50 research outputs found
Constant temperature description of the nuclear level densities
The spin and parity dependent nuclear level densities (NLD) are calculated
for medium-heavy nuclei using shell model techniques. The NLD are used to
calculate cross sections and reaction rates of interest for nuclear
astrophysics and nuclear energy applications. We investigate a new approach of
describing the shell model NLD via a constant temperature parametrization. This
approach provides new information about the effects of symmetries on the
temperature of the low-lying nuclear states, and it is shown to be more
versatile for applications
Fast, Efficient Calculations of the Two-Body Matrix Elements of the Transition Operators for Neutrinoless Double Beta Decay
To extract information about the neutrino properties from the study of
neutrinoless double-beta (0\nu\beta\beta) decay one needs a precise computation
of the nuclear matrix elements (NMEs) associated with this process. Approaches
based on the Shell Model (ShM) are among the nuclear structure methods used for
their computation. ShM better incorporates the nucleon correlations, but have
to face the problem of the large model spaces and computational resources. The
goal is to develop a new, fast algorithm and the associated computing code for
efficient calculation of the two-body matrix elements (TBMEs) of the
0\nu\beta{\beta} decay transition operator, which are necessary to calculate
the NMEs. This would allow us to extend the ShM calculations for double-beta
decays to larger model spaces, of about 9-10 major harmonic oscillator shells.
The improvement of our code consists in a faster calculation of the radial
matrix elements. Their computation normally requires the numerical evaluation
of two-dimensional integrals: one over the coordinate space and the other over
the momentum space. By rearranging the expressions of the radial matrix
elements, the integration over the coordinate space can be performed
analytically, thus the computation reduces to sum up a small number of
integrals over momentum. Our results for the NMEs are in a good agreement with
similar results from literature, while we find a significant reduction of the
computation time for TBMEs, by a factor of about 30, as compared with our
previous code that uses two-dimensional integrals.Comment: 6 pages, one figur
Angular Momentum Projected Configuration Interaction with Realistic Hamiltonians
The Projected Configuration Interaction (PCI) method starts from a collection
of mean-field wave functions, and builds up correlated wave functions of good
symmetry. It relies on the Generator Coordinator Method (GCM) techniques, but
it improves the past approaches by a very efficient method of selecting the
basis states. We use the same realistic Hamiltonians and model spaces as the
Configuration Interaction (CI) method, and compare the results with the full CI
calculations in the sd and pf shell. Examples of 24Mg, 28Si, 48Cr, 52Fe and
56Ni are discussed.Comment: 10 pages, 10 figures. Revised version. To be published in Physical
Review