Science / Periodic Table of Elements / Polonium (Po): Atomic number: 84, Atomic mass: (210) g.mol -1, Electronegativity: 2.0, Density: 9.51 g.cm-3 at 20°C, Melting point: 254 °C, Boiling point: 962 °C, Vanderwaals radius: 0.164 nm, Ionic radius: 0.102 nm (+4), Isotopes: 12, Electronic shell: [ Xe ] 4f14 5d10 6s2 6p4, Energy of first ionisation: 813.0 kJ.mol -1, Discovered by: Pierre and Marie Curie in 1898. Polonium is a radioactive, extremely rare semi-metal. It is reactive, silvery-gray, it dissolves in dilute acids, but it is only slightly soluble in alkalis. it is fairly volatile: about half of a sample of it will evaporate within 3 days (unless it is kept in a sealed container). Applications: Polonium was once used in textile mills (to eliminate static charges) and by the manufacturers of photographic plates (in brushes to remove the accumulated dust). It is used as a source of alfa-radiation for research and, alloyed with beryllium it can act as a portable source of neutrons, which normally only access to a nuclear reactor can provide. Polonium in the environment: Polonium is a very rare element in nature. it is found in uranium ores, but none extract it form these ores. Polonium is produced in about 100 g/year by bombarding bismuth with neutrons in a nuclear reactor.
Business / Finance / Principal-Only (PO): A mortgage-backed security (MBS) whose holder receives only principal cash flows on the underlying mortgage pool. All the principal distribution due from the underlying collateral pool is paid to the MORE