P reaction for the nucleosynthesis in the X-ray bursts*

Nuclear reactions in the αp-process, the sequence of (α, p) and (p, γ) reactions, are important for the nucleosynthesis in the X-ray bursts. The ²⁶Si(α, p)²⁹P reaction is one of the αp-process reactions and considered to have one of the largest effects on the light curve of the X-ray burst. However, there are not sufficient experimental data for this reaction because of the technical difficulties.

 

We performed a direct measurement of this reaction at the CNS RI beam separator (CRIB). The ²⁶Si(α, p)²⁹P reaction was measured in the high temperature region around T = 3 GK using the ⁴He thick gas target method. In spite of the large number of background events, an upper limit on the reaction cross section was obtained, which was about one order of magnitude smaller than that of the NON-SMOKER statistical model.

 

This is the first experimental evaluation of this reaction cross section by a direct measurement. Therefore, the results will be informative for determining absolute value of the cross section for high energy region and constraining the ²⁶Si(α, p)²⁹P reaction rate and the X-ray burst light curve model.

 

The analysis method and the results are discussed in this presentation.