Exploring the limits of nuclear existence for heavy proton-rich nuclei

核物理中的一个基本问题是，原子核内部可以束缚的质子和中子的数量限制是多少？这项研究提案的目的是通过比以往任何时候都更仔细地确定被称为质子滴线的准确位置来回答这个问题的关键部分。质子和中子滴线是束缚核和非束缚核之间的边界。那些在质子滴线上的人拥有如此大量的过剩质子，以至于他们非常不稳定，并试图通过质子发射的过程实现更大的稳定性。我们将研究当质子脱离束缚时，核行为是如何受到影响的。沿着原子核版图的这一遥远海岸的原子核应该会显示出与针对更稳定原子核优化的模型的预测所预期的行为最大的偏差。我们的研究将集中在质子滴线附近的原子核，即锡(Z=50)和铅(Z=82)之间的元素。从历史上看，这一区域一直是质子发射核数据的主要来源，很大程度上是因为这里的质子发射发生在一个实验可及的时间尺度上，仍然有效地与阿尔法或贝塔衰变竞争。到目前为止发现的大约30个质子发射器的一个重要特征是，它们跨越了广泛的核变形，从球形核到其他橄榄球形状的核，它们的长度比它们的宽度长50%。用简单的模型很好地描述了球形原子核的质子发射，理论描述的简单性使人们能够对这些原子核的结构有很大的了解。强变形核质子发射的理论描述必然有很大的不同，已经提出了几个模型，并与现有数据进行了比较。我们将利用新一代实验方法来研究可以在实验室中制造的最富质子的原子核，跨越整个核变形范围。我们将搜索目前尚不为科学所知的核并测量它们的质子和阿尔法衰变，首次研究选定核中的激发态，并将对重核直接质子发射的实验观测扩大到纳秒(十亿分之一秒！)甚至更短。我们的实验结果将与理论预测进行比较，以提高我们对每个原子核心的原子核复杂而迷人的世界的理解。

A fundamental question in nuclear physics is, 'what are the limits on the number of protons and neutrons that can be bound inside an atomic nucleus?' The aim of this research proposal is to answer a vital part of this question by determining more carefully than ever before the precise location of what is known as the proton drip line. The proton and neutron drip lines are the borders between bound and unbound nuclei. Those at the proton drip line have such a large excess of protons that they are highly unstable and try to achieve greater stability through the process of proton emission. We will investigate how nuclear behaviour is affected when protons become unbound. Nuclei along this distant shore of the nuclear landscape should show the greatest deviations from the behaviour expected from predictions of models optimised for more stable nuclei. Our investigations will focus on nuclei close to the proton drip line, for elements between tin (Z=50) and lead (Z=82). Historically, this region has been the primary source of data on proton-emitting nuclei, largely because here the proton emission occurs on an experimentally accessible timescale that still competes effectively with alpha or beta decay. One important feature of the 30 or so proton emitters discovered to date is that they span a wide range of nuclear deformations, ranging from spherical nuclei to others that are rugby ball shaped and are up to 50% longer than they are wide. Proton emission from spherical nuclei is well described using simple models and the simplicity of the theoretical description has allowed a great deal to be learnt about the structure of these nuclei. The theoretical descriptions for proton emission from strongly deformed nuclei are necessarily rather different and several models have been proposed and compared with the available data. We will exploit a new generation of experimental methods to study the most proton-rich atomic nuclei that can be made in the laboratory, spanning the entire range of nuclear deformations. We will search for nuclei presently unknown to science and measure their proton and alpha decays, study excited states in selected nuclei for the first time and extend experimental observations of direct proton emission from heavy nuclei to lifetimes of nanoseconds (billionths of a second!) and even shorter. The results of our experiments will be compared with the theoretical predictions in order to improve our understanding of the complex and fascinating world of the nuclei at the heart of every atom.