WEAK-INTERACTION AND NUCLEAR-STRUCTURE ASPECTS OF NUCLEAR DOUBLE-BETADECAY

Weak-interaction and nuclear-structure aspects of double beta decay ar e reviewed. Starting from effective electroweak lagrangians, decay rat es for the two-neutrino and neutrinoless modes of the nuclear double b eta decay transitions are defined and second-order perturbative expres sions for the nuclear decay amplitudes are given. Nuclear matrix eleme nts of the relevant operators are presented, as extracted from data an d from shell-model and QRPA calculations as well as from other theoret ical approximations. The analysis is performed both for the two-neutri no and neutrinoless modes of the decay. The expressions for ground-sta te-to-ground-state and ground-state-to-excited-state transitions are p resented. Updated experimental and theoretical information on beta(-)b eta(-) decays in Ca-48, Ge-76, Se-82, Zr-96, Mo-100, Cd-116, Sn-124, T e-128, Te-130, Xe-136, Nd-150, and on beta(+)beta(+), beta(+) EC and d ouble EC decays in Kr-78, Mo-92, Ru-96, Cd-106, Xe-124, Ba-130, Ce-136 is analyzed and compared with theoretical results. The relevance of s ingle-beta-decay transitions feeding some of the nuclei where double-b eta-decay transitions occur is pointed out. The systematics of various phase-space factors and extracted matrix elements is presented. (C) 1 998 Elsevier Science B.V. All rights reserved.