Re: Kinks in neutron momentum distribution

From: Joseph Comfort (
Date: Thu Apr 05 2007 - 02:49:25 CEST

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    Dear Giuseppe,

    Thank you for the suggestions about the kinks in my neutron spectum. To
    remind you, I am looking at neutrons produced by a 30-GeV beam on a Ni
    target, about 5 cm thick.

    I reanalyzed the data in terms of neutron kinetic energy, and
    specifically applied the binning of the 72 neutron groups, up to 19.6
    MeV. Above that energy, I used bins that are 20-MeV wide, cut off at
    about 6 GeV. All of the bins were put into a single array for plotting.

    The attached figure shows the results. The upper portion shows the raw
    yields per bin vs. bin #. The first 72 bins are the neutrons below 19.6
    MeV. For the lower fignure, I rescaled the number of events in each bin
    so as to reflect bins of equal width (20 MeV). Then I multiplied those
    numbers by the mean kinetic energy of the bin. I think this is close to
    your 'lethargy' quantity. There is a kink at bin 72 (19.6 MeV), and a
    second one near bin 90 (about 400 MeV). The yields between these bins
    are well above the neighbors, and have an unexpected distribution.

    I want to be able to parameterize an algorithm for generating the
    spectrum, and the kinks will make that difficult. Should I just lop off
    the extra neutrons between 20-400 MeV, and fit a smooth distribution?

    Best regards,

    Joseph Comfort                      Phone: (480)-965-6377
    Department of Physics & Astronomy   Dept.: (480)-965-3561
    Arizona State University            Fax:   (480)-965-7954
    Tempe, AZ  85287-1504               Email:

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