Study of the Extreme States with High Excitation Energy and High Spin by Ge-Si Crystal Ball.

在本项目的前期工作中，对在重离子聚变反应通道识别和选择方面有很强作用的硅探测器阵列（Si Ball）进行了改进，使其能在高束流下高负荷使用，NORDBall和改进的Si Ball的组合系统在A=80 - 90的新变形区的光谱研究中取得了显著的进展。结果建立了~（13）Mo，~（13）Nb，~（13）Nb，~（13）<87><87><85><82>Y，~（13）<81>Y，~（13）<82>Zr和~<82>（13）Sr核素的新能级结构，包括高激发态，并对其核性质进行了分析。在这个区域中，核的形变随着核子数向Z和N = 40的方向增长。发现N = 46的同位素位于球形和变形核区域之间的边界，并且N=45和46的核似乎在高激发高自旋态下强烈变形。除了上述日本-NBI合作的研究外，在九州大学串列加速器实验室还进行了大量的实验，以阐明A = 80 - 90区原子核的低激发态和基态的性质。包括新同位素的系统发现在内的丰硕成果不仅为高激发下的高自旋态提供了补充信息，而且还导致了一种新的有效方法的发展，该方法收集了这些核的全面光谱知识。

In the early stage of this project, a silicon detector array (Si Ball) which had proved to be quite powerful in the identifications and selections of the reaction channels in heavy ion fusion reaction was improved to stand the high duty use at high beam currents.The combined system of NORDBALL and the improved Si Ball brought about a dramatic progress in the spectroscopic studies of the new deformed region of A=80 90. As a result, new level structures of nucleides of ^<87>Mo, ^<87>Nb, ^<85>Nb, ^<82>Y, ^<81>Y, ^<82>Zr and ^<82>Sr including highly excited states have been established and the analysis for the nuclear properties have been carried out. The deformation of nuclei in this region grows with the nucleon number toward Z and N = 40. The isotones of N = 46 were found to lie the border between spherical and deformed nucleus regions, and the nuclei of N=45 and 46 seem to be strongly deformed at highly excited high-spin states. These experimental results have been compared with the results of cranking model calculation.Besides the above mentioned studies in Japan-NBI collaboration, lots of experiments have been carried out at the tandem accelerator laboratory of Kyushu University to clarify the properties of low-lying and ground states of the nuclei in the A = 80 -90 region. The fruitful outputs including a systematic discovery of new isotopes not only gave complementary information for the high spin states at high excitation but also led to the development of a new effective method of collecting thorough spectroscopic knowledge of these nuclei.