Birmingham Nuclear Physics Consolidated Grant

该项目是对强相互作用物质本质的探索。这项研究将探索在极端温度和密度下物质的本质，在这种情况下，原子核内的核子失去了它们的个体特征，溶解成夸克和胶子的组成部分——这种物质的状态被认为是在大爆炸后瞬间存在的。利用欧洲核子研究中心（CERN）的ALICE实验（伯明翰小组在构建触发电子装置方面发挥了主导作用）和铅核之间的碰撞，将首次详细描述这种强相互作用物质状态的性质。对这种被称为夸克-胶子等离子体的奇异物质状态的研究，将帮助物理学家更多地了解强作用力的本质和早期宇宙的演化。原子核中的核子通过强相互作用结合在一起。在核尺度上，这种相互作用是复杂的，尚未得到充分表征。然而，尽管很复杂，但还是出现了一些简单的模式，比如壳结构和幻数，或者原子核内核子簇的几何排列。由于α粒子的高度稳定性，在核内沉淀的通常是α簇。核的聚集作用是理解轻核结构的核心。例如，12C中著名的霍伊尔态，即碳在恒星中合成的状态，其结构是由三个α粒子组成的。这些系统的特征构成了该方案的一个关键要素。随着向原子核中加入越来越多的中子，达到稳定的极限，最后一个中子不再“粘”在原子核上，这个点称为中子滴线。研究接近这个极限的原子核为我们对强相互作用本质的理解提供了一个独特的测试。一种相当有趣的可能性是，水滴线上的原子核将具有相当奇特的结构，其行为就像镶嵌在中子海洋中的团簇。当前项目的部分内容将研究随着滴线的临近，集群如何发生变化。对原子核结构最精确的测试之一来自一种间接技术。原子中电子的能级在很大程度上是由原子核的性质决定的；它的总电荷，原子核的形状和半径，电荷分布和原子核的磁矩。因此，原子核相当基本的性质可以通过使用激光技术对电子能级的探测来确定。伯明翰小组在使用激光光谱技术以高精度确定核性质方面积累了近20年的经验。目前的工作将集中在由于Z=64质子子壳减弱而处于形状跃迁区域边缘的铈同位素上。为了测量这些同位素，将需要使用由光泵浦填充的亚稳态的新跃迁，以及更有效的光收集区域。

The project is an exploration of the nature of strongly interacting matter. The research will probe the nature of matter at extreme temperature and density where the nucleons inside a nucleus loose their individual identity and dissolve into their constituents of quarks and gluons - the state of matter which it is believed existed an instant after the Big Bang. Using the ALICE experiment at CERN (in which the Birmingham group have played a leading role building the trigger electronics), and collisions between Lead nuclei, the nature of this state of strongly interacting matter will be characterised in detail for the first time. The study of this exotic state of matter, known as a quark-gluon plasma, will help physicists understand more about the nature of the strong force and the evolution of the very early Universe. Nucleons in nuclei are bound via the strong interaction. On the nuclear scale, the interaction is complex and has yet to be fully characterised. Nevertheless, despite the complexity rather simple patterns emerge, such as shell structure and magic numbers or geometric arrangements of nucleons as clusters within nuclei. Due to the very high stability of the alpha-particle it is most often alpha-clusters that precipitate within the nucleus. The role of clusterisation in nuclei is central to understanding the structure of light-nuclei. For example, the famous Hoyle-state in 12C, through which carbon is synthesised in stars, has a structure which is composed of three alpha-particle. The characterisation of such systems forms a key element of the programme. As one adds more and more neutrons to a nucleus the limit of stability is reached where the last neutron no-longer 'sticks' to the nucleus, a point called the neutron drip-line. Studying nuclei close to this limit provides a unique test of our understanding of the nature of the strong interaction. One rather interesting possibility is that nuclei at the drip-line will have a rather exotic structure and behave as clusters embedded in a sea of neutrons. Part of the current programme will study how clusterisation changes as the drip-line approaches. One of the most precise tests of the structure of nuclei comes from an indirect technique. The energy levels of the electrons in an atom are largely determined by the properties of the nucleus; its overall charge, the nuclear shape and radius, the charge distribution and the magnetic moment of the nucleus. Hence, rather fundamental properties of a nucleus may be determined through an interrogation of the electronic energy levels using laser techniques. The Birmingham group has nearly 20 years accumulated experience in using laser-spectroscopy techniques to determine nuclear properties with high precision. The current work will focus on the cerium isotopes which lie at the edge of a region of shape transition due to the weakening of the Z=64 proton sub shell. To measure these isotopes new transitions using a metastable state populated by optical pumping will be needed as well as a more efficient light collection region.