Structure of nuclei far from stability

原子核结构远不稳定

• 批准号: SAPIN-2015-00049
• 负责人: Starosta, Krzysztof
• 金额: $ 7.36万
• 依托单位: Simon Fraser University
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=692847
• 关键词: Structure; nuclei; far; stability

Low-energy nuclear physics is on the verge of a significant paradigm shift in the basic understanding of its objects of study. In light nuclei it is now possible to provide ab-initio predictions of nuclear structure inspired by the Quantum Chromodynamics (QCD) theory of strong interactions, breaking a decades-long reign of phenomenological effective interactions derived from global or local fits to experimental data. These methods are used for analysis of light-ion induced reactions taking into account their structure within a unified framework; this defies the traditional separation between nuclear reaction and nuclear structure theories. At TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, sustained development in accelerators and sophisticated gamma-ray detection systems permits the study of nuclei very far from stability that tests understanding developed for stable and near-stable nuclei. A striking example is the change of nuclear shell ordering prompted by the neutron or proton excess that rearranges shell structure, often in unexpected ways, and breaks trends of observables such as spins/parities, masses, binding, and excitation energies established near stability. Configuration Interaction methods using two- and three-body interactions inspired by QCD allow the many-body nuclear problem to be solved for medium mass nuclei, including those far from stability, while density functional theories provide a further extension for investigating the validity of these interactions up to the heaviest nuclei. Current theoretical methods track errors imposed by approximations systematically, predicting trends together with uncertainties.***The goal of the proposal is to examine experimentally the dependence of nuclear interactions on the proton/neutron asymmetry as a means of validating the state-of-the-art nuclear structure theories. The research plan focuses on three areas: 1) electromagnetic transition rate studies in nuclei with equal number of protons and neutrons, in particular the benchmark 68Se nucleus, and in nuclei with extreme neutron-excess in the region of rapidly changing shape deformation, in particular 94Sr, 2) structure studies of the most neutron-rich stable nuclei near the double-beta decay candidates, in particular near 130Te, 150Nd, 154Sm and 160Gd, as well as  3) studies of neutron-induced reactions in light nuclei with nearly equal proton and neutron number, in particular elastic neutron scattering on hydrogen and deuterium. Nuclear models validated based on the provided data will be used to examine nuclear shape evolution and coexistence far from stability, nuclear matrix elements of interest to the neutrino mass measurement from neutrino-less double beta decay and Fermi constant measurement from superallowed beta decay, and presence of two- and three-body effects in neutron interactions with the lightest elements. **

在对其研究对象的基本理解方面，低能核物理学正处于一个重大范式转变的边缘。在轻核中，受量子色动力学（QCD）强相互作用理论的启发，现在有可能提供核结构的从头算预测，打破了几十年来由全局或局部拟合得出的现象有效相互作用的统治。这些方法用于分析光离子诱导反应，考虑到它们在统一框架内的结构；这违背了传统的核反应理论和核结构理论的分离。在加拿大粒子和核物理国家实验室（TRIUMF），加速器和复杂的伽玛射线探测系统的持续发展使人们能够研究远离稳定的原子核，从而测试人们对稳定和近稳定原子核的理解。一个显著的例子是由中子或质子过剩引起的核壳序的变化，它常常以意想不到的方式重新排列壳结构，并打破了可观测的趋势，如自旋/宇称、质量、结合能和接近稳定的激发能。受QCD启发，使用二体和三体相互作用的组态相互作用方法可以解决中等质量核的多体核问题，包括那些远离稳定的核，而密度泛函理论为研究这些相互作用的有效性提供了进一步的扩展，直到最重的核。目前的理论方法系统地跟踪由近似值施加的误差，预测趋势和不确定性。***该建议的目的是通过实验检验核相互作用对质子/中子不对称性的依赖，作为验证最先进的核结构理论的一种手段。研究计划主要集中在三个方面：1)质子和中子数量相等的原子核，特别是基准的68Se原子核，以及在快速变化的形状变形区域中中子极度过剩的原子核，特别是94Sr的电磁跃迁速率研究；2)双β衰变候选者附近最富中子的稳定原子核的结构研究，特别是在130Te、150Nd、154Sm和160Gd附近。3)质子和中子数几乎相等的轻核中中子诱导反应的研究，特别是氢和氘的弹性中子散射。基于所提供的数据验证的核模型将用于检查核形状演变和远离稳定性的共存，核矩阵元素感兴趣的中微子质量测量来自无中微子双β衰变和费米常数测量来自超允许β衰变，以及中子与最轻元素相互作用中的二体和三体效应的存在。**