Type of Document Dissertation Author Drumev, Kalin Author's Email Address kdrume1@lsu.edu URN etd-04112008-095727 Title Towards an Extended Microscopic Theory for the Upper-fp-shell Nuclei Degree Doctor of Philosophy (Ph.D.) Department Physics & Astronomy Advisory Committee
Advisor Name Title Jerry P. Draayer Committee Chair A. Ravi P. Rau Committee Member Jeffrey Blackmon Committee Member John Wefel Committee Member Kermit Murray Dean's Representative Keywords
- shell model
- models based on group theory
- collective levels
- upper-fp-shell nuclei
Date of Defense 2008-04-10 Availability unrestricted Abstract An extended SU(3) shell model that for the first timeexplicitly includes particles from the unique-parity
levels in nuclei is introduced. Its relevance is established through
calculations performed with realistic interactions for a group of
upper fp-shell isotopes where valence nucleons beyond the N=28=Z core
occupy levels of the normal-parity upper $fp$-shell
($f_{5/2},p_{3/2},p_{1/2}$) and the unique-parity $g_{9/2}$
intruder configuration. Specifically, the outcome suggests that
the pseudo-SU(3) symmetry is quite good throughout the region and
that only part of the configurations are relevant for the structure
of the low-lying states. The levels of the upper $fp$-shell are
handled within the framework of an m-scheme basis as well as
its pseudo-SU(3) counterpart, and respectively, the $g_{9/2}$
as a single level and as a member for the complete $gds$ shell.
More detailed analyses of the extended SU(3) model are done for
two nuclei of special interest in astrophysics, namely the waiting-point
nuclei $^{64}$Ge and $^{68}$Se. The strengths and limitations
of the theory are demonstrated by its ability to describe various
nuclear characteristics. Specifically, energy spectra, B(E2)
transition strengths and wave-function content are compared with
the realistic results. In addition, the dominance of configurations with
different distribution of particles and the role that several
newly-introduced terms play in the Hamiltonian are investigated.
The extended SU(3) approach allows one to better probe the effects
of deformation and account for these key properties of the system
within a highly-truncated model space.
The model also promises to be useful for nuclei from the
rare-earth and actinide regions. Specifically, by ensuring
a robust number of collective degrees of freedom and
Hamiltonians with a larger number of degrees of freedom,
it should allow one to give a satisfactory explanation of
the experimentally-observed existence of an abundance of
low-lying $0^{+}$ states and very strongly enhanced B(E2)
strengths found in these nuclei. This version of the theory
will extend previous results from the pseudo-SU(3) model
where the role of nucleons in the intruder levels was
relegated to a very simple renormalization of the dynamics
defined by nucleons in the normal-parity spaces only.
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