EXPERIMENTAL-DETERMINATION OF THE ANGULAR-DEPENDENCE FACTOR FOR THE DOSE-EQUIVALENT FOR PHOTONS IN CALIBRATION PHANTOMS OF PMMA

The conversion coefficients from air kerma to dose equivalent at a dep th of 10 mm in both a spherical and a slab phantom of PMMA have been d etermined for the X ray qualities: 40, 80 and 295 kV, ISO 'narrow' spe ctra and for Cs-137 gamma rays. The angular dependence factors have be en experimentally determined for the same qualities and for different angles between 0-degree and 180-degrees. The absorbed doses have been measured with thermoluminescence LiF dosemeters. The conversion coeffi cients and the angular dependence factors are generally found to agree well with calculated ones. Some minor discrepancies are found for the angular dependence factors and the 30 x 30 x 15 cm3 PMMA slab phantom .