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Title: Observation of excited states in 20Mg sheds light on nuclear forces and shell evolution

Abstract

The exotic Borromean nucleus 20Mg with N=8, located at the proton drip line provides a unique testing ground for nuclear forces and the evolution of shell structure in the neutron-deficient region. We report on the first observation of proton unbound resonances together with bound states in 20Mg from the 20Mg(d,d′) reaction performed at TRIUMF. Phenomenological shell-model calculations offer a reasonable description. However, our experimental results present a challenge for current first-principles nuclear structure approaches and point to the need for improved chiral forces and ab initio calculations. Furthermore, the differential cross section of the first excited state is compared with distorted-wave Born approximation calculations to deduce a neutron quadrupole deformation parameter of βn=0.46±0.21. This provides the first indication of a possible weakening of the N=8 shell closure at the proton drip line.

Authors:
 [1];  [1];  [1];  [2];  [2];  [2];  [3];  [4];  [2];  [5];  [6];  [7];  [8];  [8];  [5];  [2];  [2];  [9];  [2];  [2] more »;  [2];  [10];  [1];  [11];  [6];  [7];  [12];  [8];  [2];  [7];  [2];  [2];  [13];  [14];  [15];  [7];  [16];  [6] « less
+ Show Author Affiliations
  1. Saint Mary’s Univ., Halifax, Nova Scotia (Canada). Astronomy and Physics Dept.; TRIUMF, Vancouver, BC (Canada)
  2. TRIUMF, Vancouver, BC (Canada)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Physics Division; Univ. of Tennessee, Knoxville, TN (United States). Dept. of Physics and Astronomy
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Physics Division, and National Center for Computational Sciences
  5. Simon Fraser Univ., Burnaby, British Columbia (Canada). Dept. of Chemistry
  6. Saint Mary’s Univ., Halifax, Nova Scotia (Canada). Astronomy and Physics Dept.
  7. Univ. of Guelph, Guelph, Ontario (Canada). Dept. of Physics
  8. McMaster Univ., Hamilton, ON (Canada). Dept. of Physics and Astronomy
  9. TRIUMF, Vancouver, BC (Canada); Simon Fraser Univ., Burnaby, BC (Canada). Dept. of Physics
  10. High Energy Accelerator Research Organization (KEK), Tsukuba (Japan)
  11. Saint Mary’s Univ., Halifax, Nova Scotia (Canada). Astronomy and Physics Dept.; Dalhousie Univ., Halifax, Nova Scotia (Canada). Dept. of Physics and Atmospheric Science
  12. TRIUMF, Vancouver, BC (Canada); Univ. of British Columbia, Vancouver, BC (Canada). Dept. of Physics and Astronomy
  13. National Autonomous Univ. of Mexico, Mexico City (Mexico). Inst. of Nuclear Sciences
  14. Univ. of Edinburgh, Scotland (United Kingdom)
  15. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  16. TRIUMF, Vancouver, BC (Canada); Univ. of York (United Kingdom). Dept. of Physics
Publication Date:
Research Org.:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR); USDOE Office of Science (SC), Nuclear Physics (NP)
OSTI Identifier:
1502031
Alternate Identifier(s):
OSTI ID: 1493380; OSTI ID: 1546554
Report Number(s):
LLNL-JRNL-754342
Journal ID: ISSN 2469-9985; PRVCAN; 940603
Grant/Contract Number:  
AC52-07NA27344; SC0018223; AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review C
Additional Journal Information:
Journal Volume: 99; Journal Issue: 2; Journal ID: ISSN 2469-9985
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS

