Re: very principle question

From: Alberto Fasso' <>
Date: Tue, 19 Apr 2011 15:29:50 +0200

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 - 16:20:51 CEST

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