Electromagnentic probe of nuclear interactions

低能核物理最近在对其研究对象的基本理解方面经历了重大的范式转变。在轻质量和中等质量的原子核中，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。在加拿大粒子加速器中心TRIUMF，加速器和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，测试基于接近稳定的数据开发的理论和理解。一个引人注目的例子是，由中子或质子过剩引起的核壳有序性的变化，重新安排了壳结构，打破了建立在稳定附近的自旋/奇偶、质量、结合和激发能等可观测性的趋势。组态相互作用方法利用QCD激发的二体和三体相互作用，可以解决中等质量核和重质量核的多体核问题，包括那些远离稳定性的核，而密度泛函理论则将这些相互作用的应用扩展到最重的核。目前的理论方法系统地跟踪近似误差，预测趋势和不确定性，从而能够通过与实验数据的比较来直接测试QCD激发的有效相互作用。拟议计划的长期目标是提高对原子核内核子(质子和中子)之间相互作用的定量理解。短期目标是从实验上检验核相互作用对质子数(Z)和中子数(N)之间的不对称性的依赖。特别是，建议在利用西蒙·弗雷泽大学(SFU)的实验基础设施发展的同时，利用TRIUMF提供的重放射性束流执行一项精确测量电磁跃迁率的方案。在TRIUMF等待执行的实验是测量55Co和55Ni的电磁跃迁率，55Co和55Ni是质子核和中子洞核相对于闭壳56Ni，20 mg是Z=12的最缺乏中子的同位素。它还建议利用SFU的中子发生器和伽马能谱技术的发展，研究快中子引发的反应产物、裂变碎片和动力学。特别是，建议在测量裂变碎片的能量和角动量分布时部署8P光谱仪。该计划将使核科学研究人员受益，提供对验证最先进的核结构和裂变理论至关重要的信息，同时提供对高素质人员的优秀培训，这对加拿大直接有利。

Low-energy nuclear physics recently underwent a significant paradigm shift in the basic understanding of its objects of study. In light and medium mass 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. At TRIUMF, Canada's particle accelerator centre, sustained development in accelerators and gamma-ray detection systems permits the study of nuclei which are very far from stability, testing theories and understanding developed based on data obtained near stability.  A striking example is the change of nuclear shell ordering prompted by the neutron or proton excess that rearranges shell structure 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 and heavy mass nuclei, including those far from stability, while density functional theories provide an extension for application of these interactions up to the heaviest nuclei. Current theoretical methods track approximation errors systematically, predicting trends together with uncertainties, thus enabling direct tests of QCD-inspired effective interactions through comparison to the experimental data. The long-term goal of the proposed program is to improve quantitative understanding of the interactions between nucleons (protons and neutrons) inside atomic nuclei. The short-term objective is to examine experimentally the dependence of nuclear interactions on the asymmetry between the proton number (Z) and the neutron number (N). In particular, it is proposed to execute a program of precision measurements of electromagnetic transition rates using heavy radioactive beams provided by TRIUMF while taking advantage of developments of the experimental infrastructure at Simon Fraser University (SFU). Experiments awaiting execution at TRIUMF are measurements of electromagnetic transition rates in 55Co and 55Ni which are proton- and a neutron-hole nuclei with respect to closed-shell 56Ni, and in 20Mg, the most neutron deficient isotope at Z=12. It is also proposed to study products of reactions induced by fast neutrons, as well as, fission fragments and dynamics, taking advantage of the neutron generator and development of gamma-ray spectroscopy techniques at SFU. In particular, it is proposed to deploy the 8p spectrometer in measurements of energy and angular momenta distributions of fission fragments. The program will benefit researchers in nuclear science providing information crucial for validation of state-of-the-art nuclear structure and fission theories while providing excellent training of Highly Qualified Personnel which is of direct benefit to Canada.