Nuclear physics for stellar explosions

对比铁峰区重的同位素的起源的认识是核天体物理学中最活跃的领域之一。这对于爆炸性恒星环境中的核合成尤其正确，因为外来核及其反应起着至关重要的作用。在FAIR和FRIB等大型放射性束流设施进行的实验旨在测量某些奇异核的关键反应，而小型加速器设施则通过对稳定同位素的系统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HPGe γ探测器和4π求和晶体的激活和束内技术。这两种方法结合在一起对于获得核合成的可靠理论描述非常重要。该项目分为两个子项目：第一个子项目旨在深入了解重同位素的低能α-粒子透射系数及其随质子-中子不对称变化的演化。这些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，我们将在选定的同位素上研究（α,γ）和（α,n）截面。第二个子项目重点研究A=100附近质量区域的γ-强度函数，这是r过程和p过程的网络计算的重要输入。为此，我们将测量A≈100附近同位素的（p,γ）反应速率。这两个项目的实验研究将使用科隆大学的串联加速器、圣母大学的4π求和阵列HECTOR和布伦瑞克PTB的激活装置进行束流和激活研究的专用实验装置。该项目将与该领域的理论家密切合作。

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.