Half-Life and Reactions

Half-life

     The time required for half of the atoms in any given quantity of a radioactive isotope to decay is the half-life of that isotope. Each particular isotope has its own half-life. For example, the half-life of ²³⁸U is 4.5 billion years. That is, in 4.5 billion years, half of the ²³⁸U on Earth will have decayed into other elements. In another 4.5 billion years, half of the remaining ²³⁸U will have decayed. 

One fourth of the original material will remain on Earth after 9 billion years. The half-life of ¹⁴C is 5730 years, thus it is useful for dating archaeological material. Nuclear half-lives range from tiny fractions of a second to many, many times the age of the universe.

For more information on half-life and isotopes, please refer to the Isotopes Project at LBNL where you can also find the Table of Isotopes online.

Reactions

     If nuclei come close enough together, they can interact with one another through the strong nuclear force, and reactions between the nuclei can occur. As in chemical reactions, nuclear reactions can either be exothermic (i.e. release energy) or endothermic (i.e. require energy input). Two major classes of nuclear reactions are of importance: fusion and fission.

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