 In the bombardment of Lithium reaction above, the sum of the rest-masses of the reactants (the proton and the \({^7}\Li\) nucleus) is greater than the sum of the rest-masses of the products (the two \(\alpha\)-particles). However, the total kinetic energy of the reactants is less than the total kinetic energy of the products. Cockcroft and Walton’s experiment is routinely interpreted as demonstrating that the difference in the rest-masses of the products and reactants (times \(c^2)\) is equal to the difference in the kinetic energies of the products and reactants (but see  Section 4  for further discussion of this experiment as a confirmation of mass-energy equivalence).