RE: intervals in usryield card?
2013 18:59:34 +0100 (CET)
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Dear Tristan,
sorry I was not clear enough, I'll try again:
The double differential flux that you get from fluka is independent on the
bin size. It is
neutrons/unit energy/unit(second quantity). If, for instance, the "second
quantity" is an angle, the units will be
neutrons/GeV/steradian.
Now, if the bin size is 2 GeV or 1 GeV, the "neutrons/GeV" will be the same.
Instead, if you wish to nknow how many neutrons are in a given interval
DeltaE,
you'll have to multiply the neutrons/GeV * DeltaE to obtain the
"neutrons". This will depend on the bin size, and it is what you got in
the plot you sent last time.
Ciao
Paola
> Dear Paola,
>
> Thanks for the reply and trying to explain, unfortunately I am still not
> clear
>
> You said 'the bigger the interval, more the neutrons.' and I agree that
> should be the case however my experience tells me it is not.
>
> If you look at two adjacent intervals of different sizes they have almost
> the same yield despite them being significantly different in size. See
> interval 7 and interval 8 from my tab_lis output file, interval 7 has a
> yield of 4073 and interval 8 has a yield of 4045 and yet interval 7 is
> almost four time bigger than interval 8.
>
> interval double differential
> size GeV yield
> 1 1.21E-06 3174.982
> 2 1.38E-06 3161.797
> 3 1.56E-06 3325.85
> 4 1.77E-06 3498.245
> 5 2.00E-06 3751.624
> 6 2.27E-06 3749.504
> 7 2.03E-06 4073.29
> 8 5.40E-07 4045.547
> 9 1.70E-06 4003.052
> 10 5.97E-07 4347.462
> 11 6.12E-07 4093.137
> 12 1.27E-06 4150.602
> 13 2.03E-06 4227.642
> 14 3.74E-06 4196.636
> 15 2.48E-06 4435.435
> 16 8.68E-07 4525.043
> 17 8.90E-07 4733.828
> 18 4.80E-06 4609.442
> 19 5.44E-06 4898.465
> 20 6.17E-06 5074.603
>
> Many Thanks for your help
>
> Tristan
>
>
> -----Original Message-----
> From: owner-fluka-discuss_at_mi.infn.it
> [mailto:owner-fluka-discuss_at_mi.infn.it] On Behalf Of Paola Sala
> Sent: 31 January 2013 07:26
> To: Davenne, Tristan (STFC,RAL,TECH)
> Cc: paola.sala_at_mi.infn.it; fluka-discuss_at_fluka.org
> Subject: RE: intervals in usryield card?
>
> 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
>
>
> --
> Scanned by iCritical.
>
>
Paola Sala
INFN Milano
tel. Milano +39-0250317374
tel. CERN +41-227679148
Received on Sat Feb 02 2013 - 20:13:16 CET
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