Experiments on nuclear orientation at very low temperatures I, Establishment of a method of nuclear alinement and its application to cobalt-60

Abstract

Abstract Experiments have been carried out which demonstrate the possibilities of the method of ‘magnetic hyperfine-structure alinement’ for the orientation of nuclei. Single crystals of composition (1% Co, 12% Cu, 87% Zn) Rb2(SO4)2, 6H2O were cooled by adiabatic demagnetization to 0·01°K. The crystals contained a small quantity of radioactive 60Co, which decays by β-emission followed by two γ-rays in cascade. The anisotropic distribution of the γ-rays from the oriented 60Co nuclei was measured by an array of Geiger counters around the cryostat. The largest anisotropy observed was 33%, and the change in this anisotropy as the crystals warmed up to 1°K was fitted to theoretical curves where the only unknown parameter was the magnetic moment of 60Co, for which a value of 3·5 ± 0·5 nuclear magnetons was deduced.