Energy discrimination and counting electronics for computer-aided radioactive particle tracking

Computer-Aided Radioactive Particle Tracking (CARPT) is a technique to study flow in fluidized beds, bubble columns, bioreactors, and other chemical processing apparatus. It is useful where the contents of the fluid (bubbles, solids, etc.) prevent the use of optical flow visualization techniques. CARPT uses a small gamma-emitting particle having the correct density and size to move with the fluid. Emitted gammas are counted with an array of NaI detectors, and the particle's track is calculated by repeatedly determining the relative count rates. We are extending the CARPT technique by using a different isotope for each of multiple particles - this makes it possible to use energy discrimination for identification. To make multi-particle CARPT practical, we have developed an octal NIM shaping amplifier and an octal pulse processing module with a Compact PCI (CPCI) interface. Each channel of the pulse processor comprises a differential receiver, discriminator, gain stage, delay line, gated integrator, a 10-bit ADC and a single FPGA that performs as eight single channel analyzers or as a 10-bit multi-channel analyzer. The FPGA has sufficient memory to store sets of data acquired over multiple time intervals. A controller FPGA handles channel busing, acquisition timing controls and interfacing to a PLX9030 IC for PCI operations. All the electronics for a 32-detector CARPT experiment can fit in two crates with data acquisition being controlled by a CPCI processor card. Details of the electronic design and illustrative experimental results are presented.