In-the-flash pulse shape discrimination with liquid scintillators

Single neutron and gamma charge pulses were captured using a fast ADC. These data were used to populate simulated 5-µs active interrogation flash events. Analysis of these simulations revealed that long pulse tail accumulation during the flash leads to an unpredictable charge background for several microseconds after the flash. The existence of this changing background will make retrieving prompt neutron information immediately after the flash problematic. The tail accumulation is accentuated for every pulse in the flash, making the time just after the last pulse in the flash the worst possible time to measure prompt neutron data. Obtaining prompt neutron data during the flash—particularly near the beginning of the flash, where background tail accumulation is minimal—is feasible if shielding is used to control the count rates, but requires fast gamma-neutron pulse shape discrimination. A means of accentuating the pulse shape difference between neutron and gamma data is given, along with a means of compensating for the long pulse components in the dominant gamma pulses.