What matter in the original atom bomb is converted to energy?

13 January 2008

Part of the show Naked Science Q&A Show

Question

If e=mc^2 and when an atom bomb goes off some matter is converted to energy I’d like to know exactly what matter in the original atom bomb is converted to energy. Is it protons, neutrons, electrons? Is it a collection of atoms? What goes?

Answer

If you take a proton or something and make it go really, really fast - give it lots of kinetic energy then relativity says it gets heavier. In the same way if you've got lots of potential energy if you put it into a really big heavy atom like uranium then it will also get heavier. When you split up that big atom you get less potential energy and that means that the resultants (all of the protons and all of the neutrons inside) are lighter than they were before because they have less potential energy. So there are actually the same number of constituents, but the sum total weight is decreased.