Speaker
Dr
Vandana Tripathi
(Department of Physics, Florida State University, Tallahassee Fl 32306, USA)
Description
Understanding the evolution of shell structure as a function of N/Z is one main focus of current nuclear structure studies. The force behind the migration of orbitals is the monopole part of the tensor interaction. Refinement of this monopole term to increase the predictive powers of shell model calculations underscores the need for more experimental information, specially for excited states in exotic nuclei. Odd Z and odd-odd nuclei provide one of the most stringent tests of shell model predictions as many more degrees of freedom are available.
The structure of odd Z phosphorus isotopes (N = 22 – 25) were investigated at the National Superconducting Cyclotron Laboratory via the beta decay of Si isotopes. Following allowed beta decay, intruder states were populated in the P isotopes which could be identified based on the measured logft values. First gamma transitions in 38,40P were observed de-exciting the strongly populated 1+ states. These 1+ states at relatively low energy (~2MeV) with parity opposite to the 2- ground state are core excited 1p-1h states (1). The occurrence of intruder states at low energies highlights the
importance of pairing and quadrupole correlation energies in lowering the intruder states despite the N = 20 shell gap. Configuration interaction shell model calculations with the state-of-art SDPF-MU effective interaction were performed to understand the structure of these 1p1h states in the even-A Phosphorus isotopes. States in 40P with N = 25 were found to have very complex configurations involving all the fp orbitals leading to deformed
states as seen in neutron rich nuclei with N ~ 28. The calculated GT matrix elements for the beta decay highlight the dominance of the decay of core neutrons over the valence neutrons in neutron rich nuclei when neutrons and protons occupy shells of opposite parity. Unlike the even A isotopes, for the odd A isotopes the negative parity intruder states lie at higher excitation energies and the beta decay strength was found to be fragmented. Systematic discussion of the results for 37-40P will be presented highlighting the effects of adding neutrons on the shell structure.
References:
1) V. Tripathi et al., accepted in PRC, 1/24/2017
This work was supported by NSF grants PHY-1401574 (FSU) and PHY-1068217 (NSCL),
US DoE under contracts DEAC02-05CH11231 (LBNL) and DE-SC00098 (FSU) and JSPS
KAKENHI (Japan), Grants No. 25870168 and 15K05094.
Primary author
Dr
Vandana Tripathi
(Department of Physics, Florida State University, Tallahassee Fl 32306, USA)
Co-authors
Prof.
A. Volya
(Department of Physics, Florida State University, Tallahassee Fl 32306, USA)
Ms
A.L. Richard
(Institute of Nuclear and Particle Physics, Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA)
Prof.
A.O. A. O. Macchiavelli
(Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA)
Ms
B. Abromeit
(Department of Physics, Florida State University, Tallahassee Fl 32306, USA)
Dr
B.P. Crider
(National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824, USA)
Mr
C.J. Prokop
(Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA)
Dr
H. Crawford
(Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA)
Mr
K. Kravvaris
(Department of Physics, Florida State University, Tallahassee Fl 32306, USA)
Ms
N. Larson
(Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA)
Dr
N. Shimizu
(Center of Nuclear Study, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan)
Prof.
P. Fallon
(Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA)
Dr
P.C. Bender
(National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824, USA)
Mr
R. Dungan
(Department of Physics, Florida State University, Tallahassee Fl 32306, USA)
Ms
R.S. Lubna
(Department of Physics, Florida State University, Tallahassee Fl 32306, USA)
Mr
S. Yoshida
(Department of Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan)
Prof.
S.L. Tabor
(Department of Physics, Florida State University, Tallahassee Fl 32306, USA)
Prof.
S.N. Liddick
(Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA)
Prof.
T. Otsuka
(Department of Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan)
Prof.
Y. Utsuno
(Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan)