Experimental Investigation of Vibrational Excitations in 230 Th

Nuclear levels in230Th have been investigated in theβ decay of230Pa, the230Th(d, pnγ) reaction and the232Th(p, t) reaction. TheKπ=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 usualβ shape-oscillation. The branching ratios of theE2 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 ofE2 transitions from the 2 1 + to the 0 1 + band reported earlier is not confirmed. For the octupole vibrations withKπ=0−, 1−, and 2− theE1 branching ratios are analyzed in terms of the Coriolis coupling of these bands. An almost complete experimental set ofE1 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 theseE1 moments.