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Forum: Processes Involving Optical Photons
Re: Question Cerenkov photons "stuck" in parameterised geometry using v9.6p02 (Sam Blake)
Re: Feedback Re: Cerenkov photons (Gumplinger Peter)
Re: None Re: Cerenkov photons (Sam Blake)
Re: Idea Re: Cerenkov photons (Gumplinger Peter)
Re: None Re: Cerenkov photons (Sam Blake)
Date: 05 Aug, 2013
From: Sam Blake <Sam Blake>

I believe I have found the problem - it looks like I had made a mistake in setting my optical transport properties for the material that was causing the 'stuck' particle. Specifically, I have been specifying the Rayleigh scattering length as a function of photon energy.

However, as you can see below, I have only inputted 8 values after specifying a vector size of 10.

Therefore, the rayleigh scattering lengths for photon energies above 2.9804eV are being assigned a scattering length of zero, leading to the infinite sampling and zero step size. The reason it only occurs for Cerenkov-generated photons is because the scintillation photons all have energy = 2.139eV, and are hence sampling the correct 2cm scattering length.

const G4int nEntriesBC430 = 10;
  	  G4double ScntEBC430[nEntriesBC430] = { 1.0*eV, 1.9933*eV, 2.1122*eV, 2.139*eV, 2.2749*eV, 2.5200*eV, 2.8178*eV, 2.9804*eV, 3.24572*eV, 6.0*eV };

  	  G4double RIBC430[nEntriesBC430] = 		  	{ 1.58, 1.58, 1.58, 1.58, 1.58, 1.58, 1.58, 1.58, 1.58, 1.58 };
  	  G4double AbsorptionBC430[nEntriesBC430] = 	{ 3.5*m, 3.5*m, 3.5*m, 3.5*m, 3.5*m, 3.5*m, 3.5*m, 3.5*m, 3.5*m, 3.5*m }; 
-->    G4double RayleighBC430[nEntriesBC430] =  { 2.0*cm, 2.0*cm, 2.0*cm, 2.0*cm, 2.0*cm, 2.0*cm, 2.0*cm, 2.0*cm};    <-----

   myMPTBC430->AddProperty("RAYLEIGH",   ScntEBC430, RayleighBC430,  nEntriesBC430); 

After having fixed this by ensuring that 10 entries are listed for the Rayleigh scattering length, the simulations appear to be working just fine now.

Thanks once again for your help in finding the problem!

Cheers, Sam

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