$\beta -$delayed p-decay of proton-rich nuclei $^{23}$Al and $^{31}$Cl and explosive H-burning in novae*

We developed a technique to measure $\beta $-delayed proton-decay of proton-rich nuclei produced and separated with MARS at TAMU. In particular, we studied the decay of $^{23}$Al and $^{31}$Cl, both important for understanding explosive H-burning in novae. We have pulsed the beam, implanting the source nuclei moving at about 40 MeV/u in a thin Si strip detector, and then measured $\beta -$p and $\beta -\gamma $ coincidences simultaneously. The states populated above the proton threshold in $^{23}$Mg and $^{31}$S, respectively, may proton decay. They are resonances in the reaction $^{22}$Na(p,$\gamma )^{23}$Mg (crucial for the depletion of $^{22}$Na in ONe novae) and in $^{30}$P(p,$\gamma )^{31}$S (critical point in explosive H-burning in novae), but the protons emitted have very low energies, starting at about 200 keV, an experimental challenge. The setup and the results are described. The $\beta $-decay schemes were established for both nuclei, and IAS identified. The technique has shown a remarkable selectivity to $\beta $-delayed charged particle emission and shown to work even at radioactive beam rates of a few pps, for rare isotopes with lifetimes as low as 10s msec.