An electron and a positron (antielectron), both nearly at rest, collide. What particle(s) is(are) produced?
A) One photon of energy 1.02 MeV
B) Two photons of energy 511 keV
C) A pi-meson
D) A K-meson and an anti-neutrino

Question

Quizplus · Accepted Answer

When an electron and a positron collide, they can annihilate each other and produce two gamma rays (photons) of energy 511 keV each. This is because the mass of the electron and the mass of the positron each have an energy equivalent of 511 keV due to Einstein's famous equation E=mc^2. Option A is incorrect as the energy of the produced photon should be 1.02 MeV=2*511 keV instead of 1.02 MeV. Option C and D are incorrect as they involve the production of mesons, which requires much higher energies than what the interaction of an electron-positron at rest can provide.

An Electron and a Positron (Antielectron), Both Nearly at Rest