Investigation of light exotic isotopes with ultra-sensitive laser spectroscopic methods

这项应用的科学目标是测量同位素硼-8的核电荷半径。大量过剩的质子和它们的低分离能表明质子晕核的存在。这样的系统的特征是有一个中心核，其中束缚质子最少，轨道的平均距离很大。虽然中子晕核可以在几个已经被彻底研究的光系统中找到，但对硼-8的奇异结构的独立测试仍然悬而未决。核电荷半径的测定可以提供这样的测试，因为它允许以独立于模型的方式计算核心和晕质子之间的距离。为了测量核电荷半径，激光光谱是选择的方法。在这里，原子水平是用高分辨率激光系统探测的。原子核的大小对这些能级的能量有轻微的影响，通过测量不同同位素之间的跃迁能量差，可以计算出这种微小影响的大小。这需要先进的原子物理计算，最近才能用于硼系统。此外，实验的精确度也是至关重要的，这主要受到制备正确原子状态和足够数量的短寿命硼-8的限制。虽然这种技术对于较重的同位素已经很成熟，但最轻元素的低质量和高反应性特别具有挑战性。在本项目范围内，将优化阿贡国家实验室（芝加哥，美国伊利诺伊州）硼-8的生产率。此外，还将实施两个部分，以便在激光光谱学可访问的正确状态下制备放射性硼。同时，我计划更新荧光检测区域，以提供更高的灵敏度，确定实验中所需的硼-8总量。新的片段也可以在ANL进行测试，通过激光光谱学研究钯同位素链中的核结构。该装置和实验将与马萨诸塞州理工学院（MA，USA）的“外来分子和原子实验室”合作进行，由罗纳德费尔南多加西亚鲁伊斯博士领导。他们还专注于研究光，外来核，并将提供必要的科学平台和专业知识，以执行ANL的挑战性实验。

The scientific goal of this application is the measurement of the nuclear charge radius of the isotope boron-8. The large excess of protons and their low separation energy indicate the existence of a proton-halo nucleus. Such a system is characterized by a central core with the least bound proton orbiting in a large mean distance. While neutron-halo nuclei can be found in several light systems that have been investigated thoroughly, an independent test of the exotic structure of boron-8 is still outstanding. A determination of the nuclear charge radius could provide such a test, since it allowed calculating the distance between core and halo proton in a model-independent way.To measure this nuclear charge radius, laser spectroscopy is the method of choice. Here, the atomic levels are probed with high-resolution laser systems. The size of the nucleus influences the energy of these levels slightly, and by measuring the transition energy difference between different isotopes, it is possible to calculate the magnitude of this tiny effect. This requires advanced atomic physics calculations, which just recently became available for the boron system. Also, the experimental precision is crucial which is mostly limited by the preparation of the short-lived boron-8 in the right atomic state and in sufficient amounts.While such techniques are well-established for heavier isotopes, the low mass and the high reactivity of the lightest elements are particularly challenging. In the scope of this project, the production rate of boron-8 at Argonne National Laboratory (Chicago, IL, USA) will be optimized. Also, two segments will be implemented which allow to prepare the radioactive boron in the correct state which is accessible with laser spectroscopy. At the same time, I plan to update the fluorescence detection region to provide a higher sensitivity, determining the total amount of boron-8 needed in an experiment. The new segments can also be tested at ANL to investigate the nuclear structure in the palladium isotopic chain by laser spectroscopy.The setup and the experiments will be performed in collaboration with the group “Laboratory of Exotic Molecules and Atoms” at the Massachusetts Institute of Technology (MA, USA), led by Dr. Ronald Fernando Garcia Ruiz. They are also focused on studying light, exotic nuclei and will provide the necessary scientific platform and know-how to perform the challenging experiments at ANL.