LEAPS-MPS: Experimental Nuclear Structure Studies

该奖项的全部或部分资金来自《2021年美国救援计划法案》(公法117-2)。这一奖项将资助南卡罗来纳州立大学(SC State)的基础核结构物理研究项目。首席研究员和他的团队将研究质量数接近165的丰中子核和质量数接近70的所谓镜像核的结构，这些核在自然界中并不存在，但可以在加速器设施中产生。了解这些原子核对于增进对核子(质子和中子)组织成原子核的过程以及从这些组织中产生什么样的模式(长圆形、扁圆形或三轴)的认识是重要的。该项目通过将原子核加速到高能或角动量，并测量它们与其他原子核相互作用时发射的伽马和贝塔粒子辐射，加强了对这些基本问题的理解。实验将使用美国最先进的仪器和加速器设施进行。研究活动将涉及南加州州立大学的本科生；那里的学生人口中93%是非裔美国人，55%是女性。参与这项研究将准备和激励少数族裔学生继续他们的学业，进入研究生院或进入STEM领域的劳动力大军。这些学生不仅将提升自己的专业技能，成为更好的科学家，而且还将接触到国家核设施、政府实验室和医疗诊断和治疗设施等不同领域。该项目的一个中心目标是在SC州建立一个积极的核结构研究计划。该奖项支持的研究将有助于通过建立和研究原子核的基本激发模式，即伽马衰变和β衰变，来深入了解原子核的性质。实验将使用阿贡国家实验室的阿贡串列直线加速器系统(ATLAS)和加利福尼亚州稀有同位素增殖器升级(CIRU)放射性束流设施进行。伽马射线将使用世界上最强大的探测器之一(伽马斯层)进行探测。A~165质量区的丰中子核由于在88~90个中子之间形变迅速而对核结构的研究特别感兴趣。对这一质量区域内核结构的详细变化的观察继续提供对核力的洞察。A~70镜像核中的同位旋对称性破缺是本研究感兴趣的另一个主题。它还将有助于描述非常重要的核性质。伽马衰变和β衰变后的研究，辅以势能面和壳模型计算，有助于分析控制核形状的核力的影响和由此产生的单粒子轨道序列。稀土区域中变形的、富含中子的核的结构也是天体物理学领域的重大兴趣。尽管我们对r过程的理解已经取得了很大的进展，但对于A=165附近丰度的元素峰仍然难以得到令人满意的解释。对这一峰值起源的探索可能是正确识别r过程的天体物理条件的关键。为了解决这些问题，需要进行更多的实验。拟议的项目将探索A~70和165核的变形结构和其他核性质。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). This award will fund a research program in fundamental nuclear structure physics at South Carolina State University (SC State). The Principal Investigator and his group will investigate the structure of neutron-rich nuclei with mass numbers near 165 and so-called mirror nuclei with mass numbers near 70 that do not exist naturally in nature but can be produced at an accelerator facility. Understanding these nuclei is important for advancing knowledge of the process by which nucleons (protons and neutrons) organize into nuclei and what patterns (prolate, oblate or triaxial) emerge from those organizations. The project enhances understanding of these basic questions by accelerating nuclei to high energies or angular momentum and measuring gamma- and beta-particle radiation that is emitted when they interact with other atomic nuclei. Experiments will be performed using state-of-the-art instruments and accelerator facilities in the United States. The research activities will involve SC State University undergraduate students; the student population there is 93% African American and 55% female. Participation in this research will prepare and motivate minority students to continue their studies to graduate school or enter the workforce in STEM fields. These students will not only advance their professional skill set and become better scientists, but they will also be exposed to diverse areas such as national nuclear facilities, government laboratories, and medical diagnostic and treatment facilities. A central goal of the project is to build an active research program in nuclear structure at SC State. The research supported by this award will help to gain insights into the properties of nuclei by establishing and studying their basic modes of excitation i.e. gamma and beta-decays. Experiments will be performed using the Argonne Tandem Linac Accelerator System (ATLAS) and Californium Rare Isotope Breeder Upgrade (CARIBU) radioactive beam facilities at Argonne National Laboratory. Gamma-rays will be detected using one of the most powerful detectors in the world (Gammasphere). Neutron-rich nuclei in the mass region A ~ 165 are of special interest for the study of nuclear structure because of the rapid onset of deformation between 88 and 90 neutrons. The observation of detailed changes in nuclear structures within this mass region continues to provide insights into the nuclear force. The isospin symmetry breaking in the A ~ 70 mirror nuclei is another subject of interest in this study. It will also help to describe very important nuclear properties. Investigations following gamma- and beta-decays, aided by potential energy surface and shell-model calculations, are helpful to the analysis of the effects of the nuclear force governing nuclear shapes and the resulting sequence of single-particle orbitals. The structure of deformed, neutron-rich nuclei in the rare-earth region is also of significant interest for the field of astrophysics. Although much progress is being made in our understanding of the r-process, a satisfactory explanation for the elemental peak in abundance near A = 165 is still elusive. The quest to understand the origin of this peak may be key to correctly identifying the astrophysical conditions for the r-process. In order to address these issues, additional experiments are needed. The proposed project will explore deformed structures and other nuclear properties of the A ~ 70 and 165 nuclei.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.