# Which one is more efficient in producing high energy gamma rays?

According to https://apps.dtic.mil/dtic/tr/fulltext/u2/a351472.pdf the big pulsed power accelerator, HERMES III, generate electron beam with peak energy at 22 MeV and average electron energy at 16 MeV and the resulting photon energy which is bremsstrahlung radiation is approximately 2 MeV (actually 1.9 MeV) while in this link http://eprints.gla.ac.uk/80139/ this ultra compact laser driven plasma wakefield accelerator can produce more than 109 photons per pulse with a mean energy of 10 MeV. Another link https://www.nature.com/articles/s42005-018-0095-3 said laser-solid interaction generate γ-ray that reaches 0.74 PW with the brilliance of 2 × 1024 s−1 mm−2 mrad−2 (0.1%BW)−1 at 58 MeV. So, generating gamma rays using lasers is more efficient?

• To compare efficiencies one has to compare in the same units. efficiency in what? number of photons? energy of beam? – anna v Oct 17 '20 at 4:52
• It is not a value that can be quantified into an efficiency. If you want high energy photons for your experiment you choose the method that gives high energy photons, I am trying to say that efficiency is not a useful concept in this case. One cannot tell from these publications which is better. See slac.stanford.edu/pubs/beamline/26/1/26-1-kim.pdf – anna v Oct 17 '20 at 6:22
• see here for the use of he word in physics en.wikipedia.org/wiki/Efficiency#In_physics – anna v Oct 17 '20 at 6:33
• He is talking about a different thing, One would have to compare a synchrotron source of the same energy gammas to the laser source. Then if there are more gammas attained with the laser source one could say that the laser source is more efiicient. Random sources cannot be compared using the word "efficient". – anna v Oct 17 '20 at 9:26
• Take this example: it is more efficient in" time" to go by car than the bus to the next city. It is not efficient in money spent , as the gas costs more than the bus ticket. You have to define your variable. That a particular laser source reaches an energy of 105 mev cannot be compared with a source that gives 1 MeV. – anna v Oct 17 '20 at 9:38