Identification of a percolationlike critical region in the decay of excited calcium nuclei

The multidetector AMPHORA was used to investigate the reaction of 35 MeV per nucleon [sup 40]Ca ions with a [sup nat]Cu target. For 150 000 events corresponding to peripheral and midperipheral collisions, it was possible to reconstruct the primary projectilelike fragments and to calculate event by event the center of mass and the excitation energy. Comparison with a percolation simulation (charge moments, critical exponent) and a momentum ellipsoid analysis are presented and commented. No evidence for a change in disintegration mechanism with increasing excitation energy is found.