عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Dosimetry of ionizing radiations are based on standard methods issued by competent national and international organizations. Establishment of reference radiations at standard dosimetry laboratories are essential to transfer measurement standards to radiation users. This paper presents attempts made at Ionizing Radiation Division of PTB to produce a reference 20 MeV electron beam based on the German standard DIN 6800-2. The quality of the 20 MeV electron beam of a Philips SL75-20 linear accelerator (linac) is determined by a well designed plane-parallel ionization chamber, in terms of mean energy of the electron beam at the surface of a water phantom. Three types of cylindrical ionization chambers are calibrated against the primary standard of absorbed dose to water at PTB in Co-60 gamma radiation. Based on DIN 6800-2, independent measurements of absorbed dose to water are then carried out by these three calibrated chambers at a reference depth in water phantom and with reference to the dose monitoring system of the linac which consists of two other ionization chambers located in water phantom. The results are compared and a mean calibration factor for the monitor chambers with a combined standard uncertainty is determined.
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