Evidence for Nontermination of Rotational Bands in ${}^{74}\mathrm{Kr}$

Three rotational bands in ${}^{74}\mathrm{Kr}$ were studied up to (in one case one transition short of) the maximum spin $I_{\max }$ of their respective single-particle configurations. Their lifetimes have been determined using the Doppler-shift attenuation method. The deduced transition quadrupole moments reveal a modest decrease, but far from a complete loss of collectivity at the maximum spin $I_{\max }$. This feature, together with the results of mean field calculations, indicates that the observed bands do not terminate at $I=I_{\max }$.

Figure 1

Partial level scheme deduced from the current work for ${}^{74}\mathrm{Kr}$. The energy of the $\gamma$-ray transitions are given in keV and arrow widths are proportional to relative $\gamma$-ray intensities.

Figure 2

(a) Kinematic and (b) dynamic moments of inertia for the ground-state band, band A, and band B in ${}^{74}\mathrm{Kr}$ plotted versus rotational frequency.

Figure 3

Potential energy surfaces at $I=30,32,34\hslash$ calculated in the CNS formalism for the $[2,4]$ configuration. The contour line separation is 0.2 MeV. Note that the minimum remains at ${\epsilon }_2\sim 0.2$, $\gamma \sim 20°$ for all these spin values corresponding to $I_{\max }-2$, $I_{\max }$, and $I_{\max }+2$. No noncollective state can be defined for $I>I_{\max }$, and a region around the $\gamma =60°$ axis is therefore excluded from the $I=34$ surface.

Figure 4

Experimental $F(\tau )$ values for the ground-state band, band A, and band B as a function of $\gamma$-ray energy in ${}^{74}\mathrm{Kr}$. The solid line shows the calculated $F(\tau )$ values. The dashed line represents the saturation $F(\tau )$ value when the recoils leave the target.

Figure 5

(a) The measured transition quadrupole moments $Qt$ for the ground-state band (GSB), band A, and band B. (c),(d) The calculated $Qt$ values for the $[2,4]$, $[3,4](\alpha =1)$, and $[3,4](\alpha =0)$ configurations assigned to the ground-state band, band A, and band B, respectively. (b) Transition quadrupole moments of the bands in ${}^{62}\mathrm{Zn}$, ${}^{74}\mathrm{Kr}$, and ${}^{109}\mathrm{Sb}$, normalized at $I/I_{\max }=0.68$, as a function of $I/I_{\max }$.