Nuclear physics for stellar explosions

对比铁峰区更重的同位素起源的理解是核天体物理学中最活跃的领域之一。对于爆炸恒星环境中的核合成尤其如此，在那里外来核及其反应起着至关重要的作用。虽然FIRE和FRIB等大型放射束设施的实验旨在测量某些奇异原子核上的关键反应，但小型加速器设施通过对稳定同位素进行系统的精确研究做出了贡献。对于后一种方法，我们将使用高分辨率HPGeγ探测器和4个π求和晶体的激活和在束技术。这两种方法的结合对于获得可靠的核合成理论描述是很重要的。该项目分为两个子项目：在第一个子项目中，我们旨在更深入地了解重同位素的低能α粒子传输系数及其随质子-中子不对称性变化的演化。这一知识对于描述通过所谓的p过程合成富质子同位素是必要的。在我们的实验中，我们将研究选定同位素的(α，γ)和(α，n)截面。第二个子项目主要研究A=100时质量区的γ强度函数，它是关于r过程和p过程的网络计算的重要输入。为此，我们将测量同位素在Aγ100附近的(p，≈)反应率。这两个项目的实验研究将使用专门的实验装置，用于科隆大学串列加速器的束内和激活研究，圣母大学的4π求和阵列Hector，以及PTB Braunschweig的激活装置。该项目将与该领域的理论家密切合作进行。

The understanding of the origin of isotopes heavier than those in the iron peak region is one of the most active fields in nuclear astrophysics. This is especially true for the nucleosynthesis in explosive stellar environments where exotic nuclei and their reactions play a crucial role. While experiments at large-scale radioactive-beam facilities like FAIR and FRIB aim to measure key reactions on certain of those exotic nuclei, small accelerator facilities contribute via systematic precision studies on stable isotopes. We will use activation and in-beam techniques with high-resolution HPGe γ detectors and 4π-summing crystals for the latter approach. Both approaches together are important to get a reliable theoretical description of nucleosynthesis.The project is divided into two subprojects: In the first subproject we aim to gain a deeper understanding of low-energy α-particle transmission coefficients for heavy isotopes and their evolution with changing proton-neutron asymmetry. This knowledge is necessary for a description of the synthesis of proton-rich isotopes via the so called p process. In our experiments we will study (α,γ) and (α,n) cross sections on selected isotopes. The second subproject focuses on studies of the γ-strength function in the mass region around A=100 which is an important input for the network calculations on the r process and p process. For this purpose we will measure (p,γ) reaction rates on isotopes around A≈100.The experimental studies in both projects will use the dedicated experimental setups for in-beam and activation studies at the Tandem accelerator of the University of Cologne, the 4π summing array HECTOR at Notre Dame University, and the activation setup at the PTB Braunschweig. The project will be performed in close collaboration with theoreticians in the field.