How does the total mass before a nuclear reaction compare with the total mass after a nuclear reaction?

Atomically speaking, there is a small mass defect between the parent molecule and the one "achieved" after the reaction. This small amount lost is actually the energy converted and from the matter through the reaction and released as a by-product; when observed on the macro scale, this small amount of material lost results in the large atomic explosions and radioactive fallout that occurs following a nuclear detonation.