Extending the operation of a position-sensitive photomultiplier tube to 1 million counts per second

While position-sensitive photomultiplier tubes (PSPMTs), coupled to fast scintillators, are widely used as photon detectors in applications such as medical imaging systems (PET, gamma camera, etc.), where it is desirable to combine good time resolution with the capability of locating the point of photon interaction, their count rate limitations (of order of tens of thousands of cps) have precluded their use in more demanding applications. Recently, in a neutron imaging application, we found that, by using custom designed fast anode and dynode readout circuits, coupled to a fast digital pulse processing board, we could operate a PSPMT at rates approaching 1 million cps while retaining good position resolution, linearity and time resolution. These developments therefore significantly extend the range of PSPMT application.