RE: intervals in usryield card?

From: Paola Sala <paola.sala_at_mi.infn.it>
Date: Thu, 31 Jan 2013 08:26:22 +0100 (CET)

Dear Tristan
The "result" is not "strange". It is not a result.
Let me try to explain: the double differential yield gives you a fluence
per unit energy interval. This means a fluence that is (correctly)
INDEPENDENT on the energy interval that you choose to observe. Indeed,
this distribution is smooth.
Then, you "integrate" it by multiplying this times an energy interval: of
course the product will depend on the size of the interval: imagine to
have a fluence that is flat over all the energy range, this product will
be proportional to the bin size. This is perfectly normal, since you are
calculationg how many neutrons have an energy ion a given interval: the
bigger the interval, more the neutrons.
NOW, if what you want is to integrate over many bins , for instance to
get the TOTAL fluence up to a given energy , you will ADD up the
fluence*deltaE in all bins, and this will be a smooth curve as a function
of the limit of integration
(I'm afraid that all this comes from the bad habit of histogramming
packages to plot bin contents instead of values normalized to unit
interval)
Hope this helps
Ciao

Paola

> Dear Paola, Thankyou for the prompt reply and useful advice, that makes
> more sense to me now.
>
>
>
> The group boundaries controls the bin sizes and this results in
> fluctuating bin sizes. However when I integrate my double differential
> yield by multiplying by the bin size to get the neutron current I find the
> result is very noisy and fluctuates in parallel with the fluctuation in
> bin sizes. This seems to be a strange result as I wouldn't expect these
> sort of fluctuations (see attached plot). I can see that I could ignore
> the fluctuations in bin size and smooth the data but would this be
> strictly correct?
>
>
>
> Kind Regards
>
>
>
> Tristan
>
>
>
>
>
> [cid:image001.jpg_at_01CDFEDA.A3A81640]
>
>
>
>
>
> -----Original Message-----
> From: Paola Sala [mailto:paola.sala_at_mi.infn.it]
> Sent: 30 January 2013 08:35
> To: Davenne, Tristan (STFC,RAL,TECH)
> Cc: fluka-discuss_at_fluka.org
> Subject: Re: intervals in usryield card?
>
>
>
> Dear Tristan,
>
> when scoring neutrons, the code always respects the energy group
> structure that is used for low energy neutron transport. In your case,
> the energy limits chosen in the usyield card correspond to neutron groups
> from 1 (20 MeV) to 155.
>
> The details are in the manual, in the notes for the USRBDX card:
>
>
>
> 6) When scoring neutron fluence or current, and the requested energy bin
> structure overlaps with that of the low energy neutron groups, bin
> boundaries are forced to coincide with group boundaries and no bin can be
> smaller than the corresponding group. Actually, the program uses the
> requested energy limits and number of bins to estimate the desired bin
> width. The number of bins above the upper limit of the first low-energy
> neutron group is recalculated according to such width. Note that the
> lowest energy limit of the last neutron group is 1.E-14 GeV (1.E-5 eV) for
> the 260 data set.
>
>
>
> I would like to add that, if you are interested in neutrons, it is better
> to include all the energy groups in the scoring, down to the lowest
> energy.
>
>
>
> Regards
>
> Paola
>
>
>
>
>
>> Hi, I have been trying to score neutrons emerging from a target using
>
>> a double differential yield on a usryield card. On the usryield card I
>
>> specify that I want x1 variable 1 to have 99 intervals in kinetic
>> energy.
>
>> However once I have ran and looked at the result I find that I have
>
>> 155 intervals or some other number that I did not specify in my usryield
>> card.
>
>> Also the intervals are not regular in size. I selected the linear
>
>> option and so I would have thought the intervals should be equal in
>> size!
>
>>
>
>> I attach the input file and would be very grateful for any help on
>
>> this matter.
>
>>
>
>> Many Thanks
>
>>
>
>> Tristan
>
>>
>
>> --
>
>> Scanned by iCritical.
>
>>
>
>>
>
>
>
>
>
> Paola Sala
>
> INFN Milano
>
> tel. Milano +39-0250317374
>
> tel. CERN +41-227679148
>
>
>
> --
> Scanned by iCritical.
>
>


Paola Sala
INFN Milano
tel. Milano +39-0250317374
tel. CERN +41-227679148
Received on Thu Jan 31 2013 - 09:47:34 CET