A method for correcting the time-of-flight spectra for the neutron emission time and the detector efficiency

Abstract

When one measures the spectrum of a subcritical reactor by the time-of-flight method, the recorded spectrum cannot be directly compared to the calculated steady-state spectrum of the system. Indeed, there is no simple relationship between the arrival time of a neutron at the detector and its energy since the time at which the neutron leaves the reactor is not known and the energy dependence of the detector response distorts the spectrum. A method based on the detailed computation of the response of the reactor to a narrow burst source of arbitrary spectrum has been devised. It allows the calculation of a correction factor for each channel of the time analyzer. Multiplying the time-of-flight spectrum by this correction factor provides a spectrum in the flux per unit of lethargy scale which can then be compared directly to ordinary steady-state calculations.