Upper Limits of the Fission Cross Sections of Bismuth, Lead, Mercury, Gold, Iridium, and Tungsten for 14-Mev Neutrons

A photographic technique was used to set upper limits on the fission cross section of some of the naturally occurring heavy elements below radium when these are bombarded by 14-Mev neutrons; the Los Alamos Van de Graaff, utilizing the $\mathrm{T}\mathrm{}(d,n)\mathrm{}{\mathrm{He}}^4$ reaction, comprised the neutron source. It is established that the fission cross sections of the elements investigated are less than approximately ${10}^{-5\mathrm{}}$ of the cross section of ${\mathrm{U}}^{238}$.