Nuclear structure at extreme

在本研究项目中，研究了不同极端条件下的核结构。我们首先研究了高同位旋核的结构。高同位旋表明中子数大于质子数，反之亦然。同位旋的Z分量由(Z-N)/2给出，其中Z和N分别表示质子数和中子数。同位旋的大小，T，应该大于等于Tz。在中子和质子数量相等的原子核中，Tz=0，基态和低洼态为T0。低同位旋对应于在稳定线（稳定核）上或附近的原子核，在稳定线上质子和中子数相等或接近。另一方面，T较大的原子核远离稳定线，称为不稳定原子核。在过去的十年中，人们已经明确了不稳定原子核的结构与稳定原子核的结构有很大的不同。在这个项目中，我们研究了一个不稳定原子核的例子——32Mg及其附近。众所周知，N20是一个神奇的数字。因此，从稳定核的角度来看，32Mg应该是一个中子闭核，并且应该具有球形基态。这在实验和理论上都被证明是不正确的。相反，对32Mg左右的原子核的研究几乎没有。然而，我们现在可以利用东京大学小组正在开发的蒙特卡罗壳模型进行这种研究。这些研究表明，稳定原子核的变化不是突然发生的，而是逐渐发生的，有效相互作用的单极子成分在其中起着至关重要的作用。除上述研究外，还研究了包括高自旋态在内的球变形跃迁。

In this research project, the nuclear structure has been studied at variousextremes. We first investigated the structure of nuclei at high isospin. High isospin indicates situations that the neutron number is greater than theproton number or vice versa. The z-component of isospin is given by (Z-N)/2 where Z and N mean the proton and neutron numbers, respectively. The magnitude of isospin, T, should be larger than or equal to Tz. In nuclei with equal numbers of neutrons and protons, Tz=0, and the ground and low-lying states are of T0. Low-isospin corresponds to the nuclei on and near the beta stability line (stable nuclei) where the proton and neutron numbers are equal or close to each other. On the other side, nuclei with large T are far from the beta stability line, being called unstable nuclei. It has been clarified during the past ten years that unstable nuclei have structure very different from the structure of stable nuclei. In this project, we studied 32Mg, which is an example of unstable nuclei, and its vicinity. The N20 is a magic number as well known. Therefore, on the standpoint of stable nuclei, 32Mg should be a neutron-closed nucleus, and should have a spherical ground state. This has been shown to be incorrect, experimentally and theoretically. On the contrary, studies on nuclei around 32Mg have hardly been done. We can now, however, carry out such studies by using the Monte Carlo shell model being developed by the group of the University of Tokyo. By such studies, it has been clarified that the change from stable nuclei does not occur suddenly at a certain nucleus but does occur gradually, and that the monopole component of the effective interaction plays a crucial role in this. In addition to the above studies, the spherical-deformed transition has been studied including high spin states.