SCIENTIFIC AND TECHNICAL COMMUNICATIONS: PHOTON DOSE ACCUMULATION FACTOR IN CONCRETE, IRON, AND LEAD FOR 10-50 MeV MONOENERGETIC SOURCES

摘要

The use of linear electron accelerators with primary electron beam energy to 50 MeV for remote-controlled radiation therapy and flaw detection and the more stringent requirements for the radiological safety of workers and the public make it necessary to improve the methodological resources for safety planning. Here it is important to know how much the protection attenuates bremsstrahlung for this energy range taking account of the scattered radiation. Ordinarily, in engineering methods of calculating the protection from photons the scattered radiation is taken into account by means of accumulation factors. Information on the accumulation factors for different materials used for protection is limited to source photon energies below 15 MeV. We have performed calculations of the absorbed photon dose rate in air in infinite protection comprised of concrete, iron and lead with density 2.3, 7.86, and 11.3 g/cm~3 , respectively, with thickness to 30 mfp for point isotropic and flat monodirectional sources of monoenergetic photons with energy 10, 20, 30, 40, and 50 MeV.The calculations were performed by the Monte Carlo method using the MCNP-4c2 software, taking account of the dose estimated according to intersections and a local estimate of the flux. All forms of interaction of photons with matter and the contribution of the characteristic and annihilation radiation as well as bremsstrahlung to the computed dose were taken into account. The mass coefficients of attenuation of photons were used to convert from mean-free path to distance in linear dimensions.