Nuclear Reactions to Probe Structure of Exotic Nuclei

实验核物理学帮助我们了解原子中心的原子核的性质，以及元素如何在恒星及其爆炸中合成。该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。重点是加速不稳定的β衰变的原子核束，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性的原子核，它们的结合力更弱，同时也帮助我们了解稳定元素的母体是如何合成的。该项目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和博士后学者的教育，并为他们在教育和基础及应用研究方面的职业生涯做好准备。 该项目的核物理结果在天文学、了解宇宙中观测到的元素丰度、核能和国家安全、了解锕系元素裂变碎片的性质和反应方面也具有重要意义。为了扩大该项目的影响范围，主要研究者为本科生举办了关于如何准备研究生学习的讲习班，并就该研究向公众和学校进行了讲座。核物理学的前沿领域之一是远离稳定谷的原子核结构的研究。 在原子核中，单粒子轨道预计会作为中子和质子数的函数而变化，此外，对形变的存在非常敏感。 单粒子特性可以在单粒子转移反应中探测。轻离子转移反应将与库仑势垒附近的束能量和约35兆电子伏每个核子进行研究。研究将集中在N=50中子壳闭合附近的富中子核、252 Cf裂变后的加速碎片以及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）和阿贡国家实验室的阿贡串列直线加速器系统（ATLAS）中使用稀有同位素的加速束进行。 NSCL的重点是提取光谱强度，减少对理论模型参数的依赖。 在ATLAS，该小组将利用Gammaspere-ORRUBA：用于核结构研究的双探测器，通过带电粒子（用橡树岭罗格斯大学的位置敏感硅条探测器桶阵列ORRUBA测量）和伽马射线（用伽马射线管，110个康普顿抑制Ge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裂。 该小组还将进一步发展与ORRUBA耦合的闪烁体探测器测量粒子-伽马射线符合的能力。

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. The project exploits state-of-the-art instruments and accelerator facilities in the U.S. Central to this effort is enhancing the education of students and postdoctoral scholars and preparing them for careers in education and fundamental and applied research. The nuclear physics results from this project 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 fragments from fission of actinides. To expand the reach of this project, the principal investigator presents workshops to undergraduate students on how to prepare for graduate studies and gives lectures to the public and schools on this research.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. Light-ion transfer reactions will be studied with beam energies near the Coulomb barrier and about 35-MeV per nucleon. Studies will concentrate on neutron-rich nuclei near the N=50 neutron shell closure, accelerated fragments following 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 accelerated beams of rare isotopes at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University and the Argonne Tandem Linac Accelerator System (ATLAS) at Argonne National Laboratory. The NSCL focus is to extract spectroscopic strengths with reduced dependence on theoretical model parameters. At ATLAS the group will exploit Gammasphere-ORRUBA: Dual Detectors for Nuclear Structure Studies 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 Gammasphere, the array of 110 Compton-suppressed Ge gamma-ray detectors). The group will also further develop capabilities to measure particle-gamma-ray coincidences with scintillator detectors coupled to ORRUBA.