Masses and Beta-decay Studies of Neutron-rich Nuclei using the X-array and Gammasphere

¹ Physics Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
² Department of Physics, U.S. Naval Academy, Annapolis, Maryland 21402, USA
³ Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
⁴ Department of Physics and Astronomy, University of Manitoba, Winnipeg, Winnipeg, Manitoba R3T 2N2, Canada
⁵ Department of Physics, University of Chicago,y, Chicago, Illinois 60637, USA
⁶ Universitet degli Studi di Milano and INFN, Via Celoria 16, 20133 Milano, Italy
⁷ Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina and Triangle Universities Nuclear Laboratory, Duke University, Durham, North Carolina 27708, USA
⁸ Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA
⁹ Variable Energy Cyclotron Centre, India and Homi Bhabha National Institute, Training School Complex, Anushaktinagar, 1/AF Bidhan Nagar, Kolkata, 700064, Mumbai–400094, India
¹⁰ Department of Chemistry, Washington University, St. Louis, St. Louis, 63130, Missouri USA
¹¹ Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland, 20742, USA
¹² Department of Biological and Physical Sciences, South Carolina State University, Orangeburg, South Carolina 29117, USA

^* e-mail: kondev@anl.gov

Published online: 4 December 2019

Abstract

Properties of neutron-rich nuclei in the A˜160 region are important for achieving a better understanding of the nuclear structure in this region where little is known owing to diffculties in the production of these nuclei at the present nuclear physics facilities. These properties are essential ingredients in the interpretation of the rareearth peak at A˜160 in the r process abundance distribution, since theoretical models are sensitive to nuclear structure input. Predicated on these ideas, we have initiated a new experimental program at Argonne National Laboratory. During the first experiment, beams from the Californium Rare Isotope Breeder Upgrade radioactive beam facility were used in conjunction with the SATURN decay station and the X-array. We focused initially on several odd-odd nuclei, where β decays of both the ground state and an excited isomer were investigated. Because of the spin difference, a variety of structures in the daughter nuclei were selectively populated and characterized based on their decay properties. Mass measurements using the Canadian Penning Trap aimed at establishing the excitation energy of the β-decaying isomers were also carried out. Evidence was found for a change in the single-particle structure, which in turn results in the formation of a sizable N=98 sub-shell gap at large deformation. Results from the first experimental campaign using the newly-commissioned β-decay station at Gammasphere are also presented.