利用(~7Li,~6Li)反应测量^(15)N(n,γ)^(16)N天体物理反应率  

Determination of ^(15)N(n,γ)^(16)N astrophysical reaction rate via the(~7Li,~6Li) reaction

作　　者：吴志丹[1] 郭冰[1] 李志宏[1] 李云居[1] 苏俊[1] 庞丹阳[2] 颜胜权[1] 李二涛[3] 白希祥[1] 杜先超 樊启文[1] 甘林[1] 何建军[4] 金孙均[1] 景龙[1] 李龙[4] 李志常[1] 连钢[1] 刘建成[1] 谌阳平 王友宝[1] 于祥庆[4] 曾晟[1] 张立勇[4] 张伟杰[1] 柳卫平[1] 

机构地区：[1]中国原子能科学研究院,北京102413 [2]北京航空航天大学物理科学与核能工程学院,北京100191 [3]深圳大学物理科学与技术学院,深圳518060 [4]中国科学院近代物理研究所,兰州730000

出　　处：《核技术》2014年第10期59-64,共6页Nuclear Techniques

基　　金：国家自然科学基金(No.11075219;No.11321064;No.11375269;No.11275272;No.11275018);国家重点基础研究发展规划973项目(No.2013CB834406)资助

摘　　要：用Q3D磁谱仪测量了15N(7Li,6Li)16N布居16N基态和前三个激发态的角分布。通过对实验数据的扭曲波玻恩近似(Distorted wave Born approximation,DWBA)分析,导出这些态的谱因子和渐进归一化系数(Asymptotic normalization coefficient,ANC),进而用新的谱因子得到15N(n,γ)16N的天体物理反应率。结果表明,尽管15N为中子满壳核,但16N中转移中子处于2s1/2轨道的两个能级并不是很好的单粒子能级,与壳模型的理论预言结论相反。Background： Fluorine （^19F, the only stable F isotope） is a crucial element for nucleosynthetic studies since it is extremely sensitive to the physical conditions within stars. The astrophysical site of the production of fluorine is suggested to be asymptotic giant branch stars where the ^15N（n,γ）^16N reaction could affect the abundance of fluorine by competing with ^15N（α,γ）^16N. Purpose： The ^15N（n,γ）^16N reaction rate depends critically on the neutron spectroscopic factors of the four low-lying levels in ^16N. Shell model calculations and two previous measurements of the （d,p） reaction yielded the spectroscopic factors with a discrepancy by a factor of -2. The present work aims to explore these neutron spectroscopic factors via an independent transfer reaction and to determine the stellar rate of the ^15N（n,γ）^16N reaction. Methods： The angular distributions of the ^15N（^7Li,^6Li）^16N reaction leading to the first four states in ^16N were measured using a high-precision Q3D magnetic spectrograph. The neutron spectroscopic factors and asymptotic normalization coefficients （ANC） for these states in ^16N were then derived based on distorted wave Born approximation （DWBA） analysis. Results： The spectroscopic factors of these four states are extracted to be 0.96±0.09 0.69±0.09, 0.84±0.08 and 0.65±0.08, respectively. The ^15N（n,γ）^16N reaction rate was derived based on the new spectroscopic factors. Conclusion： The present result demonstrates that two levels corresponding to neutron transfers to the 2s1/2 orbit in ^16N are not as good single-particle levels as the shell model expected. The present work also might provide an independent examination to shed some light on the existing discrepancies in the spectroscopic factors and the ^15N（n,γ）^16N rate. Key words Transfer reaction, Distorted wave Born approximation （DWBA）, Spectroscopic factors, Reaction rate

关 键 词：转移反应 扭曲波玻恩近似 谱因子 反应率 

分 类 号：TL52[核科学技术—核技术及应用]