Options for photon transport

Separate section for discussion on gamma transport
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Toni Kaltiaisenaho
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Options for photon transport

Post by Toni Kaltiaisenaho » Mon Jun 29, 2015 5:12 pm

The new photon physics routines are included in version 2.1.24. The interaction physics and used methods will be described in detail in the near future. Currently, only a few input options are available but more options will be added in the future updates.

Two options exist for modelling Compton scattering. The first option is to set the Doppler broadening of the energy spectrum of scattered photons by

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set cdop <opt>
where <opt> can be 0 (off) or 1 (on). The Doppler broadening method is switched on by default. If the Doppler broadening is switched off, incoherent scattering function approximation is used for calculating the energy. In both cases, the direction of the photon is calculated using the incoherent scattering function.

At high energies, a Compton scattering event is well approximated by the Klein-Nishina equation. The Klein-Nishina method can be set by

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set ekn <E>
where <E> is the energy (in MeV) above which the Klein-Nishina equation is used for calculating both the energy and direction of the scattered photon. The default value is set to INFTY (1e+37). Below <E>, the Doppler broadening method is used if it is switched on, otherwise the incoherent scattering function approximation is used.

Thick-target bremsstrahlung approximation (TTB) is a crude approximation for modelling bremsstrahlung production by electrons and positrons. TTB is set by

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set ttb <opt>
where <opt> can be 0 (off) or 1 (on). TTB is set on by default. As a side note, the current TTB method has some limitations. Most importantly, it doesn't work well in compounds. This will be fixed in the next update.

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