ra·di·o·ac·tiv·i·ty (r  d - - k-t v -t)n. 1. Spontaneous emission of radiation, either directly from unstable atomic nuclei or as a consequence of a nuclear reaction. 2. The radiation, including alpha particles, nucleons, electrons, and gamma rays, emitted by a radioactive substance. |
radioactivity
Noun
the spontaneous emission of radiation from atomic nuclei. The radiation can consist of alpha or beta particles, or gamma rays
| radioactivity (rd--k-tv-t) The emission of radiation by unstable atomic nuclei undergoing radioactive decay. A 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. |
radioactivity
the state, property, or process of being radioactive.
See also: RadiationThe spontaneous emission of radiation, generally alpha or beta particles, often accompanied by gamma rays, from the nuclei of an unstable isotope.
ThesaurusLegend: Synonyms Related Words Antonyms
| Noun | 1. | radioactivity - the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay corpuscular radiation, particulate radiation - a stream of atomic or subatomic particles that may be charged positively (e.g. alpha particles) or negatively (e.g. beta particles) or not at all (e.g. neutrons) emission - the release of electrons from parent atoms |
Translations
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