The proton resonant properties of compound ²²Mg nucleus have been investigated by researchers of nuclear astrophysics group at the Institute of Modern Physics, Chinese Academy Sciences (IMP) using resonant elastic scattering of ²¹Na+p. Here an inverse kinematics method was utilized, that is, a ²¹Na radioactive ion (RI) beam bombards a proton target.

Researchers at IMP performed the experiment by using CRIB at the Center for Nuclear Study, the University of Tokyo. An 89 MeV ²¹Na RI beam was produced at the CRIB and bombarded an 8.8 mg/cm² thick CH₂ target. The recoiling protons were measured at scattering angles of θ_c.m.»175° and 152° by three ∆E-E silicon telescopes. The excitation function was obtained with a thick-target method over energies E_x(²²Mg)=5.5 - 9.2 MeV.

For the first time, the J^π values for ten states above the alpha threshold in ²²Mg were experimentally determined in a single consistent measurement. Researchers made three new J^π assignments and confirmed seven of the ten tentative assignments in the previous work. In addition, the levels below the alpha threshold were also measured and analyzed. The ¹⁸Ne(α, p)²¹Na reaction rate was recalculated, and the astrophysical impact of new rate was investigated through one-zone postprocessing x-ray burst calculations. It shows that the ¹⁸Ne(α, p)²¹Na rate significantly affect the peak nuclear energy generation rate and the onset temperature of this breakout reaction in these phenomena.

The stellar ¹⁸Ne(α, p)²¹Na reaction studied has being regarded as a breakout reaction from the Hot CNO cycle (HCNO) to rapid proton capture rp-process occurred in Type I x-ray bursts. The present new rate will be a great help to people in understanding the energy production, nucleosynthesis, as well as isotope abundances in such high temperature and high density stellar environment.

The results have been published in Phys. Rev. C 89, 015804 (2014).

Fig.1 Experimental center-of-mass differential cross section for resonant elastic scattering of ²¹Na+p at a scattering angle of θ_c.m.»175°. It also shows a best overall R-matrix fit. (Image by IMP)

Fig.2 Nucleosynthesis during one-zone XRB calculations. (Image by IMP)