Collaborative Research: RUI: Study of Exotic Nuclei and Neutron Detector Response

这个实验项目的主要目标是推进对奇异原子核性质的理解，本科生的参与是一个不可或缺的组成部分。实验将在密歇根州立大学（MSU）的国家超导回旋加速器实验室（NSCL）进行，使用模块化中子阵列（莫纳）和大面积多机构闪烁体阵列（丽莎），这两种阵列都是由来自莫纳合作的几个机构的本科生建造和测试的。该奖项的PI和他们的本科生团队将研究接近稳定极限的轻富中子核的结构，这将为测试当前的核结构理论模型提供数据。随着元素的同位素的核质荷比增加，同位素变得弱结合或未结合，并且与它们的稳定对应物相比，它们表现出显着不同的结构。这些不稳定的原子核是由加速核束与稳定目标的碰撞产生的，并且在MoNA-LISA塑料闪烁体探测器中中子散射的精确计算机模拟对于从这些短寿命原子核的分裂中提取物理结果至关重要。最近在洛斯阿拉莫斯国家实验室进行的中子散射实验的分析将提高这些模拟的准确性，为即将在密歇根州立大学稀有同位素束设施（FRIB）进行的高能实验做准备。 该项目的更广泛影响包括为本科生提供形成性研究机会，并在设备开发和领导方面投资莫纳协作。该奖项支持的研究将包括进行两项新实验，分析最近和未来的数据，并为FRIB高刚度谱仪使用的下一代快中子探测器的开发做出贡献。NSCL的最后两项莫纳实验将于2020年进行，以研究富中子核中的中子非束缚态。感兴趣的核是13 Be和28 F。这些实验将解决长期存在的13 Be能级结构问题，它位于已知结构变化的核图表的N=8区域，并且结合先前确定的28 F两体矩阵元素的未结合28 F状态的测量将有助于限制28 O的单中子分离能量。为了为即将到来的FRIB设施的实验做准备，2019年11月在洛斯阿拉莫斯中子科学中心（LANSCE）进行了一项实验，以测量快中子与塑料闪烁体探测器相互作用期间的中子散射和次级中子产生。这项工作将添加到最近的中子散射工作的PI暴露了一些失败的当前GEANT 4为基础的蒙特卡罗模拟包。我们的目标是改善与这些探测器的中子相互作用的建模，这将是至关重要的提高检测器的分辨率和过滤的FRIB实验的数据。这项工作也服务于更广泛的社区，因为塑料闪烁器广泛用于核物理和相关应用中的中子探测。该奖项反映了NSF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。

The main goal of this experimental program is to advance understanding of the nature of exotic atomic nuclei, with undergraduate student participation as an integral component. Experiments will be conducted at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU) using the Modular Neutron Array (MoNA) and the Large-area multi-Institutional Scintillator Array (LISA), both constructed and tested by undergraduate students from several institutions in the MoNA collaboration. The PIs of this award and their team of undergraduate students will investigate the structure of light neutron-rich nuclei near the limits of stability, which will provide data to test current theoretical models of nuclear structure. As the nuclear mass-to-charge ratio for isotopes of an element increases, the isotopes become weakly-bound or unbound, and they exhibit significantly different structure compared with their stable counterparts. These unstable nuclei are produced by collisions of an accelerated nuclear beam with a stable target, and accurate computer simulations of neutron scattering in the MoNA-LISA plastic scintillator detectors are critical for extracting physics results from the breakup of these short-lived nuclei. Analysis of recent neutron-scattering experiments conducted at Los Alamos National Laboratory will improve accuracy of these simulations in preparation for higher energy experiments soon to be conducted at the Facility for Rare Isotope Beams (FRIB) at MSU. Broader impacts of the proposed work include formative research opportunities for undergraduate students and investing in the MoNA Collaboration in terms of equipment development and leadership.Research supported by this award will consist of conducting two new experiments, analyzing recent and future data, and contributing to the development of the next generation fast neutron detector for use with the High-Rigidity Spectrometer at FRIB. Two final MoNA experiments at the NSCL will be performed in 2020 to study neutron-unbound states in neutron-rich nuclei. The nuclei of interest are 13Be and 28F. These experiments will resolve the longstanding issue of the level structure of 13Be, which is in the N=8 region of the nuclear chart known for structural changes, and measurements of unbound 28F states combined with previously determined two-body matrix elements from 28F will help place limits on the one-neutron separation energy of 28O. To prepare for experiments at the upcoming FRIB facility, an experiment was performed at the Los Alamos Neutron Science Center (LANSCE) in November 2019 to measure neutron scattering and secondary neutron production during the interaction of fast neutrons with plastic scintillator detectors. This work will add to the recent neutron scattering work from the PIs which exposed some failures of current GEANT4-based Monte Carlo simulation packages. The goal is to improve the modeling of neutron interactions with these detectors, which will be crucial for improving detector resolution and filtering of data for FRIB experiments. The work also serves a broader community since plastic scintillators are widely used for neutron detection in nuclear physics and related applications.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.