RADIOACTIVITY - The decomposition process of unstable atomic nuclei to form nuclei with higher stability is called radioactivity. The energy and particles which are released during the decomposition process are called radiation. When unstable nuclei decompose in nature, the process is referred to as natural radioactivity. When the unstable nuclei are prepared in the laboratory, the decomposition is called induced radioactivity.

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Radioactivity

What Is Radioactivity? What is Radiation?

Quick Review of Radioactivity

by Anne Marie Helmenstine, Ph.D. 

Unstable atomic nuclei will spontaneously decompose to form nuclei with higher stability. The decomposition process is called radioactivity.

The energy and particles which are released during the decomposition process are called radiation.

When unstable nuclei decompose in nature, the process is referred to as natural radioactivity.

When the unstable nuclei are prepared in the laboratory, the decomposition is called induced radioactivity.

There are three major types of natural radioactivity:

Alpha Radiation

Alpha radiation consists of a stream of positively charged particles, called alpha particles, which have an atomic mass of 4 and a charge of +2 (a helium nucleus).

When an alpha particle is ejected from a nucleus, the mass number of the nucleus decreases by four units and the atomic number decreases by two units.

For example:

²³⁸₉₂U → ⁴₂He + ²³⁴₉₀^Th

The helium nucleus is the alpha particle.

Beta Radiation

Beta radiation is a stream of electrons, called beta particles.

When a beta particle is ejected, a neutron in the nucleus is converted to a proton, so the mass number of the nucleus is unchanged, but the atomic number increases by one unit.

For example:

²³⁴₉₀ → ⁰_-1e + ²³⁴₉₁Pa

The electron is the beta particle.

Gamma Radiation

Gamma rays are high-energy photons with a very short wavelength (0.0005 to 0.1 nm). The emission of gamma radiation results from an energy change within the atomic nucleus.

Gamma emission changes neither the atomic number nor the atomic mass. Alpha and beta emission are often accompanied by gamma emission, as an excited nucleus drops to a lower and more stable energy state.

Alpha, beta, and gamma radiation also accompany induced radioactivity. 

Radioactive isotopes are prepared in the lab using bombardment reactions to convert a stable nucleus into one which is radioactive.

Positron (a particle with the same mass as an electron, but a charge of +1 instead of -1) emission isn't observed in natural radioactivity, but it is a common mode of decay in induced radioactivity.

Bombardment reactions can be used to produce very heavy elements, including many which don't occur in nature.

Anne Marie Helmenstine, Ph.D.

Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

ThoughtCo and About Education chemistry expert since 2001.

Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

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https://www.thoughtco.com/what-is-radioactivity-604312