Dear Alessandro
there is no obvious way for computing the surface of a complicated region.
However there could be a possibility (never tested... ) using the FLOOD
option in the BEAMPOS card.
This possibility works perfcetly when computing volumes for complicated
regions, on paper it could work for surfaces as well (no guarantee).
Let me explain the logic (see also the manual for the BEAMPOS card):
a) your problem should have for this purpose all regions (apart blackhole)
filled with vacuum;
b) you define a beam (whichever particle, say PHOTON's) and put a
BEAMPOS card with SDUM=FLOOD;
c) this will generate an isotropic and uniform fluence inside the sphere
with radius = WHAT(1) of the BEAMPOS card, be sure such radius
contains wholly your region;
d) the fluence so generated will be equal to 1/(pi R^2), this is an
exact analytical result;
e) you define a USRBDX, fluence-like, two-ways, estimator between the
region you want to know the surface of and the surrounding, with
normalization surface=1. It would be highly preferable/simple if the
surrounding is made of a single region (you could make an ad hoc
run/geometry for this purpose);
f) you run Fluka for sufficient primaries/cycles in order to get
a negligible statistical error on the USRBDX result (let's call
its result F);
g) since you know that F/Area should be equal to 1/(pi R^2) you
can easily derive Area
Normally this method is used in order to compute volumes using
a tracklength estimator instead of a USRBDX, and using the
equation F_track_length/Volume = 1/(pi R^2). This works perfectly
and it is sure to give the exact answer within the statistical
errors. On paper I do not see an obvious reason why it should not
work for computing an area as well, there will be numerical precision
issues since for grazing incidence a fluence boundary crossing estimator
would result into an infinite (or better a division by zero). This
is protected in the code and the influence of the necessarily
approximate protection should be small, however as I said before we
never tried this method.
Let us know if it works!
On Fri, 13 Mar 2020, Alessandro Calamida wrote:
> Dear FLUKA experts,
>
> In my geometry I have a regione that is the union of different bodies.
> Calculating the surface of it is quite complicated and so I cannot put
> the normalization factor in the USRBDX scoring.
>
> There is a FLUKA or Flair tool that allows to evaluate surfaces.
>
> I attach in the email the input of the file. The region from wich I need
> the surface is the SUPP_TRG.
>
> Best regards and thank you for your time, Alessandro Calamida.
>
>
>
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Received on Mon Mar 16 2020 - 11:51:43 CET