Nuclear Physics Rolling Grant

科学家们开始了解最微观尺度上的科学与宇宙中壮观的大规模事件之间的密切联系。令人惊讶的事实是，我们今天观察到的大多数化学元素都是从古代恒星爆炸的灰烬中产生的。这类最壮观的事件是超新星。使用非常高灵敏度的望远镜，我们可以研究从遥远的超新星喷出的物质的化学丰度，并与我们自己太阳系中发现的丰度进行比较。理解这些壮观的爆炸性天体物理事件的丰度，关键取决于涉及所谓的奇异核的核反应过程。外来核对放射性衰变是不稳定的，与自然产生的稳定同位素相比，其组成的中子和质子粒子的比例不同。直到现在，科学家们才开发出一项技术，通过这项技术，我们实际上可以产生放射性核束来重现地球上的核反应，从而推动宇宙中发生的这些大爆炸。这些奇特的原子核可以表现出光晕和中子皮等非凡的性质，这对理解中子星等天体物理对象也很重要，中子星是超新星爆炸的可能终点之一，另一个替代选择是黑洞。事实证明，奇异核的行为不像稳定核，我们需要研究它们的性质，在某些情况下，达到核存在的极限，滴线，将核反应的微观物理与我们在宇宙中观察到的物质联系起来。原子核过去被认为是液滴，后来人们意识到，由于这些系统的量子力学性质，某些数量的中子和质子，即所谓的魔术数，要稳定得多。一个很好的类比是化学体系的稳定性，比如惰性气体，在那里所有的电子都填满了一个壳层。我们的研究将探索在稳定同位素中发现的这些壳结构是否一直持续到滴线。预测在这些极端极限下会发生什么，在理论上存在很大的不确定性，因为这些极端极限发生了罕见的衰变现象。例如，这些原子核可以通过发射组成的单质子或质子对来衰变。这些过程是通过量子隧道发生的，事实证明，隧道的速度严重取决于核壳和原子核的形状--其中一些可以高度变形，这可以将量子隧道速度加快数量级！在一些区域，如近壳层闭合，存在着高于基态的奇异准稳态，这些基态具有非常高的自旋。这些状态特别揭示了壳的结构，并为研究这些奇异的衰变过程提供了一个很好的新实验室。虽然核子在核中的组装以惊人的方式表现，但人们也没有完全了解核子本身可以被激发的方式，以及它们在核内的行为如何，并影响核的性质。这是一个非常令人兴奋的领域，自然会导致考虑夸克在核子本身中的作用，以及我们如何将我们的原子核模型及其相互作用与基于量子色动力学(QCD)等现代理论的更基本的理解联系起来。这样的理论表明，存在着被称为胶球和夸克-胶子杂化的非凡的、未被发现的粒子；我们将在未来的实验中寻找这些粒子。所有这些实验都是在世界各地的原子加速器上进行的，爱丁堡小组在那里使用其设备并进行这些基本测量。许多艰苦的工作都是在爱丁堡完成的，在那里，我们使用与英国公司联合开发的产品，以及由STFC支持的大型英国实验室，构建基于硅技术的非常先进的探测器和电子系统。

Scientists are beginning to understand the intimate connections between science on the most microscopic scales and spectacular large scale events in the cosmos. It is an astonishing fact that most of the chemical elements we observe today were created from the ashes of ancient stellar explosions. The most spectacular events of this type are supernovae. With very high sensitivity telescopes we can study the chemical abundances of material ejected from distant supernovae and compare with those abundances found in our own solar system. Understanding abundances from spectacular explosive astrophysical events like these crucially depends on nuclear reaction processes involving so-called exotic nuclei. Exotic nuclei are unstable to radioactive decay, and have different ratios of constituent neutron and proton particles compared to the naturally occuring stable isotopes. Only now have scientists developed the technology whereby we can actually produce beams of radioactive nuclei to reproduce nuclear reactions here on earth driving these large explosions occuring out in the cosmos. These exotic nuclei can exhibit remarkable properties such as halos, and neutron skins which also turn out to be important in understanding astrophysical objects like neutron stars, one of the possible end points of supernovae explosions, another alternative being black holes. It turns out that exotic nuclei don't behave like stable nuclei, and we need to study what their properties are, in some cases going to the very limits of nuclear existence, the drip-lines, to connect the microscopic physics of nuclear reactions to the matter we observe in the cosmos. Nuclei used to be thought of as liquid drops and then it was realised that certain numbers of neutrons and protons, known as magic numbers, were much more stable due to the quantum mechanical nature of these systems. A good analogy is the stability of chemical systems such as the inert gases where all the electrons fill a single shell. Our studies will explore whether these shell structures found in stable isotopes persist all the way to the the drip lines. There is great theoretical uncertainty in predicting what happens at these extreme limits, where rare decay phenomena occur. For example, these nuclei can decay by emitting constituent single protons or pairs of protons. These processes occur by quantum tunneling, and it turns out the rate of tunneling critically depends on the nuclear shells and the shape of the nuclei - some can be highly deformed and this can speed up quantum tunneling rates by orders of magnitude! In some regions such as near shell closures exotic quasi-stable states exist high above above the ground-state, which have a very high spin. These states are particularly revealing about shell structures, and provide a wonderful new laboratory to study these exotic decay processes. While assemblies of nucleons in nuclei behave in remarkable ways, it is also not fully understood the ways in which the nucleons themselves can be excited, and how they behave inside nuclei, and influence nuclear properties. This is a very exciting field that naturally leads to consideration of the roles of quarks inside the nucleons themselves, and how we can connect our models of nuclei and their interactions, with a more fundamental understanding based on modern theories such as Quantum Chromo Dynamics (QCD). Such theories suggest the existence of remarkable, undiscovered, particles called glueballs and quark-gluon hybrids; we will search for these in future experiments. All these experiments are performed at atom smashers all over the world, where the Edinburgh Group takes its equipment and performs these fundamental measurements. A lot of the hard work is done back in Edinburgh where we build highly advanced detector and electronics systems based on silicon technology using products jointly developed with UK firms, and with large UK laboratories supported by the STFC.