Figure 34 in the book shows the schematic diagram for our photomultiplier tube (PMT) signal processing circuit has an analog output that is suitable for use with a sound-card-based multichannel pulse-height analyzer (MCA). However, if you already have a commercial scintillation processor that you would like to use with PRA, then you will somehow need to extend the typically narrow output pulses (e.g. 1 to 10 microseconds) so that they can be acquired through the sound card.
The simplest method is to use a passive low-pass filter. We built ours from a 100 Ohm resistor and a 0.56 uF capacitor (total capacitance of the two parallel capacitors shown in the picture below. We assembled the filter inside a Pomona Electronics 3752 mini enclosure with BNC connectors, which provides appropriate shielding from noise, as well as an easy way to inserting it in-line between the pulse processor and the PC’s sound card input.