Seminar Details

Lifetime Measurements and Pf-Shell Structure Studies Near N=Z

Charles Loelius, MSU NSCL/Physics
Thursday, April 24, 11:00 AM - 1st Guidance Committee Meeting
NSCL Lecture Hall

The structure of nuclei near the doubly magic nucleus 56Ni has provided a sensitive probe of configuration mixing across the N=Z=28 shell gap. The shell model description of nuclei in this region is well established, with the gxpf1 interaction accurately reproducing the energy levels and transition strengths of nuclei in the vicinity of 56Ni[1]. However, there remain open questions as to the effects of higher lying orbitals beyond the pf shell. In this talk the structure of even-even nuclei in the upper pf shell will be discussed, focusing on preliminary results of lifetime measurements performed at the NSCL. The B(E2) values, which can be derived from the lifetimes of excited states, reflect the effects of configuration mixing and possible contributions from intruder orbitals. Especially of importance in this region are the B(E2; 4+ → 2+), as the effects of high l orbitals may be enhanced. In particular the only prior measurement of the B(E2; 4+ → 2+) of the stable nucleus 58Ni, which used the Doppler Shift Attenuation Method (DSAM), resulted in a B(E2; → 4+ → 2+) three times larger than that predicted by a shell model calculation using the gxpf1 interaction[1][2]. In order to resolve this discrepancy, a second measurement of the lifetime of 58Ni was undertaken at the NSCL during the Gamma-Ray Energy Tracking In Beam Nuclear Array (GRETINA) campaign. The Recoil Distance Method (RDM) was employed in this measurement. The preliminary results for the 4+ lifetime of 58Ni from this experiment will be shown together with the impact of the addback analysis of the GRETINA array[3]. In addition, preliminary gamma ray spectra for new lifetime measurements of excited states of the N=Z nucleus 60Zn will be presented. Further perspectives for studies in the region will also be discussed, with a focus on a possible experiment to measure isospin non-conserving terms via lifetime measurements of the excited states of 58Zn, the mirror nucleus to 58Ni. References [1] M. Honma et al. New effective interaction for pf-shell nuclei and its implications for the stability of the N=Z=28 closed core Phys. Rev. C 69 034335 (2004) [2] O. Kenn et al. Measurements of g factors and lifetimes of low lying states in 58-64Ni and their shell model implications Phys. Rev. C 63 064306 (2001) [3] S. Paschalis et al. The performance of the Gamma Ray Energy Tracking In-beam Nuclear Array GRETINA Nucl. Instrum. Meth. A 709, 44 (2013).