I.P. Johnstone

Isomerism in 96Ag and non-yrast levels in 96Pd and 95Rh, studied in β decay

The β decay of 96Ag (Z=47,N=49) was investigated by measuring positrons, X rays as well as β-delayed protons and γ rays. The γ radiation was studied by means of germanium detectors and a NaI total-absorption spectrometer. Two β-decaying isomers in 96Ag were established with half-lives of 4.40(6) and 6.9(6) s and tentative spin–parity assignments of (8+) and (2+), respectively. For both isomers, the intensities of β transitions to low-lying levels of 96Pd (Z=46,N=50) and β-delayed proton decays to levels in 95Rh (Z=45,N=50) were measured. Several new 96Pd levels were firmly established. The level energies, their γ decays and the Gamow–Teller decay of 96Ag are compared to shell-model predictions. A new low-lying level in 95Rh was found at 680 keV excitation energy. Through a comparison with low-lying states of N=50 isotones, this level is interpreted as the first excited 7/2+ state built on the proton 9/2+ ground state. The assignments of further excited states in 95Rh are discussed.

Occupancy of spherical shells in the ground state of even 2s-1d shell nuclei

Abstract A projected Hartree-Fock calculation is carried out to estimate the occupation probabilities in ground states of even sd shell nuclei. A direct comparison with experimental occupation numbers is made possible by using Frenchs sum rules. The calculated occupation numbers are also used to calculate the matrix element 〈 g.s. | 1 · s | g.s. 〉 and the results compared with other models as well as with experimental estimates.

Decay properties of very neutron-deficient isotopes of silver and cadmium

Abstract The β-decay properties of the lightest known silver and cadmium isotopes are investigated. Data for β-delayed γ-ray emission of 95–97Ag and for β-delayed proton emission of 96Ag and 97Cd are presented. The experimental findings are compared with predictions of shell-model calculations in which a variety of model spaces and effective interactions are considered.

Retardation of E1 transitions and the neutron effective charge in 29Si

The effect of the giant dipole resonance on E1 transition rates is investigated, and an expression is derived which allows E1 effective charges to be calculated using the gamma -absorption cross section of the neighboring even- mass core. It is shown how this expression can be approximated using a sum rule in cases where the absorption cross section is not adequately known. Application is made to /sup 29/Si; using wave functions from a particle-core model, calculated E1 transition rates are in excellent agreement with experiment. (auth)

Ground state correlations in the core-particle model: Application to 37Ar

Abstract The particle-vibration model is extended to open-shell nuclei by including ground state correlations which are more general than those derived from the simple BCS treatment. The phonon renormalization due to the overlap between the single particle and collective states is also examined in detail by a shell model like technique. As an application the positive and negative parity spectra of 37 Ar are studied, and spectroscopic factors and transition rates are compared with shell model results and recent experiments. It is found that ground state correlations and in particular proton-neutron correlations are important for a correct description of spectroscopic factors. The M1 transition rates and magnetic moments are calculated taking into account M1 core polarization diagrams.

Core-polarization and open-shell effects in E6 transitions☆

Abstract The problem of isomeric E6 transitions recently measured in the fp shell is investigated. In the shell model these E6 decay rates require negative proton polarization charges and are quite anomalous in the context of usually enhanced E2 and E4 transitions. We demonstrate that usual core-polarization mechanisms cannot be invoked to explain the data and that the quadrupole deformations of the open shell that must be taken into account are instrumental in yielding negative P 6 moments.

Five-particle—one-hole states in44Sc

Abstract Odd parity levels in44Sc are investigated by coupling both proton and neutron d 3 2 holes to states of mass-45 nuclei, using projected Hartree-Fock wave functions. It is found that most particle-hole interactions taken from the literature cannot account for the observed low excitation energy of neutron hole states. Energy levels, neutron spectroscopic factors and γ-transition rates are calculated using the Erne interaction.