How does alpha decay change the nucleus of an atom?

1 Answer
Apr 15, 2016

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.



#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.