Beta-decay of nuclei near the neutron shell N = 126
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NUCLEI Theory
Beta-Decay of Nuclei Near the Neutron Shell N = 126 * I. N. Borzov** Joint Institute of Heavy Ion Research, Oak Ridge, USA Received December 23, 2010; in final form, April 26, 2011
Abstract—A self-consistent approach to the weak interaction rates is presented. It is based on the generalized energy-density functional method and continuum QRPA. The study has been made of the βdecay total energy releases, half-lives and β-delayed neutron emission branchings for recently identified near-spherical nuclei with charge numbers Z = 76−79 approaching the closed neutron shell at N = 126. Together with our previous calculations near N = 28, 50, 82 this provides an important update to the standard set of weak rates for the r-process modeling, radioactive beam experiments and advanced reactor applications. Within the fully microscopic framework a significant competition is found of the Gamow– Teller and first-forbidden decay contributions to the total half-lives. DOI: 10.1134/S1063778811100024
1. INTRODUCTION In the last years an effort has been made to develop a global approach to the β-decay properties of nuclei far from stability. The starting point is the self-consistent Finite Fermi System Theory (FFST) of A.B. Migdal [1]. An extension of the approach is based on the generalized energy-density functional (DF) theory—recent method of choice for precise electronic-structure calculations in atomic, molecular, and condensed matter systems—which is well suited for wide variety of nuclear structure calculations. The merits of the FFST idea of universality (A-independence) of the effective N N -interaction parameters are implemented in the continuum QRPA (CQRPA) framework which allows for full basis treatment of the excited states. Nuclear ground-state properties are derived within phenomenological density functional suggested by Fayans et al. (see [2]). Its DF3 version was tailored specifically for the neutron-rich nuclei [3]. An approximation to fully self-consistent treatment of the spin– isospin excited states has been implemented [3, 4]. It is assumed that, except for the spin–orbit splitting, the ground-state properties are rather insensitive to the spin and spin–isospin components of the DF. Hence, the scalar components of the DF constraining the ground-state properties can be decoupled with spin–isospin components essential for the β-decay. This allows for an independent choice of the scalar and spin–isospin effective N N interactions. In the particle–hole channel the latter is taken as sum of ∗ **
The text was submitted by the author in English. E-mail: [email protected]
the contact term with Landau–Migdal parameter g and the finite-range part of π and ρ mesonic exchange with an approximate treatment of the Δ(1232) excitations. The anzatsz was proposed by A.B. Migdal for studying the soft pionic modes in atomic nuclei and π condensation in neutron stars [1]. Last but not least, the FFST quasi-particle local charges in respect to the external fields of different symmetry account for the in-medium effects. Of prime impo
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