RE: very principle question

From: Chris Theis <>
Date: Tue, 19 Apr 2011 15:34:27 +0000

Dear Alberto,

maybe this was a mutual misunderstanding. But from "... it would not make
much sense to start a primary proton of 5 keV to be almost immediately stopped."
I inferred that you are actually referring to a range and not to an *energy*
range at which particles can be transported with more or less good accuracy.

Thanks for the explanations regarding the implementation of LPM and EPDL97.
However, this raises another question for me because the limit for the
secondary high-energy photons did not change. To my understanding, which of
course might be wrong, LPM would apply to high energetic secondaries in these
energy regions as well.

This leads me to another point which I would like to have a better
understanding of. You write:

> Why different for primary and secondary? Because the whole pattern of energy deposition, nuclear reactions etc. is dominated by primaries:=20
> transport of secondaries improves it, but is less critical. Therefore, it is more important to have "optimum" physics for primaries than for=20
> secondaries.

I fully agree with your point that primaries are more critical. However, how do you
infer the actual values for the lower limits of the secondaries? For the photons
for example we have 1 keV for primaries and 100 eV for secondaries.
What is not clear to me is on which basis this difference by a factor of
10 has been determined. To my understanding the physics for primaries& secondaries
should be the same - it is in nature - and thus, only the limit for primaries
should be the one down to which "particles can be transported with more or
less good accuracy". Don't you agree?


-----Original Message-----
From: Alberto Fasso
Sent: 19 April 2011 16:53
To: fluka-discuss (
Cc: Chris Theis; Helmut Vincke
Subject: RE: very principle question

Dear Chris,

I didn't "state that the suggested limits are related to the range of particles"!
Where did you read this statement?
They are related in some way to the *energy* range (not the range of the
particles) in which particles can be transported with more or less good

As you have noticed, that energy range has been extended for photons in
the latest FLUKA release, both at the upper and at the lower end.
At the upper end, by the implementation of the LPM effect
(Landau-Pomeranchuk-Migdal) in pair production. At the lower end, by using the EPDL97
photon cross sections from Livermore.
A warning: transport of these very low-energy photons does not take into
account special effects such as reflection by mirrors or crystals.


On Tue, 19 Apr 2011, Chris Theis wrote:

> Dear Alberto,
> Thanks a lot for your e-mail. Reading your explanations actually made
> me think about one point. On one hand you state that the suggested
> limits are related to the range of particles and of course this has not changed over the time.
> Yet, when I compare the limits of FLUKA 2008 and FLUKA 2011 for
> photons I find the following:
> Secondaries/primaries
> 2008: photons 1 keV-1000 TeV 7 keV-1000 TeV
> 2011: photons 100 eV-1000 TeV 1 keV-10000 TeV
> From the second part of your answer I take it that these changes must
> be related to substantial changes/improvements in the physics because
> we have an increase for the upper limit by a factor of 10 and a
> decrease by 7-10 for the lower limit, depending if you're looking at primaries or secondaries.
> Especially for the low energy part I would be really interested to
> know which changes allowed for this improvement. I would appreciate if
> you could provide some more background information about these changes.
> Thanks a lot
> Chris
Received on Tue Apr 19 2011 - 18:14:36 CEST

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