Answer:
He was able to prove that matter and energy are inter-convertible, and mass may be used to measure the total energy present in an object.
Step-by-step explanation:
He observed a mass defect in nuclear reaction products and the reactants. Thus, mass may be used to measure the total energy present in an object by the use of the equation;
E = m ×

Where: E is the energy, m is the mass and c is the constant speed of light.
He developed the use of nuclear reactions to generate heat energy, which has a great applications in atomic bombs.