RE: Low energy - High energy neutron spectrum

 Dear all,

Without claiming to be an expert, I usually plot neutron fluence spectra
in dependence of energy as dPhi/dln(E) = E*dPhi/dE (isolethargy plot).
In such a plot, the energy axis is logarithmic and the abscissa linear.

Best regards,
Thomas

Thomas OTTO
Head, Dosimetry Service
Radiation Protection Accelerators Meyrin
Radiation Protection Services

DG-SC
CERN
1211 Geneve 23
Switzerland
-----Original Message-----
From: owner-fluka-discuss_at_mi.infn.it =
[mailto:owner-fluka-discuss_at_mi.infn.it] On Behalf Of Anna Ferrari
Sent: jeudi, 26. f=E9vrier 2009 22:41
To: Roy Keyes
Cc: fluka-discuss_at_fluka.org; fasso_at_slac.stanford.edu
Subject: Re: Low energy - High energy neutron spectrum mismatch with =
USRTRACK

 Hi Roy,
  ok, it looks fine now!
   I send you the differential fluence distribution, that I found
   running with your input file (with minor changes), because you
   can see there all the low-energy part of the spectrum...
   it seems to me, in fact, that you cut above the secondary neutron =
peak,
   that is around 1 MeV... but maybe this is exactly what you want to =
do!

   cheers,

    Anna

> Thank you Anna and Alberto,
>
> It looks like my problem was that I was multiplying the values that=20
> Fluka gave me by the bin width (as described in the USRTRACK section=20
> of the manual...). I was in fact reading the low energy values in the =

> correct order already.
>
> At the high/low boundary, the values, when multiplied by their bin=20
> energy widths are:
>
> Low energy: 1.1050E-04 * 3.596700E-04 =3D 3.9743535e-08
>
> High energy: 9.3207E-05 * 4.0000E-03 =3D 3.728280e-07
>
> which gave me the order of magnitude mismatch.
>
> I've attached a semilog plot, which has the data plotted as Alberto=20
> suggested, and it looks much better. Now I can address my other=20
> issues :)
>
> Thanks again,
> Roy
>
>
> Anna Ferrari wrote:
>> 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=20
>> lower energy bin (20 MeV, 24 MeV); the binning of the low energy=20
>> part of the spectrum starts with the GROUP 1, that corresponds to=20
>> 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.
>>
>> cheers,
>>
>> Anna
>>
>>
>>> Hello Fluka users,
>>>
>>> I am trying to measure the neutron fluence energy spectrum of=20
>>> annihilation neutrons produced by antiprotons incident on a copper=20
>>> target. I am using USRTRACK to score the neutrons, but when I=20
>>> 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=20
>>> 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=20
>>> multiplying each bin by its energy width in GeV.
>>>
>>> I am not sure if my 0.0564 cm thick target qualifies as "very thin"=20
>>> and would lead to the artifacts mentioned in section 10.1.1 of the=20
>>> 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=20
>>> obvious mistake somewhere.
>>>
>>> Thanks,
>>> Roy
>>>
>>
>
Received on Fri Feb 27 2009 - 13:59:04 CET