Angular momentum limit of Hf isotopes produced in three fusion-evaporation reactions

摘要

The compound nucleus Hf-168 was populated in three fusion-evaporation reactions with different beam-target mass asymmetries: Ti-50 + Sn-118, Ni-64 + Ru-104 and Ge-74 + Zr-94. Due to the large negative e values of these reactions the compound nucleus is formed at low excitation energy. At three or four excitation energies for each reaction gamma -ray spectra of the evaporation residues Hf-166 to Hf-163, corresponding to the 2n to 5n exit channels, respectively. were recorded with the Ge detectors of the 8 pi -spectrometer array. The gamma -ray multiplicity and total energy were measured using the inner ball of EGO detectors. This data was used to determine the maximum angular momentum transferred to each evaporation channel, the gamma -ray decay entry region and the relative cross sections. No differences are observed between the three reactions. This is explained by the very similar dependence of the excitation energy on the angular momentum of the compound nucleus. The relative cross sections for the 2n and 3n channels are observed to be significantly larger than predicted by statistical model calculations. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 25]