A low-temperature chamber for calibrating thermal radiation detectors

A low-temperature chamber for measuring low radiation densities against an adjustable radiation background is presented which makes it possible to determine the threshold sensitivity, time constant, and the absolute absorptivity of cooled radiation detectors. The main radiation flux is generated using a model of a blackbody whose temperature can vary in the range 10-300 K; the temperature of a shield used for generating the background radiation can vary in the range 4.2-70 K. The proposed chamber and thermal-control circuit are capable of maintaining an integral radiation density of 10 to the -11th - 2 x 10 to the -6th W/sq cm (in the detector plane) with an accuracy to within 1.5%.