Dynamic chirality in the interacting boson fermion-fermion model

The chiral interpretation of twin bands in odd-odd nuclei was investigated in the interacting boson fermion-fermion model. The analysis of the wave functions has shown that the possibility for angular momenta of the valence proton, neutron and core to find themselves in the favorable, almost orthogonal geometry is present, but not dominant. Such behavior is found to be similar in nuclei where both the level energies and the electromagnetic decay properties display the chiral pattern, as well as in those where only the level energies of the corresponding levels in the twin bands are close together. The difference in the structure of the two types of chiral candidates nuclei can be attributed to different β and γ fluctuations, induced by the exchange boson-fermion interaction of the interacting boson fermion-fermion model. In both cases the chirality is weak and dynamic.

Figure 1

Twin bands calculated in the IBFFM for case A (left panels) and case B (right panels). In the upper panels the excitation energies of levels in the yrast and side band are presented. In the middle panels, the signature $S(I)$ in the yrast band is displayed. In the panels on bottom the signature $S(I)$ in the side band is presented.

Figure 2

$B(E2)$ and $B(M1)$ values calculated in the IBFFM for case A (left panels) and case B (right panels). In the upper panels $B(E2)$ values for transitions in the yrast and side band are presented. In the middle panels $B(M1)$ values for transitions in the yrast and side band are shown. In the panels on the bottom $B(M1)$ values for $\Delta I=1$ transitions from side to yrast band are presented.

Figure 3

IBFFM β and γ distributions, defined as in Ref. [7], for case A (left panels) and case B (right panels). In the upper panels the distributions for the yrast ${17}_1$ states and in the panels on bottom for the side band ${17}_2$ states are presented. The axis in the $\beta \text{−}\gamma$-plane have $\gamma =0^{°}$ and $\gamma ={60}^{°}$, while the middle line in the $\beta \text{−}\gamma$-plane marks $\gamma ={30}^{°}$.

Figure 4

IBFFM β and γ distributions, defined as in Ref. [7], for case A (left panels) and case B (right panels). In the upper panels the distributions for the yrast ${14}_1$ states and in the panels on bottom for the side band ${14}_2$ states are presented. The axis in the $\beta \text{−}\gamma$-plane have $\gamma =0^{°}$ and $\gamma ={60}^{°}$, while the middle line in the $\beta \text{−}\gamma$-plane marks $\gamma ={30}^{°}$.