SHELL EFFECTS ON FISSION-BARRIERS OF METALLIC CLUSTERS - A SYSTEMATICDESCRIPTION

We use the liquid drop model, with the stabilized jellium model, and t he Strutinsky shell correction method [Nucl. Phys. A 95, 420 (1967); 1 22, 1 (1968)], with the two-center asymmetric deformed harmonic-oscill ator potential, to evaluate fission barriers for three representative simple metal clusters (sodium, aluminum, and potassium). We obtain fis sion barrier heights as a function of size, charge, and mass asymmetry for all possible decay channels of doubly charged clusters with up to 30 atoms. We show how fragment deformations change the barrier height . For small sodium and potassium clusters we find good agreement of th e fission barriers with molecular-dynamics calculations. The critical number (cluster size for which fission competes with evaporation) is c orrectly reproduced for doubly charged clusters of the three metals co nsidered.