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A scintillation counter using pure NaI cooled to liquid nitrogen temperature has been developed. The photopeaks of Co57 γ rays (122 kev) and Cs137 γ rays (662 kev) were found to have a full width at half-height of 33% and 14%, respectively. A 7-inch quartz light pipe was used between scintillator and photomultiplier. The decay time of the fluorescent light was found to be 27 mμsec. For fast time measurements a time-to-pulse-height converter has been constructed, which operates in the range from 0–100 mμsec. The converter was used in conjunction with two scintillation counters using plastic (Pilot B) scintillators. The time resolution for the detection of annihilation γ rays was found to be 2τ0 = 2.3 mμsec. With one plastic and the cooled NaI scintillator the time resolution was found to be 2τ0 = 2.7 mμsec. The possible factors contributing to the time resolution are discussed.