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ZingPath: Nuclear Physics

Radioactive Decay

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Nuclear Physics

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Lesson Focus

Radioactive Decay


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Students learn about the concept of radioactive decay, including alpha, beta and gamma radiation.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Explain the experiment documenting nuclear decay.
  • Explain the relationship between the neutron-proton ratio and radioactive stability.
  • Learn which type of decay is likely when the neutron-proton ratio is outside the band of stability.
  • Describe the different types of radioactive emissions and the resulting products of radioactive decay.

Everything You'll Have Covered

An element's atoms can have different numbers of neutrons, constituting different isotopes. Isotopes may be stable or unstable. Unstable radioisotopes undergo radioactive decay during which they expel particles and/or energy from the nucleus to achieve a more stable form. Radioactivity can be predicted by examining the isotope's neutron-proton ratio. If this ratio lies along the band of stability, the nucleus is stable and will not decay. If the ratio lies outside the band of stability, the unstable nucleus will undergo transmutation to a more stable form.

Several types of radioactive decay exist. Very large isotopes with more than 83 protons undergo alpha decay where the nucleus emits an alpha particle consisting of two protons and two neutrons. The alpha particle is actually a helium-4 nucleus. Alpha decay reduces the mass number of the radionuclide by four while decreasing the atomic number by two, bringing it closer to (or into) the band of stability.

A beta particle, an electron emitted from the nucleus, is released in beta decay. Beta decay changes a neutron to a proton, increasing the atomic number by one while the atomic mass remains unchanged. Beta decay can be found in isotopes that lie above the band of stability, those with too many neutrons in relation to protons; these tend to be "light" isotopes with relatively low atomic numbers. In contrast, positron emission occurs in isotopes lying below the band of stability. A positron, or positive electron, is released by the nucleus, changing a proton to a neutron. This decreases the atomic number by one but keeps the atomic mass the same. (Positron emission is actually classified as a form of beta decay.) Both alpha and beta decay are accompanied by gamma emission, the release of high-energy electromagnetic rays by the nucleus.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts Students should understand the structure of an atom and the meaning of an isotope.
Course Physics
Type of Tutorial Concept Development
Key Vocabulary alpha decay, atomic nuclei, atomic number