Measurement of TVLs in lead for 4, 6 and 10 MV bremsstrahlung x-ray beams at scattering angles between 30 degrees and 135 degrees.

Measurements have been made of the transmission factors through lead for scattered radiation produced by 4, 6, and 10 MV bremsstrahlung x-ray beams incident on a polystyrene phantom; these measurements cover the range of scattering angles between 30 degrees and 135 degrees. The results show that the tenth value layer (TVL) for scattered radiation decreases sharply with increasing scattering angle and increases slightly with increasing beam energy, although at large scattering angles there is little energy dependence. TVLs range from 3.5 cm to 0.3 cm for 4 MV at scattering angles between 30 degrees and 135 degrees, from 3.8 cm to 0.6 cm for 6 MV, and from 4.2 cm to 0.7 cm for 10 MV, respectively, at scattering angles between 30 degrees and 120 degrees. Monte Carlo calculations, performed at 4 MV to simulate the transmission of scattered radiation, are in good agreement with the experimental measurements.