The Photo-Multiplier Radiation Detector

Abstract

The photo‐multiplier radiation detector consists of a commercial multiplier photo‐tube arranged to register the scintillations produced in a fluorescent screen by radiation quanta. The signal pulses thus obtained are large for alpha‐particles and other high velocity ions, much weaker for x‐rays, gamma‐rays, and high velocity electrons. The method is limited by the presence of noise pulses caused by electrons thermally emitted at the photo‐cathode; signal pulses can be discriminated from noise pulses only to the extent that their amplitudes are greater. Satisfactory detection of the weaker signal pulses has been accomplished by careful attention to (1) selection of photo‐tubes, (2) choice of fluorescent screen, (3) efficient collection of light, and (4) proper circuit design. The new detector is especially suited to narrow‐beam measurements where high counting rates are desired. However, it compares favorably with conventional detectors even when low counting rates and weak signal pulses are involved. The detector is rugged and fast, requires no special thin‐window technique, and shows high efficiency. The primary detecting medium, being a solid, has high absorption and is well defined in position. This article includes full construction details, an analysis of performance characteristics, particularly with weak signal pulses, and numerous suggestions for further improvement.