Is that what they call those "pump" thingies these days? ;-P
LOL! Not quite. It uses isotopes of boron, cadmium, and lithium sandwiched between Plexiglass plates which is then buttressed up against and alpha scintillometer.
The neutrons are captured by the sandwiched plates, which then emit an Alpha which is read by the alpha scintillometer. (zinc sulfide emits photons when struck by alpha particles which are then counted by a photomultiplier tube)
The whole assembly is then housed in a cadmium tube.