Scattering fraction of X-rays incident on a phantom from the measured energy spectra

The The scattering fraction of X-rays incident on a polymethyl- ethacrylate/aluminum phantom have been calculated from the measured spectra of the primary and scattered radiation in different directions. Constant potential X-ray equipment has been utilized to produce beams with a maximum energy in the range 40-90 keV. The energy spectra have been measured by means of an Amptek XR-100 CR system with a silicon PIN photodiode detector. The raw spectra have been corrected for the dependence of the detector efficiency on the photon energy, and utilized to determine the ambient dose equivalent (ADE) due to the primary beams and to the radiation scattered at the angles 30 degrees, 90 degrees and 150 degrees with the incident beam direction. The spectra have been calibrated in kerma units by means of the data obtained simultaneously with an ionization chamber. For the determination of the ADE, the kerma spectra (grays) was converted to sievert units through the energy dependent factors published in the ICRU 57 report. Scattering fractions were determined as the ratio of these two ADE values, according to the 453 Brazilian Health Ministry Rule. Results show that the obtained angular dependence of the scattering fractions follows nearly the same behavior of previous measurements recently published. (author)