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Gamma Decay

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This stunning image is an artist’s rendition of a gamma ray burst. A gamma ray burst is a sudden, intense flash of gamma rays given off by an extremely energetic explosion. The bursts have been observed in distant galaxies. But gamma rays also occur on Earth.

What Are Gamma Rays?

Gamma rays are electromagnetic waves. Electromagnetic waves are waves of electric and magnetic energy that travel through space at the speed of light. The energy travels in tiny “packets” of energy, called photons. Photons of gamma energy are called gamma particles. Other electromagnetic waves include microwaves, light rays, and X rays. Gamma rays have the greatest amount of energy of all electromagnetic waves. You can learn more about gamma radiation at this URL: http://www.youtube.com/watch?v=okyynBaSOtA

Gamma Rays and Radioactive Decay

Gamma rays are produced when radioactive elements decay. Radioactive elements are elements with unstable nuclei. To become more stable, the nuclei undergo radioactive decay. In this process, the nuclei give off energy and may also emit charged particles of matter. Types of radioactive decay include alpha, beta, and gamma decay. In alpha and beta decay, both particles and energy are emitted. In gamma decay , only energy, in the form of gamma rays, is emitted.

Alpha and beta decay occur when a nucleus has too many protons or an unstable ratio of protons to neutrons. When the nucleus emits a particle, it gains or loses one or two protons, so the atom becomes a different element. Gamma decay, in contrast, occurs when a nucleus is in an excited state and has too much energy to be stable. This often happens after alpha or beta decay has occurred. Because only energy is emitted during gamma decay, the number of protons remains the same. Therefore, an atom does not become a different element during this type of decay.

Q: The Figure below shows how helium-3 (He-3) decays by emitting a gamma particle. How can you tell that the atom is still the same element after gamma decay occurs?

A: The nucleus of the atom has two protons (red) before the reaction occurs. After the nucleus emits the gamma particle, it still has two protons, so the atom is still the same element.

Diagram illustrating gamma decay

Dangers of Gamma Radiation

Gamma rays are the most dangerous type of radiation. They can travel farther and penetrate materials more deeply than can the charged particles emitted during alpha and beta decay. Gamma rays can be stopped only by several centimeters of lead or several meters of concrete. It’s no surprise that they can penetrate and damage cells deep inside the body. You can learn more about the effects of gamma radiation on people at this URL: http://library.thinkquest.org/3471/radiation_effects_body.html .


  • Gamma rays are electromagnetic waves that carry photons of energy called gamma particles. They are the most energetic of all electromagnetic waves.
  • Gamma rays are produced during gamma decay of an excited nucleus. During gamma decay, the nucleus emits a “packet” of energy called a gamma particle.
  • Gamma rays are more dangerous than the particles of matter emitted during alpha or beta decay.



Review gamma decay by reading the article at the following URL. As you read, make a list of main ideas in the article.


  1. What are gamma rays?
  2. What happens during gamma decay?
  3. Explain why gamma decay occurs.

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