Citation Formats

Randhawa, J. S., Kanungo, R., Holl, M., Holt, J. D., Navrátil, P., Stroberg, S. R., Hagen, G., Jansen, G. R., Alcorta, M., Andreoiu, C., Barnes, C., Burbadge, C., Burke, D., Chen, A. A., Chester, A., Christian, G., Cruz, S., Davids, B., Even, J., Hackman, G., Henderson, J., Ishimoto, S., Jassal, P., Kaur, S., Keefe, M., Kisliuk, D., Krücken, R., Liang, J., Lighthall, J., McGee, E., Measures, J., Moukaddam, M., Padilla-Rodal, E., Shotter, A., Thompson, I. J., Turko, J., Williams, M., and Workman, O. Observation of excited states in 20Mg sheds light on nuclear forces and shell evolution. United States: N. p., 2019. Web. doi:10.1103/PhysRevC.99.021301.
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Randhawa, J. S., Kanungo, R., Holl, M., Holt, J. D., Navrátil, P., Stroberg, S. R., Hagen, G., Jansen, G. R., Alcorta, M., Andreoiu, C., Barnes, C., Burbadge, C., Burke, D., Chen, A. A., Chester, A., Christian, G., Cruz, S., Davids, B., Even, J., Hackman, G., Henderson, J., Ishimoto, S., Jassal, P., Kaur, S., Keefe, M., Kisliuk, D., Krücken, R., Liang, J., Lighthall, J., McGee, E., Measures, J., Moukaddam, M., Padilla-Rodal, E., Shotter, A., Thompson, I. J., Turko, J., Williams, M., & Workman, O. Observation of excited states in 20Mg sheds light on nuclear forces and shell evolution. United States. https://doi.org/10.1103/PhysRevC.99.021301
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Randhawa, J. S., Kanungo, R., Holl, M., Holt, J. D., Navrátil, P., Stroberg, S. R., Hagen, G., Jansen, G. R., Alcorta, M., Andreoiu, C., Barnes, C., Burbadge, C., Burke, D., Chen, A. A., Chester, A., Christian, G., Cruz, S., Davids, B., Even, J., Hackman, G., Henderson, J., Ishimoto, S., Jassal, P., Kaur, S., Keefe, M., Kisliuk, D., Krücken, R., Liang, J., Lighthall, J., McGee, E., Measures, J., Moukaddam, M., Padilla-Rodal, E., Shotter, A., Thompson, I. J., Turko, J., Williams, M., and Workman, O. Mon . "Observation of excited states in 20Mg sheds light on nuclear forces and shell evolution". United States. https://doi.org/10.1103/PhysRevC.99.021301. https://www.osti.gov/servlets/purl/1502031.
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@article{osti_1502031,
title = {Observation of excited states in 20Mg sheds light on nuclear forces and shell evolution},
author = {Randhawa, J. S. and Kanungo, R. and Holl, M. and Holt, J. D. and Navrátil, P. and Stroberg, S. R. and Hagen, G. and Jansen, G. R. and Alcorta, M. and Andreoiu, C. and Barnes, C. and Burbadge, C. and Burke, D. and Chen, A. A. and Chester, A. and Christian, G. and Cruz, S. and Davids, B. and Even, J. and Hackman, G. and Henderson, J. and Ishimoto, S. and Jassal, P. and Kaur, S. and Keefe, M. and Kisliuk, D. and Krücken, R. and Liang, J. and Lighthall, J. and McGee, E. and Measures, J. and Moukaddam, M. and Padilla-Rodal, E. and Shotter, A. and Thompson, I. J. and Turko, J. and Williams, M. and Workman, O.},
abstractNote = {The exotic Borromean nucleus 20Mg with N=8, located at the proton drip line provides a unique testing ground for nuclear forces and the evolution of shell structure in the neutron-deficient region. We report on the first observation of proton unbound resonances together with bound states in 20Mg from the 20Mg(d,d′) reaction performed at TRIUMF. Phenomenological shell-model calculations offer a reasonable description. However, our experimental results present a challenge for current first-principles nuclear structure approaches and point to the need for improved chiral forces and ab initio calculations. Furthermore, the differential cross section of the first excited state is compared with distorted-wave Born approximation calculations to deduce a neutron quadrupole deformation parameter of βn=0.46±0.21. This provides the first indication of a possible weakening of the N=8 shell closure at the proton drip line.},
doi = {10.1103/PhysRevC.99.021301},
journal = {Physical Review C},
number = 2,
volume = 99,
place = {United States},
year = {Mon Feb 04 00:00:00 EST 2019},
month = {Mon Feb 04 00:00:00 EST 2019}
}
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https://doi.org/10.1103/PhysRevC.99.021301
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