A Monte Carlo model for retrospective analysis of shield design in a diagnostic x-ray room.

Recent recommendations by the NCRP and the ICRP have lowered the nonoccupational dose limit from 5 mSv y-1 to 1 mSv y-1 [corrected]. This change has also been incorporated in the recently revised Title 10 Code of Federal Regulations, Part 20. Shielding installed in most current diagnostic x-ray rooms was based on the 5-mSv limit when rooms or corridors adjacent to the x-ray room were unrestricted areas. A computer model for evaluating shielding in a diagnostic x-ray room has been developed using the following: the Monte Carlo Code MCNP, all materials that would normally attenuate the beam in an x-ray room, realistic assumptions for work load, and a spectrum of tube potentials based on actual usage. Results indicate that most radiographic x-ray rooms with shielding designed using the conservative assumptions in NCRP 49 will meet the new standards.