Nuclear structure at extreme

在这个研究项目中，核结构已经在不同的极端进行了研究。我们首先研究了高同位旋的原子核结构。高同位旋表示中子数大于质子数或质子数大于中子数的情况。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应大于或等于Tz。在具有相同数目的中子和质子的原子核中，Tz=0，基态和低激发态都是T0。低同位旋对应于位于β稳定线上和附近的核(稳定核)，其中质子和中子数彼此相等或接近。另一方面，T较大的核远离β稳定线，称为不稳定核。在过去的十年里，人们澄清了不稳定核的结构与稳定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核的例子--32 Mg及其附近。众所周知，N20是一个神奇的数字。因此，从稳定核的观点来看，32 Mg应该是一个中子封闭的核，应该是一个球状的基态。这已经被证明是不正确的，无论是在实验上还是理论上。相反，对32 mg左右的原子核的研究却很少。然而，我们现在可以使用东京大学研究小组正在开发的蒙特卡洛壳模型来进行这样的研究。通过这些研究，阐明了从稳定核的变化不是突然发生在某个原子核上，而是逐渐发生的，并且有效相互作用的单极分量在其中起着关键作用。除了上述研究外，还研究了球形变相变，包括高自旋态。

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.