Abstract
In volume 28 of this journal, a high-temperature X-ray powder camera was described which had been designed so that the cassette could be removed for development of the film without disturbing the temperature of the specimen. A modification of that design which permits taking powder photographs at low temperatures is given here. The modification consists essentially of replacing the electrically-heated furnace assembly by an insulated cooling chamber. The chamber proper is a copper capsule which is cooled by circulating a cold gas, such as nitrogen or helium, through a helical channel. The gas is cooled by leading it through a heat exchanger consisting of a copper coil immersed in liquid nitrogen, the desired temperature being achieved by regulating the rate of flow of the gas. The cooling capsule is insulated by a hollow cylinder of foamed plastic supported within a thin-walled nylon tube. This tube, and also the concentric cassette and shaft for rotating the specimen, fit neatly into machined concentric grooves in a nylon disk which replaces the machined metal disk of the high-temperature camera. The temperature of the specimen is monitored by a thermocouple inserted into the cooling capsule on a line coaxial with the rotation axis of the specimen.
