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Forum: Processes Involving Optical Photons
Re: Question Doubts about some parameters in Detector constructiion (OpNovice) (Jaiver Salazar )
Date: 23 Nov, 2017
From: Gumplinger Peter <Gumplinger Peter>

> G4double energy_water[] = {
>      1.56962*eV, 1.58974*eV, 1.61039*eV, 1.631 .....  };

These are the optical photon energies over which you define the Mie scattering length data

>   //assume 100 times larger than the rayleigh scattering for now.
>   G4double mie_water[] = { 167024.4*m, 158726.7*m, 150742*m, ....};

This is the Mie scattering length data.

> 
>   assert(sizeof(mie_water) == sizeof(energy_water));

We assert that the array size of both are the same.

So, for example:

mie_water[1.56962*eV] = 167024.4*m

e.g. the Mie scattering length of a photon of 1.56962*eV is 167024.4*m.

>   // gforward, gbackward, forward backward ratio
>   G4double mie_water_const[3]={0.99,0.99,0.8};

> 2.the same with G4double mie_water_const[3]={0.99,0.99,0.8};, what is this?

Please, read the paragraph in the Application Developers Manual and referenced material at:

5.2.5.4. Tracking of Photons in processes/optical

under Mie Scattering

e.g.

The process requires a G4MaterialPropertiesTable to be filled by the user with Mie scattering length data (entered with the name: MIEHG) analogous to Rayleigh scattering. The Mie scattering attenuation length is the average distance traveled by a photon before it is Mie scattered in the medium and it is the distance returned by the GetMeanFreePath method. In practice, the user not only needs to provide the attenuation length of Mie scattering, but also needs to provide the constant parameters of the approximation: g_f, g_b, and r_f. (with AddConstProperty and with the names: MIEHG_FORWARD, MIEHG_BACKWARD, and MIEHG_FORWARD_RATIO, respectively; see Novice Example N06.)

The analytical expressions for Mie Scattering are very complicated since they are a series sum of Bessel functions. One common approximation made is call Henyey-Greenstein (HG). The implementation in Geant4 follows the HG approximation (for details see the Physics Reference Manual)

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1 Question: Re: Doubts about some parameters in Detector constructiion (OpNovice)   (Jaiver Salazar - 29 Nov, 2017)
(_ Note: Re: Doubts about some parameters in Detector constructiion (OpNovice)   (Jaiver Salazar - 29 Nov, 2017)
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