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tschoonj / xraylib

A library for X-ray matter interaction cross sections for X-ray fluorescence applications
https://github.com/tschoonj/xraylib/wiki
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Compton cross section for small angles is always close to zero ... #94

Closed nikhild1836 closed 5 years ago

nikhild1836 commented 5 years ago

Hi, Thank you for sharing such a useful library. I am using xraylib version '3.3.0' under Anaconda/Python3. I am getting unexpected results when querying the differential cross section for Compton scattering using the following command: DCS_Compt_CP("SiO2", 70, 0.001)

   For theta approaching zero, the returned cross section goes to zero and for theta=zero, the returned cross section is zero. I was expecting the cross section to have a maxima at theta=0. What am I missing?

Thanks!

tschoonj commented 5 years ago

To the best of my knowledge, this is entirely as expected: the incoherent scattering function SF_Compt produces zero for theta=0. Given that the differential Compton cross section is defined as the product of SF_Compt and the differential Klein-Nishina cross section, the result must be zero as well.

nikhild1836 commented 5 years ago

You are right... I just had not come across any plots showing this phenomena before. I recently found that this difference between the Klein Nishina and the Compton cross section arises because the Klein Nishina cross section is for a free electron what is being called the Compton cross section here is for an electron bound in an atom. Anyways, thank you for the quick response!