The Gamow Factor or Gamow-Sommerfeld Factor[1], named after its discoverer George Gamow, is a probability factor for two nuclear particles' chance of overcoming the Coulomb barrier in order to undergo nuclear reactions, for example in nuclear fusion. By classical physics, there is almost no possibility for protons to fuse by crossing each other's Coulomb barrier, but when George Gamow instead applied quantum mechanics to the problem, he found that there was a significant chance for the fusion due to tunneling.
This probability increases rapidly with increasing particle energy, but at a given temperature the probability of a particle having a high energy falls off rapidly, following the Maxwell-Boltzmann distribution. Gamow found that, taken together, these effects mean that for any given temperature, the particles that actually fuse are mostly in a (temperature-dependent) narrow range of energies known as the Gamow window.[2]