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Forum: Processes Involving Optical Photons
Re: Question Question about the photocathode simulation and how to Detect the photon? (Xiaodong Zhang)
Re: More Re: Question about the photocathode simulation and how to Detect the photon? (Xiaodong Zhang)
Re: Warning Re: Question about the photocathode simulation and how to Detect the photon? (Gumplinger Peter)
Re: None Re: Question about the photocathode simulation and how to Detect the photon? (Xiaodong Zhang)
Date: 03 Apr, 2012
From: Gumplinger Peter <Gumplinger Peter>

for completeness I reply to this posting:

> I use Geant4.9.4.p01. Sorry, I think I made a mistake to decode the
> value of 12. In this version, I think it should mean "StepTooSmall"

It is normal to have a step whose status is "StepTooSmall" for the so called reallocation step after the program determined that an optical photon reflects off a surface.

> When I run the program, I saw the un-correct value
> 
> PMT-windows and Photocathode interface:
> 
> theLocalPoint: (-2.39593,-1.56864,1.15e-05)
> 
> theGlobalPoint: (0.644071,7.55136,-6.87) ====> correct
> 
> theLocalNormal: (-0,-0,-1) ====> correct
> 
> theGlobalNormal: (0,0,1)

This all looks correct to me - theLocalPoint is the coordinate in the coordinate system centered about the 'local volume' (e.g. the deepest volume in the geometry hierarchy). Similarly, theLocalNormal is the direction in the coordinate system 'attached' to that local volume. The global point and normal are the coordinates and direction cosign with respect to the global coordinate system. This come in when the local volume is positioned from the origin wrt its mother and/or positioned with a rotation.

> Length of this Step: 1.54227 mm =====> step length
> 
> 6 +++++++++++++++++++++++++>>>> Status of boundary: SpikeReflection
> 
> Process name:Transportation
> 
> Length of tghis Step: 0 mm
> 
> 12 =========================>>StepTooSmall

As I said, this is to be expected upon a reflection on a geometry boundary.

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