2013 17:31:40 +0100 (CET)
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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.
Received on Fri Feb 01 2013 - 18:21:15 CET