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Forum: Processes Involving Optical Photons
Re: None Scintillation Time of Creation & YIELDRATIO (Nick Calvert)
Re: Feedback Re: Scintillation Time of Creation & YIELDRATIO (Gumplinger Peter)
Re: None Re: Scintillation Time of Creation & YIELDRATIO (Nick Calvert)
Date: 13 May, 2013
From: Gumplinger Peter <Gumplinger Peter>

Nick worked out why he was only seeing the slow component. He has been using the G4OpticalPhysics builder without making any changes. This physics builder sets the Scintillation Excitation Ratio as 0, which is overriding his yield ratio here:

http://www-geant4.kek.jp/lxr/source/processes/electromagnetic/xrays/src/G4Scintillation.cc#L388

He has manually changed this in his physics list, and the scintillation time is now as one would expect it.

However, that's quite the discovery! Turns out, there is a stark inconsistency as to what is set by default in G4Scintillation.cc (1.0):

http://www-geant4.kek.jp/lxr/source/processes/electromagnetic/xrays/src/G4Scintillation.cc#L106

and what is set by default in G4OpticalPhysics.cc (0.0):

http://www-geant4.kek.jp/lxr/source/physics_lists/builders/src/G4OpticalPhysics.cc#L68

and the examples LXe and wls for the ExcitationRatio.

The logic at:

http://www-geant4.kek.jp/lxr/source/processes/electromagnetic/xrays/src/G4Scintillation.cc#L388

is clearly written to give the YieldRatio priority in view of what is the default in the same class.

Thanks to Nick I now discovered that the LXe example is also not working as intended. It too uses the G4OpticalPhysics when, at the same time, it specifies both a FAST and SLOW component. Even in the past it SetScintillationExcitationRatio(0.0) which, as Nick pointed out, is equivalent to only getting the slow component.

I don't know what to do without maybe breaking people's code. Perhaps I can change the logic at line 388:

if ( ExcitationRatio == 1.0 || ExcitationRatio == 0.0) {

because 0.0 presently specifies just a slow component and you can't anyway specify just a fast component. A realistic value for the ExcitationRatio is anything > 0 and < 1.

Regards, Peter

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