Relative yield and period of individual groups of delayed neutrons in 233U, 235U, and 239Pu fission by epithermal neutrons

The relative yield of delayed neutrons and the half-life of their precursor nuclei in fissioning of U-233, U-235, and Pu-239 by epithermal neutrons are measured on a setup which is based on a KG-2.5 electrostatic accelerator The experimental samples are irradiated in a polyethylene cube, one face of which is irradiated by a neutron beam consisting of T(p, n)He-3 neutrons. A procedure is developed for averaging the group parameters of delayed neutrons from different series of measurements, taking account of their correlation. A comparative analysis of the data of this work and in ENDF/BVI in terms of the average half-life of the precursor nuclei of the delayed neutrons and using the dependence of the reactivity on the asymptotic period of the reactor is performed. It is shown that the data of this work agree, to within the uncertainty limits, with the recommended experimental data and differ substantially from the ENDF/BVI data.