Neutron-deficient Z ≈ N nuclei84,86Mo have been investigated using pairing-deformation self-consistent cranked shell modelcalculations up to spin I > 20 . Our calculations are in good agreement with the experimental data, indicating γ-soft triaxial shapesat low rotational frequency and well-deformed triaxial-oblate shapes at high rotational frequency for both nuclei. The shape changeis due to the alignments of the g9/2protons and g9/2neutrons.
In the framework of the projected shell model, we investigate the competition between the two-quasineutron and two-quasiproton K~π=6^+ states in the ytterbium isotopes and N =104 isotones adjacent to ^(174)Yb. The ^(174)Yb results are compared with the experimental data.The K~π =6^+ isomer observed in ^(174) Yb is assigned as an admixture of the ν7/2^-[514] ν5/2^-[512] and π7/2^+ [404]π5/2^+ [402] intrinsic structure, which explains the experimental |g K-g R | value. Similar mixing would appear in ^(174) Yb, ^(176) Hf,and ^(178) W. The low-lying K~π=6^+ states are also predicted in ^(170-178) Yb.
Using a cluster model based on the Woods-Saxon potential, alpha-particle decays from excited states in 24Mg have been system atically investigated. Calculations can in general reproduce experimental data, noticing the fact that the preformation factor P of alpha particle in alpha-decaying nuclei is of order from 100 to 10?2. This can be the evidence for the α+20Ne structure in 24Mg. Meanwhile, the results also show the existence of other configurations, such as 16O+2α. Since the calculated decay widths are very sensitive to the angular momentum carried by the outgoing cluster (α particle), our results could serve as a guide to experimental spin assignments.
It has been found that high-order deformation (e.g.β6) can have important effects on the structures of superheavy nuclei. In the present work, we investigate octupole deformation effects on superheavy nuclei with an improved potential-energy-surface (PES) calculation by including reflection-asymmetric deformations in a space of (β2 ,β3 ,β4 , β5). The calculations give various deformations including highly deformed (β2 ≈ 0.4) and superdeformed (β2 ≈ 0.7) shapes. The octupole-deformation degree of freedom mainly affects the fission barrier beyond the second minimum of PES.
In the paper we review the recent progress of studies in unstable nuclei,mainly affiliated with the facilities of radioactive ion beams in China,including both experimental and theoretical aspects of researches.Many experiments for reactions,decays and structures have been performed targeting better understandings of properties of unstable nuclei.Special experimental measurements related to nuclear astrophysics have been done to seek insights into the processes of syntheses of elements in the universe.Theoretical calculations have provided many useful predictions on the behaviors of unstable nuclei,with model developments.Studies covered many mass regions from light to superheavy nuclei,giving plenty of information about the structures of unstable nuclei,towards the limits of existence of atomic nuclei.
In this paper we study the system with three nucleons within a single-j shell, which can be described as the angular momentum coupling of a nucleon pair and the odd nucleon. The overlaps between these non-orthonormal states form a special matrix coincidental with the one obtained by Rowe and Rosensteel. They proposed a proposition related to the eigenvalue problems of that matrix and dimensions of the associated subspaces. We prove their proposition with the help of the symmetric properties of the six-j symbols. We also derive algebraic expressions for eigen energies as well as conditions for conservation of seniority through the decomposition of the angular momentum.
Recent experiments open up the possibility to investigate oblate rotation-aligned states and prolate high-K isomers in neutron-rich tungsten isotopes.In the present work,we perform the projected-shell-model calculations for A ～ 190 tungsten nuclei.The 190 W results are compared with experimental data.The observed 8 + isomer is assigned as a two-quasiproton K π = 8 + configuration.Low-lying high-K four-quasiparticle states are predicted.Of particular interest is the prediction of the K π = 20 + state in 190,192 W,which may form a long-lived spin trap.In competition with the prolate high-K states,rotational alignment leads to near-yrast collective oblate rotation.
An angular momentum projected potential-energy-surface (PES) calculation, which takes both rotational symmetry restoration and multi-quasiparticle excitation into account, is developed by using the macroscopic-microscopic model and the projected shell model (PSM). Within this method, it may become possible to modify the excitation spectra which are influenced by shape-softness of nuclei, including high-K states. As our first example, this method is adopted to study the collective and multi-quasiparticle excitations of 178Hf, and the results are in good agreement with the existing experimental data. In addition, as for the dominant structure of noncollective 6 + bands, the conflict between experimental result and the previous PSM calculation is clarified.
