Particle identification techniques

Abstract

The first time-of-flight measurements were developed to distinguish between neutrons and gamma rays following neutron interactions in matter. These early studies were mainly with very slow neutrons whose energies had been very precisely determined by mechanical choppers. Following the scattering of these neutrons by a target the measurement of the angular distribution, or attenuation coefficient, was complicated by the presence of gamma rays from the source of the neutrons or from (n, γ) reactions. The most effective method of removing this background is to time the arrival of the signals at the detector relative to the arrival of the burst of neutrons at the target. The gamma rays travel to the detector at a velocity of 3 × 108 m s-1 and so for relatively short flight paths they arrive very much earlier than the slow scattered neutrons.