Mass and charge distributions in the very asymmetric thermal neutron induced fission of the odd-Z nucleus Am-242m

Yields of light fission products (A = 68, 70-84, 87, 88, 94, 96, 98, 102 an d 106-108), their kinetic energies and nuclear charge distributions (A = 71 -84, 87 and 88) in the thermal neutron induced fission of the odd-Z nucleus Am-242m(Z = 95) were measured using the mass-separator Lohengrin at the In stitute Laue-Langevin in Grenoble (France). The mass yield curve shows a fi ne structure at A = 70, probably due to shell and/or odd-even effects affec ting also the nuclear charge distribution. The analysis of isotopic chain y ields gives evidence for a very low excitation energy of the lightest fissi on fragments observed. A preferential formation of fragments with even Z is found for this odd-Z compound nucleus, Calculated values for the local odd -even effect are comparable with those for the neighbouring even-Z fissile nuclides and increase from 13% to 30% with increasing asymmetry of the mass split (A(L) = 84 to 68 and Z(L) = 35 to 28). The neutron odd-even effect s hows a similar but less pronounced behaviour. (C) 1999 Elsevier Science B.V . All rights reserved.