An Overview about the Chemical Element Plutonium


Symbol: Pu

Atomic Number: 94

Atomic Mass: 244.0 amu (atomic mass units)

Melting Point: 639.5 C (912.65 K, 1183.1 F)

Boiling Point: 3235.0 C (3508.15 K, 5855.0 F)

Number of Protons: 94

Number of Electrons: 94

Number of Neutrons: 150

Classification: Rare Earth (Man Made)

Crystal Structure: Monoclinic

Density @ 293 K: 19.84 grams per cubic centimeter

Color: Silver

Plutonium was discovered in 1941 but, owing to wartime security measures in place at the time, the announcement of its discovery was delayed until 1946. It is a man-made or transuranium element of the actinide or actinoid series of rare earth elements. The element is named after the dwarf planet Pluto.

The American team of scientists responsible for the discovery of plutonium consisted of Glenn T. Seaborg, Joseph W. Kennedy, Edward M. McMillan and Arthur C. Wohl. Using a cyclotron, based at the University of California, they accelerated deuterons which they then fired at a target of uranium-238. The initial product of this collision was the first ever transuranium element to be made, neptunium-238. Neptunium-238 has a half-life of 2.1 days and decays by beta decay to form an isotope of the second transuranium element to be discovered, plutonium-238. This isotope has a half-life of 87.7 years and decays by alpha decay to form uranium-234. Plutonium-238 can also decay by spontaneous fission.

Since the original discovery of plutonium-238 several other isotopes have been formed with mass numbers that range from 228 to 247. All of the isotopes of plutonium are unstable. The most stable isotope formed to date is plutonium-244 with a half-life of 82,000,000 years. Plutonium-244 decays either by alpha decay to form uranium-240 or by spontaneous fission.

No natural source of plutonium has ever been found. All plutonium used in either industry or scientific research must be made by man.

Plutonium-239 will undergo a chain fission reaction when enough of the isotope is concentrated. One kilogram, if detonated completely, can produce an explosion which is equivalent to 20000 tons of conventional chemical explosive. A kilogram can also yield approximately 22 million kilowatt hours of heat energy. The energy potential of plutonium-239 has led to its use in nuclear weapons and in some nuclear reactors.

Another isotope, plutonium-238, has been used in thermoelectric generators which power long range space probes. The Cassini and Galileo probes both used plutonium-238 as a power source.

The Apollo moon landing missions used plutonium-233 to power equipment used on the lunar surface.

The long half-lives of many of its isotopes along with the amount of dangerous radiation it can produce have made plutonium contamination a serious environmental concern.