Re: [fluka-discuss]: How to get non ionizing energy loss?

From: Fasso, Alberto <>
Date: Tue, 30 Jun 2015 08:35:14 +0000

Dear Alessia,
in general, particles change energy and/or direction when they have an interaction with electrons and/or nuclei. In a Monte Carlo program, the particle movement is divided in steps:
between interactions, between a boundary crossing and an interaction, or between an interaction and a boundary crossing (boundary crossing does not change the energy and the
direction of the particle). But for charged particles, the interactions with atomic electrons are so many, that it is not convenient to simulate them all in detail. The so-called
condensed-history technique consists in averaging millions of little energy losses and of little changes of direction over a certain distance (a "step"). The average energy loss is
condensed in what is called the "stopping power", while the average change of direction is called the "multiple scattering". Such step must be neither too short, to avoid wasting CPU
time, nor too long, so that the particle energy doesn't change too much. A maximum average energy loss per step is in general from 10 to 20% (shorter if a high precision is requested).
In a step, the only cause of energy loss is ionization. Other causes (bremsstrahlung, nuclear interactions) are pointlike, and can happen only at the end of a step.
The condensed-history technique can be of Class I if all the ionization energy losses are included in the average, or of Class II if only "soft" collisions with electrons are included, and
secondary electrons with energy higher than a given threshold are transported separately (delta rays). Delta ray production (called Moller or Bhabha scattering in the case of
electrons and positrons) is pointlike, and not spread along a step.
FLUKA's treatment uses condensed-history technique of Class II (but Class I can be obtained by setting the threshold for delta ray, Moller and Bhabha production at a very high energy.
The delta ray threshold can be set with command DELTARAY for hadrons and other heavy charged particles, and with command EMFCUT for electrons and positrons.

Now answering your question: the user routine mgdraw, in ENTRY usdraw, allows you to see the pointlike energy losses of electrons and positrons.
* 208: bremsstrahlung secondaries
* 210: Moller secondaries
* 212: Bhabha secondaries
* 214: in-flight annihilation secondaries
* 215: annihilation at rest secondaries
The energy losses by ionization, which are spread along a step, can be seen in the main mgdraw ENTRY, using the variables Mtrack and Dtrack in COMMON TRACKR.
To these types of energy loss, you must add those under ENTRY endraw, which are pointlike and "artificial". These losses are not physical, ma linked to some approximation
(a particle is killed and its energy is deposited "on the spot"):
 * 20: local energy deposition (i.e. photoelectric)
* 21 and 22: below threshold
* 23: escape
* 24: time kill

I hope this can make your ideas more clear


From: <> on behalf of Saggio Alessia <>
Sent: Monday, June 29, 2015 5:17 AM
To: Stefan Roesler
Subject: Re: [fluka-discuss]: How to get non ionizing energy loss?

Hi Stefan,
thanks for your reply. Actually I found out that NIEL-DEP is the energy coming from atoms' displacements caused by impinging particles, I don't need (only) this kind of energy.

I was wondering if there is a way to know which is the process that causes the energy loss, so that I could exclude all that processes different from ionization step by step. By modifying the mgdraw routine, I printed in the file.log all the variables that can help me to understand what's really happening in my simulation (e.g. ETRACK, DTRACK, ICODE etc.) but I found no variable that says to me which is the physics energy loss process.

Moreover, which is the criterion used by FLUKA to separate the various steps? Just to be clear: in the file.log I can see a lot of steps of the same electron, in every step it loses a certain quantity of energy, but why does Fluka separate this process in so many steps? This suggests to me that in every step a certain process occurs (such as ionization, Bremsstrahlung etc.) but I'm not able to get any information about the kind of process right now. And this is what I need to do!

Hope you can help me.


----- Messaggio originale -----
Da: "Stefan Roesler" <>
A: "Saggio Alessia" <>
Inviato: Lunedì, 29 giugno 2015 9:53:25
Oggetto: Re: [fluka-discuss]: How to get non ionizing energy loss?

Dear Alessia

Yes, your assumptions are correct.

I suggest to use a USRBIN scoring for NIEL-DEP. See also an older post on
this subject


On Fri, 26 Jun 2015, Saggio Alessia wrote:

> Hi Fluka users,
> In my simulation I need to separate the energy lost by ionization
> process from that lost by other non ionizing processes. Just a little
> doubt... after a certain time passes, does all the energy lost go into
> ionization or I can always find a value of non-ionizing energy loss
> different from zero? I suppose that I'll always register a value
> different from zero because of the energy coming from nuclear breaks up
> etc... am I right?
> So, how can I get this kind of energy? Maybe I should consider the
> variable NIEL-DEP, defined as the Non Ionizing Energy Loss Deposition
> (GeV), but how to use it? It is not clear to me.
> Thank you in advance
> Cheers
> Alessia
> __________________________________________________________________________
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Received on Tue Jun 30 2015 - 12:15:25 CEST

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