Experimental Study Of High-Spin States In ～(156)Tm And ～(155)Tm

In recent years, as unique candidate to study the residual interaction between quasi-proton and quasi-neutron, the investigation of odd–odd nuclei have attract more and more interest. The level structures of odd–odd nuclei more complicated than even–even and odd A nuclei. It is more difficult to investigate the high-spin states of odd–odd nuclei due to their complicated level structure are uncertain. This results that some model calculations can not be examined timely. In transitional region, nuclei with neutron number N≥88 generally exhibit strong collectivity due to their prolate shape whereas those with N≤86 more appears as aligned single-particle configuration with non-collective rotation. In this region one may also expect the coexistence of different nuclear shapes and study shape evolution, described by collective and non-collective rotational models. The odd-odd nucleus, (156)~Tm with N=87, makes a good candidate for such studies. This thesis mainly concerns the in-beam γ-ray spectroscopic techniques and their applications in the study of high-spin level structures of N=87 (156)~Tm and 155Tm nuclei. (1)High spin study of odd-odd nucleus (156)~Tm The high spin states of (156)~Tm are populated by performing 142Nd(19F,5n)(156)~Tm fusion-evaporation reaction (E(19F )=122.5MeV), and the 19F beam is delivered from the HI-13 Tandem Accelerator at China Institute of Atomic Energy(CIAE). The detecting array consists of 14 HP(Ge) detectors and 1LEPs. The total two-fold coincidence events is about 1.7×108. The level ordering was made through consideration ofγ-ray intensity balance together withγ-ray excitation function. A two-dimensional angular correlation matrix was also constructed from coincidence data with detector at 450 as one axis and detector at 900 as the other. Gamma-ray intensities in spectra gated on quadrupole transitions were used to extract DCO ratios. The old level scheme of 156Tm is modified. 20 levels and 19 transitions have been added in the new level scheme in which spin and parity of energy levels are up to (34-). (2) High spin study of nucleus 155Tm At the same time, the high spin states of 155Tm are populated and studied. The new 17 levels and 17 transitions have been in the new level scheme in which spin and parity of energy levels are up to (57/2+). (3) Theory calculation The level structures of high spin states of odd-odd nucleus 156Tm are explained by the empirical shell model, OXBASH program and TRS program. The calculations from 21-to 16-with the four-quasi-particle empirical shell model are consistent with experimental results. The level energies below 17-calculated by OXBASH program are lower than experimental results. The deformation parameters of β2 obtained from the TRS calculations are from 0.120 to 0.165 while the rotational frequencies of ω=0.000~0.672. The nucleus 156Tm is a weakly deformed shape. The high spin states of odd-odd nucleus 156Tm are deduced between collective and non-collective motion states. The lower levels of odd-odd nucleus 156Tm are near non-collective motion states, and the higher levels are near collective motion states. On the side, the level structures of high spin states of nucleus 155Tm are calculated by the three-and five-quasi-particle empirical shell model,...