Equivalence of mass and energy
We have already referred on page 82 to Einstein’s theory of the equivalence of mass and energy. In 1905 he had shown that the relationship between mass and energy is given by the equation,
Apart from its importance as the first completely man-controlled splitting of the atom, Cockcroft and Walton’s experiment also provided the first piece of experimental evidence for the truth of Einstein’s equation.
When a nucleus disintegrates the sum of the masses of the fragments produced is always slightly less than the mass of the original nucleus. This loss in mass appears as energy of the fragments. Cockcroft and Walton calculated the total energy of the two flying helium particles and showed that it was related to the loss in mass when the lithium nucleus disintegrated, exactly in accordance with Einstein’s equation.