The Scintillation Counter
The scintination counter is a relatively new instrument for the detection and measurement of nuclear and atomic radiations. Light produced in a fluorescent material by the incident particle or quantum Is picked up by a photomultiplier tube. The resultant photoelectric emission is amplified in the photomultiplier by a series of secondary-emission stages. This paper is a review of the present state of knowledge regarding the characterstics of the counter and the details of Its operation.
Microsecond Measurement of the Phosphorescence of X‐Ray Fluorescent Screens
Microsecond square‐wave x‐ray pulses, repeated a thousand times a second, were obtained by operating an x‐ray tube directly from a radar pulser. The phosphorescent build‐up and decay of light emitted by fluorescent materials when irradiated by the x‐ray pulses was observed with a multiplier phototube connected to an oscilloscope. Oscillograms of CaWO4 (radiographic intensifying screen) and BaSO4 indicate simple exponential response, with decay to 1/eth intensity in 6 and 0.8 microseconds, respectively. MgWO4 and Patterson B (fluoroscopic) and D (photofluorographic) screens were found to complete their main response to microsecond excitation in 10 to 100 microseconds, but their decay is not exponential.
The phosphorescence of various solids
Ultra-violet radiation absorbed by a solid may be dissipated either as heat or as luminescence. If the electrons involved in the absorption transitions return to the ground state in a time not greater than 10-6 sec., the resulting emission is described as fluorescence. Delayed return is generally referred to as phosphorescence, and it is the chief object of this paper to describe some measurements of the decay law for various solids, together with some associated measurements of photoconductivity. A preliminary account of this work has already been published (Randall and Wilkins 1939).