Alpha Decay

The nuclear disintegration process that emits alpha particles is called alpha decay. An example of a nucleus that undergoes alpha decay is uranium-238. The alpha decay of U-238 is

In this nuclear change, the uranium atom (²³⁸U₉₂) transmuted into an atom of thorium (Th90234) and, in the process, gave off an alpha particle. Look at the symbol for the alpha particle: He24. Where does an alpha particle get this symbol? The bottom number in a nuclear symbol is the number of protons. That means that the alpha particle has two protons in it which were lost by the uranium atom. The two protons also have a charge of +2

. The top number, 4, is the mass number or the total of the protons and neutrons in the particle. Because it has 2 protons, and a total of 4 protons and neutrons, alpha particles must also have two neutrons. Alpha particles always have this same composition: two protons and two neutrons. Another alpha particle producer is thorium-230.

These types of equations are called nuclear equations and are similar to the chemical equivalent discussed through the previous chapters.