D. C. Zheng

Double Gamow-Teller strength in nuclei

The Gamow--Teller transition strength from ({ital N},{ital Z}) to ({ital N}{minus}2,{ital Z}+2) nuclei is studied using extended space shell-model calculations. The notion of a giant double Gamow--Teller state is introduced. The application of these ideas to double beta-decay and pion double charge exchange is introduced. A good signature in light-medium mass nuclei of the double Gamow--Teller mechanism in pion double charge exchange from the {ital J}=0 ground state of an even--even nucleus is the excitation of both {ital J}=0{sup +} and {ital J}=2{sup +} states in the final nucleus. {copyright} 1989 Academic Press, Inc.

Nuclear structure studies of double Gamow-Teller and double beta decay strength

Abstract The double Gamow-Teller strength distribution is evaluated microscopically in a series of light and medium mass nuclei using the shell model approach. The specific 2β decay transition from the ground state to ground state is computed in all the nuclei considered and the model dependence of the result is studied. The importance of the coherence when summing over the intermediate states is studied and is found to be a crucial factor in most of the double Gamow-Teller transitions. The effects of SU(4) symmetry breaking are studied using several models and types of interactions. This breaking is much larger in medium mass nuclei (A = 44) than in the lighter nuclei (A = 8, 12, or 20). The behaviour of double Gamow-Teller ground state to ground state transition amplitudes on the size of the model space is found to be complicated and to be different for different nuclei. The probabilities of studying double Gamow-Teller strength in combined (p, n) and (n, p) experiment, in pion double charge-exchange, and charge-exchange reactions are discussed.

An excited superdeformed band of 80Zr in Skyrme Hartree-Fock calculations

Abstract Both experiment and theory yield the result that the ground band of 80Zr is superdeformed with an axis ratio of approximately 3 2 . In this work excited bands are considered with Skyrme Hartree-Fock approach. Using the Skyrme 3 interaction an excited spherical state is calculated at an excitation energy of 8.6 MeV and an excited superdeformed band with an axis ratio of about 2 1 is obtained with a band-head energy of 8.5 MeV. Relative to the (excited) spherical state, the ground state band consists of a 12-particle-12-hole state and the excited deformed band consists of a 16-particle-16-hole excitation. Other topics such as the kinetic energy anomaly, the monopole shrinkage, and the Bertsch formula for deformation are discussed.

Comparison of the Nilsson and Skyrme Hartree-Fock results for the properties of highly deformed states in nuclei☆

A Comparison of the Nilsson model and the Skyrme Hartree-Fock model for studying highly deformed states in nuclei is made. The states constructed are the 4-particle, 4-hole and 8-particle, 8-hole states in 40Ca and the linear alpha chain states in 12C and 16O. The deformations obtained in the two approaches are remarkably similar. The change in the radius of the np-nh state in 40Ca relative to the ground state is smaller in the Skyrme Hartree-Fock model than in the Nilsson model, indicating monopole shrinkage in the former approach, hence volume non-conservation. Whereas the energies of the 4p−4h states are nearly the same in the two approaches, the 8p−8h is at too high an energy in the Nilsson model. For the linear chain states in 12C and 16O, the Skyrme 3 Hartree-Fock approach gets the energies of the projected Jπ = 0+ states a factor of two too high while the results of the Nilsson model are in surprisingly good agreement with experiments. The quadrupole moment in momentum space (Qp) for the ground state and the metastable highly deformed states is discussed.

Variable volume parameters for the radii and kinetic energies of superdeformed states

Abstract In Hartree-Fock calculations for 40Ca with certain Skyrme interactions, the difference of kinetic energy between a deformed np−nh state and the spherical ground state is often much larger than what is predicted by a volume conserving deformation. To explain the results the volume parameter ( ω x ω y ω z ) 1 3 must be different for an np−nh state than it is for the ground state.

A model study of finite range three-body interactions

Abstract An interaction consisting of a two-body attractive Gaussian and three-body repulsive Gaussian is applied to study the ground state and four-particle excitation state of 4He. This may be regarded as an extension of the Skyrme interactions (T. H. R. Skyrme, Philos. Mag., 1 (1956), 1043; Nucl. Phys., 9 (1959), 615; D. Vautherin and D. M. Brink, Phys. Rev. C, 5 (1972), 626) all of which have zero range three-body terms. Up to a certain point, increasing the range a3 of the three-body term results in a deeper and sharper minimum for the energy of the four-particle excitation. However if a3 becomes too large relative to the two-body range a2, a phenomenon, which we call pseudo-collapse, comes into play. In contrast to the above, when an interaction consisting of a short range two-body repulsion and long range two-body attraction is used, there is no relative minimum in the energy of the four-particle excitation. Thus, not all states obtained in usual shell model calculations may really exist.