Systematic investigation of quadrupole properties in deformed and transitional nuclei

In the present work, we address a long-standing problem in nuclear physics on how to decipher the nature of collective motion from electromagnetic transition probabilities. A systematic analysis of the $B(E2)$ transitions is performed for thirty nuclei using the triaxial projected shell model (TPSM) approach. It is shown that $I \rightarrow (I-2)$ transitions for the $\gamma$-bands depict a staggering phase and this phase reverses with the inclusion of the quasiparticle excitations for all the nuclei, except for the six nuclei of $^{76}$Ge, $^{112}$Ru, $^{170}$Er, $^{182}$Os, $^{192}$Pt and $^{232}$Th. This feature is analogous to the energy staggering phase obtained for these nuclei. It is noted that the energy staggering phase with even-spin-down (odd-spin-down), which is considered as a signature of $\gamma$-softness ($\gamma$-rigidity), corresponds to even-spin-up (odd-spin-up) staggering phase of the $B(E2)$ transitions. Further, TPSM predicted values for both energies and transition are shown to be in good agreement with the corresponding experimental values.Comment: 24 pages, 28 figure

Triaxial projected shell model approach for negative parity states in even-even nuclei

The triaxial projected shell model (TPSM) approach is generalized to investigate the negative parity band structures in even-even systems. In the earlier version of the TPSM approach, the quasiparticle excitations were restricted to one major oscillator shell and it was possible to study only positive parity states in even-even systems. In the present extension, the excited quasiparticles are allowed to occupy two major oscillator shells, which makes it possible to generate the negative parity states. As a major application of this development, the extended approach is applied to elucidate the negative parity high-spin band structures in $^{102-112}$Ru and it is shown that energies obtained with neutron excitation are slightly lower than the energies calculated with proton excitation. However, the calculated aligned angular momentum ($i_x$) clearly separates the two spectra with neutron $i_x$ in reasonable agreement with the empirically evaluated $i_x$ from the experimental data, whereas proton $i_x$ shows large deviations. Furthermore, we have also deduced the transition quadrupole moments from the TPSM wavefunctions along the negative-parity yrast- and yrare- bands and it is shown that these quantities exhibit rapid changes in the bandcrossing region.Comment: 14 pages, 17 figure