Re: EMFCUT, basic understanding check

From: Giuseppe Battistoni <>
Date: Sat, 9 Apr 2011 14:15:01 +0200 (CEST)

Dear Betrand
I think that you are choosing correctly the thresholds.
For a more general case, however, you should instead
look carefully at the question of
the so called "electronic equilibrium". For this topic please
refer to the lecture on "Physics Optimizations and Proper Threshold
Settings" given at the 2010 Advanced Course in Ericeira:
go to

As far the values that you adopt are concerned, I add that probably you
can even raise them a bit, if you need to speed
up calculation time.
If I were in your shoes I would made a check of what happens
to the dose in air as a function of the prod. cut in tungsten.
I would not be surprised if you will find that a 1 MeV cut will
give practically equivalent results to the 100 keV case, with a benefit
of reduced calculation time.
In order to proceed to furrher optimization, let me also add that
there could be advantages in giving different values for e+/e- with
respect to photons: tracking time for e+/e- is heavily affected by
energy cuts, while time for photons is much less affected.
Therfore, if you need it, you can lower thresholds for photons with
only a very reduced penalty.

Best regards
        Giuseppe Battistoni

On Thu, 7 Apr 2011, Bertrand H. Biritz wrote:

> Dear FLUKA users,
> After re-reading the manual, googling through the threads and also
> reading the latest presentations from the Heidelberg course I wanted to
> verify that I am using the EMFCUT card for my simulation correctly.
> The basic geometry is a 4 MeV electron beam goes through a bore in a
> tungsten cube with a target inside, the tungsten being the shielding. I
> am interested in scoring the DOSE-EQ in air outside of this target to
> see how much radiation a person would receive when standing a certain
> distance away from the target.
> Via the EMFCUT card I set the production threshold in air to 1keV but
> for tungsten I set it to 100keV (the default, if I am not mistaken). The
> reason I increasing it in tungsten is I am not really interested in what
> happens inside of the shielding, rather how many particles escape it.
> If I understood slide 5 ("Production Thresholds" ) of the EM lecture
> correctly, then the amount of energy lost per step by a primary particle
> is the same regardless of the specified threshold. With the EMFCUT card
> one just specifies if this energy is used to create delta rays, by
> setting the threshold accordingly.
> Is this correct? Will the spectrum of particles which make it past the
> shielding be nearly unaffected by what the production threshold is set
> to inside of the shielding?
> I say "nearly" as a delta ray produced near the exiting surface of the
> shielding will be able to make it out and the higher the threshold the
> more energetic the delta rays (although I would imagine the probability
> is also less for producing these).
> Am I completely misunderstanding this?
> Sincerely,
> Bertrand
> P.S. In the manual for EMFCUT it says the FUDGEM parameter must be set
> to 1 if the cutoff is larger than 100keV, yet on slide 6 the Heidelberg
> EM presentation (and also that of 2009 and 2008) it says 10keV. Which
> one is correct?
Received on Sat Apr 09 2011 - 15:01:01 CEST

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