 If the scattering at the sample is not elastic but changes the neutron velocity, the rephasing will become incomplete and a loss of final
polarization results, which depends on the distribution of differences in the time, which the neutrons need to fly through the symmetric first (coding) and second (decoding)precession zones.The time differences occur due to a velocity change acquired by non-elastic scattering at the sample.The distribution of these time differences is proportional (in the linearization approximation which is appropriate for quasi-elastic high resolution spectroscopy) to the spectral part of the scattering function S(Q,ω).