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Keywords: rayleigh
Forum: Physics List
Re: Idea Coherent Diffusion of gamma in physics list (Alain Ferragut)
Re: Feedback Re: Coherent Diffusion of gamma in physics list (Wellisch, J.P.)
Re: None Re: Coherent Diffusion of gamma in physics list (Alain Ferragut)
Date: 09 Jul, 2003
From: michel maire <michel maire>

User Alain FERRAGUT wrote:

>> Hi, Let's take the case of lead for gamma energy of about 100 keV. For
>> this example, I will take the "Compilation of X-Ray Cross section" from
>> Lawrence radiation Laboratory (Livermore). These are old data from 1969
>> but still good enough for our discussion. What do we see in this table ?
>> 
>> At 100keV :
>>    --> PhotoCrossSection    = 1777 barns/atom
>>    --> CoherentCrossSection (Rayleigh) = 67.27 barns/atom
>>    --> IncoherentCrossSection (Compton) = 34.34 barns/atom
>> 
>> It is true that, compared to photoelectric effect, coherent diffusion of
>> gamma is very small. But, on the other hand, Compton diffusion is taking
>> into account by the physics list (LHEP_PRECO_HP), although the cross
>> section of Compton process is very small compared to photo effect. It is
>> even smaller than coherent scattering. So, it is logical to include
>> Rayleigh process if Compton process is included, even far above 1keV
>> gamma energy.

I admit that one would include Rayleigh to be coherent.

The standard em package, inherited from Geant3, is designed to provide an as efficient as possible shower development in the GeV->TeV region. Such showers are not very sensitive to the details of low energy gamma

processes: including Rayleigh would degrade the efficiency for pratically
nothing. However, it is our plane to include in 'standard' an implementation of Rayleigh which would provide a good compromise between accuracy and efficiency. You can include the lowEnergyRayleigh, which need the dataset G4EMLOW

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