Measurement and evaluation of X ray dose equivalent rates in mazesof medical electron accelerator facilities

Dose equivalent rates for X rays in mazes of 7 medical electron accelerator facilities producing X rays of 6, 8 or 18 MV were measured using the 2570/1A FARMER dosimeter and FJ- 347A X-Y dosimeter, which were calibrated at National Bureau of Standards. The measurement results indicate that X ray dose equivalent rate reaches maximum at the inner entrance of the maze and the ratio of the dose equivalent rate to the absorbed dose rate from the useful beam at the isocenter is more than 5.5 × 10-5 as the distance from the inner entrance to the isocenter is less than 5.2m. The dose equivalent rates decrease gradually with increasing distance. The dose equivalent rates in tunnel of the maze are less than 10-6 of the absorbed dose rate from the useful beam at the isocenter. The variation of dose equivalent rates in mazes with cross-sectional areas and path lengths of the mazes follows an exponential attenuation law. The dose equivalent rates in these mazes were also evaluated using a model given in this paper, and compared with the measurements.