DOES THE COMPOUND NUCLEUS REMEMBER ITS WAY OF FORMATION - HOT GDR SPECTROSCOPY IN THE YB-DY REGION

A difference method has been applied to determine the first chance GDR photon emission accompanying a deexcitation of the hot compound syste ms of Yb-162 and Dy-158 produced in heavy ion fusion reactions with 3 various projectile-target combinations. The GDR difference yield has t urned out to be surprisingly small for the heaviest projectiles (Ti) b eing in dramatic conflict with the statistical model (code CASCADE) pr ediction, while for the lightest beam (O) an agreement with the model has been observed. For the intermediate (Si) projectiles a strong depe ndence of the difference yield on the transferred angular momentum has been noticed. With increasing I the difference yield decreases and re aches zero for the highest transferred I(50 ($) over bar h). Recently additional checks with better definition of the fusion events applying the PPAC and CS HPGe detectors have been performed.