Nuclear Reaction Studies for Nuclear Structure and Nucleosynthesis

实验核物理学帮助我们了解原子中心的原子核的性质，以及这些元素是如何在恒星和恒星爆炸中合成的。这个项目通过将原子核加速到高能量，并测量它们与其他原子核相互作用时发出的伽马和带电粒子辐射，增强了我们对这些基本问题的理解。研究的重点是对衰变不稳定的原子核加速束，其寿命短至几秒钟。原子核之间的相互作用使我们了解原子核的性质，特别是那些远离稳定的、束缚较弱的原子核，同时也帮助我们了解稳定元素的母体是如何合成的。这个项目将有助于促进我们对远离稳定谷的原子核结构和反应的理解，以及它们在恒星和爆炸中的合成。它将利用美国最先进的仪器和加速器设施。这项工作的核心是加强学生的教育，为他们从事教育、基础研究和应用研究做好准备。预期的核物理结果在天文学上也很重要，可以了解宇宙中观察到的元素的丰度，对于核能和国家安全也很重要，可以了解裂变碎片的性质和反应。拟议活动的结构旨在对研究生的教育和培训产生积极影响。该项目还将通过寻找女性或来自其他代表性不足背景的早期职业科学家，帮助提高核科学工作人员的多样性。这些早期职业学者参加前沿研究和开发一系列仪器，将为他们在高等教育、基础和应用研究、国家实验室和工业领域的职业生涯做好准备。核物理学的前沿领域之一是对远离稳定谷的原子核结构的研究。在原子核中，单粒子轨道随着中子数和质子数的变化而变化，此外，对变形的存在非常敏感。单粒子特征可以在单粒子转移反应中探测到，并且在计算中子捕获反应的直接分量时很重要，中子捕获反应负责合成比铁重的元素。光离子转移反应将用能量接近库仑势垒和每核子约40兆电子伏特的放射性离子束进行研究。研究将集中在N=50中子壳闭合附近的富中子核、252Cf自发裂变后的加速碎片和对理解恒星核合成及其爆炸很重要的轻核。这些研究将在密歇根州立大学的国家超导回旋加速器实验室（NSCL）、阿贡国家实验室的ATLAS加速器设施和圣母大学的核科学实验室用放射性离子束进行。NSCL的重点是限制在富含中子的原子核中结合中子的势的形状，从而在减少对理论模型参数的依赖的情况下提取光谱强度。带电粒子和同步伽马辐射都将用灵活配置的探测器来测量。在ATLAS上，将利用gammassphere -ORRUBA：用于实验结构研究的双探测器，通过带电粒子（用ORRUBA测量，ORRUBA是橡树岭罗格斯大学位置敏感硅条探测器的桶阵列）和伽马射线（用大型、高度分段的锗伽马射线探测器阵列测量）之间的重合测量来探测单粒子强度的碎片。罗格斯大学领导的努力将得到ORRUBA合作其他成员领导的努力的补充。这些结果将与不稳定核结构的理论预测进行比较，并作为恒星核合成及其爆炸的计算输入。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Experimental nuclear physics helps us to understand the properties of the nuclei at the center of atoms and how the elements are synthesized in stars and their explosions. This project enhances our understanding of these fundamental questions by accelerating nuclei to high energies and measuring gamma and charged particle radiation that is emitted when they interact with other atomic nuclei. The focus is on accelerating beams of atomic nuclei that are unstable to beta decay, living for times as short as seconds. The interactions between atomic nuclei informs our understanding of the properties of atomic nuclei, especially those far from stability that are more weakly bound, as well as helping us to understand how the parents of the stable elements were synthesized. This project will serve to advance our understanding of the structure of and reactions on atomic nuclei away from the valley of stability and their synthesis in stars and their explosions. It will exploit state-of-the-art instruments and accelerator facilities in the U.S. Central to this effort is enhancing the education of students and preparing them for careers in education and fundamental and applied research. The anticipated nuclear physics results are also of importance in astronomy, to understand the abundance of elements observed in the cosmos, and for nuclear energy and national security, to understand properties of and reactions on fission fragments. The structure of the proposed activities is designed to have a positive impact on the education and training of graduate students. The project will also serve to enhance the diversity of the nuclear science workforce by seeking out early career scientists who are women or come from other under-represented backgrounds. The participation of these early career scholars in the forefront research and the development of arrays of instruments would prepare them for careers in higher education and fundamental and applied research, at national laboratories and in industry. One of the frontier areas of nuclear physics is the study of the structure of atomic nuclei far from the valley of stability. In atomic nuclei the single-particle orbitals are expected to change as a function of neutron and proton number and, in addition, are very sensitive to the presence of deformation. Single-particle characteristics can be probed in single-particle transfer reactions and are important in calculating the direct component in neutron capture reactions that are responsible for the synthesis of elements heavier than iron. Light-ion transfer reactions will be studied with radioactive ion beams with energies near the Coulomb barrier and about 40-MeV per nucleon. Studies will concentrate on neutron-rich nuclei near the N=50 neutron shell closure, accelerated fragments following spontaneous fission of 252Cf and light nuclei important for understanding the synthesis of nuclei in stars and their explosions. These studies will be carried out with radioactive ion beams at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University, the ATLAS accelerator facility at Argonne National Laboratory and the Nuclear Science Laboratory at the University of Notre Dame. The focus at NSCL is to constrain the shape of the potential that binds neutrons in a neutron-rich nucleus and, therefore, extract spectroscopic strengths with reduced dependence on theoretical model parameters. Both charged particles and coincident gamma radiation will be measured with flexible configurations of detectors. At ATLAS, Gammasphere-ORRUBA: Dual Detectors for Experimental Structure Studies will be exploited to probe the fragmentation of single-particle strength with coincidence measurements between charged particles (measured with ORRUBA, the Oak Ridge Rutgers University Barrel Array of position-sensitive silicon strip detectors) and gamma rays (measured with large, highly segmented germanium gamma-ray detector arrays). The Rutgers-led efforts will be complemented by efforts led by other members of the ORRUBA collaboration. The results will be compared with theoretical predictions of nuclear structure away from stability and disseminated as input into calculations of nucleosynthesis in stars and their explosions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.