恒星中子源^(13)C(α,n)^(16)O反应的研究

Study of Neutron Source Reaction ^(13)C(α,n)^(16)O in Stars

13 C(α,n)16 O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17 O 6.356 MeV1/2+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)17 O转移反应角分布,确定了影响13C(α,n)16 O反应最关键、最不确定的17 O(Ex=6.356MeV)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%。

13 C（α,n）16 O 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 resonancein17O plays an important role in the 13C（α,n）16O reaction .The 13C（11B , 7 Li）17 O angular distributions were measured using HI-13 tandem accelerator and Q3D magnetic spectrograph , and then used to determine the α-width of the subthreshold resonant state w hich is currently the most uncertain parameter for determining the 13 C （α,n）16 O reaction rate .By using the present α-width ,the astrophysical S-factor and the stellar rate of the 13C（α,n）16 O 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 .