Abstract
This paper describes an apparatus for cooling an iron foil containing a radioactive impurity to a temperature in the range of 0.012 to 0.026°K by thermal contact with an adiabatically demagnetized chromium potassium alum salt pill. The purpose of the demagnetization is to orient the nuclei of the radioactive impurity. A superconducting solenoid is used to produce the high magnetic field required to remove the entropy from the chrome alum. The apparatus uses two helium Dewars—a large one which contains the superconducting magnet and a small one which contains the salt pill, the 1°K helium bath, and the radioactive sample. The salt pill is formed by pressing a mixture of chrome alum and Octoil S around 5000 0.076-mm-diam copper wires. The salt is supported by a graphite cylinder and helium exchange gas is used to establish heat contact between the salt and the 1°K helium bath. In one form of the apparatus the chrome alum salt and the sample are surrounded by a copper can which is cooled to 0.1°K by contact with a manganese ammonium sulfate salt pill located in the fringe field of the superconducting magnet. With the chrome alum pill alone, the sample temperature is 0.019 to 0.026°K; with the guarded salt pill the sample temperature is 0.012 to 0.016°K.
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