Abstract
The exotic Borromean nucleus Mg20 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 Mg20 from the Mg20(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.
| Original language | English |
|---|---|
| Article number | 021301 |
| Journal | Physical Review C |
| Volume | 99 |
| Issue number | 2 |
| DOIs | |
| State | Published - Feb 4 2019 |
Funding
The authors express sincere thanks to the TRIUMF beam delivery team. The support from NSERC, Canada Foundation for Innovation and the Nova Scotia Research and Innovation Trust is gratefully acknowledged. TRIUMF receives funding via a contribution through the National Research Council Canada. Support from RCNP for the target is gratefully acknowledged. It was partly supported by the Grant-in-Aid Program of the Japanese government under Contracts No. 23224008 and No. 14J03935. We thank J. Simonis, K. Hebeler, and A. Schwenk for providing the EM interaction 3N matrix elements used in this Rapid Communication and for valuable discussions. Computations were performed with an allocation of computing resources at the Jülich Supercomputing Center (JURECA). This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Award No. DE-SC0018223 (SciDAC-4 NUCLEI) and the Field Work Proposals No. ERKBP57 and No. ERKBP72 at Oak Ridge National Laboratory (ORNL). This research used resources of the Oak Ridge Leadership Computing Facility located at ORNL. J.E. gratefully acknowledges financial support from the German Academic Exchange Service (DAAD Postdoc program). This work has been partially supported by U.S. DOE Award No. DE-SC0018223. ORNL is managed by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 for the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive paid-up irrevocable world-wide license to publish or reproduce the published form of this Rapid Communication or allow others to do so for U.S. Government purposes.
| Funders | Funder number |
|---|---|
| U.S. Department of Energy | |
| Office of Science | |
| Nuclear Physics | ERKBP57, DE-SC0018223, ERKBP72 |
| Lawrence Livermore National Laboratory | DE-AC52-07NA27344 |
| Oak Ridge National Laboratory | |
| Nova Scotia Research Innovation Trust | 14J03935, 23224008 |
| UT-Battelle | DE-AC05-00OR22725 |
| Natural Sciences and Engineering Research Council of Canada | |
| Canada Foundation for Innovation | |
| Deutscher Akademischer Austauschdienst |