Decay mechanism and lifetime of $^{67}$Kr

TL;DR

This paper investigates the unexpectedly short lifetime of $^{67}$Kr, proposing that its decay mechanism is a transition between true and sequential two-proton emission, which constrains the energy levels involved.

Contribution

It introduces a new interpretation of $^{67}$Kr decay as a transition dynamic, challenging previous assumptions of true 2p emission and refining energy level estimates.

Findings

Decay mechanism is a transition between true and sequential 2p emission.

Ground state energy of $^{66}$Br is constrained to 1.35-1.42 MeV.

Revised decay understanding explains the shorter observed lifetime.

Abstract

The lifetime of the recently discovered $2p$ emitter $^{67}$Kr was recently found considerably below the lower limit predicted theoretically. This communication addresses this issue.Different separation energy systematics are analyzed and different mechanisms for $2p$ emission are evaluated. It is found that the most plausible reason for this disagreement is a decay mechanism of $^{67}$Kr, which is not "true $2p$" emission, but "transition dynamics" on the borderline between true $2p$ and sequential $2p$ decay mechanisms. If this is true, this imposes stringent limits $E_r=1.35-1.42$ MeV on the ground state energy of $^{66}$Br relative to the $^{65}$Se-$p$ threshold.