Band structure of high spin states in the A approximately 70 region

A wide variety of collective band structures have been reported in the A approximately 70 mass region which has become a very important testing ground for nuclear models. The general trends of the low energy spectra in nuclei with N approximately 50 as first studied in this region have been described in anharmonic vibrator models. Then strong evidence for shape coexistence was reported in 72Se. Very recently shape coexistence has been reported in 74Kr but with a reversal in the near spherical and deformed shapes. The ground state of 74Kr is reported to be strongly deformed even more so than the super ground state deformation recently reported for 100Sr. Positive and negative parity bands to high spin have been observed in these nuclei. The influence of the gsub(9/2) orbital in these bands has been well established in both even-even and odd-mass nuclei. The crossing of the ground state band with two quasi-particle bands based on (gsub(9/2))2 configurations is understood to be the cause of backbending in the yrast moments of inertia. Now a second backbending of the moment of inertia is observed in 74Kr where levels are reported to tentative 20+, the highest spin observed in this region. The authors discuss some new techniques and recent results of heavy-ion, in-beam spectroscopy studies in this region. (Auth.)