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Idea Re: Can I use optical surface to reflect X-ray or gamma photon? 

Forum: Processes Involving Optical Photons
Re: Question Can I use optical surface to reflect X-ray or gamma photon? (Huagang Yan)
Date: 05 Jan, 2017
From: Michael H. Kelsey <Michael H. Kelsey>

On Thu, 05 Jan 2017 19:19:12 GMT, Huagang Yan wrote:
> I need to construct a broad uniform radiation field by using mirrors.
> However, physical mirrors do not reflect high energy photons. Is it
> possible to use an optical surface in Geant4 to artificially reflect the
> X-rays? If yes, how do I accomplish this?

Optical surfaces in Geant4 are only effective with incident particles of type "G4OpticalPhoton". X-rays and gamma rays are of type "G4Photon", and all of the actual physics processes which generate or interact those particles only recognize G4Photon tracks.

If you are interested in completely ignoring the actual physics of X-rays or gamma-rays on material, you can "hack" what you need, in a couple of ways.

1) Define your optical surfaces with properties that cover the energy range of what you want (e.g., energy bins up to keV or MeV).

2) In your primary generator action, create G4OpticalPhotons with any energy (wavelength, frequency) you want, and let them go. They will not participate in any of the normal EM processes, but will participate in optical processes.

3) If you have some other system generating the X-rays using regular G4 EM processes, then you can "convert" them, in your G4UserTrackingAction. In ::PreUserTrackingAction(), just look for new tracks with particle type G4Photon, and modify them to have G4OpticalPhoton instead. Now they won't participate in normal EM (see (2), above), but will respect your optical surfaces.

Obviously, this is all completely non-physical, but it lets you do the ray-tracing you want.

  -- Michael Kelsey

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