A systematic investigation of the optimum conditions for the design and operation of a gas scintillation counter has been made. The gases studied were xenon, krypton, argon, helium, and various gas mixtures. Both a 6292 and a quartz window K1306 phototube were used with and without quaterphenyl as a wavelength shifter. Under optimum conditions an energy spread of less than 4% is obtainable for the Po210&agr; particles. The application of the gas scintillation counter as a fast ``slow neutron detector,'' using the reaction B10(n,&agr;)Li7, and its usefulness as a fast fission detector have been examined and discussed.