Study of unusual fission-mass distributions, a < 200, using ∼ 200 MeV proton and 3He fission

Recent studies of proton-induced fission of targets 80 < A < 200 have indicated unusual fission-mass distributions near A = 140. They have continued measurements with protons E = 190 MeV, and added 3He, E = 270 MeV, at the Indiana University Cyclotron. The target nuclei included Nb, Ag, La, Ce, Pr, Nd, Dy, and heavier targets. Targets were made from ultrapure materials to minimize heavy contaminants. ΔE and E combined with TOF information (relative to the cyclotron beam, Δt ≤ 0.8 nsec) was used to separate and identify coincident fission fragments, determine their angular correlations and deduce approximate Z, M, and determine the kinetic energy release (TKE). Selected ΔE - E spectra, ΔZ/Z distributions, angular distributions and cross sections are presented