Composite Delayed Neutron Energy Spectra for Thermal Fission of ²³⁵U

Composite delayed neutron energy spectra from the thermal neutron fission of ²³⁵U have been measured for eight delay-time intervals between 0.17 and 85.5 s. Our experimental technique combines a helium-jet and tape transfer system with a beta-neutron time-of-flight spectrometer. The neutron energy range of 0.01 to 2.0 MeV is spanned with ⁶Li-glass, plastic, and liquid scintillators. Spectra are compared to ENDF/B-V as well as to individual precursors' data and average energies are tabulated for the present and previous compilations. An equilibrium spectrum is also calculated and compared to ENDF/B-V and individual precursor measurements.