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arXiv 1508.05660nucl-ex
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探测$^{26}$ Mg核的天体物理重要态以研究$s$过程的中子源

Probing astrophysically important states in $^{26}$Mg nucleus to study neutron sources for the $s$-Process

R. Talwar, T. Adachi, G. P. A. Berg, L. Bin, S. Bisterzo, M. Couder, R. J. deBoer, X. Fang, H. Fujita, Y. Fujita, J. Gorres, K. Hatanaka, T. Itoh, T. Kadoya, A… 展开作者

R. Talwar, T. Adachi, G. P. A. Berg, L. Bin, S. Bisterzo, M. Couder, R. J. deBoer, X. Fang, H. Fujita, Y. Fujita, J. Gorres, K. Hatanaka, T. Itoh, T. Kadoya, A. Long, K. Miki, D. Patel, M. Pignatari, Y. Shimbara, A. Tamii, M. Wiescher, T. Yamamoto, M. Yosoi

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摘要：

$^{22}$ Ne（$α$，n）$^{25}$ Mg反应是大质量恒星慢中子俘获过程（$s$ -过程）的主要中子源，它与$^{13}$ C（$α$，n）$^{16}$ O一起，对渐近巨星分支（AGB）恒星的$s$ -过程产生中子有贡献.然而，该反应是吸热的并且直接与$^{22}$ Ne（$α,γ)^{26}$ Mg辐射捕获）竞争。由于$^{26}$ Mg在α和中子分离能附近的能级结构的不确定性，这两种反应的不确定性都很大。这些不确定性正在影响理论恒星模型中s过程核合成的计算。过去的间接研究已经成功地确定了能量，$γ$射线和中子宽度的$^{26}$镁状态在感兴趣的能量区域。但是，高库仑势垒阻碍了共振强度的直接测量，共振强度由这些状态的$α$宽度决定。本实验的目的是通过$α$转移技术来确定临界共振态和精确测量$α$宽度。因此，使用日本大坂RCNP的Grand Raiden光谱仪分别对固体$^{26}$ Mg靶和$^{22}$ Ne气体靶进行了$α$ -非弹性散射和$α$ -转移测量.在目标区域（10.61 - 11.32 MeV）中，观察到高于$α$阈值的六个能级（E $_x$ = 10717 keV、10822 keV、10951 keV、11085 keV、11167 keV和11317 keV）。速率在两个反应通道中由E $_x$ = 10951、11167和11317 keV处的状态的共振贡献主导。E $_x$ =11167 keV对（$α,γ$）率的影响最大，因此对s过程环境中中子产生的预测起着重要的作用。

英文摘要：

The $^{22}$Ne($α$,n)$^{25}$Mg reaction is the dominant neutron source for the slow neutron capture process ($s$-process) in massive stars and contributes, together with the $^{13}$C($α$,n)$^{16}$O, to the production of neutrons for the $s$-process in Asymptotic Giant Branch (AGB) stars. However, the reaction is endothermic and competes directly with the $^{22}$Ne($α,γ)^{26}$Mg radiative capture. The uncertainties for both reactions are large owing to the uncertainty in the level structure of $^{26}$Mg near the alpha and neutron separation energies. These uncertainties are affecting the s-process nucleosynthesis calculations in theoretical stellar models. Indirect studies in the past have been successful in determining the energies, $γ$-ray and neutron widths of the $^{26}$Mg states in the energy region of interest. But, the high Coulomb barrier hinders a direct measurement of the resonance strengths, which are determined by the $α$-widths for these states. The goal of the present experiments is to identify the critical resonance states and to precisely measure the $α$-widths by $α$ transfer techniques . Hence, the $α$-inelastic scattering and $α$-transfer measurements were performed on a solid $^{26}$Mg target and a $^{22}$Ne gas target, respectively, using the Grand Raiden Spectrometer at RCNP, Osaka, Japan. Six levels (E$_x$ = 10717 keV , 10822 keV, 10951 keV, 11085 keV, 11167 keV and 11317 keV) have been observed above the $α$-threshold in the region of interest (10.61 - 11.32 MeV). The rates are dominated in both reaction channels by the resonance contributions of the states at E$_x$ = 10951, 11167 and 11317 keV. The E$_x$ =11167 keV has the most appreciable impact on the ($α,γ$) rate and therefore plays an important role for the prediction of the neutron production in s-process environments.

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