Element Plutonium, Pu

Plutonium had been discovered in 1940 by Edwin M. McMillan, Joseph W. Kennedy, and Arthur C. Wahl at the Berkeley Laboratory of the University of California by bombardment of uranium oxide U₃O₈ with deuterons highly accelerated in the 60-inch Berkeley cyclotron. Later was found out that this reaction yields a short-lived Neptunium-238 isotope which, in his turn, produces Plutonium-238 with 50 years half-life. One year later Joseph W. Kennedy, Glenn T. Seaborg, Emilio Segre and Arthur C. Wahl had synthesized more important isotope, Plutonium-239 via bombardment of uranium with deuterons highly accelerated in the cyclotron. Plutonium-239 is a product of Neptunium-238 fission. It emits alpha-radiation; its half-life period is 24,000 years. The pure substance was first isolated in 1942.

Plutonium isotopes with mass numbers from 232 to 246 are currently known. Traces of Plutonium-247 and Plutonium-255 are found in thermonuclear explosion dust. Alpha-radioactive Plutonium-244 is the most long-lived isotope with T_1/2= 80.8 million years. Half-life periods of all plutonium isotopes are much shorter than the Earth's age; the first plutonium with appeared at the origin of the Earth had been already completely decayed. However traces of Plutonium-239 constantly appear after beta-decay of Neptunium-239 which, in its turn, is yielded by uranium-neutron nuclear reaction (including space neutrons). That's why uranium ores contain traces of plutonium.

Plutonium is concentrated in sea organisms; the accumulation coefficient, which is ratio of concentrations in organism and in the environment, is 1000-9000 for seaweeds, approximately 2300 for mixed plankton, up to 380 for mollusks, 1000 for starfish, 5, 570, 200 and 1060 for fish muscles, bones, liver and stomach, respectively. Terrestrial plants receive plutonium mainly through root system accumulating it until 0.01% of the entire mass. In human organism it is found mostly in liver and skeleton bones where it is concentrated.