北大核科学论坛第320期

报告题目: Decline and Fall of Low Energy Time-Dependent Quadrupole Vibrations
报告人: Prof. John Sharpey-Schafer  University of the Western Cape, South Africa
报告时间:  2017515日(周一)下午3:30
报告地点: 北京大学物理学院7802会议室(物理西楼217)
报告摘要:The present wealth of experimental data on the structure of deformed atomic nuclei challenges the original interpretation by Bohr and Mottelson of low-lying excited Kπ=0+ and Kπ=2+ rotational bands as β and γ vibrations of the quadrupole shape. We show that the first excited Kπ=02+ bands are pairing isomers with seniority zero lowered into the pairing gap by configuration dependent pairing to form a second vacuum (SV) analogous to the ground state vacuum. These bands are 2p-2h single particle configurations and have nothing to do with nuclear “vibrational collectivity”. In contrast, the first excited Kπ=2+ bands, that are found in all quadrupole deformed nuclei, are collective and exist as a consequence of the triaxial nuclear shape. We discuss the experimental evidence that has led to the demise of the interpretation of data in terms of low energy quadrupole surface vibrations of the mean nuclear shape. In summary, rotational bands arise because of the breaking of spherical symmetry and the first excited Kπ=2+ bands arise because of the breaking of axial symmetry.  Indeed the experimental data point to the conclusion that the low energy excited states in deformed nuclei are dominated by the nuclear shape and that interpretations in terms of vibrations or phonons are misleading.
联系人:孟杰(mengj@pku.edu.cn)
        张双全(sqzhang@pku.edu.cn)