Daughter Isotope Definition - Chemistry Glossary

What Is a Daughter Isotope?

Alpha decay schematic
In alpha decay, a parent nucleus decays into a daughter nucleus and an alpha particle.

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A daughter isotope is the product which remains after an original isotope has undergone radioactive decay. The original isotope is termed the parent isotope. A daughter isotope is also known as a daughter product, daughter nuclide, decay product, or radio-daughter.


For example, uranium-238 decays along what is called a decay chain:

238U → 234Th → 234mPa → ... → 206Pb

Uranium-238 is the parent isotope, while thorium-234, protactinium-234m, and lead-206 are all daughter isotopes.

Daughter Isotopes and Half-Life

The half-life of an isotope is used to predict the time half of a sample will decay into a daughter isotope, but it cannot predict when an individual atom will decay into a daughter product. However, the nature of the decay product(s) form is highly predictable.


  • Peh, W. C. G. (1996). "The Discovery of Radioactivity and Radium." Singapore Medical Journal. 37 (6): 627–630. 
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Helmenstine, Anne Marie, Ph.D. "Daughter Isotope Definition - Chemistry Glossary." ThoughtCo, Aug. 29, 2020, thoughtco.com/definition-of-daughter-isotope-in-chemistry-605861. Helmenstine, Anne Marie, Ph.D. (2020, August 29). Daughter Isotope Definition - Chemistry Glossary. Retrieved from https://www.thoughtco.com/definition-of-daughter-isotope-in-chemistry-605861 Helmenstine, Anne Marie, Ph.D. "Daughter Isotope Definition - Chemistry Glossary." ThoughtCo. https://www.thoughtco.com/definition-of-daughter-isotope-in-chemistry-605861 (accessed March 9, 2021).