<prompt> Which of the following is the most penetration beam?Electron beam8 MV photons18 MV photonsProton beam  <response>: The order of penetration power is ? rays electrons a paicles. Here the 18MeV photon will have more energy than 8MeV photon. Ref: Essentials of Environmental Health, By Robe H. Friis, 2011, Page 191 