Compton background

Figure 13.3 Relative MDA as a function of relative efficiency for coaxial p-type detectors and a fixed counting time. Case where Compton background, is dominant (recalculated...

Compton background produced by Bi-207 y- lines and estimated backseat tering distributions (b) 14.2 MeV neutrons at 5 kV/cm. The structure above the dashed line is due to accidental coincidences between neutron tag triggers and Bi-207 events in the cell. 

It is important to note that expression (23) can be applied to the crystalline phase intensities only if we include, in the first integral, its own smooth diffuse background and not just the intensity belonging to the crystalline peaks. In fact, a pure crystalline sample also has a smooth background due to the incoherent inelastic scattering (i.e. Compton scattering), the TDS, disorder scattering and, very often, unresolved tails of overlapped peaks. 

Expression (25) describes the smooth background belonging to a crystalline phase due to the incoherent (or Compton) scattering and the TDS or disorder scattering. The last contribution in (25) is very approximate because it is known that the TDS has a very complicated shape with very large peaks centered in the same position as the Bragg ones [56]. 

Scattered radiation. In a transmission experiment, the Mossbauer sample emits a substantial amount of scattered radiation, originating from XRF and Compton scattering, but also y-radiation emitted by the Mossbauer nuclei upon de-excitation of the excited state after resonant absorption. Since scattering occurs in 4ti solid angle, the y-detector should not be positioned too close to the absorber so as not to collect too much of this unwanted scattered radiation. The corresponding pulses may not only uimecessarily overload the detector and increase the counting dead time, but they may also affect the y-discrimination in the SCA and increase the nonresonant background noise. 

The relativistic derivation of the relationship between the Compton cross section and the Compton profile leads to a further correction factor [7]. Finally a background subtraction and a normalization of the valence profiles to the number of valence... 

I is the measured intensity, J the Compton profile, M the multiple scattering contribution, K the energy dependent correction factor, B the background, C the normalization constant and Zvai the mean number of valence electrons. Figure 3 shows a valence Compton profile of Cu obtained by this procedure. 

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