radioactivity

American  

[rey-dee-oh-ak-tiv-i-tee] / ˌreɪ di oʊ ækˈtɪv ɪ ti /

noun

Physics, Chemistry.

1. the phenomenon, exhibited by and being a property of certain elements, of spontaneously emitting radiation resulting from changes in the nuclei of atoms of the element.

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radioactivity British  

/ ˌreɪdɪəʊækˈtɪvɪtɪ /

noun

1. the spontaneous emission of radiation from atomic nuclei. The radiation can consist of alpha, beta, and gamma radiation

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radioactivity Scientific  

/ rā′dē-ō-ăk-tĭv′ĭ-tē /

1. The emission of radiation by unstable atomic nuclei undergoing radioactive decay.

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radioactivity Cultural  

1. The emission of elementary particles by some atoms when their unstable nuclei disintegrate (see half-life). Materials composed of such atoms are radioactive. (See alpha radiation, beta radiation, and gamma radiation.)

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Closer Look

In the nuclei of stable atoms, such as those of lead, the force binding the protons and neutrons to each other individually is great enough to hold together each nucleus as a whole. In other atoms, especially heavy ones such as those of uranium, this energy is insufficient, and the nuclei are unstable. An unstable nucleus spontaneously emits particles and energy in a process known as radioactive decay. The term radioactivity refers to the particles emitted. When enough particles and energy have been emitted to create a new, stable nucleus (often the nucleus of an entirely different element), radioactivity ceases. Uranium 238, a very unstable element, goes through 18 stages of decay before becoming a stable isotope of lead, lead 206. Some of the intermediate stages include the heavier elements thorium, radium, radon, and polonium. All known elements with atomic numbers greater than 83 (bismuth) are radioactive, and many isotopes of elements with lower atomic numbers are also radioactive. When the nuclei of isotopes that are not naturally radioactive are bombarded with high-energy particles, the result is artificial radioisotopes that decay in the same manner as natural isotopes. Each element remains radioactive for a characteristic length of time, ranging from mere microseconds to billions of years. An element's rate of decay is called its half-life. This refers to the average length of time it takes for half of its nuclei to decay.

Etymology

Origin of radioactivity

First recorded in 1895–1900; radio- + activity

Explanation

The emission of energy in a stream of particles or waves is radioactivity. While radioactivity can be useful in science and medicine, exposure to high doses of it is dangerous. Archaeologists can learn the age of certain fossils by measuring their radioactivity — or more specifically, the amount of radioactive carbon they contain. Radioactivity is what creates nuclear power, and doctors also use it in radiation therapy, to kill cancer cells. Too much radioactivity is bad for our bodies, though, since it can damage our DNA. The word comes from radioactivité, which was coined by Marie and Pierre Curie in 1898.

Example Sentences

That process releases huge amounts of energy, no carbon emissions and limited radioactivity.

From The Wall Street Journal • Dec. 18, 2025

The Burevestnik’s radioactivity could make it easy to detect.

From The Wall Street Journal • Oct. 28, 2025

The camera will then pick up the radioactivity in such a way that doctors can see how, for example, a cancer has spread.

From BBC • Feb. 26, 2025

The Cabrera Services report noted the radioactivity at the Albany Bulb is consistent with other landfills that accept construction debris, which may contain naturally radioactive material, such as granite.

From Los Angeles Times • Dec. 2, 2024

Alvarez seconded Nahmias’s perception that the cyclotron was used “as a radioactivity factory first of all because great numbers of new radioisotopes could be discovered that way with very little effort.”

From "Big Science" by Michael Hiltzik

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