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Factors of merit for radiation detectors Unwin, Alexander Matthew

Abstract

A discussion is given of the many uses of photo-conductive cells, especially of those of the lead sulphide type. A Factor of Merit for radiation detectors as proposed by Clark Jones is presented, which is intended to cover all types of detectors, and which is applied to the lead sulphide cells studied. Other Factors of Merit are also mentioned. From information obtained the Factors of Merit are evaluated for the cells. These Factors of Merit are found to vary with the temperature of the cell layer. It is found that limiting noise is not due to Johnson noise, but rather to radiation fluctuations; and that the ultimate sensitivity has been reached in some cells. The cells are assumed to be type II detectors according to Clark Jones's classification. It is found that the engineering limit proposed by R. J. Havens does not apply here. Particularly good agreement between various expressions for the Factor of Merit is shown, assuming a type II detector. A description of the apparatus is given in some detail. A black body radiator and associated temperature control, a 900 cycles per second tuned amplifier, a wide band preamplifier and a multi vibrator used in measuring time constants of such cells are described. The methods of measurement of responsivity to noise ratio, of noise, of time constants, frequency response curves and spectral response of a detector are outlined. It is found that the black body is optically aligned; tests show that the response of a cell is directly proportional to the intensity of the illumination.

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