If electrons is at light speed, how easy it is to gain a bit more speed and slow time. Since everything else is in motion, when the electron returns from such short trip in time, it well find itself free from the nucleus as everything have literally moved on. This is a Whacko Jump. A jump in time, resulting in ionization.
Why not then all other particles, protons do the same? Too Much Mass??
Hydrogen has an exposed nucleus, maybe its proton can be made to jump by shooting a high speed particle at it.
Mayby then we can begin to quantify such jumps and have a better understanding of how mass is involved in the process. Obviously, momentum and kinetic energy, where else does the mass term appears.