Study Of High Spin States In The Nucleus ～(155)Tm

¹⁵⁵Tm, far away from double magic nucleus, belongs to the rare-earth nuclei. The highspin information of ¹⁵⁵Tm is rare by far. Through this thesis new levels were deduced.¹⁵⁵Tm ,with Z=69 and N=86, exhibiting the evolution of collectivity and non-collectivity. Onthe other hand, the study of ¹⁵⁵Tm must be helpful for the studies of its isotones andisotopes.The experiment has been performed in the HI-13 tandem accelerator at the China Instituteof Atomic Energy. The high spin states of ¹⁵⁵Tm have been populated via heavy-ion fusionevaporation reaction 142Nd(19F,6n)¹⁵⁵Tm. The target was a self-supporting foil with 2.2mg/cm2thickness. The detecting array consists of 14 Compton suppressed HPGe-BGO spectrometersand one LEPs. Single γ-ray spectra were collected at beam energy from 110MeV to 125MeVfor excitation function measurement. A γ-γ coincidence experiment was performed at beamenergy of 122.5MeV and beam current of 15nA. About 1.7×108 coincident events ?w?ith fold≥2 were collected during 100 hours beam time. Treee Eγ-Eγ matrixes were found, one wassymmetrical, the others were unsymmetrical matrixes. From the coincidence analysis, newlevel schemes of ¹⁵⁵Tm were deduced which included 28 new ?γ-rays and 26 new levels, andthe level scheme extended up to an excitation energy of 7.7MeV and a spin of 61/2-.The thesis consists of four chapters. Firstly introduces the ordinary instances about highspin states, then explains the in-beam γ-ray spectroscopic techniques and their applications inthe study of high-spin level structures of ¹⁵⁵Tm nuclei,finally discusses the high spin states of¹⁵⁵Tm with systemic comparision,empirical shell model and OXBASH programme.