P. C. Sood

Microscopic structures of parity doublets in the151Pm,153Eu and155Eu nuclei

Microscopic structures of the proposed parity doublet bands in the odd-proton Z=61151Pm and Z=63153, 155Eu nuclei are examined using the quasiparticle phonon nuclear model Hamiltonian including the residual pairing and multipole-multipole interactions. Octupole correlations between intrinsic nonrotational states are studied to check the suggested assignments of parity doublet partners in these nuclei. We conclude significant octupole correlations between a pair ofKπ = 1/2± doublets in each of these nuclei, with somewhat weaker correlations betweenKπ = 3/2± bands in both the Eu isotopes. No octupole connection between the lowestKπ = 5/2± bands is found; however, significant octupole collectivity, built on the low-lying 5/2− bands, is predicted in the higher-lying 5/2+ bands which contain the 5/2+ [402] fragmented strength.

Characterization of isomers of the nucleus154Pm

Consideration of the expected two-quasiparticle structures and their estimated band head energies, and the selection rules for beta transition rates for the154Nd →154Pm →154Sm decays are used to deduce the configurations for the isomers and the low-spin structures in the neutron rich doubly odd nucleus61154Pm93. The 2.68 m high spin isomer and the 1.73 m low spin isomer are respectively assigned the spin-parity 4+ and 1+ with the configuration {p:5/2− [532↑] +n:3/2− [521↑]} with the 2.68 m isomer lying lower in energy, and thus forming the154Pm ground state. Two-quasiparticle character of the beta-connected states in154Nd decay and154Pm decay is discussed.

Deformed Odd-Odd Nuclei: Matrix Elements for the Residual p-n Interaction and Patterns of Alternating Perturbations in Level Spacings

The application of a simple semi-empirical model is discussed in terms of interpreting experimental nuclear structure data for twelve of the best characterized odd-odd deformed nuclei. An essential part of this modeling is to calculate values of the Gallagher-Moszkowski splittings and Newby shifts, the observables that arise from the n-p residual interaction in odd-odd nuclei. Assumptions regarding the form for this n-p force are traced historically. The predictive power of a favored form of the n-p force, one that includes a central force with short-and long-range components, a tensor force, and some effects of core polarization, is examined in light of experimental data obtained since its formulation. A data set of forty-two experimentally-determined Newby shifts has been reviewed as to the reliability of each entry. Exceptions to a recently proposed rule for the a priori determination of the sign of a Newby shift are discussed. Evidence is presented for the existence of an odd-even staggering or signature effect in the rotational spacings of many K - bands (with K > 0). By use of corioliscoupling calculations, it has been possible to reproduce the staggering observed in some of the K - rotational bands of 156Tb, 168Tm, 176Lu, 182Ta, and 182Re.

THE LEVEL STRUCTURE, SPINS AND PARITIES OF 223Ac

The spin-parity assignments of 223Ac are discussed based on a critical reexamination of the experimental data and the theoretical calculations.

Deuteron-induced reaction studies of the nuclear structure of178Hf

The level structure of178Hf is interpreted on the basis of the population of the states following178Hf (d, d′),177Hf (d, p) and179Hf (d, t) reactions. Evidence for quadrupole and octupole vibrational bands and unmixed and intermixed two-quasiparticle configurations is presented.

