D. S. Brenner

Empirical proton-neutron interaction energies. Linearity and saturation phenomena

Abstract A method to extract empirical proton-neutron interaction energies for individual protons and neutrons as well as integrated valence p-n interaction strenghts is discussed. The results give direct experimental support to the N p N n scheme, verifying the linearity of the p-n interaction against N p N n early in a shell and its subsequent saturation. They also reflect the behavior i of recently calculated quadrupole p-n strengths which account for the empirical saturation in B (E2: 0 1 + → 2 1 + ) values, and point to the importance of the monopole p-n interaction as well.

The enigma of 114Cd. A classical case of ambiguities in quantum mechanical state mixing

Abstract Lifetime measurements of levels near 2 MeV in 114 Cd give quantitative evidence for collective 3-phonon vibrational states. An analysis of the level scheme reveals a remarkable ambiguity with origins in the basic properties of quantum mechanical mixing.

Empirical p-n interactions: global trends, configuration sensitivity and N=Z enhancements

Abstract Empirical proton-neutron (p-n) interaction strengths are extracted for all nuclei with well-known binding energies. Particularly large interaction strengths are noted for N=Z nuclei: they result primarily from the T=0 component of the interaction and are discussed in terms of both schematic and realistic shell model calculations. Also, the observed micro-structure of the p-n interaction in doubly magic and deformed regions sheds light on both the orbit sensitivity and on the role of monopole and quadrupole components of the p-n interaction.

Observation of 0+ states in 118Cd and the systematics of intruder states

Abstract The structure of 118 Cd was studied through the decay of 118 Ag by angular correlation, γ-γ coincidence, and γ-multiscaling measurements. The results showed the existence and E2 decay properties of two new 0 + states at 1285.8 and 1615.0 keV. They were interpreted in terms of a schematic model calculation of all the even Cd isotopes which is based on simple properties of a quadrupole interaction and which involves the mixing of normal vibration-like and intruder rotation-like 2p-4h configurations.

IBA calculations near the Z = 64 subshell

Abstract It has recently been shown that the effects of the Z = 64 subshell are important for nuclides with N ⩽ 88 but disappear as N approaches 90, due to the influence of neutron-proton interactions. IBA-2 calculations show excellent agreement with experimental energy systematics if the effective reduction in valence bosons caused by the Z = 64 subshell closure is explicitly included. The deduced parameters then behave as predicted by the microscopic basis of the IBA-2 model, in contrast with previous studies.

COULOMB EXCITATION OF RADIOACTIVE NUCLEAR BEAMS IN INVERSE KINEMATICS

Two techniques for determining B(E2:01+ → 21+) values using low-energy Coulomb excitation of Radioactive Nuclear Beams in inverse kinematics are presented. One method, applicable if the lifetime of the excited state is ∼1 ns, uses a linear array of NaI(Tl) detectors to measure the decay curve, and thus the 21+ state lifetime, for Coulomb excited radioactive beam nuclei as they decay in flight downstream from a carbon excitation target. In the second method, useful when lifetimes are short, <1 ns, or for low intensity beams, a through-well NaI(Tl) detector is used to measure the Coulomb excitation cross section from which the B(E2:01+ → 21+) value is calculated. The results of test experiments with beams of stable Os isotopes are presented.

Shell structure in empirical p-n interactions: comparison with Nilsson and shell model calculations

Abstract Calculations of the variations of residual proton-neutron (p-n) interaction matrix elements for three different mass regions are presented within the frameworks of two approaches, the Nilsson and shell models, which differ substantially in the basis states and interactions used. The excellent agreement obtained with experiment in both approaches points to the simplicity of the underlying physics in terms of orbital overlap arguments.

Linearity of nuclear level energies with the P-factor

Abstract It is shown that isotopic sequences of 2 1 + level energies, for elements from Zr to the actinides, are linear against the factor P = N p N n (N p +N n ) . This linearity is interpreted in terms of a simple two-level model. The P -factor also provides a linearization scheme for intruder 0 + energies in the Pb region.

A simple shell model interpretation of the evolution of structure in pre-collective nuclei☆

Abstract The evolution of structure in pre-collective nuclei from oxygen to actinides is studied in terms of the structural signature R 4 2 ≡ E(4 + 1 ) E(2 + 1 ) in singly magic nuclei. A simple physical interpretation of these empirical trends is discussed in terms and illustrated with schematic shell model calculations. The basic idea does not depend on details of the calculations but rather invokes only very general features of nuclear shell structure and the fact that the nuclear force is short-range and attractive.

Parabolic energy dependence of odd-odd multiplets in N=83 nuclides

The splitting and the displacement of low-lying πg72νf72 and πd52νf72 multiplets in the odd-odd N = 83 isotones are found to be described by a quadrupole interaction between the odd proton and odd neutron. The quenching and inversion of the πd52νf72 parabola is found to arise from the quasiparticle blocking effect as the occupancy of the d52 orbital changes.