The decay property of Na20 was studied using a Mg20 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 Na20. 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 Ne19+p as was expected before. The half-life time of Mg20 is determined to be 11417 ms. The stellar reaction rate of Ne19(p,)20Na is also discussed based on the present experimental result.
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