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Forum: Physics List
Re: Question region cut (V. Grabski)
Re: None Re: region cut (michel maire)
Date: 24 Oct, 2003
From: Varlen Grabski <grabski@fisica.unam.mx>

Hello,
Seems that 10 cm changes a lot?

Index : 4     used in the geometry : Yes     recalculation needed : No
 Material : quartz
 Range cuts        :  gamma 1.2 m      e- 1.2 m      e+ 1.2 m
 Energy thresholds :  gamma 10.4498 MeV    e- 894.291 MeV    e+ 851.321
MeV
 Region(s) which use this couple :
    layer_0

>> Index : 4     used in the geometry : Yes     recalculation needed :
No
> >>  Material : quartz
> >>  Range cuts        :  gamma 1.3 m      e- 1.3 m      e+ 1.3 m
> >>  Energy thresholds :  gamma 2.88022e+295 J      e- 1.01145 GeV    e+ 962.847 MeV
> >>  Region(s) which use this couple :
> >>     layer_0

Regards,
Varlen

On Fri, 2003-10-24 at 09:14, michel maire wrote:
> *** Discussion title: Physics List
> Email replies to PublicHyperNews@slac.stanford.edu must include:
>   In-Reply-To: <"/phys-list/31/1"@geant4-hn.slac.stanford.edu>
>   Subject: ...change this to be about your reply.
> 
> User V. Grabski wrote:
> 
> >> Hello, I have a problem with region cut setting. For the cut 1.3 m the
> >> energy thresholds calculations for the gamma is strange.
> >> 
> >> Index : 4     used in the geometry : Yes     recalculation needed : No
> >>  Material : quartz
> >>  Range cuts        :  gamma 1.3 m      e- 1.3 m      e+ 1.3 m
> >>  Energy thresholds :  gamma 2.88022e+295 J      e- 1.01145 GeV    e+ 962.847 MeV
> >>  Region(s) which use this couple :
> >>     layer_0
> >> 
> >> What I can do to correct this? Thanks, Varlen
> 
>  It is not related to region, but to the range -> energy relation.
> 
>  For e-/e+ the relation is monotonic, and as big is the range, you can
>  compute a corresponding energy. 
>  (As you as seen in your case ~1 m -> ~1 GeV)
> 
>  For Gamma, the relation is no more monotonic, due to a small valley in
>  the total cross section between the regions of Compton dominant and
>  pair production dominant, and after the cross section is flat.
>  Therefore if the cut in range, i.e. the Absoption length, is too big
>  we set the energy to DBL_MAX. Of course, this will prevent any brems
>  production.
> 
>  See PhysicsReferenceManual 
>  -> electromagnetic/miscellaneous/conversion range-energy
> 
>  We can imagine some trick to overcome this situation. But it would be
>  somewhat arbitrary. 

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