Transistor Form of Nuclear Particle Detector

Abstract
A transistor form of nuclear particle detector has been fabricated using 20,000 ohm-cm p-type silicon. With such high resistivity silicon and a wafer 10 mils thick, a bias voltage of 30 to 40 volts extends the depletion layer almost completely through the wafer, leaving a thin p-region so that the whole wafer becomes a transistor. A particle entering the device through the collector depletion layer produces ionization in this layer which is quickly swept out. The charge separation is such that the emitter is forward biased and a transistor pulse current flows subsequent to the collector diode current. The current time characteristics of the device will be shown and the gain of the device will be considered both for light radiation and particle pulse signals. From a detailed consideration of the gain-bias characteristics the lifetime in the base of the transistor can be calculated. This will be compared to the response time of the unit. The detector surface has been shown to have sensitivity variations by comparing the gain of the device obtained with a small light beam at several points on the surface. Variations in sensitivity are indicated by the shape of the resolution curves. Signal to noise ratios obtained are comparable to those realized with good amplifiers and similar area diodes. This, combined with noise and gain data, indicates that the device is amplifying the signal and the collector junction noise current by the same factor. Typical gain figures are 200 to 300.

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