Understanding the Half Life of Plutonium

Plutonium is a radioactive element discovered in 1940 by Seaborg, McMillan, Kenned, and Wahl when they bombarded uranium with deuteron atoms using the 60-inch cyclotron at Berkeley, California. It is a transuranic element with the atomic number 94.

For all industrial processes plutonium is considered a man-made element. However, plutonium occurs in very small amounts within pitchblende, the ore used to supply uranium. By small amount this is very small amount in that according to the European Nuclear Society pitchblende contains one Plutonium-239 atom per 1 trillion or more uranium atoms in pitchblende.

Radioactive elements decay by the loss of particles or energy. The Health Physics Society states that the types of radioactive decay are:

* alpha – loss of a particle similar to a helium atom

* beta – loss of a particle similar to an electron

* gamma – loss of energy – gamma rays

The effect of radioactive decay is the transformation of one element to another.  The rate of this transformation can be measured as the half-life of the element. A half-life of 10 years means that after 10 years half of the original amount of the element has been transformed to the new element. Therefore 10 grams of element A will form 5 grams of element B in ten years. The remaining 5 grams of element A will yield 2.5 grams of B in the next ten years and a further 1.25 after the next ten years.

Plutonium-239 is one of a number of isotopes of the element. All isotopes contain the same number of electrons and protons but different numbers of neutrons. While all isotopes normally have similar chemical properties they differ markedly in their half-lives. The Jefferson Lab Science Education site lists the half-lives of plutonium isotopes by alpha decay ranging from plutonium-229 at around 2 microseconds to plutonium-244 at 80,000,000 years

Most isotopes of plutonium decay by alpha decay although some if the exceed critical mass may be subject to nuclear fission, which may results in a large spontaneous release of energy. This type of energy release may be harnessed in nuclear reactors or used in nuclear devices. From the Institute of Energy and Environmental Research both plutonium-239 and plutonium-241 are fissile materials. and can be split by both slow (ideally zero-energy) or fast neutrons to form two new nuclei releasing energy and more neutrons It is this type of reaction that allows the chain reaction used in nuclear reactors.