High-spin proton alignments and evidence for a second band with enhanced deformation in ${}^{171}$Hf

High-spin properties of the nucleus ${}^{171}$Hf were studied through the ${}^{128}$Te(${}^{48}$Ca,5$n$) reaction. Previously known bands have been extended to significantly higher spins and four new bands have been extracted from these data. The results are discussed within the framework of the cranked shell model aided by a comparison with level structures in the neighboring nuclei. The band crossings at rotational frequencies $\sim$500 keV are interpreted as caused by the alignments of $h_{11/2}$ and $h_{9/2}$ proton orbitals. Band ED2 exhibits an alignment pattern similar to that of band ED1 which was reported in a recent paper and proposed to be built on a second potential energy minimum involving the deformation-driving proton $i_{13/2}\otimes h_{9/2}$ configuration. It is likely that band ED2 is also associated with a deformation enhanced with respect to that of the normal deformed structures. Further experimental investigation is needed to ascertain the nature of this band.

Figure 1

Partial level scheme for ${}^{171}$Hf. Arrow widths are proportional to the relative intensities of the $\gamma$ rays. Energies are in keV and tentative transitions are shown with dashed lines.

Figure 2

Partial level scheme for ${}^{171}$Hf displaying the high-$K$ bands.

Figure 3

Fourfold coincidence spectra for (a) band ED2, and the high-spin regions of (b) band B and (c) band H. The spectrum of band ED2 is a sum of triple coincidence gates on all band members. The spectra of bands B and H are sums of triple gates on transitions above levels $35/2^{+}$ and $31/2^{-}$, respectively.

Figure 4

Fourfold coincidence spectra for the high-$K$ bands, (a) band HK1 and (b) HK2, triple gated on the $M1$ transitions in each band. The $M1$ transitions are marked with plus signs (“+”), and the ND yrast transitions are marked with crosses (“$\times$”). The “#” symbols in the HK1 spectrum denote contaminations from neighboring nuclei. The star symbol (“$*$”) in the HK2 spectrum denotes the 149-keV peak, which is the lowest $M1$ transition in band HK1.

Figure 5

Representative fourfold coincidence spectra for the high-spin regions of bands (a) X1, (b) X2+X3, (c) X2+X4, and (d) MAB. The star symbols (“$*$”) denote the interband linking transitions. Spectra of bands X1 and MAB are sums of triple gates on all band members. The spectrum of bands X2+X3 is a sum of triple gates on all transitions in band X3. The spectrum of bands X2+X4 is a sum of coincidence gates between transitions in band X2 and X4.

Figure 6

Quasiparticle diagrams for neutrons (upper panel) and protons (lower panel) for ${}^{171}$Hf calculated at ${\epsilon }_2=0.225$, ${\epsilon }_4=0.03$, and $\gamma =0^{\circ }$. The levels are labeled by parity and signature as $(+,+1/2)$ solid lines, $(+,-1/2)$ dotted lines, $(-,+1/2)$ dot-dashed lines, and $(-,-1/2)$ dashed lines.

Figure 7

Alignments for the bands in ${}^{171}$Hf. The dashed line represents the alignment observed in the ground-state band in ${}^{170}$Hf. The plot of band ED2 is based on assumed spin values; see text for details.

Figure 8

Excitation energies, minus a rigid-rotor reference, as a function of spin for the bands in ${}^{171}$Hf. The plot of band ED2 is based on assumed excitation energy and spin values; see text for details.

Figure 9

Experimental $B\left(M1\right)/B\left(E2\right)$ ratios (data points) compared to theoretical values (lines) for bands HK1 and HK2.

Figure 10

Dynamic moments of inertia $J^{\left(2\right)}$ as a function of rotational frequency for bands ED1 and ED2 in ${}^{171}$Hf and band SD1 in ${}^{172}$Hf [16].