恒星中子源13C（α，n）16O反应的研究

Abstract

13C（α，n）16O是渐进巨星支（AGB）星中慢速中子俘获（s）过程的主中子源反应，而17O 6.356 MeV 1/2＋阈下共振对13 C（α，n）16 O反应影响很大。本文使用 HI-13串列加速器和Q3D磁谱仪，首次测量了13C （11B ，7Li）17O转移反应角分布，确定了影响13C（α，n）16O反应最关键、最不确定的17O（Ex ＝6.356 MeV）阈下共振态的α宽度，从而得出天体物理能区13 C （α，n）16 O反应的天体物理 S因子和反应率，澄清了国际上已有S因子数据间高达25倍的巨大分歧。AGB星s过程核合成网络计算表明：新反应率数据导致恒星中铅的丰度增加了25％。

13C(??,n)16O is the main neutron source reaction of slow neutron capture (s) process in asymptotic giant branch (AGB) stars. The 6.356 MeV 1/2+ subthreshold resonance in 17O plays an important role in the 13C(??,n)16O reaction. The 13C(11B, 7Li)17O angular distributions were measured using HI-13 tandem accelerator and Q3D magnetic spectrograph, and then used to determine the ??-width of the subthreshold resonant state which is currently the most uncertain parameter for determining the 13C(??,n)16O reaction rate. By using the present ??-width, the astrophysical S-factor and the stellar rate of the 13C(??,n)16O reaction were derived. This shed some light on the existing discrepancies up to a factor of 25 in S-factors derived from different authors. The simulation of s-process in AGB stars shows that the new reaction rate produces 25% more Pb than the CF88 compilation.