Re: x-Rays Transport

From: Alberto Fasso' <>
Date: Mon, 13 Jul 2009 10:29:33 -0700 (PDT)

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Dear Ali,

I send my answer to the list, although you sent your mail directly to
me. Please keep all your correspondence on the list, so that anybody
can answer and other users can profit of the answer.

Your input file is full of errors. Remember what I told you?
"Without the input file, we can only guess, and the possible causes are
thousands". And indeed, there were many, difficult to guess.

First of all the geometry cannot work: the three regions Dum,
Target and Det are nearly completely overlapping. The purpose of the Dum
region is not clear, since it is never used, but maybe you intended to
use it in a next run. The easiest way to make a correct geometry in
your case is to define a cylinder, and to cut it with one or two planes.

Then there is a lot of confusion about energies. You say "I want to
simulate the transport of x-rays having E=100 keV", but in the BEAM
command you set the photon energy = 1.D-6, which is 1 keV, not 100.
By the way, the lower limit of photon transport is 1 keV, so starting
with that energy will never work. You need the primary photons to have at
least 7 keV (it is written in the manual).
Then, with EMFCUT you set the transport limit to 1.D-7, which is 0.1 keV,
again too low. Fortunately the program resets it to an acceptable value,
but I have an impression that you have made a general mistake in
converting keV to GeV. For instance, you request a USRBDX with energy limits
1.0D-8 and 2.0D-6: which means between 10 eV and 2 keV: of course you will
never score anything. The lower limit must not be lower than 1.E-6, and of
course you cannot expect to get a "spectrum" between 1 and 2 keV!

Other odd things, probably doing no harm, but difficult to understand:
- why do you request Leading Particle Biasing (EMFCUT, WHAT(3)=255.)?
   The purpose of LPB is to accelerate the simulation of showers, but
   there are no showers at 100 keV and less. (In addition,if you request it,
   use EMF-BIAS, and not EMFCUT which is the obsolete way)
- Why do you give command EMF, which is useless with the DEFAULTS you are
   using (PRECISIO)? And by the way, the DEFAULTS I would recommend for
   your problem is not PRECISIO, but EM-CASCA.
- and finally, never start a particle on a boundary!

Best regards,


On Sun, 12 Jul 2009, Ali Koosha wrote:

> Dear Dr Fasso
> Thanks for your attention.
> I want to simulate the transport of x-rays having E=100 keV, but it does
> not work.
> It seems that "Pcut" could not be lower than 1.0E-3 MeV, even in the case
> of using another value via EMFCUT. I attached my input files, if you think
> it can help.
> On Sun, Jul 5, 2009 at 9:02 PM, Alberto Fasso' <>
> wrote:
> Dear Ali,
> First of all (and this applies not only to you, but to all
> users
> writing to this list) it is useless to ask questions about a
> problem without sending also at least the input file. Without
> the
> input file, we can only guess, and the possible causes are
> thousands.
> But perhaps in this case you are luckier, and my guess can be
> successful.
> 100 keV are lower than the transport and production thresholds
> set by
> most defaults. You should set both thresholds lower yourself
> using
> command EMFCUT, once with SDUM = PROD-CUT (for production) and
> once
> with SDUM blank, for transport. Read carefully the manual about
> that
> command (please notice that transport thresholds are set by
> region, and production thresholds are set by material).
> Another important thing: the thresholds you are using are
> reported in
> the .out file. Check that they are how you want them.
> ======================================================================
> Productions thresholds are reported as follows:
> 1 Quantities/Biasing associated with each media:
> Rho = 2.35000 g/cm**3 Rlc= 9.84627 cm
> Ae = 1.51100 MeV Ue = 5766.71 MeV
> Ap = 0.333333 MeV Up = 5766.20 MeV
> (Ae = production threshold for electrons, expressed as _total_
> energy, i.e.
> kinetic plus mass. In this example, 0.001 GeV kinetic.
> Ap = production threshold for photons)
> Transport thresholds are reported as follows:
> 1 Correspondence of regions and EMF-FLUKA material numbers and
> names:
> Region EMF FLUKA
> Ecut = 1.5110E+00 MeV, Pcut = 3.3333E-01 MeV, BIAS
> = F, Ray. = F, S(q,Z) = T, Pz(q,Z) = F
> (Ecut = transport transport threshold for electrons, expressed
> as _total_
> energy
> Pcut = transport transport threshold for photons)
> ======================================================================
> Kind regards,
> Alberto
> On Sun, 5 Jul 2009, Ali Koosha wrote:
> Dear Fluka experts
> I want to perform a simulation of x-rays (~100 keV)
> beam incident on a
> simple Cu thin/thick target;
> but my attempts failed to attain a non-zero output
> from the code, under the
> following conditions:
> source = a monodirectional "PHOTON" annular beam
> having nominal energy of
> ~100keV
> geometry = a simple rcc
> score = surface and track estimate of "PHOTON"s
> flux
> misc = turn EMF. It seems that x-rays don't
> transport
> at all.
> --
> Alberto Fasso`
> SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
> Phone: (1 650) 926 4762 Fax: (1 650) 926 3569
> Best Regards
> Ali Koosha

Alberto Fasso`
SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
Phone: (1 650) 926 4762   Fax: (1 650) 926 3569
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Received on Mon Jul 13 2009 - 22:27:38 CEST

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