Jirina Stone

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).

Abstract:

The odd-odd [Formula Presented] nuclide, [Formula Presented] has been produced in the [Formula Presented] reaction at 125 MeV. Recoiling fragments separated by their [Formula Presented] values were implanted onto the tape of a moving tape collector and transported to a shielded position between two plastic β detectors and two Ge γ-ray detectors where β-γ coincidences were recorded as a function of time. γ rays with energies of 279 (100%), 504 (90%), and 713 (40%) keV, previously identified as yrast transitions in daughter [Formula Presented] were observed and found to decay with a half-life of 5.8 (6) s. From the relative intensities of the γ-rays, a spin and parity of [Formula Presented] and [Formula Presented] are assigned to the parent state in [Formula Presented] undergoing β decay. A production cross section of [Formula Presented] has been determined for [Formula Presented] by comparison of the counting rates with those of other reaction products with known cross sections. An upper limit of 500 keV can be set for the energy of this level relative to a possible highly deformed [Formula Presented] ground state. From this limit, it can be inferred that [Formula Presented] pairing is considerably quenched relative to such pairing in adjacent odd-odd [Formula Presented] Two-quasiparticle rotor model calculations have been used to account for the structure of [Formula Presented] and adjacent nuclides. © 1998 The American Physical Society.