Abstract
A detailed study of the positive parity yrast and yrare rotational bands in 77Rb is presented. Using the reaction 40Ca( 40Ca, 3 p) and the EUROGAM I spectrometer, γγγ coincidences enabled us to follow both bands over a large spin range and to measure many E2 strengths. The moments of inertia and transition quadrupole moments indicate that a more deformed band ( ϵ 2 ≈ 0.38) is crossed by a less deformed one ( ϵ 2 ≈ 0.29). Since the yrare band starts at the extremely low spin value of I = 9 2 , the conventional band crossing mechanism of two aligning high- j quasiparticles is excluded. The frequency-dependent equilibrium shapes were calculated with Nilsson-Strutinsky type calculations using a diabatic tracing of configurations near the neutron Fermi level. This is the first observation of such a band crossing.
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