Narrow Results

Collective rotational bands were observed for the first time in neutron-rich odd–odd ${}^{142}$La by means of $\gamma$-$\gamma$-$\gamma$ and $\gamma$-$\gamma$-$\gamma$-$\gamma$ coincidence measurements of prompt fission $\gamma$ rays from ${}^{252}$Cf using multi-detector array Gammasphere. Similarity between the yrast band of ${}^{142}$La and those of neighboring ${}^{144}$La, ${}^{144}$Ce was found and interpreted as quasiparticle excitations. PES calculations suggested triaxial deformation for the ground state of 142La. Considerable triaxial and near zero octupole deformations were deduced for the yrast band of ${}^{142}$La by the TRS model calculations. The band-crossing observed in the yrast band of ${}^{142}$La was interpreted to be caused by alignment of the (h${}_{11/2}$)² proton pair, and the crossing frequency was best reproduced by the TRS calculations taking into account triaxial deformations. In contrast to the interpretations for the band crossing of ${}^{142}$La, alignments of the (i${}_{13/2}$)² neutron pair were found to be responsible for the band-crossing of the yrast band in the neighboring even-N ${}^{143}$La, and triaxial degree of freedom was found to play a more significant role than octupole deformations in the nucleus, although its ${\beta }_3$ values deduced are large.

In a terminating band, the nucleon number changes in a specific orbital not only lead to deformation changes of the band but also the type of the band termination is impressed. In this work, we consider the role of the orbitals near the Fermi surface in some of the nuclei with $A\sim 160$; such as Dy ($Z=66$), Ho ($Z=67$) and Er ($Z=68$) isotopes. Our results show that the contribution of the number of the proton holes in the core is very effective to energy cost at the end of the rotational bands and then, termination type. Change the number of the protons on high-$j$ orbitals ($h_{11/2}$) in $N=88$ isotones and also, the neutrons on high-$j$$i_{13/2}$ and low-$j$$f_{7/2}{h}_{9/2}$ neutron orbitals do not affect in the type of termination. They cause only to move up or down the terminating bands in energy.

The differential cross-sections of the ⁹Be(α,α)⁹Be* scattering (E_lab(α) = 30 and 90 MeV) with excitation of ⁹Be states 2.43 MeV, 2.78 MeV, 5.59 MeV and 7.94 MeV were obtained. The question of the formation of the third rotational band based on the 2.78 MeV state is considered. The new excited state 3.82 MeV in the ⁹Be with an assumed spin-parity Jπ = 3/2- were observed.

Rotational bands of ²⁵⁰Fm, ^252,253,254No and ²⁵¹Md are studied by the cranked shell model with particle-number conserving treatment for monopole and quadrupole pairing correlations. Observed bands are reproduced very well by theoretical results. Backbendings of kinematic moment of inertia and the alignment of high-j orbital are investigated.

High spin states of ¹¹⁶Sb were populated using the ¹¹⁴Cd(⁷Li, 5n) fusion evaporation reaction at a beam energy of 48 MeV. The previously reported rotational bands, built on πg_9/2 ⊗ νh_11/2 and πg_9/2 ⊗ νd_5/2 configurations, have been extended and a new ΔI = 1 band has been identified.

Rotational structure and observed long bands in ¹²⁵Xe are investigated with the configuration-dependent cranked Nilsson-Strutinsky approach. The observed long bands, especially the unconnected long bands are compared with the calculated configuration assigned to the band and the agreement between experiment and theory at high spin is remarkable. The observed long bands are confirmed as highly deformed and their properties are explained theoretically. There is shape coexistence within the same configuration from low spin to intermediate spin. Possible normal deformed bands with rotation around the intermediate principal axis in several interesting configurations of ¹²⁵Xe are discussed. The calculated results indicate ¹²⁵Xe is near prolate at high spin with large deformation of ε₂ ∼0.36, and may rotate around the intermediate principal axis at low spin with ε₂ ∼0.20 and γ ∼ −40°.

Differential cross-sections of the ¹¹B + α inelastic scattering at E(α) = 65 leading to the most of the known ¹¹B states at the excitation energies up to 14 MeV were measured. The data analysis was done by DWBA and in some cases by the modified diffraction model allowing determining the radii of the excited states. The radii of the states with excitation energies less than ~ 7 MeV with the accuracy not less than 0.1-0.15 fm coincide with the radius of the ground state. This result is consistent with the traditional view of the shell structure of the low-lying states in ¹¹B. Most of the observed high-energy excited states are distributed among four rotational bands. The moments of inertia of band states are close to the moment of inertia of the Hoyle state of ¹²C. The calculated radii, related to these bands, are 0.7 - 1.0 fm larger than the radius of the ground state, and are close to the radius of the Hoyle state. These results are in agreement with existing predictions about various cluster structure of ¹¹B at high excitation energies. The state with the excitation energy 12.56 MeV, I^π = 1/2⁺, T = 1/2 and the root mean square radius R ~ 6 fm predicted in the frame of the alpha condensate hypothesis was not found. The observed level at 12.6 MeV really has T = 1/2, probably, I^π = 3/2⁺ and the radius close to that of the ground state.