In this series of pictures, an ultraviolet light is being used to excite the liquid. The liquid is clear and a beam of light from a standard flashlight leaves no trace, but a beam from a UV light makes a trace in the fluid, seen as a blob or track. A 25mW green laser will make a beam in the liquid, but a 5mW red one does not seem to work at all. The color is not quite right in the pictures. The track looks blue and the spot where the light stops on the bottom of the can looks violet.
The long cylindrical metallic tubes are BF3 and BF3 B10-lined neutron counting tubes. These are made similar to the usual Geiger tube but with a different fill gas, case material, and fill pressure.
Another image shows some plastic scintillating material sitting on top of the NEN PSD fluid canister. The plastic scintillators work like the fluid.
I would like to have shown all of these items in operation but there is nothing special to demonstrate them with around here, although the usual background radiation would probably be enough. An experiment for another time.
If the Geiger counter has a sensitivity of 1x, then here are the sensitivities of various scntillation crystals when used with photomultiplier tubes:
30x Plastic Scintillator (presumably the fluid as well)
100x NaI(Tl) Sodium iodide activated with Thallium
125X CsI Cesium iodide
200X BGO Bismuth germanate