Fast-Neutron-Induced Fission Cross Sections ofPu241andAm243

The cross sections for neutron-induced fission of ${\mathrm{Pu}}^{241}$ for neutrons of energies from 0.02 to 1.80 Mev and of ${\mathrm{Am}}^{243}$ for neutrons of energies from 0.3 to 1.7 Mev have been determined. The determination was made by measuring the ratio of each cross section to that of ${\mathrm{U}}^{235}$ using a back-to-back gas scintillation counter.