Plutonium By Sean Byrne

History The production of plutonium and neptunium by bombarding uranium-238 with neutrons was predicted in 1940 by two teams working independently. Plutonium was first produced and isolated on February 23, 1941 by deuteron bombardment of uranium in the 60-inch cyclotron at Berkeley. The discovery was kept secret due to the war. It was named after Pluto, having been discovered directly after neptunium.                             Glenn Seaborg

Chemical & Physical Properties General Name, Symbol, Number plutonium, Pu, 94 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery white                 Standard atomic weight (244)  g·mol−1 Electron configuration [Rn] 5f6 7s2 Electrons per shell 2, 8, 18, 32, 24, 8, 2 Physical properties Phase solid Density (near r.t.) 19.816  g·cm−3 Liquid density at m.p. 16.63  g·cm−3 Melting point 912.5 K (639.4 °C, 1182.9 °F) Boiling point 3505 K (3228 °C, 5842 °F) Heat of fusion 2.82  kJ·mol−1 Heat of vaporization 333.5  kJ·mol−1 Heat capacity (25 °C) 35.5  J·mol−1·K−1

General Information 244Pu is the nucleon-richest atom that naturally occurs in the Earth's crust. Plutonium has been called "the most complex metal" and "a physicist's dream but an engineer's nightmare"for its peculiar physical and chemical properties. It has six allotropes normally and a seventh under pressure, each of which have very similar energy levels but with significantly varying densities, making it very sensitive to changes in temperature, pressure, or chemistry, and allowing for dramatic volume changes following phase transitions The most significant isotope of plutonium is 239Pu .

General Information All 15 plutonium isotopes are radioactive, and most emit relatively weak alpha radiation which can be blocked even by a sheet of paper. The main isotopes of plutonium are: Pu-238, (half-life 88 years, alpha decay) Pu-239, fissile (half-life 24 000 years, alpha decay) Pu-240, fertile (half-life 6 560 years, alpha decay) Pu-241, fissile (half-life 14.3 years, beta decay) Pu-242, (half-life 376 000 years, alpha decay) Pluto was considered to be a planet at the time (though technically it should have been "plutium", Seaborg said that he did not think it sounded as good as "plutonium"). Seaborg chose the letters "Pu" as a joke, which passed without notice into the periodic table.

Uses By Man The isotope 239Pu is a key fissile component in nuclear weapons, due to its ease of fissioning and availability. The critical mass for an unreflected sphere of plutonium is 16 kg, but through the use of a neutron-reflecting tamper the pit of plutonium in a fission bomb is reduced to 10 kg. Complete detonation of plutonium will produce an explosion equivalent to the explosion of 20 kilotons of trinitrotoluene (TNT) per kilogram.                                              Hanford Site plutonium production reactors along the Columbia River during the Manhattan Project.

Uses By Man The isotope plutonium-238 (238Pu) has a half-life of 88 years and emits a large amount of thermal energy as it decays. These characteristics make it well suited for safe electrical power generation for devices which must function without direct maintenance for timescales approximating a human lifetime. It is therefore used in radioisotope thermoelectric generators such as those powering the Cassini and New Horizons (Pluto) space probes. 238Pu has been used successfully to power artificial heart pacemakers, to reduce the risk of repeated surgery. It has been largely replaced by lithium based primary cells, but as of 2003 there were somewhere between 50 and 100 plutonium-powered pacemakers still implanted and functioning in living patients.

Chemistry It displays five ionic oxidation states in aqueous solution: Pu(III), as Pu3+ (blue lavender) Pu(IV), as Pu4+ (yellow brown) Pu(V), as PuO2+ (thought to be pink; this ion is unstable in solution and will disproportionate into Pu4+ and PuO22+.) Pu(VI), as PuO22+ (pink orange) Pu(VII), as PuO52- (dark red); the heptavalent ion is rare and prepared only under extreme oxidizing conditions. Plutonium reacts readily with oxygen, forming PuO and PuO2, as well as intermediate oxides. It reacts with the halogens, giving rise to compounds such as PuX3 where X can be F, Cl, Br or I; PuF4 and PuF6 are also seen. The following oxyhalides are observed: PuOCl, PuOBr and PuOI. It will react with carbon to form PuC, nitrogen to form PuN and silicon to form PuSi2.

Compounds Plutonium reacts readily with oxygen, forming PuO and PuO2, as well as intermediate oxides. It reacts with the halogens, giving rise to compounds such as PuX3 where X can be F, Cl, Br or I. The following oxyhalides are observed: PuOCl, PuOBr and PuOI. It will react with carbon to form PuC, nitrogen to form PuN and silicon to form PuSi2. Plutonium like other actinides readily forms a dioxide plutonyl core (PuO2). In the environment, this plutonyl core readily complexes with carbonate as well as other oxygen moieties (OH-, NO2-, NO3-, and SO4-2) to form charged complexes which can be readily mobile with low affinities to soil. PuO2(CO3)1-2 PuO2(CO3)2-4 PuO2(CO3)3-6 PuO2 Plutonium also readily shifts valences between the +3, +4, +5 and +6 states. It is common for some fraction of plutonium in solution to exist in all of these states in equilibrium.