Speakers
Description
The average energy and multiplicity of prompt $\gamma$-rays from near thermal neutron induced fission of $^{235}$U have been measured using the STEFF detection setup at both the high-flux ILL research reactor and the neutron time-of-flight facility n_TOF. As highlighted by the NEA High Priority Request List, these quantities are of importance to the heating of non-fuelled elements of a reactor core and concerted efforts have been made in recent years to improve the available data. STEFF is capable of measuring both fission fragment's energy and velocity, a so-called $2E2v$ device and the fragment velocities and energies are used to provide a clean and precise timing signal for a fission event. The central chamber is surrounded by an array of 11 127$\times$102 mm NaI scintillators which are used to record the time and energies of $\gamma$-rays within a time window centered around the identified time-of-fission. Both prompt fission $\gamma$'s and those originating from secondary interactions by prompt fission neutrons are detected and a method is given here to distinguish between the two based on both the detection time and energy. Details on the full analysis methodology and procedures will be presented and a comparison of the results from the two experiments at thermal neutron energies will be given in order to quantify and investigate any systematic uncertainties associated in each case, particualrly with regard to the functioning of STEFF in the high $\gamma$-ray background environment associated with EAR2 at n_TOF. The final results will be given and shall be compared to other recent measurements and evaluations.