Angular correlation, electron-photon measurements

It is still necessary to perform the measurements at two different scattering geometries. Angular correlation functions were measured for photon azimuthal angles of (j) = tt (in the electron... 

If there is more than one particle emitted in the scattering process, and one or more of these (electron, photon, etc.) are detected in coincidence with the scattered electron, then the cross sections are also differential with respect to the energy and angular distributions of these secondary particles. Such measurements are called correlation measurements, since the cross section depends on the correlation between say the angles (or energies, or spin directions) of the final particles. 

The angular correlation PAS measurement is based on the evaluation of the 511 keV y-photon distribution. The total momentum of both y photons arising during the moment of annihilation is equal to the momentum of the annihilated (e+, e ) pair. Because the is thermalised before the annihilation in the material, its momentum can be neglected. Therefore, the angular distribution of the y-photon pairs depends on the local electron momentum distribution in the observed material. This fact is frequently used in the study of mechanical, thermal or radiation-induced defects in materials [131]. 

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