碳氮氧循环中关键天体反应19F(p,gamma)20Ne的实验研究

宇宙中的大部分恒星都属于第I星族，其内部除了H和He以外还有C、N、O、F等元素。大质量I族星由于温度密度较高，主要通过CNO循环进行氢燃烧。19F(p,g)20Ne反应是氢燃烧从CNO循环突破到A>20核区唯一可能的通道，对理解氢燃烧过程中的催化剂流失至关重要。目前该反应在Gamow窗口内尚无直接测量数据，反应截面只能通过高能区数据外推得到，误差可达一个数量级。本项目将对19F(p,g)20Ne在Gamow能区的反应截面进行首次直接测量，将误差降到20%以下。实验将在西安交通大学新建成的400kV高压强流离子加速器上进行。我们将用强流质子束轰击19F靶，用NaI阵列和高纯锗Clover探测器测量19F(p,g)20Ne反应放出的伽玛射线，扫描Ep=150~345keV能区的反应截面。利用实验精确测定的截面数据重新计算19F(p,g)20Ne反应率并研究其天体物理意义。

Most of the stars in the universe are Population I stars which, in addition to H and He, contain heavy elements such as C, N, O, and F. Due to the higher temperature and density, massive Population I stars convert hydrogen to helium via the CNO cycles. Here, 19F(p,g)20Ne is the unique breakout reaction from the CNO cycles to the A>20 mass region, which makes it very important to the catalysts loss during the hydrogen burning. By so far, no direct measurement has been performed within the Gamow window. The cross section used in the reaction rate calculation was extrapolated based on the high-energy data, but with an uncertainty factor up to 10. In this project, the 19F(p,g)20Ne cross section in the Gamow window will be directly measured for the first time. The experiment will be performed at the 400-kV high-voltage intense ion beam accelerator at Xianjiaotong University. The 19F targets will be bombarded by the high-current proton beam, and the gamma-rays be detected by the NaI array and Clover detectors. The cross section in the energy region of Ep=150~345keV will be scanned, with an aimed statistical uncertainty better than 20%. The thermonuclear 19F(p,g)20Ne reaction rate will be calculated and the astrophysical implications be revealed based on the firmer experimental data.