A 5 kg mass of 239Pu contains about 12.5 ×10 24 atoms. Īlpha decay, the release of a high-energy helium nucleus, is the most common form of radioactive decay for plutonium.
It has a low melting point (640 ☌) and an unusually high boiling point (3,228 ☌). Unlike most metals, it is not a good conductor of heat or electricity. This, the most common structural form of the element ( allotrope), is about as hard and brittle as gray cast iron unless it is alloyed with other metals to make it soft and ductile. At room temperature plutonium is in its α ( alpha) form. Plutonium, like most metals, has a bright silvery appearance at first, much like nickel, but it oxidizes very quickly to a dull gray, although yellow and olive green are also reported.
The Fat Man bombs used in the Trinity nuclear test in July 1945, and in the bombing of Nagasaki in August 1945, had plutonium cores. Producing plutonium in useful quantities for the first time was a major part of the Manhattan Project during World War II that developed the first atomic bombs. Plutonium isotopes are expensive and inconvenient to separate, so particular isotopes are usually manufactured in specialized reactors. It is a heat source in radioisotope thermoelectric generators, which are used to power some spacecraft. Plutonium-238 has a half-life of 87.7 years and emits alpha particles. The presence of plutonium-240 limits a plutonium sample's usability for weapons or its quality as reactor fuel, and the percentage of plutonium-240 determines its grade ( weapons-grade, fuel-grade, or reactor-grade). Plutonium-240 exhibits a high rate of spontaneous fission, raising the neutron flux of any sample containing it. Trace quantities arise in natural uranium-238 deposits when uranium-238 captures neutrons emitted by decay of other uranium-238 atoms.īoth plutonium-239 and plutonium-241 are fissile, meaning that they can sustain a nuclear chain reaction, leading to applications in nuclear weapons and nuclear reactors. Plutonium is the element with the highest atomic number to occur in nature. Wartime secrecy prevented the University of California team from publishing its discovery until 1948. Since uranium had been named after the planet Uranus and neptunium after the planet Neptune, element 94 was named after Pluto, which at the time was considered to be a planet as well. First, neptunium-238 ( half-life 2.1 days) was synthesized, which subsequently beta-decayed to form the new element with atomic number 94 and atomic weight 238 (half-life 88 years). Plutonium was first synthetically produced and isolated in late 1940 and early 1941, by a deuteron bombardment of uranium-238 in the 1.5-metre (60 in) cyclotron at the University of California, Berkeley. It is radioactive and can accumulate in bones, which makes the handling of plutonium dangerous. When exposed to moist air, it forms oxides and hydrides that can expand the sample up to 70% in volume, which in turn flake off as a powder that is pyrophoric. It reacts with carbon, halogens, nitrogen, silicon, and hydrogen. The element normally exhibits six allotropes and four oxidation states. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94.
0 kommentar(er)
