Dear Zhiyuan,
There is no general number of particles, it depends on the problem under
consideration.
The number of cycles should be at least 5 because the statistical errors
are evaluated by Fluka when the results from different cycles are
combined, at the end of the runs: the variance is calculated from the
weighted variance among all different cycles from all runs of the same
input . This procedure has no meaning if the number of cycles is too small.
The driving quantity for statistics is the total number of events, the
product Nt = N * Nr *Ns
The random seed does not influence at all the statistical error.
This said, the actual value of the statistical error depends on how many
times a detector receives a signal.
No signal means no statistics even after an infinite number of primaries.
In your case, the 250 MeV proton beam stops a few centimeters before the
end of the target.
Products of proton nuclear interactions will stop before or slighly
after the proton range, within the target, except for neutrons.
Detectors placed downstream the target, will "see" only the few neutrons
and the even fewer charged hadrons produced by neutron reinteractions. I
doubt that you will ever be able to achieve some statistical
significance on charged hadrons, even using biasing.
Regards
Paola
On 6/9/21 5:33 AM, 梅志远 wrote:
>
> Dear experts,
>
> I recently ran a simulation by Fluka. Unfortunately, I found the
> statistical errors of the results (the concerned particles' flux
> scoring by the USRTRACK cards)were very big!
>
> I have tried many ways to reduce the errors. However, the drop of the
> errors are unapparent. I have some questions about the statistical
> errors of calculating results:
>
>
> 1) How many primary particles should I set in the START card to obtain
> a reasonable result? I have tried to set the primary particles equal
> to 1E8. However, the errors are still unacceptable.
>
>
> 2) If the number of primary particles in the START card is N, the
> number of cycles to run is Nr, and the number of spawned jobs is Ns, I
> found the number of 'total' primary particles in the result filesNt =
> N * Nr *Ns. So, what is the most crucial numbers influencing the
> statistical errors, N or Nt?
>
>
> 3) The Fluka manual says that the cycles of run should be 4 or 5 to
> obtain the statistical errors. If I run the FLUKA project by a
> spawning ways, the 'total' cycles of run should equal Nr * Ns. I
> really want to know how should I set the cycles of run to be 4 or 5.
> Should I directly set Nr = 4, or should I set Nr * Ns = 4? How dose
> the number of spawned jobs Nsaffect the statistical errors?
>
>
> 4)Do the random number seeds in RANDOMIZ cards affect the statistical
> errors of the results? Should I adopt different seeds in different
> cycles of run to obtain a more reasonable results? If I should, how
> can I implement it.
>
>
> I have attached my inp files here.
>
>
> Any help is appreciated!
>
>
> Best regards
>
> Zhiyuan
>
>
> --
>
> Zhiyuan Mei
> meizhiyuan_at_hust.edu.cn
>
> /---------------------------------------------------
> Institute of Applied Electromagnetic Engineering(IAEE)
> Huazhong University of Science and Technology(HUST)
> Address: Luoyu Road 1037, Wuhan, China
> Tel: +86-155-2701-7168
> /---------------------------------------------------
>
>
>
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Received on Wed Jun 16 2021 - 22:48:35 CEST