Jirina Stone

Abstract:

A new method is introduced designed to facilitate study of matrix elements in complex β-decay through the measurement of asymmetric β-emission from a low-temperature polarised source. The method involves coincident detection of the β-emission with subsequent γ-transitions to tag the β-spectrum component. The method is demonstrated by application to the decay of 140La.

Abstract:

Shell-model and deformed Hartree-Fock plus BCS calculations are reported for even-even nuclei 18-30O, 18-36Ne, and 20-42Mg; shell-model calculations additionally included 38,40Ne and 44,46,48Mg. Ground-state binding energies and 2+1 quadrupole moments are calculated by both models. Shell-model calculations, aided by a new truncation method, include 2+1 excitation energies and magnetic moments. Hartree-Fock calculations with SkI6, RATP, Z*σ, and SkX Skyrme forces include ground-state deformations and rms radii; SkI6 gives the best overall agreement with experiment. The two models are compared with each other and with experiment. Two-neutron separation energies, evidence for a neutron halo or skin in heavy O isotopes, and deformation of Ne and Mg isotopes are discussed. Both models indicate disappearance of the shell gap at N = 28 (Mg), and the shell model does so additionally at N = 20 (Ne and Mg).