3.62 Gamma Decay
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. Ingamma 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:TheFigure3.112 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.
FIGURE 3.112
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.think
quest.org/3471/radiation_effects_body.html.
Summary
- 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.
Vocabulary
- gamma decay: Type of radioactive decay in which a nucleus emits energy in the form of gamma rays.