Two-proton capture on the ${}^{68}$Se nucleus with a new self-consistent cluster model

Abstract

We investigate the two-proton capture reaction of the prominent rapid proton capture waiting point nucleus, ${}^{68}$Se, that produces the borromean nucleus ${}^{70}$Kr (${}^{68}$Se$+p+p$). We apply a recently formulated general model where the core nucleus, ${}^{68}$Se, is treated in the mean-field approximation and the three-body problem of the two valence protons and the core is solved exactly. The same Skyrme interaction is used to find core-nucleon and core valence-proton interactions. We calculate $E2$ electromagnetic two-proton dissociation and capture cross sections, and derive the temperature dependent capture rates. We vary the unknown $2^{+}$ resonance energy without changing any of the structures computed self-consistently for both core and valence particles. We find rates increasing quickly with temperature below $2-4$~GK after which we find rates varying by less than a factor of two independent of $2^{+}$ resonance energy. The capture mechanism is sequential through the $f_{5/2}$ proton-core resonance, but the continuum background contributes significantly.

Comments: 7 pages, 4 figures