الفهرس 
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Abstract
The linear accelerator (linac) is the primary tool in external beam radiotherapy, which generates continuous energy Bremsstrahlung gamma rays when energetic electrons hit a high Z material such as tungsten or lead. High energy photon beam (>10 MeV) are preferred if doses should be delivered to larger depths (e.g., for the treatment of prostate cancer) and to enhance the skin sparing. Photoneutrons are produced when the incident photon energy is above the threshold energy of the (ɤ, n) reaction. This threshold depends on the atomic number of the target (e.g., 7.42 MeV for tungsten) lead to the production of unwanted neutrons that contaminate the photon field.