Measurement of the prompt fission γ-rays from slow neutron-induced fission of 235U with STEFF

The average energy and multiplicity of prompt γ-rays from slow neutron-induced fission of 235U have been measured using the STEFF spectrometer at the neutron time-of-flight facility n_TOF. The individual responses from 11 NaI scintillators were corrected for multiple γ-ray interactions, prompt fission neutrons and background counts before being deconvolved to estimate the emitted spectrum of prompt fission γ-rays. The results give an average γ-ray energy E¯γ of 1.71(5) MeV and multiplicity ν¯γ of 2.66(18) considering γ-rays emitted within the energy range 0.8–6.8 MeV. The n_TOF data has a slightly larger E¯γ and smaller ν¯γ than other recent measurements, however the product of the two is in agreement within quoted uncertainties.