Extended R-matrix description of two-proton radioactivity

TL;DR

This paper develops an extended R-matrix framework to describe various mechanisms of two-proton radioactivity, successfully reproducing experimental half-lives and predicting promising candidate nuclei for future studies.

Contribution

It introduces decay width formulae for multiple decay mechanisms within the extended R-matrix approach, enhancing understanding of two-proton radioactivity.

Findings

Reproduces experimental half-lives of $2p$ radioactivity.

Predicts $^{71}$Sr and $^{74}$Zr as promising candidates for future research.

Provides an upper limit for the decay width of $^{18}$Mg's $4p$ emission.

Abstract

Two-proton ($2p$) radioactivity provides fundamental knowledge on the three-body decay mechanism and the residual nuclear interaction. In this work, we propose decay width formulae in the extended R-matrix framework for different decay mechanisms, including sequential $2p$ decay, diproton decay, tri-body decay, and sequential two-diproton decay. The diproton and tri-body formulae, combined with information on the two-nucleon transfer amplitude and Wigner single-particle reduced width, can reproduce well experimental $2p$ radioactivity half-lives. For the case of $^{67}$Kr, theoretical predictions for direct $2p$ decay give much larger half-lives than the recent measurement from RIKEN. A combination of direct and sequential $2p$ emission is analyzed by considering a small negative one-proton separation energy and a possible enhanced contribution from the $p$-wave component. The present method predicts that $^{71}$Sr and $^{74}$Zr may be the most promising candidates for future study on $2p$ radioactivity. Our model gives an upper limit of 55(4) keV for the decay width of $4p$ emission in recently found four-proton resonant nuclide, $^{18}$Mg, which agrees with the observed width of 115(100) keV.