Masses and $\ensuremath{\beta}$-Decay Spectroscopy of Neutron-Rich Odd-Odd $^{160,162}\mathrm{Eu}$ Nuclei: Evidence for a Subshell Gap with Large Deformation at $N=98$

Masses and $β$ -Decay Spectroscopy of Neutron-Rich Odd-Odd ${}^{160, 162}{Eu}$ Nuclei: Evidence for a Subshell Gap with Large Deformation at $N = 98$

D. J. Hartley, F. G. Kondev, R. Orford, J. A. Clark, G. Savard, A. D. Ayangeakaa, S. Bottoni, F. Buchinger, M. T. Burkey, M. P. Carpenter, P. Copp, D. A. Gorelov, K. Hicks, C. R. Hoffman, C. Hu, R. V. F. Janssens, J. W. Klimes, T. Lauritsen, J. Sethi, D. Seweryniak, K. S. Sharma, H. Zhang, S. Zhu, and Y. Zhu

Phys. Rev. Lett. 120, 182502 – Published 4 May 2018

Abstract

The structure of deformed neutron-rich nuclei in the rare-earth region is of significant interest for both the astrophysics and nuclear structure fields. At present, a complete explanation for the observed peak in the elemental abundances at $A \sim 160$ eludes astrophysicists, and models depend on accurate quantities, such as masses, lifetimes, and branching ratios of deformed neutron-rich nuclei in this region. Unusual nuclear structure effects are also observed, such as the unexpectedly low energies of the first $2^{+}$ levels in some even-even nuclei at $N = 98$ . In order to address these issues, mass and $β$ -decay spectroscopy measurements of the ${}^{160}{Eu}_{97}$ and ${}^{162}{Eu}_{99}$ nuclei were performed at the Californium Rare Isotope Breeder Upgrade radioactive beam facility at Argonne National Laboratory. Evidence for a gap in the single-particle neutron energies at $N = 98$ and for large deformation ( $β_{2} \sim 0.3$ ) is discussed in relation to the unusual phenomena observed at this neutron number.

Received 19 January 2018
Revised 27 March 2018

DOI:https://doi.org/10.1103/PhysRevLett.120.182502

Physics Subject Headings (PhySH)

Beta decay Binding energy & masses Electromagnetic transitions

Nuclear Physics

Authors & Affiliations

D. J. Hartley¹, F. G. Kondev², R. Orford^2,3, J. A. Clark^2,4, G. Savard^2,5, A. D. Ayangeakaa^2,*, S. Bottoni^2,†, F. Buchinger³, M. T. Burkey^2,5, M. P. Carpenter², P. Copp^2,6, D. A. Gorelov^2,4, K. Hicks¹, C. R. Hoffman², C. Hu⁷, R. V. F. Janssens^2,‡, J. W. Klimes², T. Lauritsen², J. Sethi^2,8, D. Seweryniak², K. S. Sharma⁹, H. Zhang⁷, S. Zhu², and Y. Zhu⁷

¹Department of Physics, U.S. Naval Academy, Annapolis, Maryland 21402, USA
²Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
³Department of Physics, McGill University, Montréal, Québec H3A 2T8, Canada
⁴Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
⁵Department of Physics, University of Chicago, Chicago, Illinois 60637, USA
⁶Department of Physics, University of Massachusetts-Lowell, Lowell, Massachusetts 01854, USA
⁷Department of Physics, Zhejiang University, Hangzhou, China
⁸Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA
⁹University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada

^*Present address: Department of Physics, U.S. Naval Academy, Annapolis, Maryland 21402, USA.
^†Present address: Universit degli Studi di Milano and INFN, Via Celoria 16, 20133 Milano, Italy.
^‡Present address: Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA and Triangle Universities Nuclear Laboratory, Duke University, Durham, North Carolina 27708, USA.