Decay property ofNa20for the onset mechanism of the rapid-proton process

The decay property of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Na}$ was studied using a ${}_{}{}^{20}{}_{}{}^{}\mathrm{Mg}$ beam to learn better the onset mechanism of the rapid-proton process. The delayed protons were successfully measured, which correspond to one of the possible $1^{+}$ states in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Na}$. There is no clear beta decay to the first excited $1^{+}$ state above the proton threshold, suggesting that this state would not be the s-wave resonance in the thermal reaction of ${}_{}{}^{19}{}_{}{}^{}\mathrm{Ne}$+p as was expected before. The half-life time of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Mg}$ is determined to be 114±17 ms. The stellar reaction rate of ${}_{}{}^{19}{}_{}{}^{}\mathrm{Ne}$(p,γ${)}^{20}$Na is also discussed based on the present experimental result.