High-spin yrast structure of ${}^{159}$Ho

An investigation of the yrast structure of the odd-$Z$ ${}^{159}$Ho nucleus to high spin has been performed. The ${}^{159}$Ho nucleus was populated by the reaction ${}^{116}$Cd(${}^{48}$Ca,$p4n\gamma$) at a beam energy of 215 MeV, and resulting $\gamma$ decays were detected by the Gammasphere spectrometer. The $h_{11/2}$ yrast band has been significantly extended up to $I^{\pi }=75/2^{-}$ (tentatively $79/2^{-}$). A lower frequency limit for the second ${\left(h_{11/2}\right)}^2$ proton alignment was extracted consistent with the systematics of this alignment frequency, indicating an increased deformation with neutron number in the Ho isotopes. The energy-level splitting between the signature partners in the $h_{11/2}$ structures of the Ho isotopes and the neighboring $N=92$ isotones is discussed.

Figure 1

Partial level scheme for ${}^{159}$Ho of the lowest energy structure based on the $h_{11/2}$ $7/2^{-}\left[523\right]$ proton orbital. Energies are given to the nearest kiloelectronvolt. Parentheses and dotted lines indicate tentative assignments.

Figure 2

$\gamma$-ray spectra obtained from sums of triple gates set on the low-spin interband and intraband transitions and (a) the $\alpha =-1/2$ transitions above $(43/2^{-})$ and (b) the $\alpha =+1/2$ transitions above $(41/2^{-})$ in ${}^{159}$Ho. Photopeaks labeled with squares correspond to the low-energy interband transitions. Photopeaks labeled with triangles in (a) correspond to transitions associated with the $\alpha =+1/2$ signature partner, and photopeaks labeled with asterisks in (b) correspond to transitions associated with the $\alpha =-1/2$ signature partner. Energies labeled in parentheses indicate tentative transitions.

Figure 3

Aligned angular momentum $i_x$ as a function of rotational frequency $\hslash \omega$ for (a) the $h_{11/2}$ band in ${}^{159}$Ho and the yrast band in ${}^{160}$Er, and (b) the $h_{11/2}$ band in ${}^{157}$Ho and ${}^{159}$Ho. A common reference [14] was extracted through a variable moment-of-inertia fit to the ground-state band of ${}^{160}$Er with Harris parameters [15, 16] of ${\mathcal{J}}_0=23{\hslash }^2$ MeV${}^{-1}$ and ${\mathcal{J}}_1=58{\hslash }^4$ MeV${}^{-3}$.

Figure 4

Energy-level splitting as a function of spin for the $7/2^{-}\left[523\right]$ signature partner bands in ${}^{155}$Ho [24], ${}^{157}$Ho [17, 18], ${}^{159}$Ho, ${}^{161}$Ho [25], ${}^{163}$Ho [26], and ${}^{165}$Ho [27].

Figure 5

Energy-level splitting as a function of spin for the $\pi h_{11/2}$ signature partner bands in the $N=92$ isotones ${}^{155}$Eu [28], ${}^{157}$Tb [28], ${}^{159}$Ho, ${}^{161}$Tm [29], ${}^{163}$Lu [30], and ${}^{165}$Ta [31].