Problem No 9
Electron, initially at rest, is accelerated with a voltage , where is the electron's rest mass, – the elementary charge, – the speed of light, and – a dimensionless number. The electron hits a motionless positron and annihilates creating two photons. The direction of one emitted photon defines the direction of the other one. Find the smallest possible value of the angle between the directions of the two emitted photons (express it in terms of and provide a numrical value for ).