RE: [fluka-discuss]: Energy deposition attribution

From: Alberto Fasso' <>
Date: Mon, 25 May 2015 08:47:13 -0700 (PDT)

There is a thing that should be clear to everybody: in real life (i.e. not
in a Monte Carlo code) ALL THE ENERGY is always deposited by electrons!
Also energy lost in CSDA: only, if the electron energy is small enough,
one ignores them and considers only the energy LOST by the charged particle,
disregarding the fact that that energy is not deposited directly, but is
imparted to electrons (possibly many of them) which in turn deposit it.
In a Monte Carlo code, electrons of very low energy are not tracked, but
their energy is deposited at the point where the electrons would be set in
motion. How low is "a very low energy"? In FLUKA, the threshold depends
on the DEFAULT used (in your case HADROTHE), or can be set by the
DELTARAY command, but in any case cannot be lower than 1 keV.

Therefore, defining the dose attributed to a specific particle (defined in
AUXSCORE) is a useful fiction, but a fiction. And that dose depends on the
value of the threshold for delta ray production: a threshold that cannot be
set to less than 1 keV. If we could transport electrons with any energy
(we can't!) we would not have any CSDA. In extreme terms, no dose can be
attributed to a particle that is not an electron. What you get with
AUXSCORE has no absolute meaning, but depends on an arbitrary threshold
that you choose.


On Mon, 25 May 2015, Staffan Engdahl wrote:

> Thank you for the fast response!
> Yes, that was also my initial guess and I have run a simulation where I
> discard all electrons using the DISCARD card (see the attached input card) and
> it is obvious that the "missing" dose comes from electrons.
> As you mention, most energy is deposited by delta rays due to the low
> production threshold.
> Does this mean that the dose attributed to a specific particle (defined in the
> AUXSCORE) only comes from the energy lost in the CSDA? Meaning that the dose
> from delta rays produced in inelastic interactions with the same specific
> particle is not attributed to that particle?
> Best regards,
> Staffan Engdahl
> -----Original Message-----
> From: Alberto Fasso' []
> Sent: den 25 maj 2015 11:37
> To:
> Cc: Staffan Engdahl
> Subject: Re: [fluka-discuss]: Energy deposition attribution
> I guess that the missing energy deposition is due to electrons. You are using the default HADROTHE, which has a threshold for delta ray production of
> 100 keV. Therefore, most of the energy is deposited by delta rays.
> You can easily check this in two ways:
> 1) use AUXSCORE to add deposition by electrons
> 2) use command DELTARAY to set the threshold to infinity (i.e., an energy higher than that of the beam). With delta ray suppressed, the sum of all curves should coincide with the total
> Alberto
> On Mon, 25 May 2015, Staffan Engdahl wrote:
>> Dear FLUKA experts,
>> I have a query regarding how energy deposition is attributed to
>> different particles in FLUKA.
>> I attach a plot of laterally integrated energy deposition (IDD) of a
>> parallel 450MeV/u carbon beam on a cylindrical water phantom. I have
>> used USRBIN to score the energy deposition in a cylindrical mesh. I
>> used AUXSCORE to discriminate between particle species and one USRBIN
>> without particle discrimination (blue curve). After summation of the
>> energy depositions from all scored particles I end up with the black
>> curve. This means that I get a rather large difference between total
>> energy scored and the summed energy from the major beam constituents.
>> (I did not include the 12C in the summed dose)
>> One would expect some disagreement between the curves due to some
>> minor secondaries from inelastic interactions (and recoils?) but not to this extent?
>> Question: To which particle species could the dose difference between
>> the blue and the black curve be attributed?
>> See my attached input card for more details on the simulation.
>> Thanks in advance!
>> Best Regards,
>> Staffan Engdahl

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 May 25 2015 - 19:05:55 CEST

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