Theoretical study of the decay-out spin of superdeformed bands in the Dy and Hg regions

Decay of the superdeformed bands have been studied mainly concentrating upon the decay-out spin, which is sensitive to the tunneling probability between the super- and normal-deformed wells. Although the basic features are well understood by the calculations, it is difficult to precisely reproduce the decay-out spins in some cases. Comparison of the systematic calculations with experimental data reveals that values of the calculated decay-out spins scatter more broadly around the average value in both the $A \approx$ 150 and 190 regions, which reflects the variety of calculated tunneling probability in each band.Comment: 6 pages 4 figures (30 PS files). To appear in Proc. of NS2000 (Nuclear Structure 2000) conf., at MSU, 15-19 Aug., 200

Efficient Method for Quantum Number Projection and Its Application to Tetrahedral Nuclear States

We have developed an efficient method for quantum number projection from most general HFB type mean-field states, where all the symmetries like axial symmetry, number conservation, parity and time-reversal invariance are broken. Applying the method, we have microscopically calculated, for the first time, the energy spectra based on the exotic tetrahedral deformation in $^{108,110}$Zr. The nice low-lying rotational spectra, which have all characteristic features of the molecular tetrahedral rotor, are obtained for large tetrahedral deformation, \alpha_{32} \gtsim 0.25, while the spectra are of transitional nature between vibrational and rotational with rather high excitation energies for $\alpha_{32}\approx 0.1-0.2$Comment: Trivial mistakes are correcte

On the Response Function Technique for Calculating the Random-Phase Approximation Correlation Energy

We develop a scheme to exactly evaluate the correlation energy in the random-phase approximation, based on linear response theory. It is demonstrated that our formula is completely equivalent to a contour integral representation recently proposed by Donau et al. being numerically more efficient for realistic calculations. Numerical examples are presented for pairing correlations in rapidly rotating nuclei.Comment: 4 pages, 4 figure

High-K Precession modes: Axially symmetric limit of wobbling motion

The rotational band built on the high-K multi-quasiparticle state can be interpreted as a multi-phonon band of the precession mode, which represents the precessional rotation about the axis perpendicular to the direction of the intrinsic angular momentum. By using the axially symmetric limit of the random-phase-approximation (RPA) formalism developed for the nuclear wobbling motion, we study the properties of the precession modes in $^{178}$W; the excitation energies, B(E2) and B(M1) values. We show that the excitations of such a specific type of rotation can be well described by the RPA formalism, which gives a new insight to understand the wobbling motion in the triaxial superdeformed nuclei from a microscopic view point.Comment: 14 pages, 8 figures (Spelling of the authors name was wrong at the first upload, so it is corrected

Simple model for decay of superdeformed nuclei

Recent theoretical investigations of the decay mechanism out of a superdeformed nuclear band have yielded qualitatively different results, depending on the relative values of the relevant decay widths. We present a simple two-level model for the dynamics of the tunneling between the superdeformed and normal-deformed bands, which treats decay and tunneling processes on an equal footing. The previous theoretical results are shown to correspond to coherent and incoherent limits of the full tunneling dynamics. Our model accounts for experimental data in both the A~150 mass region, where the tunneling dynamics is coherent, and in the A~190 mass region, where the tunneling dynamics is incoherent.Comment: 4 page

Spreading Width for Decay out of a Superdeformed Band

The attenuation factor F responsible for the decay out of a superdeformed (SD) band is calculated with the help of a statistical model. This factor is given by 1/F = (1 + Gamma(down) / Gamma(S)). Here, Gamma(S) is the width for the collective E2 transition within the superdeformed band, and Gamma(down) is the spreading width which describes the mixing between a state in the SD band and the normally deformed (ND) states of equal spin. The attenuation factor F is independent of the statistical E1 decay widths Gamma(N) of the ND states provided that the Gamma(N) are much larger than both Gamma(down) and Gamma(S). This condition is generically met. Previously measured values of F are used to determine Gamma(down).Comment: Submitted to Physical Review Letter