A model for radiation shielding at a typical diagnostic X-ray facility in Tanzania.

This study presents a radiation shielding model for the diagnostic x-ray facility at Muhimbili Medical Centre. The developed model combines the influence of scattered and leakage radiation levels. The estimation of scattered radiation is based on the interaction of the output of an x-ray machine with the patient and objects within the x-ray room. These interactions lead to the scattering of radiation on the patient surface hence the radiation exposure at the reference points. Some fraction of output is transmitted through the patient, table, and film cassette assembly on the way to the floor where again the scattering process takes place. The leakage radiation is estimated on the basis of the measured leakage radiation level. An area monitoring survey was also carried out at the same reference points, using well calibrated themoluminescent dosimeters. The developed model predicts dose equivalents within # 15% of the observed values at 3 m distance. Beyond the walls of x-ray rooms, a model proposed by McGuire (1986) has been found to agree well with the area monitoring data. The occupational exposure at the Medical Centre is 89% lower than the maximum permissible limit, while the exposure to the public is 20% higher than the acceptable level.