During radioactive decay, an unstable nucleus will emit alpha or beta particles. We can describe the changes by using nuclear equations. The format for a nuclear equation is:
Atom before decay ⮕ atom after decay + radiation emitted
In nuclear decay equations, the sum of the mass and atomic numbers should be the same before and after the reaction.
During alpha decay, the alpha particle is emitted from an unstable nucleus. Due to the +1 charge of each proton, the charge of the nucleus decreases by 2. Also, the atomic number decreases by 2 and the mass number decreases by 4.
The diagram below shows uranium undergoing alpha decay.
When uranium-238 undergoes alpha decay, it forms thorium-234. The nuclear equation is:
Beta decay affects the overall charge of the nucleus. During this process, a neutron in the nucleus transforms into a proton, and an electron (beta particle) is emitted. Since the proton number increases by 1, the positive charge of the nucleus increases. However, the mass number does not change.
As the atomic number changes, a completely different element is formed.
Below is an example of an equation for beta decay:
A beta particle is a high-speed electron, so it has no mass. This means that the mass number does not change. Since a neutron changes into a proton during beta decay, the atomic number of the atom increases by 1.