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Enriched targets of 187Re and 185Re were bombarded with α-particles of energy between 23.0 and 42.8 MeV. The levels characteristic of 189Ir and 187Ir produced by the (α, 2n) reaction were studied. The positive parity bands built on the 3 2 + ground state and on the 1 2 + first excited state in both nuclei were observed and interpreted as bands built on the 1 2 +[402] and 1 2 + [400] Nilsson states. The negative parity levels form two independent systems: the first one possesses characteristics typical of a rotation-aligned band and is interpreted as belonging to the h 9 2 orbital; the second one is connected with the 11 2 − isomeric state which originates from the h 11 2 orbital. The possibility of a triaxial shape for this h 11 2 . level system is discussed. In 189Ir a 3.2 ms isomeric state of 2333 keV excitation energy has been found and, as a by-product, some information has been gathered on the 4.1 ms isomer in 188Ir.

The influence of the reaction mechanism and of the nuclear structure at high angular momentum on the γ-ray deexcitation process is studied for Dy nuclei produced in a (40–80 MeV) and 12 C (80–110 MeV) induced reactions on 154, 155, 158, 160 Gd and 146, 150 Nd targets, respectively. The quasi-continuum (q.c.) γ-ray spectra for selected exit channels are decomposed into collective and statistical parts for which the γ-ray energies, the multiplicities and partly the multi-polarities are determined. Large differences in the constitution of the q.c. γ-ray cascades and in the population strengths of high-spin yrast states in 152 Dy and 156 Dy are attributed to nuclear structure effects at high angular momentum. This constitution and the centroids of the γ-ray entry regions in the energy versus angular-momentum plane are also evaluated as functions of beam energy and projectile. The γ-ray multiplicities and both coordinates of the entry region centroids increase initially with bombarding energy and then level off or even decrease at the highest energies. The observed increase is reproduced by a statistical-decay model, but at the higher bombarding energies strong deviations occur which are discussed in view of the reaction mechanisms, including incomplete fusion and non-equilibrium neutron emission, particularly absorptive breakup.

High-spin levels of the rotation-aligned bands built on the ${h}_{\frac{9}{2}}$ subshell in $^{183}\mathrm{Ir}$ and $^{185}\mathrm{Ir}$ have been populated by ($\ensuremath{\alpha}, 6n\ensuremath{\gamma}$) and ($\ensuremath{\alpha}, 4n\ensuremath{\gamma}$) reactions. In $^{183}\mathrm{Ir}$ a rapid increase in the apparent moment of inertia has been observed at high spins. The implication of this result for the interpretation of backbending phenomena in even nuclei in this mass region is discussed.

Level properties of 185Ir were investigated by in-beam γ-spectroscopy using (α, 4n) and (α, 6n) reactions with E, ranging from 41 to 77 MeV. A well-developed system of levels built on the h 9 2 Subshell is excited. A band built on the 11 2 − isomeric state is also observed. In distinction from heavier Ir isotopes, only a single positive parity band is developed to high-spin states. Two isomers with T 1 2 = 120 ns and 40 ns are found for excitation energies above 2.2 MeV. The experimental results are discussed in terms of rotational models including the Coriolis coupling and providing for a stable triaxial shape of the 185Ir nucleus.

Various channels from the 14 N + 159 Tb reaction at 140 MeV were studied using γ-particle coincidences combined with γ-ray multiplicity measurements. A wide class of binary reactions ranging from typical incomplete fusion processes to few-nucleon capture reactions was selected and investigated. Energy spectra, absolute cross sections and average γ-ray multiplicities were measured for a large number of reaction channels. From a detailed kinematical analysis it was found that all the reactions quite precisely satisfy the “recoil formula” of Siemens et al. for hard-grazing collisions. It is attempted to describe this wealth of reaction data on the common footing of the sum-rule model that combines the idea of partial statistical equilibrium with a generalized concept of critical angular momentum. The experimental results seem to confirm the basic assumptions of the model.