Direct observation of E0 transitions in 188Pb through in-beam spectroscopy

Competing configurations, assigned with three different shapes, are mixed at low angular momentum in the neutron-deficient 188Pb nucleus. Here, we present a simultaneous conversion electron and γ-ray in-beam spectroscopic precision measurement employing the sage spectrometer. The level energy of the first excited state, 0+2, has been determined at 591(1) keV through direct measurement of conversion electrons. By using the intensity of the observed 0+2→0+1 transition to the ground state, the feeding of the 0+2 state has been determined for the first time, which suggests the 0+2state is the head of the predominantly prolate band. The compositions of the 4+2→4+1and 2+2→2+1 inter-band transitions have been determined, indicating configuration mixing between the bands.