Spectral measurements of gamma-ray-induced secondary electron fields

Recent developments in beta-particle spectrometers have resulted in instruments that are capable of directly measuring the energy distribution of the recoil electrons that are produced as a result of gamma-ray interactions with matter. A two-detector spectrometer system has been developed that measures the energy distribution of high-energy electron radiation fields while simultaneously (actively) rejecting the system's response to the gamma-ray component of the field. The first detector, sensitive primarily to electrons, is located in front of a scintillation-based spectrometer so that the incident electrons must traverse it before interacting with the scintillation detector. The first detector is used to gate the spectrometer to accept only those interactions induced by energetic electrons. Proper design of the gating detector minimizes its gamma-ray sensitivity. A system rejection ratio, the ratio of the number of rejected gamma-ray-induced spectrometer pulses to the number of leakage pulses recorded, of ∼300 to 1 has been demonstrated for low-energy gamma-ray fields. In the work described in this paper, energy distribution measurements were made of the secondary electron field produced by irradiation of metal foils with 661.6-keV photons