We have measured the mass-yield distribution from the fission of ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$ induced by 14.8-MeV neutrons. Seventy-five fission products from ${}_{}{}^{66}{}_{}{}^{}\mathrm{Ni}$ to ${}_{}{}^{169}{}_{}{}^{}\mathrm{Er}$ were detected. From these measurements we obtained the total chain yields for 49 mass numbers and constructed the mass-yield curve. Absolute fission yields were obtained by using the ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}\mathrm{}(n,f)\mathrm{}$ monitor reaction. The total yield determined from each half of the mass-yield curve is 0.984. From the agreement in these two methods we conclude that our yield determination is accurate to approximately 4%. The peak-to-valley ratio is 5.5, a significantly larger value than the ratio of 4.1 found for 14.8-MeV neutron fission of ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$. This difference agrees with the trend noted previously for 14.8-MeV neutron fission of uranium isotopes. A number of independent fission yields were measured. Values of $Z_p$ inferred from these yields agree with those estimated from independent-yield systematics, but are approximately 0.1 charge unit greater than predicted. Several partial isomer yields and isomer ratios were measured. These results provide additional information about the fractional production of isomeric states either directly from fission or from $\beta$ decay. The absolute photon intensity for the 342-keV transition in the decay of ${}_{}{}^{111}{}_{}{}^{}\mathrm{Ag}_{}^g{}_{}{}^{}$ was measured to be 0.0668(±5%).

NUCLEAR REACTIONS, FISSION ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}\mathrm{}(n,f)\mathrm{}$, $E=14.8\mathrm{}$ MeV; measured fission yields, deduced fission mass distribution. Measured independent fission yields and partial isomeric yields. ${}_{}{}^{111}{}_{}{}^{}\mathrm{Ag}_{}^g{}_{}{}^{}$ measured $I_{\gamma }$.

• Received 8 July 1977

DOI:https://doi.org/10.1103/PhysRevC.16.1907