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Minor changes in the assignments of gamma rays following the alpha decay of228Pa in two previous studies make possible a reinterpretation of224Ac into two alternative level schemes. The resulting level structures arise from the reflection asymmetric configurations π3/2±(0.0 −0.3)−ν3/2±(−0.1 0.6), π5/2±(0.0 −0.2)±ν3/2±(−0.1 0.6) and π5/2±(0.0 −0.2)±ν1/2±(0.2 −0.1 3) which give rise to eitherK=0± or 1±,K=4±,K=2± andK=3± parity doublet bands. The bands with appreciable band structure, namelyK=0± or 1± andK=3±, have average parity doublet splittings of 11.0 and 5.8 keV respectively. These are extremely small values and suggest that224Ac is the most octupole deformed nucleus studied thus far. A method of calculating the parity doublet splitting in odd-odd nuclei is suggested and tested for224Ac. It seems to work remarkably well. The systematics of the hindrance factors for the bands with extended band structures confirm their interpretations as band structures. Finally, the two alternative level schemes are analyzed in the framework of the axially-symmetric rigid rotor model including the Coriolis interaction.

Alpha recoil sources of221Rn were used to study the level structure of217Po and the ground state of213Pb. The half-life of217Po was measured to be (1.6±0.2) s. When combined with unpublished data, an alpha-decay hindrance factor (HF) of 1.3 was obtained for the alpha-decay, strongly suggesting a g9/2 → g9/2 transition between217Po and213Pb ground states. Alpha-gamma coincidence studies confirm the previously observed 11/2+ band head in217Po. It is suggested that an unobserved 9/2+ ground state lies below the 11/2+ state in217Po and an attempt is made to observe connecting links between these two parts of the217Po level scheme.

The level structures populated in alpha decay of all odd-Z-even-N nuclei withZ=(83–93) andN=(126–142) up to 500 keV are presented. More data on the 4n+3 nuclear sequences are given from215Bi to235Np. Particular emphasis is placed on the hindrance factors to alpha decay in interpreting the level structures in term of the shell model, the octupole-quadrupole model and the Nilsson model. The level structures and the hindrance factors go through transition region in which mixtures of the properties of two different nuclear models are appropriate. These transition regions represent a challenge to nuclear theorists to develop more all-encompassing nuclear models.

The interchange of two sets of spins in the level structure of219Ra observed following the alpha decay of223Th and the suggestion that the ground state of219Ra was not observed in the heavy ion reaction spectroscopy208Pb(14C, 3n), allow the correlation of these levels which were previously unconnected. The resulting level structure is interpreted in terms of $$K = \tfrac{1}{2}^ \pm $$ and $$K = \tfrac{5}{2}^ \pm $$ parity doublet bands which evolve from anomalous rotational structures into vibrational-like structures with alternating spins and parities. The level structure of219Ra is successfully interpreted both in terms of octupole deformed (e 3=0.08) Nilsson levels and in terms of intermediate coupling using normal Nilsson levels with very strong octupole correlations. The levels in219Ra are then compared to the corresponding levels in a series of isotopic and isotonic nuclei to trace the collapse of octupole-quadrupole deformed nuclear structure into the more degenerate shell-model spectroscopy.

The remarkable features of the spectra of the odd-A Fr isotopes from213Fr (with 126 neutrons) through225Fr (with 138 neutrons) serve as a sequence of examples for the application of a variety of nuclear models. As the shapes vary from spherical to spherical with strong octupole correlations to octupole-deformed, the corresponding symmetry breaking leads to increasingly complex spectra. Of considerable interest is the fact that the219Fr 9/2− ground state has the character of an h9/2 shell model state while still having the rotational properties appropriate as a legitimate member of a reflection asymmetric K=1/2− band. It is also possible to follow the expansion of the more degenerate shell model states into the less degenerate reflection asymmetric states. This results from dramatic decreasing in decoupling parameters with increasing mass number.

Energies of the first 2+, 3− and 4+ states of even-even nuclei are plotted against proton and neutron number. Using this systematics, shell effects and the corresponding quadrupole and hexadecapole collectivity and deformation effects are compared and contrasted. Also, the correspondingB(E2),B(E3) andB(E4) values are plotted against neutron number and their very different systematics compared. Among the new results are the presence of hexadecapole collectivity at the 82 proton and neutron closed shells and the presence of the maximum values ofB(E4) at neutron numbers 10, 90–92 and 140–146. Finally, the systematics of the hexadecapole (K=4+) vibrations is compared with that of the quadrupole (K=2+) gamma vibrations in the quadrupole deformed rare earth region.

The octupole-octupole interaction has been added to the old pairing-plus-quadrupole model. Symmetries of the HF mean field are discussed. It is shown that under the assumption of the S-symmetry of the HF mean field, only two quadrupole and two octupole parameters have non-zero expectation values in HFB ground state. A detailed analysis of two possible approaches to the HFB treatment of the model Hamiltonian is presented.

Experimental evidence from the spectroscopy of155Gd and153Sm for the theoretically predicted quadruplet band structure, with band parity sequences (+−−+) and (−++−), is examined.

A cranked Hartree-Fock-Bogolubov formalism for a description of collective rotational states, which includes the n-p residual interaction along with pairing and is applicable to a neutron-proton system, is presented. A delta force form is used for the n-p residual interaction. A simple model is then developed where the valence neutrons and the valence protons occupy i13/2 and h11/2 orbitals, respectively. Results of these calculations are presented to show the effect of n-p interaction on the phenomenon of bandcrossing. Within the limits of such a restrictive model (which is particularly applicable to the (h11/2) p(i13/2) n bands in odd-odd nuclei) we find evidence for a shifting of the first bandcrossing frequency to a larger value. We find that n-p interaction may also affect many other phenomena in the high spin region.

The energy levels in the188Re nucleus were studied using the189Os(t, α)188Re reaction at triton energy Et=15·1 MeV. The energy of the excited states and the corresponding relative cross-sections were determined. The experimental relative intensities were compared with the theoretical DWBA predictions, calculated with the Nilsson model. The pairing effect and the Coriolis interaction in the residual as well as in the target nucleus were considered. Assignment of low-lying observed states was suggested. In contradiction with the DWBA predictions low intensity was found for excitation of the ground state rotational band and the ground state in the188 Re nucleus was not observed at all.

Levels in210Bi were studied using the reaction209Bi(n, γ)210Bi thermal neutrons. Ten configurations were studied — the fourth through the thirteenth in order of increasing energy. Gamma rays from 63 to 4285 keV were observed using three different modes of observation. Fifty-seven states with energies, spins and parities were assigned to configurations in210Bi. The experimental multiplets were compared with the theoretical calculations of Kim and Rasmussen and Herling and Kuo.