It is a drawback of scintillation counting with crystals that large-sized crystals are found not to be very transparent. They exhibit a considerable light scattering which gives rise to additional absorption. This drawback could be overcome if instead of crystals one were able to use liquids, which can be applied in large thicknesses without considerable absorption. In the course of the investigation of the fluorescent efficiency of liquid solutions when excited by gamma-radiation and by neutrons,
special solutions were used which exhibited a fluorescent efficiency high enough to make them applicable for counting work. (Extracted from the introductory part of the paper.).
Another invention of liquid scintillation counters.