RE: very principle question

From: Chris Theis <>
Date: Tue, 19 Apr 2011 14:30:02 +0000

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:

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

-----Original Message-----
From: Alberto Fasso
Sent: 19 April 2011 15:30
To: fluka-discuss (
Cc: Helmut Vincke; Chris Theis; Stefan Roesler
Subject: Re: very principle question

Dear Helmut,

those are not thresholds! They are *suggested* transport limits.
The "further transport" is the same for primaries and secondaries.
Common sense tells you that if the transport threshold of protons
(yes, this time I am talking about an actual threshold) is 1 keV, it would not
make much sense to start a primary proton of 5 keV to be almost immediately
stopped. But it can be done, nothing prevents you to do it: it would just be silly.
On the other hand, if in the course of a hadronic cascade a 5 keV secondary
  proton is generated, transporting it makes sense.

There is also another reason. The transport limits you are referring to
are due to the fact that the accuracy of transport and interaction models
becomes gradually worse as energy gets close to them. But they are not "sharp"
limits: the physics of proton transport is not "good" at 101 keV and "bad"
at 99 keV. The limits reported in the manual are just an indication to the
user of *about* the lowest primary or secondary energy which can give you
good results. Why different for primary and secondary? Because the whole pattern of
energy deposition, nuclear reactions etc. is dominated by primaries: transport
of secondaries improves it, but is less critical. Therefore, it is more
important to have "optimum" physics for primaries than for secondaries.
For the same reason, with some DEFAULTS the threshold for performing
multiple scattering is lower for primaries than for secondaries.


On Mon, 18 Apr 2011, Helmut Vincke wrote:

> Dear FLUKA users and authors
> When I am looking at the transport limits of FLUKA I see different=20
> limits for secondary and primary particles.
> The lower threshold for secondaries is always below the corresponding=20
> lower threshold of primary particles (differences up to a factor 1E4).
> From my understanding the origin of the particle (either produced in=20
> an interaction or started from a given point by the user) should not=20
> make a difference for the further transport of this particle.
> I attach the transport limits of FLUKA, as they are listed in the manual.
> I would be grateful if you could explain me the difference.
> Thanks in advance
> Best regards
> Helmut
> Transport limits listed in the FLUKA memory:
> Secondary particles Primary particles
> charged hadrons 1 keV-20 TeV (*) 100 keV-20 TeV (*) (**)
> neutrons thermal-20 TeV (*) thermal-20 TeV (*)
> antineutrons 1 keV-20 TeV (*) 10 MeV-20 TeV (*)
> muons 1 keV-1000 TeV 100 keV-1000 TeV (**)
> electrons 1 keV-1000 TeV 70 keV-1000 TeV (low-Z
> materials) (**)
> 150 keV-1000 TeV (high-Z materials) (**)
> photons 100 eV-1000 TeV 1 keV-10000 TeV
> heavy ions<10000 TeV/n<10000 TeV/n
> (*) upper limit 10 PeV with the DPMJET interface
> (**) lower limit 10 keV in single scattering mode
Received on Tue Apr 19 2011 - 17:16:01 CEST

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