Understanding Energy-Mass Equivalence: Element Formation Explained

[GeneralOJB]

What defines what element results when energy is converted into matter? i.e. the protons/electrons/neutrons

 

[mathman]

When energy (high energy gamma rays) is converted to matter, the usual process is pair production (particle plus anti-particle). Which product depends primarily on the amount of energy involved. The lowest energy possible is to produce an electron-positron pair, which requires 1.022 Mev.

http://en.wikipedia.org/wiki/Pair_production