In radioactive decay, what is the typical trend of parent and daughter isotopes over time?

• A. The amount of parent decreases while the amount of daughter increases
• B. Both remain fixed
• C. The amount of daughter decreases while parent increases
• D. The sum remains constant with no change

Answer: (A)

In radioactive decay, unstable nuclei transform into a more stable form. As this happens, the number of parent nuclei decreases because each decay takes one away, and the number of daughter nuclei increases because that decay produces one daughter. In the common simple case where the daughter is stable, the parent count drops over time while the daughter count rises, so the composition shifts from mostly parent to mostly daughter. The total number of atoms in the system (parent plus daughter) stays the same in a closed system, since a decay just repackages an atom as a different nucleus. This is why the typical trend is a decreasing parent and an increasing daughter.