoring Organization:: USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26); USDOE National Nuclear Security Administration (NNSA); National Science Foundation (NSF); Science and Technology Facilities Council

Grant/Contract Number:: SC0020451; NA0003180; FG02-08ER41556

OSTI ID:: 1604421

Journal Information:: Physical Review C, Journal Name: Physical Review C Journal Issue: 3 Vol. 101; ISSN PRVCAN; ISSN 2469-9985

Publisher:: American Physical Society (APS)Copyright Statement

Country of Publication:: United States

Language:: English

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