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 ($\alpha ,xn\gamma$) reactions on enriched Se targets with $x=2, 3, \mathrm{and} 4$. The data are in-beam and radioactive $\gamma$ spectra, angular distributions, relative and absolute excitation functions and ∼3-nsec time distributions. All transitions in the ground-state bands are ≳95% prompt (≳3 nsec) except for ${}_{}{}^{84}{}_{}{}^{}\mathrm{Kr}$, in which the 6 → 4, 4 → 2, and 2 → 0 transitions have the same intensities of long-lived (≳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.