# Re: [fluka-discuss]: Asymmetrical results and high error percentage

From: <alfredo.ferrari_at_mi.infn.it>
Date: Sun, 1 May 2022 18:21:44 +0200

Dear Jyoti

the bins where you see high results with large statistical errors are
those that on you x-y plane are exactly below the annular air regions
gapxx.

Therefore it is not surprising you see a much larger radiation leakage in
correspondence with those air gaps.

Furthermore the results are symmetric within the large statistical errors,
for example the first two cases in your pdf file have a combined
statistical error of ~40% which means they are uncertain by a factor 2 or
larger, indeed they differ well within that range.

At a very superficial examination, your problem is dominated by
"channeled" leakage through those annular air gaps.

Best regards
Alfredo

> Dear FLUKA Experts,
>
> In the attached input file, I want to score Dose-Eq. at z=56 (top surface)
> of the geometry. I used four USRBIN cards:
>
> x-y-z, z= 56 to 57, y = -0.5 to 0.5, x = -59.5 to 59.5 (119 bins), Volume
> of one bin: 1cc
> x-y-z, z= 56 to 58, y = -1 to 1, x = -59 to 59 (59 bins), Volume of one
> bin: 8cc
> x-y-z, z= 56 to 57, x = -0.5 to 0.5,y = -59.5 to 59.5 (119 bins), Volume
> of one bin: 1cc
> x-y-z, z= 56 to 58, x = -1 to 1,y = -59 to 59 (59 bins), Volume of one
> bin: 8cc
>
> The dose-eq. values near the air gap (i.e., x = 32.5 to 32.7 and x = -32.5
> to -32.7) have increased suddenly to very large value (e.g, from
> 0.00026mR/h to 0.00268mR/h). Also, the values at x = -32.6 are not same as
> the values at x = 32.6 even when the geometry is symmetrical.
>
> First, I kept 25 source pencils (odd number), the values were different at
> x = 32.6 and -32.6. So, I kept 40 pencils (even number), then also values
> are different. I even tried increasing the NPS from 5E07 to 2E08, but
> values are still different. Why is it so?
>
> What can I do to improve the values (I already tried increasing bin volume
> and NPS)?
> Am I doing something wrong in biasing? Or is there any other method of
> biasing which may improve my results?
>