COLLECTIVE E1 TRANSITIONS IN EVEN-A RA, TH, AND U-NUCLEI

Transitions between rotational states of the ground-state and lowest K (pi) = 0- bands in Ra-226 Th-224-232 and U-230,U-232 were studied by g amma-ray and conversion-electron spectroscopy following (d, pn) and (a lpha, xn) reactions in beam, and following the (p, xn) production of r adioactive Pa isotopes out of beam. Coincidence measurements allowed t o establish the level schemes and to determine E1/E2 branching ratios which can be interpreted in terms of the ratios of intrinsic electric dipole to quadrupole moments, D0/Q0, of a rigid rotor. This ratio was found to be independent of spin from I = 8 to 19 for 226Th, whereas th ere is an indication that it increases for 224Th in the same spin regi on by almost a factor of two. For the transitional nuclei Ra-226 and T h-228 no spin-dependence was found for spins up to I = 11 and 13, resp ectively. For the reflection-symmetric nucleus Th-230 the D0/Q0 ratios are consistent with the rotational predictions if the Coriolis coupli ng to the K(pi) = 1- band is taken into account.