[Triumf-seminars] TRIUMF Special Seminar, Mon 2010-05-03 at 14:00

[postmaster at admin.triumf.ca]

Date/Time: Mon 2010-05-03 at 14:00  

Location: Auditorium  

Speaker: Dr. Heather Crawford - Hausser Fellowship finalist (NSCL)  

Title: "Beta-Decay and Isomeric Properties of Neutron-Rich Sc and Ca Isotopes Near N=32 and 34"  

Abstract: Dr. Heather Crawford is on the short list of applicants for the TRIUMF Otto Ha"usser Fellowship.

Beta-decay and Isomeric Properties of Neutron-Rich Sc and Ca Isotopes Near N=32 and 34
   The beta decay and isomeric properties of neutron-rich 21Sc and 20Ca isotopes near neutron number N=32 and N=34 have been studied at NSCL.  The low-energy structures of nuclei in this region are stabilized by the presence of a sub-shell closure at N=32, a result of the gap between the neutron 2p3/2 level and the higher-lying 2p1/2 and 1f5/2 levels.  A gap is also predicted between the 2p1/2 and 1f5/2 orbits, suggesting a possible additional sub-shell closure at N=34 in the 20Ca and 22Ti isotopes [1].  While experimental evidence for 56Ti [2] suggests that such a gap is not present for Z=22, the presence or absence of this sub-shell closure in the Ca isotopes remains an open question.  The lack of protons in the 1f7/2 orbit in the 20Ca isotopes may result in a continued monopole shift of the neutron 1f5/2 orbital, leading to a significant gap between the neutron 1p1/2 and 1f5/2 states.
The low-energy level structures of 53,54,56Sc, deduced from beta decay and isomer data collected at NSCL with the Beta Counting System [3] combined with 16 detectors from the Segmented Germanium Array [4], will be presented.  The results are interpreted in the framework of basic particle-particle and particle-hole coupling, and compared to shell-model calculations using the GXPF1 effective interaction [5].  Decays from an isomeric state in 56Sc have permitted identification of new levels in this nuclide, located one proton and one neutron outside of 54Ca.  The ordering and origin of these low-lying levels provides insight into the possible N=34 sub-shell gap in the Ca isotopes.  Isomeric and delayed beta rays in 54Sc, as well as the low-level structure of 53Sc populated following beta decay of 53Ca, give additional support for the N=32 sub-shell closure at Z=20.  

[1] T. Otsuka et al., Phys. Rev. Lett. 87, 082502 (2001).  
[2] S.N. Liddick et al., Phys. Rev. Lett. 92, 072502 (2004).
[3] J.I. Prisciandaro et al., NIM A 505, 140 (2003).
[4] W.F. Mueller et al., NIM A 466, 492 (2001).
[5] M. Homna et al., Phys. Rev. C 65, 061301(R) (2002).
  

Dr. Cerfon and Dr. Crawford are the two finalists for the TRIUMF Otto Hausser Fellowship.