Rejection of Nal Pulse Pile-Up in Linac Bremsstrahlung Measurements

A pulse pile-up rejection system was developed and used successfully with a NaI gamma spectrometer to measure the bremsstrahlung spectral distribution from a 0.2-radiation-length gold-tungsten target bombarded by high energy electrons from a pulsed electron linear accelerator. The system utilizes a double differentiation technique to reject those scintillation events where more than one gamma ray is detected during a single linac pulse. The pulse pile-up rejection circuit was used effectively over a gamma energy range of 0.25 Mev to 21 Mev and increased data collection speed by about a factor of 20. The performance of the system agrees with theoretical predictions calculated on the basis of Poission statistics. Gamma spectral distributions measured with the system at the EG&G linac are presented to demonstrate utilization of the system.