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

Photoatomic and photonuclear reactions

  1. Mar 23, 2013 #1
    Grettings to all,
    I'm interested to know which are the main interaction between:

    1.gamma-atom, also known like photoatomic reactions
    2.gamma-nuclei, photonuclear reactions. e.g photofission

    Thank you!
  2. jcsd
  3. Mar 23, 2013 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    The photo-atomic reaction implies a gamma-electron reaction. The two possibilities are 1) complete absorption of the gamma photon, photoelectric absorption, in which the electron obtains an energy equivalent to the energy of the gamma less the binding energy of the electron, and 2) scattering, generally known as Compton scattering, in which the gamma photon scatters off the electron with less energy (longer wave length) and the electron absorbs that energy and moves to a higher energy level or is ejected from the atom.

    With respect to the nucleus, there are two possibilities: 1) pair production, which has a threshold approximately equal to two electron rest masses (+ some recoil energy of the atom, which is very low because of the nuclear mass) and 2) photoneutron emission, which has a threshold equal to the binding energy of the 'last' neutron, which is just a way of saying the smallest binding energy level. In the case of a deuteron, an interaction with a gamma of sufficient energy (~2.226 MeV), causes photodissociation, and similarly for 9Be, a gamma of ~1.666 MeV causes photoemission of a neutron producing 8Be, which is unstable and which promptly dissociates into 2 alpha particles.
  4. Mar 23, 2013 #3
    Thank you very much for the answer good Astronuc.
    Can you tell me where i can find a short description of these phenomena e.g cross section for all nuclides.
    For a good understanding i need to write equation of reaction U238+gamma.
    Which is main of interaction process between gamma and U238?
  5. Mar 23, 2013 #4


    User Avatar
    Staff Emeritus
    Science Advisor

    The main interaction is energy dependent, but for gammas less than 1.0222 MeV, the main interactions would be Compton scattering and photoelectric absorption.

    Chapter 1 Radiation Sources, IV. Sources Of Electromagnetic Radiation, C. Photoneutron sources , p. 23

    Chapter 2 Radiation Interactions, III. Interaction of Gamma Rays, pp. 47-51

    From Glenn F. Knoll, Radiation Detection and Measurement, Fourth Edition, Wiley, 2010

    See also - http://www.bnl.gov/ncss/files/ppt/Gamma%20Ray%20Interactions_%20week%202%20Tuesday%20lecture.ppt [Broken]

    Cross-sections would be available from various laboratories or catalogs of radiation sources, or taken from MCNP code (Los Alamos National Lab), or

    IAEA - http://www-nds.iaea.org/photonuclear/
    Last edited by a moderator: May 6, 2017
  6. Mar 25, 2013 #5
    Thank a lot, these books are very useful.
    What formula might be applied to compute binding energy of 'last' neutron or binding energy level for nuclei shells?
    When take place reaction such as:(gamma,p), (gamma,He3), (gamma,2n), (gamma,alpha)
    Last edited: Mar 25, 2013
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook