Measurement of the Prompt Fission $$\gamma $$-Rays from Slow Neutron-Induced Fission of $$^{235}$$U with STEFF

The average energy and multiplicity of prompt $$\gamma $$ γ -rays from slow neutron-induced fission of $$^{235}$$ 235 U 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 $$\gamma $$ γ -ray interactions, prompt fission neutrons and background counts before being deconvolved to estimate the emitted spectrum of prompt fission $$\gamma $$ γ -rays. The results give an average $$\gamma $$ γ -ray energy $${\bar{E}}_{\gamma }$$ E ¯ γ of 1.71(5) MeV and multiplicity $$\bar{\nu }_{\gamma }$$ ν ¯ γ of 2.66(18) considering $$\gamma $$ γ -rays emitted within the energy range 0.8–6.8 MeV. The n_TOF data has a slightly larger $${\bar{E}}_{\gamma }$$ E ¯ γ and smaller $$\bar{\nu }_{\gamma }$$ ν ¯ γ than other recent measurements, however the product of the two is in agreement within quoted uncertainties.