Total cross sections for fast neutrons by a time of flight method

Abstract

A time of flight method for the determination of total cross sections for fast neutrons has been realized by detecting neutrons twice along their path by stilbene scintillation counters. The time interval between the pulses of the two counters is measured by a delayed coincidence circuit and determines the energy of the neutrons between the counters. The experimental arrangement and its properties with respect to efficiency, energy resolution and background are discussed. The time resolution was limited by the low efficiency of the coincidence circuit for resolving times smaller than 4 nanoseconds. The method has been tested by measuring with an average energy resolution of 20% the total cross section of sulphur between 400 and 1200 keV. The results are compared to earlier measurements and to the optical model. Further possibilities of the method are discussed.