Abstract
IN a recent communication, the possibility of using photoconductive lead sulphide cells for the measurement of rapidly varying surface temperatures has been emphasized1. For this purpose it is, of course, desirable that the response time of the measuring instrument be sufficiently small, and it is therefore of interest to see whether on theoretical grounds it is possible to decrease the response time of the cells. In this connexion it is important to remember that the conduction electrons can be captured both by the ionized impurities (n per c.c.), the number of which increases with increasing temperature, and by interstitial ions. At ordinary temperatures the equilibrium number of the latter (Frenkel defects) is very small ; however, under suitable conditions of manufacture, a large number (M per c.c.) corresponding to a high-temperature equilibrium can be 'frozen-in'. The number of conduction electrons released by radiation (I per c.c. per sec.) and heat agitation (A per c.c. per sec.) is then determined by the equation the capture coefficients of the ionized impurities and interstitial ions being assumed equal for the sake of simplicity. The time ta taken ta obtain the fraction a of the full asymptotic response is, therefore, given by .
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References
Lee, E., and Parker, R. C., Nature, 158, 518 (1946).
Mott and Gurney, Electronic Processes in Ionic Crystals (Oxford, 1940).
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HEPNER, W. Response of Photoconductive Lead Sulphide Cells. Nature 159, 96 (1947). https://doi.org/10.1038/159096a0
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DOI: https://doi.org/10.1038/159096a0
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