H. Nakada

Parity dependence of nuclear level densities

A simple formula for the ratio of the number of odd- and even-parity states as a function of temperature is derived. This formula is used to calculate the ratio of level densities of opposite parities as a function of excitation energy. We test the formula with quantum Monte Carlo shell model calculations in the (pf+g(9/2)) shell. The formula describes well the transition from low excitation energies where a single parity dominates to high excitations where the two densities are equal.

Particle-Number Reprojection in the Shell Model Monte Carlo Method: Application to Nuclear Level Densities

We introduce a particle-number reprojection method in the shell model Monte Carlo that enables the calculation of observables for a series of nuclei using a Monte Carlo sampling for a single nucleus. The method is applied to calculate nuclear level densities in the complete (pf+g{sub 9/2}) -shell using a good-sign Hamiltonian. Level densities of odd-A and odd-odd nuclei are reliably extracted despite an additional sign problem. Both the mass and the T{sub z} dependence of the experimental level densities are well described without any adjustable parameters. The odd-even staggering observed in the calculated backshift parameter follows the experimental data more closely than do empirical formulas. (c) 1999 The American Physical Society.

Isospin decomposition of the Gamow-Teller strength in Cu-58

Abstract The Gamow-Teller (GT) strength excited by a (p, n)-type reaction on a nucleus with isospin T0 and N > Z is shared by isospin components T0 − 1, T0 and T0 + 1. A good energy resolution (3He, t) reaction on 58Ni revealed the fine structure of the GT strength in 58Cu. The isospin of each level constituting the fine structure was assigned by comparing to results from inelastic electron and proton scatterings and (n, p)-type reactions, thus resolving the isospin structure of the GT strength in 58Cu. The ratio of the summed GT strengths among the three isospin components is well described by a shell-model calculation.

E2 properties of nuclei far from stability and the proton-halo problem of 8B.

[ital E]2 properties of [ital A]=6--10 nuclei, including those of nuclei far from stability, are studied by a (0+2)[h bar][omega] shell-model calculation which includes [ital E]2 core-polarization effects explicitly. The quadrupole moments and the [ital E]2 transition strengths in [ital A]=6--10 nuclei are described quite well by the present cal- culation. This result indicates that the relatively large value of the quadrupole moment of [sup 8]B can be understood without introducing the proton halo in [sup 8]B. An interesting effect of the 2[h bar][omega] core-polarization is found for effective charges used in the 0[h bar][omega] shell model; although isoscalar effective charges are almost constant as a function of nucelus, appreciable variations are needed for isovector effective charges which play important roles in nuclei with high isospin values.

Spin projection in the shell model monte carlo method and the spin distribution of nuclear level densities.

We introduce spin projection methods in the shell model Monte Carlo approach and apply them to calculate the spin distribution of level densities for iron-region nuclei using the complete (pf + g9/2) shell. We compare the calculated distributions with the spin-cutoff model and extract an energy-dependent moment of inertia. For even-even nuclei and at low excitation energies, we observe a significant suppression of the moment of inertia and odd-even staggering in the spin dependence of level densities.

Heavy deformed nuclei in the shell model Monte Carlo method.

We extend the shell model Monte Carlo approach to heavy deformed nuclei using a new proton-neutron formalism. The low excitation energies of such nuclei necessitate low-temperature calculations, for which a stabilization method is implemented in the canonical ensemble. We apply the method to study a well-deformed rare-earth nucleus, 162Dy. The single-particle model space includes the 50-82 shell plus 1f_{7/2} orbital for protons and the 82-126 shell plus 0h_{11/2}, 1g_{9/2} orbitals for neutrons. We show that the spherical shell model reproduces well the rotational character of 162Dy within this model space. We also calculate the level density of 162Dy and find it to be in excellent agreement with the experimental level density, which we extract from several experiments.

Tensor-force effects on single-particle levels and proton bubble structure around the Z or N=20 magic number

Applying the semi-realistic

Crossover from vibrational to rotational collectivity in heavy nuclei in the shell-model Monte Carlo approach.

NN

Microscopic nuclear level densities from Fe to Ge by the shell model Monte Carlo method

interactions that include realistic tensor force to the Hartree-Fock calculations, we investigate tensor-force effects on the single-particle levels in the Ca isotopes. The semi-realistic interaction successfully describes the experimental difference between

Semi-realistic nucleon-nucleon interactions with improved neutron-matter properties

\varepsilon(p1s_{1/2})