Backscatter peak

Finally, the fundamental unit of concentration obtained by RBS is in atoms/cm or concentration in the sample-versus-bachscattering energy loss. To convert the profile of a backscattering peak into a depth profile it is necessary to assume a density for the material being profiled. For single-element films, such as Si, Ti, and W, an elemental density can be assumed for the film and an accurate thickness is obtained. In the case of multi-elemental films with an unknown density, a density for the film is calculated by summing the density of each element, normalized to its concentration. The accuracy of this assumption is usually within 25%, but for some cases the actual density of the film may vary by as much as 50%— 100% from the assumed density. It is useful to note that ... 

In the pulse-height distributions of Compton interactions of y-rays in scintillation detectors there are two prominent features usually present (1) the Compton edge, which corresponds to the maximum energy that can be transferred to an electron by the y-ray, and (2) the backscatter peak, which corresponds to the absorption of a photon which has been scattered through 180° in the material surrounding the detector. 

Fig. 5.12. Energy of Compton edge and backscattered peak for gammas of energy <0.7 MeV.

The Compton edge of a -y-ray peak falls at 0.95 MeV. What is the energy of the photon What is the energy of the backscatter peak ... 

Backscatter peak - Compton scattering through a large angle, giving rise to a broad distribution at about 200 keV. 

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