Dose Profile and Uncertainty Analysis of Narrow Beam X-Rays and Collimated 137cs Source used at the Secondary Standards Dosimetry Laboratory of the Ghana Atomic Energy Commission

Abstract

The study highlighted the importance of dose standardization to ensure that radiation measurements are linked to the international system. The half value layer (HVL) was determined and compared with ISO 4037 values and the values quoted on the calibration certificate of the reference ionization chamber to verify whether the X-ray machine is emitting correct energies. The percentage (%) deviation of the HVL obtained for the various X-ray emitting beam qualities are within the acceptable limits except for the 60 kV which was subsequently modified by using 0.7 mm Al. The dose profiles for the narrow beam X-rays and the collimated 137Cs source were established. The difference resulting from the theoretical and measured values is generally less than 10% in the useful range of 1 to 2m. The dose profiles generated provides standardized beam output characteristics that can be used to calibrate dose rate monitoring equipment, TLDs and other dosimetry systems. The uncertainty analysis indicated that most of the calibration factors with the associated uncertainties for the set of survey meters calibrated at the Secondary Standards Dosimetry Laboratory of Ghana Atomic Energy Commission are within the acceptable limits. The uncertainties ranged from 0.03 to 17% with the majority of them ranging from 0.03 to 6.0 % with only a few of them more than 6.0 %.