Re: compare-bdx and yield results

From: Anna Ferrari <>
Date: Mon, 6 Jun 2011 13:34:44 +0200 (CEST)

Dear Ertan,

first of all thank you for having resent the summary file of your results
(I put it in attachment).

You wanted to calculate the number of positrons exiting your target.
You correctly did it using two different estimators:

a) with the USRYIELD card you estimated the particle yield calculated
respect to the beam direction, expressed as double differential
distribution (in energy and in solid angle in your case);

b) with the USRBDX card, choosing the scoring of the current you computed
the same quantity, as double differential distribution in energy and in
solid angle and calculated respect to the normal to the boundary surface.

After having run FLUKA you gave the FLUKA output files in input to the
corresponding post-processing programs to finally obtain the summary
output files ([]_tab.lis, []_sum.lis) with the computed distributions.
You have to take care because there are done some integrations.
Let's concentrate only on the total responses.
You must observe (it is written in the []_sum.lis file) that while the
USRYIELD results for the total response have been integrated in energy and
mantained as differential in angle (even if you used a sigle angular
bin they are always given "per steradian"), the USRBDX results are
integrated in energy and in angle (they are given both as "part/cm2 per
primary" and as "part per primary", but not anymore "per steradian").

Results from a) and b) in your []_sum.lis file have therefore a different
Total responses from a) are given in part/sr per primary particle.
You get: 1.594 E-2 part/sr per primary.
To obtain the fully integrated total response you have still to integrate
over the solid angle, that for you is 4pi (you considered 1 bin in solid
angle:(0,pi) ).
Then you get 0.200377 particles per primary that is exactly the result in b)
after the integration over the boundary surface.

I saw that you used also the USRBDX card with the fluence scoring. The
fluence estimator has a different physical meaning: you weight in this
case each exiting positron with 1/cos(theta) (where theta is the angle of
the positron track respect to the normal to the boundary surface) because
the fluence at the boundary surface is the density of particle tracks in
an infinitesimal thickness at that boundary (see the first pages of:

useful also for a comparison of all the estimators).
In this case you obtain therefore a total response a bit higher then in
the case of current scoring (you would obtain the same results only if all
the positron tracks were exiting perpendicularly to the surface).

Hope it helps,
bests regards,


Anna Ferrari
Helmholtz-Zentrum Dresden-Rossendorf
01314 Dresden (Germany)

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> Hi Fluka experts
> I want to learn relationship between the usrbdx and usryield results
> in my work the electrons hit on the target and I try to find some
> information about the positrons after the target (for example number of
> positron etc)
> So I obtained some results but I cannot interpreted
> I remember that the usrbdx and usryield results should be compatible
> is it true
> My results attached
> May you help me please about the my usrbdx and usryield results
> Thank you so much for your help
> Ertan ARIKAN

Received on Mon Jun 06 2011 - 17:33:20 CEST

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