Slow-Neutron Cross Sections of ${\mathrm{Pu}}^{240}$, ${\mathrm{Pu}}^{242}$, and ${\mathrm{Am}}^{243}$

Measurements of the total cross sections of ${\mathrm{Pu}}^{240}$, ${\mathrm{Pu}}^{242}$, and ${\mathrm{Am}}^{243}$ have been made using the Argonne "fast chopper." The results on ${\mathrm{Pu}}^{240}$ include only the resonance structure which could be studied through the ${\mathrm{Pu}}^{240}$ impurity in some samples of ${\mathrm{Pu}}^{239}$ which were used in an exhaustive study of the latter nuclide. The values of the resonance parameters of the resonances at 1.053, 20.4, and 38.2 ev comprise these results. The studies of ${\mathrm{Pu}}^{242}$ and ${\mathrm{Am}}^{243}$ were made possible by the separation of these nuclides from samples of ${\mathrm{Pu}}^{239}$ which had undergone extensive neutron irradiation. Resonances were observed at 2.65 and 53.6 ev in ${\mathrm{Pu}}^{242}$ and at 0.976, 1.353, 1.74, 3.42, 5.12, 6.54, 7.84, 10.3, 12.8, 13.1, and 15.3 ev in ${\mathrm{Am}}^{243}$. Resonance parameters are reported for all of these resonances and in addition, the resonance capture integrals derived from these parameters are compared with the results of other measurements of these quantities.