Research on High Spin Structures of N=79 Isotones in A=135 Nuclear Region

Key words: 
• nuclear structure /
• high spin state /
• shape transition /
• oblate deformation

Abstract: The progress of research on the high spin states at N=79 isotopes 135Ba， 1³⁷Ce and ¹³⁹Nd in A=135 neutrondeficient region by the research group of Tsinghua University has been reviewed. The experiments were carried out by using inbeam γray spectroscopy technology and heavy ion nuclear reactions ¹³⁰Te(⁹Be， 4n)， ¹²⁴Sn(¹⁸O， 5n) and 128Te(¹⁶O， 5n) at China Institute of Atomic Energy (CIAE). The high spin level schemes of these nuclei have been expanded. The results indicate that the lower spin states of these nuclei originated from νh-111/2 hole state coupling with the neighboring eveneven nucleus cores. All the deformation parameters γ values of these three isotones are larger than 30°， which indicates that they have triaxial deformation with oblate side. The prolateoblate transition in Ba， Ce and Nd isotopic chains indeed happens between N=77 and N=79. Through systematical comparison with the neighboring isotones， the configurations for some middle spin state levels have been assigned. At the high spin states， one oblate band in 137Ce and three ones in 139Nd with γ≈ -60° were discovered. The origination and structural character of these oblate bands have been discussed.