Structure of nuclei far from stability

低能核物理在对其研究对象的基本理解方面即将发生重大的范式转变。在轻核中，现在有可能从量子色动力学(QCD)的强相互作用理论出发，提供原子核结构的从头算预测，打破了几十年来从全局或局部拟合到实验数据的唯象有效相互作用的统治地位。这些方法用于分析光离子诱导反应，在统一的框架内考虑了它们的结构；这打破了核反应和核结构理论之间的传统分离。在加拿大粒子和核物理国家实验室TRIUMF，加速器和复杂的伽马射线探测系统的持续发展使人们能够研究非常不稳定的原子核，从而测试对稳定和近稳定原子核的理解。一个明显的例子是由中子或质子过剩引起的核壳层有序性的变化，它通常以意想不到的方式重新排列壳层结构，并打破了接近稳定的自旋/奇偶、质量、结合和激发能等可观测参数的趋势。在QCD的启发下，利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(包括那些远离稳定性的核)的多体核问题，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近似造成的误差，预测趋势和不确定性。*该提议的目标是通过实验检验核相互作用对质子/中子不对称性的依赖性，作为验证最先进的核结构理论的手段。研究计划集中在三个领域：1)质子和中子数目相等的核，特别是基准68Se核，以及快速形状形变区域中具有极高中子过剩核的电磁跃迁率研究，特别是94Sr，2)双β衰变候选者附近，特别是130Te，150Nd，154Sm和160Gd附近最富含中子的稳定核的结构研究，以及3)质子和中子数几乎相等的轻核中中子诱发反应的研究，特别是弹性中子在氢和氘上的散射。根据所提供的数据验证的核模型将用于检查远离稳定性的核形状演化和共存、由无中微子双β衰变测量中微子质量的感兴趣的核矩阵元素和由超允许的β衰变测量费米常数，以及在中子与最轻元素相互作用中是否存在二体和三体效应。**

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. **