RE: very principle question

From: Helmut Vincke <>
Date: Tue, 19 Apr 2011 15:03:51 +0000

Dear Alberto

Thanks for your answers. However, your answer triggers some more detailed
questions and comments:

5 keV protons: if it is almost immediately stopped depends on the
composition and above all the density of the material. Moreover, the upper limit
for charged protons (as primary) is 100 keV, an energy which is sufficient to
cross the whole gas volume of a TEPC detector.

The difference of secondaries and primaries is much stronger for anti-neutrons,
namely a factor of 10000. Can you tell me the explanation for that one?

We have even another case where we have a factor of 10 for the upper
transport limit: namely photons: primary: 10000 TeV in contrary to secondaries:
1000 TeV. Please tell us if this is a spelling mistake. In case it isn't
please explain the reason.

As a user I would like to have a list telling me the limits of reliability
(this term needs to be defined by the one who provides the list) of FLUKA
for each particle type. No matter if any other part of the particle history
or if other secondaries are dominating the quantities I score.


-----Original Message-----
From: Alberto Fasso=20
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
> limits for secondary and primary particles.
> The lower threshold for secondaries is always below the corresponding
> lower threshold of primary particles (differences up to a factor 1E4).
> From my understanding the origin of the particle (either produced in
> an interaction or started from a given point by the user) should not
> 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 - 17:52:01 CEST

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