Study of nuclear deformations at angular momenta close to the liquid-drop limit

In an attempt to investigate shapes of 161Ho nuclei formed in 37Cl + 124Sn collisions, at angular momenta close to or beyond the liquid-drop limiting value (approx.=90 (h/2π)), first results from the measurement of p and α emission correlated with the nuclear spin axis were obtained. 1. At 254 MeV bombarding energy and in coincidence with the fission channel, particle emission prior to fission (Msub(α)approx.=Msub(p)approx.=0.13) displays an anisotropy by an order of magnitude too small to be described by emission from a spherical nucleus. Analysis yields quadrupole deformation parameters vertical strokedeltavertical stroke approx.= 0.6-0.8 in the angular momentum window 87 (h/2π)<=I<=100 (h/2π), corresponding to axis ratios 2.1-2.7 of a superdeformed ellipsoid. 2. At 200 MeV, with selection of residue events, particle correlations measured in the crystall ball with respect to the spin axis - obtained as the symmetry axis of the E2 deexcitation pattern - require small deformation parameters vertical strokedeltavertical stroke approx.= 0.2 only, nearly independent of I in the interval 22 (h/2π)<=I<=58 (h/2π). Whether the observations indicate a critical behaviour (superbackbending), or whether the extreme deformations reflect shapes specific to the dissipative mechanism of ''fast fission'', remains to be investigated. (orig.)