High-spin rotational structures in ${}^{76}\mathrm{Kr}$

High-spin states in ${{}^{36}{}_{76}\mathrm{Kr}}_{40}$ have been populated in the ${}^{40}\mathrm{Ca}$(${}^{40}\mathrm{Ca}$,4p)${}^{76}\mathrm{Kr}$ fusion-evaporation reaction at a beam energy of 165 MeV and studied using the Gammasphere and Microball multidetector arrays. The ground-state band and two signature-split negative parity bands of ${}^{76}\mathrm{Kr}$ have been extended to $~30\hslash$. Lifetime measurements using the Doppler-shift attenuation method show that the transition quadrupole moment of these three bands decrease as they approach their maximum-spin states. Two signatures of a new rotational structure with remarkably rigid rotational behavior have been identified. The high-spin properties of these rotational bands are analyzed within the framework of configuration-dependent cranked Nilsson-Strutinsky calculations.

Figure 1

γ-ray spectra obtained by summing pairs of double coincidence gates set on in-band transitions in (a) the ground-state band of ${}^{76}\mathrm{Kr}$, (b) the α = 0 signature of Band C, and (c) the α = 1 signature of Band C. In each case, the in-band transitions are denoted by an asterisk.

Figure 2

γ-ray spectra obtained by summing pairs of double coincidence gates set on in-band transitions in (a) the α = 0 signature of Band D, (b) the α = 1 signature of Band D, (c) the α = 0 signature of Band E, and (d) the α = 1 signature of Band E. In each case, the in-band transitions are denoted by an asterisk.

Figure 3

Level scheme derived from the present data set. γ-ray transition energies are given to the nearest kiloelectron volt and arrow widths are proportional to relative γ-ray intensities. Levels are grouped into five bands, labeled A to E, in addition to the ground-state band.

Figure 4

Upper panel shows the sum of the background subtracted γ-ray spectrum in coincidence with a double gate set on the 1001- and 1192-keV transitions in Band C and the 1257-keV linking transition. Lower panel shows the background subtracted γ-ray spectrum in coincidence with a double gate set on the 1001- and 1192-keV transitions in Band C. The 1257-keV transition links Band C and the ground-state band (GSB).

Figure 5

Experimental $F(\tau )$ values as a function of γ-ray energy for the ground-state band (filled circles) in ${}^{76}\mathrm{Kr}$. The solid lines in plot (a) show the calculated $F(\tau )$ values for various constant transition quadrupole moments ($Q_t=1.5$, 2.0, and 2.5 $e\hspace{1em}b$). The solid line in plot (b) shows the calculated $F(\tau )$ value, considering that $Q_t$ varies as a function of spin (see text). The dashed line represents the $F(\tau )$ value reached by the recoils that leave the target.

Figure 6

Lineshape fit in ${}^{76}\mathrm{Kr}$ for the ground-state band transition, 1189 keV, from the backed-target data. The top, middle, and bottom panels correspond to lineshapes at the mean angles 145°, 90°, and 35°, respectively.

Figure 7

(a) Kinematic and (b) dynamic moments of inertia for the ground-state band and Band C in ${}^{76}\mathrm{Kr}$ plotted versus rotational frequency.

Figure 8

(a) Kinematic and (b) dynamic moments of inertia for Band D in ${}^{76}\mathrm{Kr}$ plotted versus rotational frequency.

Figure 9

(a) Kinematic and (b) dynamic moments of inertia for Band E in ${}^{76}\mathrm{Kr}$ plotted versus rotational frequency.

Figure 10

Energies of high-spin collective configurations in ${}^{76}\mathrm{Kr}$ relative to an $I(I+1)$ reference plotted versus spin from (a) experiment and (b) configuration-dependent cranked Nilsson-Strutinsky calculations. Solid (dashed) lines represent positive (negative) parity, and closed (open) symbols denote signature $\alpha =0$ $(\alpha =1)$. In panel (b) terminating states are encircled, whereas the maximum spin states that do not terminate are indicated by large squares. The calculated bands are labeled by $[p,n]$, where $p(n)$ is the number of $g_{9/2}$ protons (neutrons). The band label has been added next to the assigned configuration. A second even spin [3,4] configuration lower in energy for the spin range $I\approx 25\text{−}30$ is shown by a thinner line and smaller closed squares. Note that the absolute normalization for experiment and calculations is different

Figure 11

Calculated deformation trajectories for ${}^{76}\mathrm{Kr}$. The deformations are shown for each fourth spin value except for the band terminating at $I^{\pi }={26}^{+}$, where the $I^{\pi }={24}^{+}$ state is also shown.

Figure 12

Top panel shows the measured transition quadrupole moments $Q_t$ for the ground-state band and Band D. Lower panel shows the calculated $Q_t$ values for the [2,4] and [3,4] configurations that are interpreted as the ground-state band and Band D, respectively.