Re: simulating low energy EM showers

Hi Corey,

Could you, please, let us know which version of Geant4 VMC you use? In case you used v 2.8, could you check if the problem persists with trunk? Recently, there was found a bug in the optical physics list in v 2.8 and it is now fixed in svn trunk.

Thank you,

Ivana

Corey Reed wrote:
> Hi,
>
> I was wondering if any expert may be able to help guide my investigation
> in the right direction. A quick summary of my problem: 15 MeV positrons
> don't seem to be fully tracked if they are ~2 meters away from my
> detector objects, shown by the plot
> http://www.nikhef.nl/~cjreed/poslenVsRad.gif
>
> I would appreciate very much any advice!
>
>
>
> Details:
>
> I am trying to simulate positrons of 10-20 MeV in water. My geometry
> consists of a large tank of water (cylinder dz=dr=25 meters) and 3 PMT
> detectors about 60 cm from the origin.
>
> I throw the positrons evenly in a 5 meter sphere about the origin.
>
> However, it seems that when the photon is thrown 2.5 meters or more away
> from the origin, the positron track length is always less than 0.3cm!
> (It should be ~9cm in water.)
>
> Looking at the location of positrons which eventually produce an optical
> photon that hits one of my active detectors, as shown in this plot:
>
> http://www.nikhef.nl/~cjreed/posxyWithHit.gif
>
> There seems to be some strange cutoff at 2.5m
>
> This is more visible if I plot the radial distance of the positron
> vertex from the origin:
>
> http://www.nikhef.nl/~cjreed/posRdists.gif
>
> (red = thrown, teal = op-photon gets to cathode, blue = photoelectron
> produced)
>
> Finally, the positron track length vs the radial vertex position:
>
> http://www.nikhef.nl/~cjreed/poslenVsRad.gif
>
>
> I am using the physics lists "emStandard+optical" with:
>
> /mcPhysics/rangeCuts 0.1 mm
>
> /mcPhysics/setCerenkovMaxPhotons 100
> /mcPhysics/setTrackSecondariesFirst True
>
> /mcPhysics/selectOpProcess Scintillation
> /mcPhysics/setOpProcessActivation True
> /mcPhysics/setScintillationYieldFactor 1.0
>
>
> Thanks!
>
> - Corey
>

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e-mail:  Ivana.Hrivnacova_at_cern.ch
address: Institut de Physique Nucléaire, 91406 Orsay, France
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