6 Jun
2015
6 Jun
'15
10:24 a.m.
Correcting my mistake: I said "The quoted formula, once the dimensions are corrected, gives E > mc^2. Spontaneous pair creation requires E < -2 mc^2." In this context, spontaneous pair creation only requires E < 0, provided that rest energy is included in E. I was confusing this with a different situation. If a nucleus is sufficiently charged that the binding energy of an electron in its lowest level exceeds 2 mc^2, then it is energetically favorable to create a pair, keep the electron, and eject the positron. This requires Z = 137 for a point nucleus, Z = 170 for a real nucleus. Positron production in collisions of heavy nuclei has been observed. -- Gene