Extended R-matrix description of two-proton radioactivity
Zhaozhan Zhang · Cenxi Yuan · Chong Qi · Boshuai Cai · Xinxing Xu
Two-proton () 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 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 radioactivity half-lives. For the case of Kr, theoretical predictions for direct decay give much larger half-lives than the recent measurement from RIKEN. A combination of direct and sequential emission is analyzed by considering a small negative one-proton separation energy and a possible enhanced contribution from the -wave component. The present method predicts that Sr and Zr may be the most promising candidates for future study on radioactivity. Our model gives an upper limit of 55(4) keV for the decay width of emission in recently found four-proton resonant nuclide, Mg, which agrees with the observed width of 115(100) keV.