Mass-energy equivalence: E=mc2
This pair of scales would show that an alpha particle is lighter than the two neutrons and two protons that make it up. This ‘mass defect’ can be translated into an energy difference by multiplying by c2. The resultant energy is known as the binding energy: in the case of two protons and two neutrons, 28 million electronvolts. This substantial value of binding energy represents less than 1% of the internal energy (or mass) of the alpha particle.
Jean_Marc Faday (CNRS/Images-Média)