Investigations of Exotic Nuclei with Large Arrays

用大阵列研究奇异核

• 批准号: SAPIN-2016-00045
• 负责人: Andreoiu, Corina
• 金额: $ 1.82万
• 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: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=616813
• 关键词: Investigations; Exotic; Nuclei; Large; Arrays

Almost every element on earth was formed at the core of a star. Nuclear reactions continually convert light elements into heavier ones, but the exact mechanism and astrophysical site where this takes place remain unclear. This situation arises because there are many ambiguities concerning the exact nature of the nuclear strong force, which is responsible for binding the protons and neutrons together at the centre of an atom. A primary goal of contemporary nuclear physics is to reveal a comprehensive unified description of this force so that we can understand the origin and evolution of all nuclear matter. The vast majority of elements existing on earth are stable nuclei, forming the so-called valley of nuclear stability. These stable nuclei are well described in the nuclear shell model developed by Nobel laureates M. Goppert-Mayers and J. H. Jensen in the late 1940s. This model has successfully explained many experimental observations, including the existence of the so-called magic numbers, a special set of proton and neutron numbers (2, 8, 20, 28, 82 and 126) that brings extra stability to nuclear matter, similar to the electron configurations of the noble gases in chemistry. For decades, the shell model has been the backbone to our understanding of nuclear structure. In recent years, experimental investigations of nuclei with larger numbers of neutrons compared to protons have revealed new magic numbers in these exotic nuclei. The challenge is to understand why exactly the magic numbers shift with different combinations of protons and neutrons, and to successfully predict whether other more exotic nuclei that might only exist for fractions of a second can be formed far from stability. The evolution of shell structure could lead to a new frontier of nuclear stability comprehension. In order to develop new models that will describe the structure of nuclear matter far from stability, the evolution of magic numbers, and the creation of elements in stars, scientists need detailed knowledge of nuclear masses, lifetimes, and decay probabilities. Experimental nuclear science, such as that described in this proposal, is responsible for the critical gathering of information for nuclei situated far from stability. In particular, the multitude of tin nuclei makes an excellent case study because they all have a magic number of 50 protons, and many tin isotopes exist far from stability with neutron numbers beyond the magic number of 82. The proposed experiments will take place mainly at TRIUMF in Vancouver, BC. Unstable nuclei are created on-site with the world’s largest cyclotron. These nuclei are then investigated with large state-of-the-art detectors that are able to observe the radiation emitted when the nuclei decay. The information extracted from these experiments provides clues into the nuclear matter and produces essential information for nuclear astrophysics about the creation of elements in the universe.

地球上几乎所有的元素都是在恒星的核心形成的。核反应不断地将轻元素转化为更重的元素，但发生这种转换的确切机制和天体物理位置尚不清楚。这种情况的出现是因为对于核强力的确切性质有许多模糊的地方，核强力负责将原子中心的质子和中子结合在一起。现代核物理的一个主要目标是揭示这种力的一个全面统一的描述，以便我们能够理解所有核物质的起源和演化。 地球上存在的绝大多数元素都是稳定核，形成了所谓的核稳定谷。这些稳定的原子核在诺贝尔奖获得者M.Goppert-Mayers和J.H.Jensen于20世纪40年代末发展的核壳模型中得到了很好的描述。这个模型成功地解释了许多实验观测，包括所谓幻数的存在，这是一组特殊的质子和中子数(2、8、20、28、82和126)，它给核物质带来额外的稳定性，类似于化学中惰性气体的电子构型。几十年来，壳模型一直是我们理解核结构的支柱。近年来，对具有比质子更多的中子的原子核的实验研究揭示了这些奇异原子核中的新魔数。我们面临的挑战是弄清楚为什么神奇的数字会随着质子和中子的不同组合而变化，并成功地预测其他可能只存在几分之一秒的更奇异的原子核是否可以形成远离稳定性的原子核。壳层结构的演变可能导致核稳定性理解的一个新的前沿。 为了开发新的模型来描述远离稳定性的核物质的结构、幻数的演化以及恒星中元素的产生，科学家们需要详细的核质量、寿命和衰变概率的知识。 实验核科学，如本提案中所描述的，负责为远离稳定的原子核收集关键信息。特别是，锡原子核的众多是一个很好的案例研究，因为它们都有50个质子的魔数，而且许多锡同位素的存在远远不稳定，中子数超过了82的魔数。拟议的实验将主要在不列颠哥伦比亚省温哥华的TRIUMF进行。不稳定的原子核是用世界上最大的回旋加速器在现场创造的。然后用大型最先进的探测器对这些原子核进行研究，这些探测器能够观察到原子核衰变时发出的辐射。从这些实验中提取的信息提供了了解核物质的线索，并为核天体物理学提供了关于宇宙中元素创造的基本信息。