Experimental investigation of vibrational excitations in 230Th

Nuclear levels in 230Th have been investigated in the β decay of 230Pa, the 230Th(d, pnγ) reaction and the 232Th(p, t) reaction. The Kπ = 0+1, 2+1, and 2+2 bands with band heads at 635, 781, and 1010 keV were observed up to the 8+, 9+, and 7+ levels, respectively. A second excited 0+ level was identified at 1297 keV which might be interpreted as the usual β shape-oscillation. The branching ratios of the E2 transitions from the 0+1, 2+1, and 2+2 bands are explained in the framework of the rotational model by taking into account the coupling of these bands with the ground-state band, and the coupling between the 0+1 and 2+1 band. A strong enhancement of E2 transitions from the 2+1 to the 0+1 band reported earlier is not confirmed. For the octupole vibrations with Kπ 0-, 1-, and 2- the E1 branching ratios are analyzed in terms of the Coriolis coupling of these bands. An almost complete experimental set of E1 transition moments from these negative-parity bands to the 0+g, 0+1, and 2+1 bands was obtained. It is suggested that octupole correlations might be important in explaining these E1 moments. (orig.)