What Are Radioactive Isotopes?

Radioisotopes can be useful, but they are also often dangerous.
Radioisotopes can be useful, but they are also often dangerous. (Image: Jupiterimages/Creatas/Getty Images)

Radioactive isotopes, also called radioisotopes, are atoms with a different number of neutrons than is usual, making them unstable. A radioisotope's nucleus decays, emitting alpha, beta and gamma rays until the isotope reaches stability. Once it’s stable, the isotope may become another element entirely, such as when uranium decays into lead. The random nature of radioactivity means it’s impossible to know exactly when an individual atom will decay.

How Many?

At present, about 200 radioactive isotopes are used on a regular basis, and while some are long-lasting and easily obtained, others are very unstable and decay into other isotopes in a few hours or less.

How Are They Manufactured?

Radioactive isotopes can be manufactured in several ways; most commonly, by bombarding a substance with neutrons in a small nuclear reactor; an excess of neutrons makes the substance radioactive. Some isotopes are produced in a cyclotron in which protons are added to the atomic nucleus, resulting in an excess of protons; this also produces radioactivity.


Radioactive isotopes are useful because they produce alpha, beta and gamma rays. The radiation’s penetrating power depends on its energy, particle mass, and the object’s density. These properties lead to many practical applications in science, medicine and industry. The type and strength of radiation needed as well as an isotope’s lifetime determine its uses in various fields.

Medical Uses

Radioactive isotopes are powerful tools used to diagnose and treat a variety of illnesses. For example, chromium-51, which produces gamma rays, helps in classifying blood cells and measuring protein loss in the human body. Cobalt-60, a substance that gives off both gamma and beta radiation, is often used in cancer treatment. Oxygen-18 and technetium-99 are used as biological tracers, helping doctors find hidden tumors in various parts of the human body; as the diseased tissue absorbs the tracer substance, the telltale radiation marks the tumor’s location.

Uses in Archaeology and Industry

Scientists use radioactive isotope elements such as carbon-14, used to establish the age when a living organism died; lead-210, used to date ice and sediments under 150 years old, and potassium-40 to establish the age of rocks and minerals. Chlorine-36 helps measure the age of ground water up to about a million years. In industry, radioisotopes are used as fuel for nuclear power plants, in the manufacturing of smoke alarms, tracing factory waste that may cause pollution, and predicting the behavior of heavy metals in water. Sodium-24 and magnesium-27, for example, are used to locate leaks in water pipes, while iridium-192 is used in radiography devices.

Other Uses

Radioisotopes are used to study biological processes in plant life for agriculture, and to treat and preserve food, making it safer for consumption and prolonging its shelf life.

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