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

在我们对原子核微观结构的理解的历史发展中，最重大的进展之一是在50多年前取得的，当时发现核子(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，正是其他核子本身有效地产生了每个核子在其内运动的势。多年来，实验结果表明，所谓的核壳模型适用于大量的核，特别是那些靠近封闭壳层的核，它们对应于核能能级的能级间隙。然而，最近的实验结果表明，对于富含中子的核，特别是在中子数8、20和28附近的核，壳层间隙变小(壳层猝灭)，幻数，即与闭合壳层相对应的核子数不再有效。此外，还出现了新的神奇数字。壳体模型的极限检验是本工作的目标之一。核物理学家试图回答的问题包括：这些元素的起源是什么？以及“为什么构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的形成过程。核壳模型在回答这些问题上发挥了重要作用。根据一些理论，对于锡的50个质子和82个中子的同位素周围的中子过剩的核(丰中子核)，壳模型必须进行修正。例如，对于其中一种同位素镉-130，它有48个质子和82个中子，已经预测到壳层猝灭。令人惊讶的是，最近的实验研究表明，对于这种镉的同位素，壳模型确实仍然有效。这种行为是镉同位素的特例，还是该区域原子核的普遍行为？回答这个问题的一种方法是建立富含中子的邻近同位素的激发态，例如钯(有46个质子)。本提议涉及首次对丰中子钯同位素在中子数82附近的激发态进行实验研究，以测试壳层闭合的稳健性。我们将在原子序数Z=50以下的丰中子区研究的另一个现象是磁旋转，这是一种新的核激发模式，与自然界中观察到的最快的磁转子相对应。目前的研究将导致对潜在微观结构的更好理解。感兴趣的核将通过多核子转移反应来填充，这些反应是由一束高能的96Zr离子束与厚的124Sn靶相互作用产生的。意大利莱格纳罗国家实验室的XTU串列Van de Graaff和Alpi直线加速器的组合将被用来将96Zr离子加速到576 MeV的能量。将使用40个康普顿抑制的锗探测器组成的GAP阵列来研究二元反应碎片的伽马射线衰变。最后，实验结果将使我们能够全面分析先前在莱格纳罗国家实验室使用Clara/Prisma探测器系统的相关实验。目前的实验将允许为早期实验中研究的质量数约为110的丰中子核建立必要的伽马射线符合关系。在这个质量区域中，我们将继续研究N=50和N=82魔中子数之间的原子核形状的演化。

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shell gaps become small (shell quenching) and the magic numbers, nucleon numbers corresponding to closed shells, are no longer valid.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.