Jolly Roger :
Bouncing back to the subject of the carbon atom you mentioned earlier, another possible way you might get ordinary garden variety C 12 to go unstable and break apart is by photo – fission (instead of being able to use neutrons like you can with certain isotopes of heavy atoms, carbon absorbs more neutrons than it emits, causing the chain reaction to wind down to a stop. Trying to fission carbon with neutrons is like trying to burn wet wood soaked with lots of water). With photo – fission, absorption of a highly energetic photon is used to excite atoms enough to destabilize them. However, this requires a highly energetic gamma ray, and I don’t know if you could ever get more energy out by the E = MC2 mass conversion…… than the amount of energy it takes to produce the high energy gamma ray necessary to break carbon apart.