M.A. HASSAN*, M.H. GABER**, E. ESMAT*, H.I. FARAG***, H.M. EISSA*

*National Institute for Standards (NIS), Giza, Egypt
**Biophysics Department, Faculty of Science, Cairo University, Egypt
***National Cancer Institute, Cairo, Egypt

Abstract. Experimentally determined values of X-ray backscatter factors were performed using NE 2571 cylindrical ionization chamber. Measurements were made for X-rays generated at voltages between 100 kV and 300 kV with different thickness and type of filters. To study the influence of the irradiation geometry on the backscatter factors, the measurements were performed for different photon beam field diameters at the phantom front face, at a fixed source-to-phantom distance of 1m. Measured results are analyzed and discussed in comparison with measured and calculated values given in the cited references.

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