Alpha decay
The key idea
Alpha decay is a nuclear transformation in which an unstable nucleus emits an alpha particle, a helium-4 nucleus containing two protons and two neutrons.
Why it matters
The parent loses two units of atomic number and four units of mass number, giving a simple conservation check for nuclear equations.
A picture to remember
The parent loses two units of atomic number and four units of mass number, giving a simple conservation check for nuclear equations.