S. Pittel

Towards a unified microscopic description of nuclear deformation

Abstract Nuclear deformation, as it occurs in both light and heavy nuclei, is discussed in a unified microscopic shell-model framework. The short-range 3 S 1 neutron-proton interaction plays an important role in this discussion.

Systematic study of deformed nuclei at the drip lines and beyond

An improved prescription for choosing a transformed harmonic oscillator (THO) basis for use in configuration-space Hartree-Fock-Bogoliubov (HFB) calculations is presented. The new HFB+THO framework that follows accurately reproduces the results of coordinate-space HFB calculations for spherical nuclei, including those that are weakly bound. Furthermore, it is fully automated, facilitating its use in systematic investigations of large sets of nuclei throughout the periodic table. As a first application, we have carried out calculations using the Skyrme Force SLy4 and volume pairing, with exact particle number projection following application of the Lipkin-Nogami prescription. Calculations were performed for all even-even nuclei from the proton drip line to the neutron drip line having proton numbers Z=2,4,...,108 and neutron numbers N=2,4,...,188. We focus on nuclei near the neutron drip line and find that there exist numerous particle-bound even-even nuclei (i.e., nuclei with negative Fermi energies) that have at the same time negative two-neutron separation energies. This phenomenon, which was earlier noted for light nuclei, is attributed to bound shape isomers beyond the drip line.

Hartree-Fock-Bogolyubov study of deformation in the ZrMo region

Abstract Hartree-Fock-Bogolyubov calculations are carried out for the even Mo isotopes, to assess quantitatively the role of the isoscalar neutron-proton interaction in producing deformation in nuclei with large neutron excesses.

Nuclear physics of dark matter detection

We describe the elastic scattering of weakly interacting dark matter particles from nuclei, with laboratory detection in mind. We focus on the lightest neutralino (a neutral fermion predicted by supersymmetry) as a likely candidate and discuss the physics needed to calculate its elastic scattering cross section and interpret experimental results. Particular emphasis is placed on a proper description of the structure of the proposed detector nuclei. We include a brief discussion of expected count rates in some detectors.

Neutron-proton correlations in an exactly solvable model

We examine isovector and isoscalar neutron-proton correlations in an exactly solvable model based on the algebra SO(8). We look particularly closely at Gamow-Teller strength and double β decay, both to isolate the effects of the two kinds of pairing and to test two approximation schemes: the renormalized neutron-proton quasiparticle random phase approximation (QRPA) and generalized BCS theory. When isoscalar pairing correlations become strong enough a phase transition occurs and the dependence of the Gamow-Teller β+ strength on isospin changes in a dramatic and unfamiliar way, actually increasing as neutrons are added to an N=Z core. Renormalization eliminates the well-known instabilities that plague the QRPA as the phase transition is approached, but only by unnaturally suppressing the isoscalar correlations. Generalized BCS theory, on the other hand, reproduces the Gamow-Teller strength more accurately in the isoscalar phase than in the usual isovector phase, even though its predictions for energies are equally good everywhere. It also mixes T=0 and T=1 pairing, but only on the isoscalar side of the phase transition.

Microscopic study of the shape transition in the zirconium isotopes

Abstract The shape transition in the Zr isotopes is investigated in the framework of the Shell Model. The neutron-proton interaction between selected orbitals is found to be instrumental for the onset of deformation in this neutron-rich region.

Quadrupole deformations of neutron-drip-line nuclei studied within the Skyrme Hartree-Fock-Bogoliubov approach

We introduce a local-scaling point transformation to allow for modifying the asymptotic properties of the deformed three-dimensional Cartesian harmonic oscillator wave functions. The resulting single-particle bases are very well suited for solving the Hartree-Fock-Bogoliubov equations for deformed drip-line nuclei. We then present results of self-consistent calculations performed for the Mg isotopes and for light nuclei located near the two-neutron drip line. The results suggest that for all even-even elements with

The microscopic Interacting Boson Model for nondegenerate orbits

Z

Exactly Solvable Models for Atom-Molecule Hamiltonians

=10--18 the most weakly-bound nucleus has an oblate ground-state shape.

Boson mappings and four-particle correlations in algebraic neutron-proton pairing models

Abstract The microscopic Interacting Boson Model formalism is outlined and a general procedure is described for deriving the parameters of the model when the valence orbits are nondegenerate. This latter technique involves expanding pair creation operators for J = 0 (or J = 2) correlated pairs in terms of J = 0 (or J = 2) pair creation operators for individual orbits. This expansion enables us to relate matrix elements for the multi-orbit problem to matrix elements for individual orbits for which the well-known Racah-seniority reduction formulae apply. Our calculated results for the parameters of the boson-boson quadrupole-quadrupole interaction show a definite relationship to the underlying subshell structure of each major shell, in agreement with the phenomenological results. It is also discovered that the results obtained using particle states are not the same as those obtained using hole states, due to the truncation scheme used to extablish the correlated J = 0 and J = 2 pairs.