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Question ProcessHit being called with step points outside volume 

Forum: Hits, Digitization and Pileup
Date: Mar 13, 08:45
From: Sergio Losilla <Sergio Losilla>

Hi,

I am observing something I did not expect. I have this G4Box with the following extent:

          Min bounds (mm):          -1.0250000000000011e+02 -1.0250000000000011e+02 -2.2204460492503131e-14
          Max bounds (mm):           1.0750000000000011e+02  1.0750000000000011e+02  2.4100000000000003e+02

with a sensitive detector attached to it. Sometimes ProcessHits gets called when both the PreStepPoint and the PostStepPoint are located outside the volume.

What I have observed is that this happens with a series of electron multiple scattering and ionization steps, with the first step happening inside the volume.

For example, this is some debugging information reported from a series of ProcessHits:

          Track ID: 4
          Particle type: e-
          Process: msc
          Volume: Energy Deposition Grid
          PreStepPosition (mm):      2.6934043593914865e+01 -1.2301722949817044e+01  5.3104086883068446e-15
          PostStepPosition (mm):     2.6917978050042727e+01 -1.2296560936845795e+01 -4.0353906987950286e-02

          Track ID: 4
          Particle type: e-
          Process: msc
          Volume: Energy Deposition Grid
          PreStepPosition (mm):      2.6917978050042727e+01 -1.2296560936845795e+01 -4.0353906987950286e-02
          PostStepPosition (mm):     2.6851608596360958e+01 -1.2284143949119052e+01 -2.1246248611655932e-01

...

          Track ID: 4
          Particle type: e-
          Process: eIoni
          Volume: Energy Deposition Grid
          PreStepPosition (mm):      2.1505300429019215e+01 -1.2437761048433565e+01 -1.0967299306487321e+01
          PostStepPosition (mm):     2.1506268196140923e+01 -1.2447058581141297e+01 -1.0995601681213966e+01

          Track ID: 4
          Particle type: e-
          Process: eIoni
          Volume: Energy Deposition Grid
          PreStepPosition (mm):      2.1506268196140923e+01 -1.2447058581141297e+01 -1.0995601681213966e+01
          PostStepPosition (mm):     2.1525478176840299e+01 -1.2465976307976618e+01 -1.1000048031860869e+01

          Track ID: 4
          Particle type: e-
          Process: eIoni
          Volume: Energy Deposition Grid
          PreStepPosition (mm):      2.1525478176840299e+01 -1.2465976307976618e+01 -1.1000048031860869e+01
          PostStepPosition (mm):     2.1531384827331596e+01 -1.2468889707710611e+01 -1.1022813550720395e+01

Notice that the last steps are happening as far as 1.1 cm outside of the volume!

Is there anything I am missing?

Best regards,

Sergio

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1 None: Re: ProcessHit being called with step points outside volume   (Makoto Asai - Mar 13, 09:08)
(_ None: Re: ProcessHit being called with step points outside volume   (Sergio Losilla - Mar 13, 10:36)
(_ None: Re: ProcessHit being called with step points outside volume   (Makoto Asai - Mar 13, 10:50)
(_ None: Re: ProcessHit being called with step points outside volume   (Sergio Losilla - Mar 18, 06:57)
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