Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Are gamma rays produced in fusion reactions?

  1. May 13, 2010 #1
    Lots of articles and papers I read talk about the gamma rays produced during fusion reactions. And yet, when I look at equations for fuel cycles, the sum of the energies of the fusion products equals the total energy liberated.

    Since this implies that all of the energy released in the fusion reaction is in the form of kinetic energy carried by the reaction products, where do gamma rays fit in? Are they produced afterward, as syncrotron or bremsstrahlung radiation?

    Either way, does anyone know how much energy is carried as gamma rays for various fuel cycles, or can point me to a website that does? I'm especially interested in the 3He-3He cycle.

  2. jcsd
  3. May 13, 2010 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    Gamma emission occurs in the reaction: p + d -> He3 + γ


    The distinction between gamma rays and X-rays is somewhat arbitrary, since a 100 keV gamma is the same as a 100 keV X-ray. The distinction is related to the origin. X-rays are generally defined at those photons originating from atomic reactions, i.e. transitions from atomic electrons, with photon energies above ultraviolet. Brehmstrahlung (braking radiation) originates from free electrons accelerating in a nuclear electric field. Synchrotron radiation is probably distinguished from gamma radiation since it is usually originating from an accelerated proton or light nucleus.

    Gamma emission occurs in the (p,γ) reactions of the CNO cycle.
  4. May 14, 2010 #3
    So what you're saying is, aside from a few reactions, and discounting synchrotron and braking radiation, the equations are right and the energy generally is carried as kinetic energy?

    The sources I read must have been referring to bremsstrahlung x-rays. That explains why I wasn't able to find any better data on these fusion gamma rays.

    This actually makes it easier for me, since I'm self-teaching myself nuclear
    physics, and this is one less channel to keep in mind.
    Last edited: May 14, 2010
  5. May 14, 2010 #4


    User Avatar
    Staff Emeritus
    Science Advisor

    In the fusion of light elements, the reactions involve a restructuring the nuclei, and in general the resulting energy is 'carried as kinetic energy'.

    Usually a confined plasma implies a magnetic field (as opposed to inertial confinement), and the motion of electrons about the field lines produces 'cyclotron radiation'.



    Brehmsstrahlung radiation is also possible and occurs when free electrons are accelerated by nuclear charges (protons and nuclei).

    FYI - http://casa.colorado.edu/~wcash/APS3730/notes.htm

    Gamma rays are more likely when fusion involves nuclei heavier than B, e.g., C, N, O. Of course, if free neutrons are present, they can be absorbed in (n, γ) reactions.
    Last edited: May 14, 2010
  6. May 14, 2010 #5


    User Avatar
    Science Advisor

    I think it's not so difficult to calculate the energy fraction that is carried away by a gamma ray photon. If one takes the mean energy of p and d in the sun (based on the temperature) and uses the masses of p, d and He3 one can calculate the energy of the gamma ray photon.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Are gamma rays produced in fusion reactions?
  1. Fusion reaction (Replies: 6)