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Transitions between rotational states of the ground-state and lowest K π = 0 − bands in 226 Ra, 224–232 Th and 230,232 U were studied by gamma-ray and conversion-electron spectroscopy following (d,pn) and ( α , x n) reactions in beam, and following the (p, x n) production of radioactive Pa isotopes out of beam. Coincidence measurements allowed to 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, D 0 / Q 0 , of a rigid rotor. This ratio was found to be independent of spin from I = 8 to 19 for 226 Th, whereas there is an indication that it increases for 224 Th in the same spin region by almost a factor of two. For the transitional nuclei 226 Ra and 228 Th no spin-dependence was found for spins up to I = 11 and 13, respectively. For the reflectionsymmetric nucleus 230 Th the D 0 / Q 0 ratios are consistent with the rotational predictions if the Coriolis coupling to the K π = 1 − band is taken into account.

The nuclear structure of 225Th has been studied using the reaction 226Ra(α, 5n) 225Th at a beam energy of 50 MeV. In-beam γγ, e−e−, e−n and e−γ coincidences have been measured, along with γ-ray and electron intensities, and these have been used to establish a decay scheme up to spin 39/2ħ and excitation energy 2494 keV. Parity doublets have been observed, forming two “quasimolecular bands”, along with enhanced E1 transitions linking states of opposite parity. γ-branching ratios have been measured and an average value of |D0/Q0| = (0.51±0.06)×10−3fm−1 has been deduced. The results are compared with calculations incorporating odd multipole degrees of freedom in the description of the nuclear shape.

High-spin states in 224,226,228Th were investigated using conversion-electron and γ-ray spectroscopic methods following 226 Ra (α, x n ) reactions. The Kπ = 0+ and 0− rotational bands are observed, which in 224,226Th merge into a single band characteristic for reflection asymmetric shape. The systematics of the level energies and El transition rates of 220–230Th are discussed in terms of a stable octupole deformation.

The rotational bands built on the excited 112− levels in 191Au and 193Au were investigated in (α,4n) reactions with in-beam γ-ray and conversion electron spectroscopy. Half-lives of the rotation-aligned levels in these bands were determined from e−e− time spectra, which were measured with a new double-orange spectrometer. In addition, some information on the magnetic moments of the rotation-aligned levels was obtained from integral perturbed angular distribution measurements. Finally, the previously unknown low-energy 312− → 272− transition in 191Au was identified from conversion electron measurements. From these data it is concluded that the rotation-aligned Hg cores have predominantly νvi1322 structure, contrary to the earlier suggestion of a πh1122 core structure.