Segregation of Polonium in Bismuth Crystals

Single crystals of bismuth containing polonium as an impurity are studied in order to determine the distribution of the polonium. Number-distance relations for α-particles emitted normally through cleavage surfaces afford the means of investigation, measurements being made with a Geiger counter. When present in very small concentrations polonium is found to be segregated into small regions which have nearly regular spacings when viewed in several directions. These average spacings, (0.54±0.03)μ for planes parallel to the (111) plane and (0.90±0.1)μ for planes parallel to the (111̄) plane, are unaffected by the speed of growth of the bismuth crystal and by subsequent heat treatment. The addition of tellurium suppresses alternate layers parallel to the (111) plane and removes all evidence of layers parallel to the (111̄) plane.