University of the West of Scotland Nuclear Physics Group Consolidated Grant

自从欧内斯特·卢瑟福的开创性实验证明了原子核的存在以来，几乎整整100年了。在接下来的一个世纪里，里程碑式的发展，如1940年代核壳模型的建立，1960年代重离子加速器的建造，以及核探测器技术的重大进步，坚定地确立了核物理作为一项处于科学研究前沿的国际活动。在过去的几十年里，对远离稳定谷的奇异原子核的性质的研究已经取得了相当大的实验进展。在这项综合拨款申请中描述的研究方案包括对远离稳定性的原子核的结构和性质的研究。我们研究方案的主要目的之一是更好地了解稳定谷丰中子和丰质子一侧的奇异核的结构和行为。在理论计算的支持下，最近的实验观察已经开始表明，富中子核的结构可能与那些接近稳定的核的结构不同。例如，众所周知的幻数序列，对应于核壳结构中的能隙，现在被认为是随着中子的极端过剩而在原子核中发生变化。在中子数N=20附近，这种变化的证据已经令人信服，预计在N=28、50和82的其他壳层间隙中也会有类似的影响。我们将使用伽马射线和带电粒子能谱技术研究丰中子核中壳层能隙的演化。在质量数A~100以上，静电斥力使稳定核的中子比质子多。在双魔术Sn100核上方的富质子核是那些中子和质子数量几乎相等的核。众所周知，这些原子核通过奇异的衰变模式衰变，例如质子发射。对这些衰变性质的光谱研究可以提供有关原子核在其基态和最初几个激发态的性质的宝贵信息。我们的研究计划将包括通过研究A~110附近的粒子衰变和伽马射线能谱来研究A~110附近的富质子核。我们研究计划的另一个方面将致力于研究原子核的裂变。裂变是一种集体衰变模式，最常与铀区的重核有关，但在我们的研究中，我们将研究铅区奇异核的β延迟裂变，这些核距离稳定很远(约20-25个中子)，最近才能通过实验获得放射性束流的发展。研究β-延迟裂变的性质，如裂变碎片的质量分布，将提供有关低激发能下的核结构和壳层效应的重要信息。在我们研究计划的一个相关部分中，我们将使用放射性At束流来研究其他核结构效应，如形状共存。我们的研究方案有几个主题，将使用不同的方法。首先，我们的实验将在大型国际设施中使用最先进的设备进行。伽马射线能谱提供了研究奇异核结构的最佳方法之一，在这里，我们将开发Legnaro国家实验室、GSI和GANIL的新型Agata伽马射线跟踪光谱仪。我们研究的另一部分将利用芬兰Jyväskylä的Jurogam伽马射线能谱仪和Ritu反冲分离器。我们研究β-延迟裂变的方案将利用欧洲核子研究中心Isolde设施和日本宇宙航空研究开发机构实验室的放射性同位素束流。此外，我们将利用在伊索尔德开发的新的阿司坦束。

It is almost exactly 100 years since Ernest Rutherford's pioneering experiments which demonstrated the existence of the atomic nucleus. In the century that has followed, landmark developments, such as the inception of the nuclear shell model in the 1940s, the construction of heavy-ion accelerators in the 1960s, and major advances in nuclear-detector techniques, have firmly established nuclear physics as an international activity at the forefront of scientific research. In the past few decades, the quest to understand the properties of exotic nuclei ever further from the valley of stability has led to considerable experimental progress. The programme of research described in this Consolidated Grant application covers research into the structure and properties of atomic nuclei that lie far from stability. One of the main aims of our research programme is to achieve a better understanding of the structure and behaviour of exotic nuclei on both the neutron-rich and proton-rich sides of the valley of stability. Recent experimental observations, supported by theoretical calculations, have begun to suggest that the structure of neutron-rich nuclei may be different from those near stability. For example, the well known sequence of magic numbers, corresponding to energy gaps in nuclear shell structure, is now thought to change in nuclei with an extreme excess of neutrons. The evidence for such a change is already convincing around neutron number N=20, and similar effects are expected for the other shell gaps at N=28, 50, and 82. We will study the evolution of shell gaps in neutron-rich nuclei using both gamma-ray and charged-particle spectroscopy techniques. Above mass number A~100, electrostatic repulsion causes stable nuclei to have more neutrons than protons. Proton-rich nuclei just above the doubly-magic Sn100 nucleus are those with near equal numbers of neutrons and protons. These nuclei are known to decay by exotic decay modes such as proton emission. Spectroscopic study of the properties of these decays can give invaluable information about the properties of the nucleus in its ground state and in the first few excited states. Our research programme will include studies of proton-rich nuclei around A~110 by investigating their particle decays and by gamma-ray spectroscopy. Another aspect of our research programme will be devoted to studying fission of the nucleus. Fission is a collective mode of decay most commonly associated with heavy nuclei in the uranium region, but in our research we will study the beta-delayed fission of exotic nuclei in the lead region that lie very far from stability (by ~20-25 neutrons) and which have only recently become experimentally accessible with the development of radioactive beams. A study of the properties of beta-delayed fission, such as the mass distributions of the fission fragments, will give important information about nuclear structure and shell effects at low excitation energy. In a related part of our research programme, we will use radioactive At beams to study other nuclear-structure effects such as shape coexistence. Our research programme has several themes which will use different methodologies. Primarily, our experiments will be carried out using state-of-the-art apparatus at large international facilities. Gamma-ray spectroscopy offers one of the best methods of studying the structure of exotic nuclei, and here we will exploit the new AGATA gamma-ray tracking spectrometer at Legnaro National Laboratory, GSI and GANIL. Another part of our research will make use of the Jurogam gamma-ray spectrometer with the RITU recoil separator at Jyväskylä in Finland. Our programme to study beta-delayed fission will make use of beams of radioactive isotopes from the ISOLDE facility at CERN and at the JAEA laboratory in Japan. Furthermore, we will exploit the development of new radioactive beams of astatine at ISOLDE.