What are Radionuclides?
(sometimes called a radioisotope) is an atom
with an unstable nucleus
. An unstable nucleus means that the atom’s ratio of neutrons
is unbalanced, which gives it too much energy. To become more stable, the atom changes the number of neutrons or protons, or both. To make this change, the atom emits (gives off) energy in the form of radiation. This process of radiation emission that allows the atom to become stable is called radioactive decay.
Alpha particle leaving the nucleus due to radioactive decay. Credit: EPA.gov (click to enlarge)
How do radioactive decay and radiological half-life work together?
determines how long it takes for half of the atoms in a given mass to decay
into another form. Depending on the radionuclide, the half-life can range from fractions of a second to billions of years.
Radioactive decay will continue until the nucleus is balanced. The rate at which radioactive materials decay varies greatly among radionuclides. A highly radioactive substance (one that has a short half-life) decays more quickly than a less radioactive substance (one that has a longer half-life).
Examples of half-lives of certain radioactive elements:
- Carbon-14, which is used for dating fossils, has a half-life of 5,730 years.
- Plutonium-239 has a half-life of 24,000 years.
- Uranium-238, the most prevalent isotope in uranium ore, has a half life of about 4.5 billion years.
- Americium-241, which is used in smoke detectors, has a half-life of 432.7 years.
- Radon-222 has a half-life of 3.82 days.
Alpha, beta, and gamma rays are released during radioactive decay. Sometimes neutrons or positrons (a positive electron) are released. Protons from the nucleus of an atom are not released during typical radioactive decay. The U.S. Environmental Protection Agency (EPA) and other regulatory agencies generally limit radiation exposures from specific sources to the public to levels well under 100 millirem (mrem).
Hundreds of different radionuclides exist. Some of the more familiar ones are radon, uranium, and radium. The EPA website Commonly Encountered Radionuclides provides fact sheets on the 12 most commonly used radionuclides.
Related Information on this web site