Measurement and Analysis of Ground-State Band Transitions and2+′States inKr78,80,82,84from (α,xnγ)

Abstract

Ground-state band levels to ${6}^{+}$ in $^{84}\mathrm{Kr}$, ${6}^{+}$ in $^{82}\mathrm{Kr}$, ${8}^{+}$ in $^{80}\mathrm{Kr}$, and ${10}^{+}$ in $^{78}\mathrm{Kr}$ have been identified with 20-65-MeV ($\ensuremath{\alpha},xn\ensuremath{\gamma}$) reactions on enriched Se targets with $x=2, 3, \mathrm{and} 4$. The data are in-beam and radioactive $\ensuremath{\gamma}$ spectra, angular distributions, relative and absolute excitation functions and \ensuremath{\sim}3-nsec time distributions. All transitions in the ground-state bands are \ensuremath{\gtrsim}95% prompt (\ensuremath{\gtrsim}3 nsec) except for $^{84}\mathrm{Kr}$, in which the 6 \ensuremath{\rightarrow} 4, 4 \ensuremath{\rightarrow} 2, and 2 \ensuremath{\rightarrow} 0 transitions have the same intensities of long-lived (\ensuremath{\gtrsim}200-nsec) component in addition to the prompt component. Multipole mixing ratios of three other transitions in $^{82}\mathrm{Kr}$ are obtained from the angular distributions. The systematics of level energies in the ground-state bands of various Se, Kr, Mo, and Ru isotopes are analyzed with a phenomenological equation. This reveals three limiting types of nuclei.