Status Report on the Development of the ASCOP Photomultipiers

This paper describes the "ASCOP" line of photomultipliers derived from the design for Schlumberger Well Surveying Corporation which was presented at the last Scintillation Counter Symposium. High-temperature photomultipliers of various sizes are now in production and are used extensively in oil well radioactivity logging. Resolution measurements up to 165°C have been made with NaI(Tl) crystals and a CRT light pulser. A complete line of photomultipliers for the far ultraviolet is described, including tubes with LiF windows up to 2" in diameter. Cs-Sb cathodes or spectrally selective" solar-blind" Cs-Te cathodes are used. Photomultipliers for scintillation counting range from 3" to 11/4" in diameter. They combine good cathode sensitivity and uniformity, good electron collection and low dark current. Resolution data are presented. Tubes of this type have been successfully used for scintillation counting in various earth satellites.