Very low energy protons from $\beta $-delayed p-decay of proton-rich nuclei for nuclear astrophysics*

We developed a technique to measure very low energy protons from the beta-delayed proton-decay of proton-rich nuclei produced and separated with the MARS recoil separator at TAMU. A simple setup consisting of a telescope made of a thin double sided Si strip detector (p-detector) backed or sandwiched between two thick Si detectors ($\beta $-detectors) was designed. The source nuclei are slowed down from 30-40 MeV/u and implanted in the middle of the thin p-detector. The excited states populated in daughter nucleus above the proton threshold are resonances in the radiative proton capture leading to that nucleus; therefore, beta-decay can be a useful mechanism to study these resonances. In particular, we have studied $^{23}$Al and $^{31}$Cl and got information on the resonances of $^{22}$Na(p,$\gamma )^{23}$Mg and $^{30}$P(p,$\gamma )^{31}$S reactions, both important in novae. We studied different W1 and BB2 p-detectors, 45-140 $\mu $m thick, made by MSL, and found that thinner detectors with a small cell size are best to measure proton energies as low as 2-300 keV.