Study Of High Spin Spectroscopy In Odd-Odd¹³⁰Cs Nucleus

The nucleus is an unique multi-body system that can be excited in many kinds ofquantum mechanics ways. The competition and interaction between the single particlemovement and collective movement is the important factor which determines thenuclear structure. The neutron-deficient nuclei in the A¹30mass region lie in atransitional region between the primarily spherical Sn（Z=50） nuclei and the welldeformed La（Z=57） and Ce（Z=58） nuclei. In this region, the proton Fermi level liesnear the bottom of the h11/2shell favoring prolate shapes（γ=0°, Lund convention）,while the neutron Fermi surface is towards the top of the h11/2shell, driving the nucleustowards a negative γ shape. The deformation-driving properties of h11/2neutrons andprotons are therefore conflicting and a given nucleus may have either a prolate, oblateor triaxial shape depending on the configuration. It is a hot spot for the studies of thehigh-spin states which shows rich structural characteristics with the above features. Inthis thesis, by means of in-beam nuclear spectroscopy experiments, we focus on thestudies of the odd-odd nuclei,¹³⁰Cs. All these nuclei are γ soft. They will show richstructural phenomena of various nuclear characteristics, since the shapes of thesenuclei would be strongly influences by the quasi-particles in various Nilsson orbits.Through the study of these phenomena, you can deepen the understanding of thesenuclides, enrich the systematic of nuclear spectroscopy of the whole A¹30high-spinstates and contribute to the nuclear theory and improve further.The first part of the thesis gives a brief introduction of the development onnuclear structure, high-spin populating and the models of nucleus, as well as thecharacteristics of the high-spin level structure of A¹30mass region nuclei.The second part of the thesis introduces concepts and experimental methods ofthe in-beam γ-ray spectroscopic techniques, such as the widely used methods topopulate high spin states of atomic nucleus, as well as the issues concerning off-linedata analysis.In the third part of the thesis, a study of high spin level structure of¹³⁰Cs isconducted using the data obtained from¹24Sn (¹⁰B,4n) and¹24Sn(¹¹B，5n)reactions atthe beam energy of47and58MeV, respectively. After unfolding, the γ-γ coincidence events are sorted into three symmetric two dimensional Eγ-Eγmatrixes together withthree asymmetric DCO ratio matrixes. In the data pre-handling stage, excitationfunctions of the two experiments are calculated using Cascade; Efficiency calibrationfor the detector array is carried out with standard radioactive source133Ba and152Eu,the two efficiency curves are normalized at the energy point of400keV. A newhigh-spin level structure of¹³⁰Cs had been made depends on the information ofcoincidence, energy, intensity and DCO ratios of the γ rays. And the first observationsof the γ-transitions are stated in detailed and discussed about the essence of physics.The achievements for this work are outlined below:1. The level scheme from the present work is a significant extension with theaddition of about50new transitions to that reported in the earlier works. Theπd5/2υh11/2band has been extended to higher spin and several new bands have beenestablished. In addition, the structure of the unfavored signature of the h11/2g7/2band below the band-crossing has been revealed in the present work. Depending onthese new observations, the ordering of the102.9and804.1keV transitions establishedby R.Kumar et al. has been reversed in the present work. Furthermore, we haveobserved several new γ-transitions in the low states.2. Four new bands have been established in the present work, and three of themare tentatively assigned to the h11/2d5/2（h11/2）2, h11/2d5/2and h11/2h11/2configuration. Band6and8both show only dipole in-bands transitions. However, thelowest observed state energies of these two bands are quite different. Therefore, weassign band6and8as four-and two-quasiparticle bands respectively. Depend on theenergies and DCO ratios of the newly observed γ-transitions, we assign the spin andparity to the bands that first observed in the present work.3. Band8decays via the177.6and306.7keV two transitions into the yrast band;by means of the two transitions we confirm the energy of5isomer. As a consequence,spin assignments for the observed bands in¹³⁰Cs can be made in a convincing way.Therefore,¹³⁰Cs can be taken as a reliable reference for the adjacent odd-odd nuclei incases where the spin assignments for the rotational bands have to be made by resortingto systematic. We found that the spins assignment to πh11/2υh11/2band of^120,122Cs byMoon et al. is not agree with the systematics of excitation energy.4. The structure of the unfavored signature of band5has been established more completely in the present work by means of three new γ-transitions were observed inband. Furthermore, we have observed several additional liking transitions from thisband to lower sates. The spins of this band were reassigned according to our measuredDCO ratios; however, there is serious disagreement between the spin assignmentsproposed in our and Kumar’s study. Not only the DCO ratios, but also the signaturesplitting is supported our conclusion.The fourth part of the thesis summarizes the already achieved results in thepresent work.