# How does alpha decay work?

Jul 29, 2016

Alpha decay is a process that some unstable nuclei use to become more stable.

#### Explanation:

During alpha decay, a nucleus emits a particle that consists of two protons and two neutrons — an alpha (α) particle, which is also a helium nucleus.

Since the atom loses two protons, it changes to a different element.

Its atomic number ($Z$) decreases by two units.

The atom loses two nucleons (protons and neutrons), so its mass number ($A$) decreases by four units.

For example, an atom of uranium-238 (with 92 protons) becomes an atom of thorium-234 (with 90 protons) when it undergoes alpha decay.

$\text{_92^238"U" →color(white)(l) _90^234"Th" +color(white)(l) _2^4"He}$