Competition Between Particle-Hole and Particle-Particle Correlations in Forbidden Electron Capture: the Case of ${}^{123}$Te

Abstract

The K-electron capture half-life of ${}^{123}$Te has been recently measured to be $t_{exp}^K=2.4\times 10^{19}$ yr, and constitutes the longest half-life ever measured in a single $\beta$-transition of any nuclear species. We have calculated this second unique forbidden transition within the framework of the proton-neutron quasi-particle random phase approximation, making use of Skyrme-type effective interactions. A strong cancellation effect between particle-hole and particle-particle correlations is found. The model, without any renormalization of the force, provides a lower limit for the K-electron capture half-life of $\sim 10^{17}$ yr, which unambiguously rules out the old experimental values of $10^{13}-10^{14}$ yr. A few percent increase of the particle-particle matrix elements of the Skyrme interaction allows to reproduce the experimental findings.

Comments: Completely revised version, 10 pages, Latex Re-submitted to Physical Review Letters on April 1997. Some minor errors corrected, many experimental inputs used