Production and crystal growth of isotopic rare-earth metals

Abstract

Large single crystals of high-purity rare-earth metal isotopes 154Sm, 163Dy, and 170Er were obtained by grain growth during high-temperature annealing. Isotopic separation produced about 60 g each of the isotopes in metal oxide form. The isotopic enrichment was 99.5, 96.9, and 96.1% for the 154Sm, 163Dy, and 170Er, respectively. The metal was formed by high-temperature reduction and distillation. Collection efficiency was about 92%, and the total impurity content was <500 ppm by weight. The metal was cast into a button in a water-cooled copper mold using a high-purity, arc-melting facility. Melt losses were about 50 mg for 163Dy and 170Er and 200 mg for 154Sm. The buttons were sealed in argon-filled tantalum cans, heated by induction, and annealed for 96 h at 917, 1375, and 1450 °C for the Sm, Dy, and Er, respectively. Any metal lost from the button was recoverable from the tantalum can interior. The resultant specimens had five to eight single crystal grains. The largest, 163Dy, was about 2.5 × 2.5 × 0.5 cm. All buttons had one or two grains large enough for neutron diffraction experiments. The substructure misorientation was <0.3° as measured by neutron diffraction.