A Few Remarks of additional shielding on Electron Linac Radiation Oncology Facilities --- Measurements and Analysis on Angular Distribution of Dose Rate around Targets Bombarded by 18, 25, 34 MeV Electrons

Dose rate measurements have been performed around the cupper, tungsten and aluminum targets bombarded by 18, 25 and 34 MeV electrons. The detectors were set at 500 mm from the target and the angles were 0, 30, 60, 90 and 120 degrees in the direction to the beam line. Three kinds of detectors were applied for the measurements, miniature ionization chamber and glass dosimeter for photons, and CR-39 for neutrons, respectively. The measured results were compared with calculated ones by using the Monte Carlo calculation code MCNP5. Very good agreements were obtained in the case of ionization chamber and glass dosimeter, when the influence of electrons scattered by the target were involved in the calculation. However, some discrepancies for the dose rate of neutrons were observed.