Studies of the rotational behaviour of nuclei by continuum gamma ray techniques

Non-spherical (i.e. deformed) nuclei exhibit different modes of excitation. One salient feature, inherent to the deformed shape, is the rotational mode of excitation. Thus a rotational band structure may be built on different intrinsic states. These bands are described by moments of inertia J through E=k2/2J I(I+1) where E is the excitation energy and I is the total or the collective spin. The present thesis deals with the effective moment of inertia Jeff(2), which can be extracted after corrections to the 'side-feeding' of the rotational states. A band moment of inertia J(2)band is also deduced from experiments using two-dimensional γγ ray energy correlations. The variations of these moments of inertia with the rotational frequency are studied by means of in-beam γ-ray spectroscopy techniques. The interplay between the single particles and the collective motion in the alignment of spin is also investigated. The studies are carried out by means of compound nuclear reactions for neutron deficient nuclei around A=130. Particular attention is paid to the states originating from the neutron i13/2 shell model state. Comparisons of the calculated values of Jeff(2) are made with data. The calculations are based on the Cranked Nilsson Strutinsky Model combined with Monte-Carlo methods. A drastic shape change is found, with an occupation at high spins (I>30 h) of a very deformed shape (ε2 ≅ 0.32), for all the nuclei studied. (orig.)