the number at the lower left is the atomic number, or z number.
Uranium-238 is an isotope, which undergoes alpha decay to produce Thorium and gamma rays.
In order to write an equation for a nuclear reaction, we must first establish some basic rules.
Each of the elements involved in the reaction is identified by the chemical symbol. The number at the upper right is the mass number, also known as the A number.
Nuclear reactions can be described mathematically in much the same way as chemical reactions.
We commonly express these reactions by equations, although there is a unique difference in the nature of the reactions.