A scintillation counter used in a vacuum chamber for a liquid hydrogen target

To measure charge exchange and charged-prong annihilation cross sections in the low momentum $\text{pp}$ reaction, we used a cylindrically shaped scintillation counter surrounding the liquid hydrogen target. It was contained in a target vacuum chamber and was optically coupled to a photomultiplier tube outside the vacuum chamber by a lucite light guide. Optical coupling between the scintillator and the lucite light guide was attained by a half-cylinder lucite piece. An analysis of this optical coupling method is also described.