Jovan Vukanić

Simplified model of low energy x-ray backscattering

The reflection of x-rays from a half space is studied within the framework of a model that assumes multiple isotropic scattering of photons without energy loss. An exactly solvable analytical expression for the angular distribution of reflected photons is derived. The range of validity of the model was determined by the Monte Carlo simulation thereby incorporating energy loss and angular dependences. For water as a scatterer, in the energy range from 10 to 60 keV, which is often used in x-ray diagnostics, the two approaches differ by at most 5%. The analytic results, confirmed by the Monte Carlo simulation, show that the angular distribution of reflected photons for energies greater than 30 keV--where multiple scattering events dominate--may be represented by a cosine law, within a few per cent of accuracy.

Influence of anisotropy of Compton scattering on low energy x-ray reflection

The reflection of x-rays from a semi-infinite water target, for energies ranging from 10 to 60 keV, often used in x-ray diagnostics, is investigated by Monte Carlo simulation. The same process was also treated analytically as the classical albedo problem for isotropic scattering without energy loss. Good agreement of results for the angular distribution of reflected photons of the two approaches is obtained for higher photon energies from the energy range considered. Multiple collision scattering dominates at higher energies, leading to isotropization of the photon distribution. Discrepancies between the isotropic scattering model and Monte Carlo results appear at the lower part of the energy range. Monte Carlo results show that at these energies photon reflection is governed mainly by single collisions and that these discrepancies are caused by anisotropy of the distribution of single backscattered photons. It is shown that the inclusion of the anisotropy of single Compton backscattering in the analytical model greatly improves the agreement with Monte Carlo results.

A theoretical analysis of reflection of X‐rays from water at energies relevant for diagnostics

The reflection of X‐rays from a semi‐infinite water target, for energies used in X‐ray diagnostics, is treated by the analog Monte Carlo simulation. In the developed procedure it was possible to calculate separately contributions of photons scattered, before reflection, fixed number of times with target electrons. It turned out that multiple collision type of reflection dominates at all energies investigated, whenever the absorption is small. The same process was also treated analytically as the classical albedo problem for isotropic scattering without energy loss. Very good agreement of results of the two approaches is obtained.