Development of multiframe detectors for ultrafast radiography with 800 MeV protons

We constructed two small-area pixelated detectors, which can record signals produced by 800-MeV proton beam micropulses with a repetition rate of 358 ns. The first detector was built around a two-dimensional (2-D) photodiode array. The array was illuminated by light emitted by a monolithic 1.7-mm-thick lutetium oxy-orthosilicate (LSO) scintillator and imaged by a simple optical system. The other detector was a hydrogen ion chamber operated at 1 to 2.5 atm. The anode was divided into an array of 8×8 1 mm² pixels. The fast positive-ion drift velocity in hydrogen helps to minimize the space charge build up. However, for beam pulses spaced in time closer than 1 μs, there appears to be a substantial accumulation of space charge. The electronic readout chain, for each of the 64 channels, consisted of an externally clocked fast-gated integrator and an amplifier coupled to an on-board analog-to-digital converter (ADC) and a first-in-first-out storage (FIFO). The detectors were tested with beam pulses up to 4×10⁶ protons per mm² delivered in 30 to 120 ns wide microbursts