A weight Problem in uniform sampling

From: SEMON Laurent (laurent.semon@synchrotron-soleil.fr)
Date: Thu Jun 21 2007 - 09:17:50 CEST

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Hello dear's users of Fluka,

=20

I try to sample a synchrotron source for Fluka calculations and i use
for that source.f . I perform an uniform sampling over my energy range
[1:500] keV and this sampling is very efficient (I manage to sample all
the energies).=20

My problem comes from the weight calculation. I use the formula w =3D
N(E)/A*(Emax-Emin) where A is the integral of the spectra over the
energy interval [Emin:Emax] and N(E) the number of photons per second
per keV as function of energy. For the lowest energies (for example 2
keV) N(E)=3D10E+20 and w=3D145 but for the highest energies (500 keV for
example) N(E)=3D10E-10 and w=3D10E-24!!!

With this huge weight interval Fluka calculations never converge.

=20

My questions are:

=20

1) Is it possible to perform good calculations with this huge weight
interval even if the spectra sampling is good?

=20

2) If an uniform sampling is not desirable for this type of spectra
(because of the huge weight interval), do you recommends a better
function that 1/N(E) to biase the spectra ?

=20

Thank you very much for all informations ...

=20

Best regards

=20

Laurent

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Hello dear’s users of =
Fluka,

I try to sample a synchrotron source for Fluka
calculations and i use for that source.f . I perform an uniform sampling =
over
my energy range [1:500] keV and this sampling is very efficient (I =
manage to
sample all the energies).

My problem comes from the weight calculation. =
I use
the formula w =3D N(E)/A*(Emax-Emin) where A is the integral of the =
spectra over the
energy interval [Emin:Emax] and N(E) the number of photons per second =
per keV
as function of energy. For the lowest energies (for example 2 keV) =
N(E)=3D10E+20
and w=3D145 but for the highest energies (500 keV for example) =
N(E)=3D10E-10 and
w=3D10E-24!!!

With this huge weight interval Fluka =
calculations never
converge.

My questions are:

1) Is it possible to perform good calculations =
with
this huge weight interval even if the spectra sampling is =
good?

2) If an uniform sampling is not desirable for =
this
type of spectra (because of the huge weight interval), do you recommends =
 a
better function that 1/N(E) to biase the spectra ?

Thank you very much for all informations =
…

Best regards

Laurent

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Next message: SEMON Laurent: "Option EMF-BIAS"

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Reply: Chris Theis: "RE: A weight Problem in uniform sampling"
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