Development of a measurement reference standard for neutron energies between 1 MeV and 20 MeV using time of flight method at the AMANDE facility

The variation of the response of instruments as a function of neutron energy has to be determined in well-characterized mono-energetic neutron fields. These fields are measured in terms of neutron fluence and mean energy of the mono-energetic neutron peak, providing values that are required to determine the related dosimetric quantities. At the IRSN AMANDE facility, the reference measurement standard for neutron energy is based on the time of flight (ToF) method, i.e. on a determination of the neutron velocity, requiring a pulsed beam and fast detectors. In this study, we describe the experimental and theoretical aspects of the development of this method for neutron energies above 1 MeV using liquid scintillators. We present the adopted experimental protocol and give full details of the estimation of uncertainties associated with the neutron energy measurement. To extract as accurately as possible the mean energy from the experimental neutron ToF distribution, a simulated energy distribution is fitted to the measurements. This simulation includes a detailed analysis of the energy resolution, taking into account all the contributions influencing the ToF measurements. Comparison with neutron energy calculated from kinematics leads to the conclusion that the ToF method at the AMANDE facility can be considered as a reference measurement standard for neutron energies between 1 MeV and 20 MeV, with a relative uncertainty lower than 1.5%. (authors)