Fission ofBi209by 36.1 -MeV Protons: Search for an Asymmetric Component in the Mass Distribution, and Neutron-Emission Results

A thin deposit of ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ was bombarded with 36.1-MeV protons from the Oak Ridge isochronous cyclotron and correlated energies of fission-fragment pairs were measured with silicon surface-barrier detectors. The mass-yield distribution obtained from these energies was compared with the radiochemical results of Sugihara, Roesner, and Meadows; we do not confirm the existence of the small asymmetric peak that appears in the wings of their distribution. Studies of statistical uncertainties and dispersion effects in our experiment indicate that they are not large enough to wash out such peaks. The average number of neutrons emitted as a function of fragment mass was obtained from a cumulative yield calculation and is consistent with an earlier measurement for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$-induced fission of ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$. Pre-neutron-emission mass and kinetic energy distributions are presented.