Birmingham Nuclear Physics Consolidated Grant

该项目是对强相互作用物质本质的探索。这项研究将探索物质在极端温度和密度下的性质，在这种情况下，原子核中的核子失去了各自的身份，并溶解到它们的夸克和胶子成分中--人们认为这种物质状态在大爆炸后一瞬间就存在了。利用欧洲核子研究中心的Alice实验(伯明翰小组在建立触发电子设备方面发挥了主导作用)以及铅核之间的碰撞，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，将有助于物理学家更多地了解强力的性质和非常早期的宇宙的演化。原子核中的核子通过强相互作用被束缚。在核规模上，这种相互作用是复杂的，尚未得到充分的描述。然而，尽管很复杂，但还是出现了相当简单的模式，例如壳层结构和魔数，或者核子作为原子核内的团簇的几何排列。由于阿尔法粒子的稳定性很高，在原子核内沉淀的往往是阿尔法团簇。原子核中的簇化作用是理解轻原子核结构的核心。例如，著名的12C中的霍尔态，通过它在恒星中合成碳，其结构由三个阿尔法粒子组成。这类系统的特点构成了该方案的一个关键要素。当人们将越来越多的中子添加到原子核中时，稳定性达到极限，此时最后一个中子不再“粘”在原子核上，这一点被称为中子滴线。研究接近这一极限的原子核为我们理解强相互作用的本质提供了一种独特的测试。一种相当有趣的可能性是，滴线上的原子核将具有相当奇怪的结构，并表现为嵌入中子海洋中的团簇。当前计划的一部分将研究集群化如何随着滴线的临近而变化。对原子核结构最精确的测试之一来自于一种间接技术。原子中电子的能级在很大程度上取决于原子核的性质；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，可以通过使用激光技术对电子能级的询问来确定原子核的基本性质。伯明翰集团在使用激光光谱技术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位于形状转变区域边缘的Ce同位素，这些区域是由于Z=质子亚壳的减弱而引起的。为了测量这些同位素，将需要使用由光抽运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.