Mass, charge and energy distributions in the very asymmetric fission of 249Cf induced by thermal neutrons

Abstract Fission yields of fragments with mass numbers A = 69–87 and fragment kinetic energies for A = 74–87 in the very asymmetric neutron induced fission of 249 Cf have been measured using the mass separator Lohengrin at the Institut Laue-Langevin in Grenoble. The chain yields observed in this very light mass region are considerably higher than predicted. An evaluation of the isotopic yields shows a strong increase of the proton odd-even effect from 7% to 17% with increasingly asymmetric fission. The neutron odd-even effect is increasing from 4% to 10%. These observations and a narrowing of the average nuclear charge distribution can be explained by a decreasing excitation energy with increasing asymmetry of the fission process.