Re: Low energy - High energy neutron spectrum mismatch with USRTRACK

From: Anna Ferrari <>
Date: Thu, 26 Feb 2009 16:08:36 +0100 (CET)

 Hello Roy,

> I suspect I am making an obvious mistake somewhere.

 you are right. There is not a discontinuity in your high energy-low
 energy neutron spectra, simply you did not correctly read
 the output file: you have read the low-energy part in the inverse mode.

 The results of the high energy part are written starting with the lower
 energy bin (20 MeV, 24 MeV); the binning of the low energy part of
 the spectrum starts with the GROUP 1, that corresponds to the
 higher energy interval (19.6 MeV, 20 MeV).
 Your contents are: 1.105 10^-4 in the bin (19.6,20)
                     9.32 10^-5 in the bin (20,24)

 and you will find a continous behaviour.

 Just two suggestions more:
 1) in your .inp file you have set the USRTRACK card with: linear
    binning in (0, 0.2) GeV, 50 bins. For neutrons FLUKA will force
    the binning to fit with the 260 neutron groups (logaritmically
    binned) between the thermal region and 20 MeV; above 20 MeV
    you get 45 linear energy bins. If you want to better control
    your linear binning in the high energy part, you can use
    the USRTRACK in two steps, for the two energy ranges.

 2) you can also use a non-formatted output (using a negative number in
    what(3)) and then run the post-processing program ustsuw (see the manual
    for the details): in this way you will get - between other outputs -
    a file [output]_tab.lis, which shows in the first two columns the energy
    boundaries, in the third the corresponding bin content and in the last
    one the statistical error.



> Hello Fluka users,
> I am trying to measure the neutron fluence energy spectrum of
> annihilation neutrons produced by antiprotons incident on a copper
> target. I am using USRTRACK to score the neutrons, but when I calculate
> and plot the "low" and "high" energy parts of the spectrum together,
> there is a large mismatch in the spectrum at 20 MeV (see attached plot).
> I am using the 260 group low energy neutron transport library and am
> scoring up to 0.2 GeV. To obtain the fluence energy spectrum, I am
> multiplying each bin by its energy width in GeV.
> I am not sure if my 0.0564 cm thick target qualifies as "very thin" and
> would lead to the artifacts mentioned in section 10.1.1 of the Fluka
> manual.
> If anyone has any idea why I am seeing such a disjointed spectrum, I
> would greatly appreciate hearing back. I suspect I am making an obvious
> mistake somewhere.
> Thanks,
> Roy
Received on Thu Feb 26 2009 - 16:33:55 CET

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