Dear Vladimir,
At first glance, I think you are experiencing the result of an
unfortunate choice of region importance values:
- Note that with the first biasing card you are setting importance 0.5
from regions RmodL (number 5) to Rshell (number 6).
Then, with the second card, you set importance 2 from region RmodR
(number 4) to region Rbox (number 7), overriding what you intended to
do with the previous card.
Thus, regions in your geometry will have importance of either 1 or 2,
but never 0.5 as you intended. This will allegedly just result in
"wasting" a bit of CPU time.
- To make sure you control what importance is assigned to which region,
search in the output file for "Particle importances" or, for a more
visual approach, note that in Flair you can display the value of the
importance assigned to each region in a new layer in the Geometry tab.
Let us know if you need help with this.
- A few of your USRYIELD cards score neutrons from Rbox to subsequent
regions Rcount1, Rcount2, Rcount3, respectively, at various positions
X within Rbox. However, whereas Rbox has importance 2, your regions
Rcount1, Rcount2, Rcount3 have importance 1. I fail to understand the
virtue of this and would suspect it can actually be detrimental: some
neutrons that were initially "split" then play Russian roulette when
they cross into Rcount1, thwarting your efforts somewhat.
- Try a consistent scheme (assign increasing importance to subsequent
regions) and maybe a bit more aggressive, i.e., importance 2 in RmodR,
4 in Rshell, 8 in Rbox (and the counters). You may also want to
effectively cut Rbox at various values of x (this is a very long
region with considerable attenuation) and assign increasing
importances to the farther regions.
Cheers,
Cesc
On Mon, Jul 29 2019, at 08:46 +0300, babintsev wrote:
>
>
> Dear experts,
> I want to enlarge neutron statistics on the right side
> of the target with the same number of beams:
> lead box in moderator ... and 3 counters on the right side
>
> For this I use biasing : divide moderator into 2 parts : left and right
> I use W= 2 to the right side
> = 1/2 for the left side in moderator
>
> Then I compare results before biasing and after that.
>
> Results :
> () Total number of low energy neutron interactions: 6025716
> with biasing
>
> ... it was 3525982
> no biasing
>
> () CPU - approximately the same
>
> () N neutrons in the counters is less with biasing !?
>
> example with counter-3 (C3) :
> 1.5200707E-02 +/- 2.631857 % (no biasing)
>
> 1.3233015E-02 +/- 9.833910 % with biasing
>
> ------------------------
>
> so, I think that these are strange results
>
> May be I have errors somewhere ?
>
> thank you
> Vladimir
>
--
Francesc Salvat Pujol
CERN-EN/STI
CH-1211 Geneva 23
Switzerland
Tel: +41 22 76 64011
Fax: +41 22 76 69474
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Received on Wed Jul 31 2019 - 17:19:34 CEST