SYSTEMATICS OF SUPERDEFORMATION FROM A~8 TO A~248

The systematics of superdeformation (∈≈0.6) is studied throughout the mass regions from A~8 to the fission isomers with A~242, including the recently observed superdeformed nuclei with A~152 and ~192. Strong shell effects are calculated which are described in a shell energy landscape in terms of valleys of stability which proceed from oblate through spherical to normal-deformed (∈≈0.25–0.3) and on to superdeformed and hyperdeformed (∈≈0.86) shapes with increasing nucleon number. Local minima in these valleys are calculated for prolate nuclei with 4, 10, 16, 28–32, 40–44, 60–66, 80–86, 110–116 and 140–150 neutrons and/or protons when the ratio of the major to minor axes is ≈ 2:1 and the deformation ∈≈0.6. Although the local minima represent the regions of greatest stability, the shell energy valleys should be viewed as more or less continuous structures in which a variety of different deformations can occur. Other local minima in the valleys of the shell energy landscape are observed for oblate (∈≈−0.75) and hyperdeformed nuclei. When shell effects are added to the liquid-drop potential in the Nilsson-Strutinsky formalism, spherical and normal deformation shapes tend to predominate. However, superdeformed, oblate and hyperdeformed shapes are also predicted. In the case of superdeformed nuclei, shell effects predominate over the liquid-drop potential for the light nuclei creating superdeformed ground states. In intermediate-mass nuclei, the liquid-drop potential predominates and superdeformation is only observed at fairly high energy and at high spins where the superdeformation is stabilized. In the heaviest nuclei, the combined effect of the Coulomb potential and the fissionability of the liquid drop causes the potential to reach a maximum at ∈≈0.6. The shell effect then produces a second minimum 2–3 MeV above the ground state with its coexisting spectroscopy. Existing experimental data throughout the nuclear periodic table are shown to be in remarkable agreement with theoretical expectations. Predictions of new regions of superdeformation are presented.

EVIDENCE FOR THE COEXISTENCE OF INTRINSIC REFLECTION ASYMMETRY AND REFLECTION SYMMETRY IN 155Eu AND 153Eu

The inverted odd-even staggering of the differential radii of the Eu isotopes from neutron number 88 through 93, and the Kπ = 5/2± parity doublets with magnetic moments tending towards the hybridized limit and with connecting enhanced El transitions in l55Eu and 153Eu suggest the existence of intrinsic reflection asymmetry in the ground state of the Eu isotopes. The average splitting energy between 3 parity doublets in 155Eu is 63.8 keV, while it is 97.4 keV for the one parity doublet in 153Eu. Decoupling parameters of the Kπ = 1/2± parity doublet bands in l55Eu have opposite signs but are approaching the same absolute value as expected for intrinsic reflection asymmetric nuclei. However, the presence of the 3/2 [411] bands with octupole vibrations ~530 keV above also implies the coexistence of reflection symmetric spectra in the low energy regions of both 155Eu and 153Eu.

Systematic investigation of hexadecapole collectivity in even-even nuclei

Energies of the first 2+, 3− and 4+ states of even-even nuclei are plotted against proton and neutron number. Using this systematics, shell effects and the corresponding quadrupole and hexadecapole collectivity and deformation effects are compared and contrasted. Also, the correspondingB(E2),B(E3) andB(E4) values are plotted against neutron number and their very different systematics compared. Among the new results are the presence of hexadecapole collectivity at the 82 proton and neutron closed shells and the presence of the maximum values ofB(E4) at neutron numbers 10, 90–92 and 140–146. Finally, the systematics of the hexadecapole (K=4+) vibrations is compared with that of the quadrupole (K=2+) gamma vibrations in the quadrupole deformed rare earth region.

Configurational assignments inHo168and comparison withHo166

Comparison of the six states recently observed in {sup 168}Ho with the states in {sup 166}Ho suggests configurational assignments for all six states. The validity of these assignments is strengthened by the allowed unhindered beta decay of {sup 168}Dy to the two 1{sup +} states in {sup 168}Ho and by microscopic theoretical calculations of the quasiparticle structure of the corresponding states in {sup 166}Ho and {sup 168}Ho.

Configurational assignments in Ho 168 and comparison with Ho 166

Comparison of the six states recently observed in {sup 168}Ho with the states in {sup 166}Ho suggests configurational assignments for all six states. The validity of these assignments is strengthened by the allowed unhindered beta decay of {sup 168}Dy to the two 1{sup +} states in {sup 168}Ho and by microscopic theoretical calculations of the quasiparticle structure of the corresponding states in {sup 166}Ho and {sup 168}Ho.