Making metallic berkelium

Metallic 249Bk, mass 740 μg, has been made as a film on a tantalum substrate by reducing the oxide with thorium. The evaporated-metal yield was 85%, while the yield on the substrate was 72%. The metal has a double hexagonal close-packed structure of α-La type, parameters a = (0.3412 ± 0.0002) nm, c = (1.1060 ± 0.0006) nm, c/2a = 1.621 ± 0.002. The metallic radius is 0.1702 ± 0.0001 nm, x-ray density 14.86 ± 0.03 g/cm3. The oxidation under various conditions has been examined