Nuclei Of High Spin Rotation Structure

One of the most interesting and intriguing aspects of nuclei is the interplay between collective and single-particle degrees of freedom. To understand these nuclear features, investigations of nuclei are carried out to the extremes of angular momentum, to superheavy nuclei, to extreme neutron-proton ratios and to higher excitation energy. The new generation of high resolution, full solid angle gamma-ray detector arrays have opened up a window for detailed studies of high spin states for varied region.Configuration-dependent cranked Nilsson-Strutinsky (CNS) approach, which is a macroscopic-microscopic method and has proven to be very successful in the description of the various facets of rotating nuclei and many low-energy nuclear phenomena, has been introduced. In order to investigate nuclear high spin states over a very large spin range up to band termination more efficiently, the pairing correlation of nucleons is neglected. Virtual crossings of two single-particle orbitals with a weak interaction have been removed to avoid the very large fluctuations in the single particle angular momenta and/or single particle wave functions, and angular momentum non-conservation due to the cranking term, which means diabatic orbitals are constructed. A sum of the rotating liquid drop energy and shell energy corrections calculated by Strutinsky procedure gives the total nuclear energy at specified deformation and spin. Calculations are performed self-consistently within 4-Dimensional parameter space (ε₂,γ,ε₄,ω). There are a number of important advantages with respect to the quantitative description of band termination phenomena in comparison with the effective microscopic theories. The CNS approach could determine the different fixed configurations accurately and follow them as a function of spin, handle the existence of large deformation changes and coupling scheme changes that occur within the fixed configurations, include the coexistence of competing configurations having different deformations in the yrast region at a specified spin, and determine accurately the relative energies of the different subshells to define the proper configurations that are lowest in energy. With a set of standard parameters, the CNS approach can predict new nuclear structure phenomenon in the high spin region very reliably.For the investigation of rotational bands at low spin, the pairing correlations, which is one of the most important residue interaction in nuclei, should be included in the CNS approach. BCS method is applied to treat pairing interactions approximately. In this case, the removal of virtual interaction needs special treatment. With pairing included CNS(PCNS) approach, it is convenient to study rotational phenomena at low spin, such as backbending, signature splitting, quasi-particle deformation driving force.¹²⁵Ce is the nearest nucleus among odd-A cerium isotopes to proton drip line of which the rotational bands can be observed. Deformations of ¹²⁵Ce and ^127,129 Ce are moderate. The high spin states of these nuclei received high attention in last decades. They provide experimental test for well deformed nuclei near the proton drip line.The CNS approach has been used to investigate rotational structures of (¹25,127,129) Ce isotopes. The CNS calculations indicate that ^125,127,129Ce with yrastconfigurations are near axial deformed, and the shape of ¹²⁵Ce with negative parity yrast configuration is soft toγdeformation. For each yrast configuration of ^127,129Ce, there are two minima on the potential energy surface. Particularly for configuration of ¹²⁹Ce with negative parity andα= -(1/2), the second minimum in energy is similar to the first one, so there would be triaxial and normal axial deformed shape coexistence in ¹²⁹Ce. Signature splitting and shape evolution as a function of spin are also calculated. Only positive parity yrast bands of ¹²⁵Ce show large signature splitting. Based on the calculations, proper configurations are assigned to these observed yrast bands and the bandhead of positive parity bands of ¹²⁵Ce is also clarified. The CNS calculations are in good agreement with experimental results when spin is over 15h. However, CNS approach without pairing can not explain abnormal signature splitting in the backbending region.The rotational bands of ^125,127,129Ce are calculated by PCNS approach. Appropriate pairing parameters are selected. It is shown that the PCNS approach improves theoretical results greatly at low spin. The tendency of band, energy, signature splitting and exact spin value at which backbending happened can be well reproduced. The abnormal signature splitting of positive parity yrast bands in ¹²⁵Ce can be interpreted as the crossing of two bands with one and three quasi-particles. However, comparing to the CNS approach, the PCNS results in the high spin region are questionable where energy levels are dense and the coupling and/or mixing between orbitals are strong.The superdeformed or highly deformed band terminations in ³⁸K, ³⁶Ar, ³⁴S and ³⁵Cl have been studied by the CNS approach. Some possible superdeformed band terminations are predicted, especially the superdeformed band terminates at I = 19(?) and aboutε₂ = 0.39 (withε₂ (?)0.50 when I≤9(?)) in ³⁸K, and all of them are favorable for observation. The tendency of these bands in energy with spin increasing favors band termination, so superdeformed bands terminating would be smooth. The calculated superdeformed band is in good agreement with observed one in ³⁶Ar confirms that the calculated results are reliable.