Measurement of Double-Differential Neutron Emission Spectra from Uranium-238

Abstract

We have performed the measurement of neutron emission spectra from ²³⁸U using a time-of-flight technique, and deduced the following data; (1) the prompt fission neutron spectra for 2 MeV incident neutrons at two emission angles of 90° and 135°, (2) the double-differential neutron emission cross sections at the incident energies of 1.2, 2.0, 4.2, 6.1 and 14.1 MeV. The emission spectra and the cross sections for scattering process were also deduced by subtracting the fission neutrons from the experimental spectra. The experimental results were compared with other experiments and the evaluations of JENDL-3 and ENDF/B-IV.

From the fission spectrum data ranging from 2 to 12 MeV, we have derived the best fit parameters for the Maxwellian and Watt type distribution functions. The experimental spectra are described with the Maxwellian spectrum with temperature of 1.24–1.26 MeV and are softer than both evaluations.

The spectra and cross sections for inelastic-scattering showed substantial disagreement with the evaluations concerning the discrete levels between 0.5 and 1.2 MeV, and continuum neutrons due to evaporation and pre-equilibrium processes. The secondary neutron angular distributions at 14 MeV incident energy were reproduced fairly well with the systematics.

KEYWORDS:

• double-differential cross section
• neutron emission
• uranium-238
• 1.2–14.1 MeV incident energy
• experimental data
• time-of-flight method
• fission neutrons
• Maxwellian distribution
• Watt distribution
• inelastic scattering
• discrete inelastic scattering
• continuum neutrons
• pre-equilibrium reaction
• neutron spectra
• angular distributions
• coupled-channel theory analysis