Experimental determination of barrier transmission factors for different shielding materials unders high energy X-rays

Broad beam barrier transmission factors for lead, steel and ordinary concrete materials have been determined at 4, 6 and 10 MV photon energies in a linear accelerator device by means of measurements for design purposes of primary radiation shielding. In the setup where these factors were obtained, the distance from the source to barrier (SDD) was set to be 100 cm. A farmer type ionization chamber was used as the detector in the measurements. In the measurement set-up, the detector was placed 30 cm away from the outer wall of the barrier in a 2-4 cm thick solid phantom made of water equivalent material in the centre of the beam to provide adequate build-up. In the study, radiation transmission factors for concrete material were measured in field areas between 3*3-10*10 cm2. Then, using these values, TVL values of the corresponding field areas of concrete were calculated and the change of TVL values with respect to the field area TVL was evaluated. In addition, three different measuring setups where the distance from source to detector was varied as 130, 230 and 330 cm were studied for measuring barrier-free relative dose values at each beam energy and the dependence of these values on the effective field size were also examined. As a result, it has been observed that the broad beam conditions develop after 20*20 cm2 field area. In the study, TVL values were also obtained for lead, steel and concrete materials at a distance of 130 cm source to detector distance and at device field area of 10*10 cm2 and these values were adjusted to those in the literature for 40*40 cm2 to obtain TVL values of these materials for the maximum available field area. The narrow and broad beam TVL values determined in this study were found to be in good agreement with the literature.