Evolution of shell structure of Z < 50 neutron-rich nuclei near the N=82 closed shell.

N=82 闭合壳层附近 Z < 50 富中子核的壳层结构演化。

• 批准号: ST/I000208/1
• 负责人: Robert Chapman
• 金额: $ 0.79万
• 依托单位: University of the West of Scotland
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FI000208%2F1
• 关键词: Evolution; shell; structure; 50; neutron

One of the most significant advances in the historical development of our understanding of the microscopic structure of the atomic nucleus was made more than 50 years ago, when it was shown that nucleons (protons and neutrons) occupy orbitals in much the same way as electrons do around the nucleus. In this case, it is the other nucleons themselves which effectively generate a potential within which each nucleon moves. Over the years, experimental results have shown that the so-called 'nuclear shell model' is valid for a great number of nuclei, in particular those near closed shells, which correspond to gaps in the nuclear energy levels. However, recent experimental results have shown that, for neutron-rich nuclei, particularly those near neutron numbers 8, 20 and 28, the shell gaps become small (shell quenching) and the magic numbers, nucleon numbers corresponding to closed shells, are no longer valid. In addition, new magic numbers appear. The test of the limits of the shell model is one of the objectives of the present work. Questions nuclear physicists try to answer include: 'What is the origin of the elements?' and 'Why are the atomic elements that make up our world distributed in the quantities we observe?' The answers to these questions will help us to understand the processes involved in the creation of nuclei in the cosmic furnace. The nuclear shell model plays an important role in answering these question. According to some theories, the shell model has to be modified for nuclei with an excess of neutrons (neutron-rich nuclei) around the isotopes of tin with 50 protons and 82 neutrons. For example, for one of those isotopes, cadmium- 130, which has 48 protons and 82 neutrons, shell quenching had been predicted. Surprisingly, recent experimental studies have shown that the shell model is indeed still valid for this isotope of cadmium. Can this behaviour be an exceptional case for the cadmium Isotopes or is it a general behaviour for nuclei in the region? One way to answer this question is by establishing the excited states of neutron-rich neighbouring isotopes such as palladium (with 46 protons). The present proposal is concerned with the first experimental study of the excited states of the neutron-rich palladium isotopes near neutron number 82 to test the robustness of the shell closure. An additional phenomenon which we will study in the neutron-rich region below atomic number Z = 50 is 'magnetic rotation', a new mode of nuclear excitation which corresponds to the fastest magnetic rotor observed in nature. The present study will lead to an improved understanding of the underlying microscopic structure. The nuclei of interest will be populated using multinucleon transfer reactions which result from the interaction of a beam of energetic 96Zr ions with a thick target of 124Sn. The combination of the XTU tandem Van de Graaff and the ALPI linear accelerator at the Legnaro National Laboratory in Italy will be used to accelerate the 96Zr ions to an energy of 576MeV. The gamma-ray decay of the binary reaction fragments will be studied using the GASP array of 40 Compton-suppressed germanium detectors. Finally, the results of the experiment will allow a comprehensive analysis of a previous related experiment which used the CLARA/PRISMA detector systems at the Legnaro National Laboratory. The present experiment will allow essential gamma-ray coincidence relationships to be established for neutron-rich nuclei studied in the earlier experiment with mass numbers around 110. In this mass region we will continue to study the evolution of nuclear shape between the N = 50 and N = 82 magic neutron numbers.

在我们对原子核微观结构的理解的历史发展中，最重要的进展之一是在50多年前，当时人们发现核子（质子和中子）占据轨道的方式与电子围绕原子核的方式大致相同。在这种情况下，是其他核子本身有效地产生了一个势，每个核子在这个势中运动。多年来，实验结果表明，所谓的“核壳模型”对大量的原子核都是有效的，特别是那些接近封闭壳层的原子核，它们对应于原子核能级的间隙。然而，最近的实验结果表明，对于富中子核，特别是那些接近中子数8，20和28的核，壳层间隙变小（壳层猝灭），幻数，对应于封闭壳层的核子数，不再有效。此外，新的魔法数字出现了。壳模型的极限的测试是本工作的目标之一。核物理学家试图回答的问题包括：“元素的起源是什么？”为什么组成我们世界的原子元素以我们观察到的数量分布？“这些问题的答案将有助于我们理解宇宙熔炉中原子核产生的过程。核壳层模型在回答这些问题中起着重要的作用。根据一些理论，壳模型必须被修改为在具有50个质子和82个中子的锡同位素周围具有过量中子的核（富中子核）。例如，对于其中一种同位素镉-130，它有48个质子和82个中子，已经预测了壳层淬火。令人惊讶的是，最近的实验研究表明，壳模型确实仍然适用于镉的这种同位素。这种行为是镉同位素的一个特例，还是该区域原子核的一般行为？回答这个问题的一种方法是建立富中子的邻近同位素的激发态，如钯（有46个质子）。目前的建议是关注的第一个实验研究的激发态的富中子钯同位素中子数82附近的壳封闭测试的鲁棒性。我们将在原子序数Z = 50以下的富中子区研究的另一种现象是“磁旋转”，这是一种新的核激发模式，对应于自然界中观察到的最快的磁转子。目前的研究将导致更好地了解潜在的微观结构。感兴趣的原子核将使用多核子转移反应填充，该反应由高能96 Zr离子束与124 Sn厚靶的相互作用产生。XTU串联货车de Graaff和意大利Legnaro国家实验室的ALPI线性加速器的组合将用于将96 Zr离子加速到576 MeV的能量。将使用由40个康普顿抑制锗探测器组成的GASP阵列来研究二元反应碎片的伽马射线衰变。最后，实验的结果将使人们能够对以前在莱尼亚罗国家实验室进行的一项使用了ARMA/PRISMA探测器系统的相关实验进行全面分析。目前的实验将允许基本的伽马射线符合关系，以建立在较早的实验中研究的质量数约为110的富中子核。在这个质量区域，我们将继续研究N = 50和N = 82魔中子数之间的核形状的演化。