Question

How does alpha decay change the nucleus of an atom?

Answer 1

Alpha decay means giving off an alpha particle, which has two protons and two neutrons. So the atomic number drops by two and the mass number drops by 4.

Explanation:

Example:

`U^{238}` -> `Th^{234}+He^{4}`

Uranium has an atomic number of 92, thotium an atomic number of 90, and we see the decrease by 4 in mass number. `He^{4}` is the alpha patticle, which is also a helium-4 nucleus.