The nuclear refrigeration of copper

Nuclear refrigeration experiments have been performed on samples containing 0.93 g-atom of copper. After demagnetization to a field of 800 G from initial conditions of 25 kG and 16 mK, lattice temperatures of less than 1 mK were reached. The temperature of the copper nuclei was measured with a pulsed nuclear magnetic resonance thermometer. The lattice temperature was then calculated from this value and the experimentally determined heat leak of 0.10±0.02 erg/sec. An attempt to measure the lattice temperature directly by observing the anisotropy in the angular distribution of the rays emitted by 1 µCi of ⁵⁴ MnZN was not successful. A number of solutions of the differential equations describing nuclear refrigeration have been obtained and were used to simulate experiments with various heat leaks and final magnetic fields. Calculations have also been fitted to the experimental results wherever possible.