RE: Photoneutron Yield

From: Mario Santana Leitner (
Date: Thu Feb 01 2007 - 18:57:02 CET

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    I didn't fully understand your issue. Anyway, here is what I know about the angular distribution of photoneutrons.
    - If the neutrons come exclusively from evaporations then you should find an isotropic distribution.
    - Fast direct photohadrons are observed with a peak at 90\deg
    - Typically neutrons below 2.5 MeV should be almost isotropic.
    - For energies below about 50 MeV the dipolar absorption is the only direct mechanism and thus the angular spectrum is symmetric around 90\deg
    - For higher energies multipolar absorptions take place and the peak shifts towards a smaller angle, e.g. 60\deg
    - Some references:
      *) Gordon S. Mutchler. "The Angular Distributions and Energy Spectra of Photoneutrons from Heavy Elements." Requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology. February 1996.
      *) G. A. Price and D. W. Kerst. "Yields and Angular Distributions of some Gama-Neutron Processes." Physical Review 77(6), March 1950
      *) H.L. Poss. "Note on Angular Asymmetries in (gamma,n) Reactions." Health Physics 70 (1950)
      *) G.C. Reinhard and W.D. Whitehead. "Angular Distribution of Fast Photoneutrons." Nuclear Physics 30 pp 201-214 (1962).

    hope this helps


    -----Original Message-----
    From: on behalf of Sunil C.
    Sent: Wed 1/31/2007 6:36 AM
    Subject: Photoneutron Yield
    Hi All
    I am calculating photoneutrons from a thick target at angles from
    forward to backward, using a simple beam (energy 2.0 GeV)
    target setup.USERYIELD cards are used to score the double differential
    yields. I find that total neutron/sr/e (integrated over energy) peaks
    at 90 deg ad is symmetrical about it. I have not seen any literature
    depecting this behaviour. In Stevenson et al. NIM 216 1983 99-103, such an
    anisotropy is explained away by subtracting the background contribution.
    They have commented about an experiment where such behaviour is known to
    ocuur at low energies. The incident eenrgy was much higher compared to
    what I am doing now.

    I would like to know what the experts in this field think about it.


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