Precision measurement of prompt fission neutron spectra of 235U, 238U, and 239Pu

Prompt neutron spectra from fission of 235U, and 239Pu have been measured at incident neutron energies of 0.10, 0.18, 0.53 and 2.07 MeV. A major effort was made to obtain an accurate experimental determination of the efficiency and energy response function of the time-of-flight neutron detector in the energy range 0.15 to 15 MeV. The spectra have been analytically described by the so called Watt distribution, as well as with a Maxwell distribution. It is shown that the Watt relation gives a somewhat better description of the spectra than the Maxwell formula. The angular correlation between incident-neutrons and fission-neutrons was measured for 235U and 238U at an incident neutron energy of 2.07 MeV. The data indicate some slight anisotropies, being rather small or even negligible for 235U and somewhat more pronounced for 238U. The results show that the shape of the neutron energy distribution is independent of the angle of observation. 4 figures, 1 table