Measurement and Analysis of Ground-State Band Transitions and 2+'States in 78, 80, 82, 84Kr from (α,xnγ)
Ground-state band levels to 6+ in 84Kr, 6+ in 82Kr, 8+ in 80Kr, and 10+ in 78Kr have been identified with 20-65-MeV (α,xnγ) reactions on enriched Se targets with x=2, 3, and 4. The data are in-beam and radioactive γ 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 84Kr, 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 82Kr 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.