RE: very principle question

Alberto,

Since you repeated already in the mail to me that those limits are *indications*,
*suggestions*, *guidelines*, then you should write that also in the manual instead
of using the term "limit". And now I really start splitting hair: check the
definition of the word limit in the oxford dictionary. They do not mention
the words *indications*, *suggestions*, *guidelines in that respect.
( http://oxforddictionaries.com/definition/limit ).

However, in your last email you almost totally missed or ignored the point of
our question. Chris and I are not concerned about the term "limits" we are
just puzzled that the secondaries have limits which partly strongly differ
from those listed for primaries. A factor of up to 10000 is not just a small
difference and I believe that I am not the only user who wants to understand
the difference of the "two flavors" of one particles when it comes to
the very low energy range.

Also the upper limit for primary photons of 10000 TeV compared to the upper
limit of 1000 TeV for secondary photons appears strange to me. This would mean:
a 10000 TeV primary photon producing a cascade containing photons of an energy
above 1000 TeV leads directly to a photon energy range where you recommend
not to use the code for secondaries. This however reduces the upper limit
for primary photons somehow to absurdity.
Nevertheless, thank you very much for your trials to explain me the complicated
matter of energy limits in FLUKA. I believe now to know where the difference of
primaries and secondaries comes from but I will refrain from outlaying my
interpretation here or from further bothering you with my questions.

Helmut

-----Original Message-----
From: Alberto Fasso
Sent: 19 April 2011 20:02
To: fluka-discuss (fluka-discuss_at_fluka.org)
Cc: Chris Theis; Helmut Vincke
Subject: RE: very principle question

Chris,

again...! Please see my answer to Helmut.
Why are you both so concerned about those limits?
With most objects you purchase, you get some recommendations by the manufacturer.
For the tires of a car, the owner's manual gives you the maximum recommended pressure.
If it says it 32 lbs of pressure, does it mean that you cannot inflate them at 33 lbs?
Would that be dangerous? And why 32 and not 30?
The manufacturer doesn't tell you, but you are satisfied that his experience has
shown that value to ensure maximum safety and minimum wearing.

So, please take these recommendations in the same way. They are not compulsory,
they are just *recommendations*

Alberto

On Tue, 19 Apr 2011, Chris Theis wrote:

> 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: transport of secondaries improves it, but is less critical. Therefore, it is more important to have "optimum" physics for primaries than for 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=20
> 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?
>
> Chris
>
> -----Original Message-----
> From: Alberto Fasso
> Sent: 19 April 2011 16:53
> To: fluka-discuss (fluka-discuss_at_fluka.org)
> 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 accuracy.
>
> 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.
>
> Alberto
>
> 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 Wed Apr 20 2011 - 09:27:09 CEST