Measurements of delayed fission neutron spectra of 235U, 238U and 239Pu with proton recoil proportional counters

The delayed fission neutron spectra of 235 U, 333U and 239 Pu were measured for different time intervals after fission with proton recoil proportional counters. For these measurements, the spectra of the various time groups were determined. 14 MeV neutrons and, for 235 U, also thermal neutrons were used to induce fission. Where published experimental group spectra were available, comparisons with these results were made.