Hi Emilio,
you are estimating neutron yield which is n/p. Therefore the error on
neutron yield should be Sqrt[n/p] instead of Sqrt[n]/p.
This also explains why you observe, from the statistical experiment you
did, the difference by a factor of 3 ( ~ Sqrt(10^6/10^5) ).
Finally, it is perfectly normal for the neutron yield to fluctuate with
changing dimensions if one considers the parasitic absorption, given the
high neutron absorption cross section of tungsten.
Cheers,
Nikhil
On Sun, Oct 23, 2016 at 11:42 AM, <emilio_at_impcas.ac.cn> wrote:
> Dear FLUKA experts,
>
> I am simulating the neutron production from a cylindrical W target using a
> 400 MeV proton beam; using the loop function, I change the radius R and the
> length L of the cylinder, scoring the total neutron produced.
>
> At first, I tried with 10^5 proton; however I found some weird results
> (the neutron yield was decreasing and then increasing again changing L);
> for this reason I increased the primary particles up to 10^6, and the
> results were more consistent (you can find the imput cards in the attached
> files).
>
> My problem is that the difference between the two bunch of simulations
> seems too large to be explained with statistical fluctuation: in the file
> "Neutron Yield 400 MeV.pdf" you can find the neutron yield n/p with 10^5
> (solid curves) and 10^6 (dashed curves) protons; each color corresponds to
> a different radius. I also included the error bar due to the statistical
> fluctuation, calculated as Sqrt[n]/p, where n is the number of neutrons !
> scored, p is the number of proton. There are several points at 6 and more
> sigma's, which is not possible with 30 datapoints. In general it looks like
> the statistical fluctuations are roughly 3 times larger than what expected
> with Sqrt[n].
>
> Is it not correct to assume that the statistical error would be Sqrt[n]?
> Am I using some biasing that I am not aware of?
>
> Thank you for your help
> Emilio Ciuffoli
>
>
>
>
>
>
__________________________________________________________________________
You can manage unsubscription from this mailing list at
https://www.fluka.org/fluka.php?id=acc_info
Received on Mon Oct 24 2016 - 16:51:34 CEST