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 nonoc cupational dose limit from 5 mSv-1 to 1 mSv-1. This change has also be en incorporated in the recently revised Title 10 Code of Federal Regul ations, 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 evaluati ng shielding in a diagnostic x-ray room has been developed using the f ollowing: the Monte Carlo Code MCNP, all materials that would normally attenuate the beam in an x-ray room, realistic assumptions for work l oad, and a spectrum of tube potentials based on actual usage. Results indicate that most radiographic x-ray rooms with shielding designed us ing the conservative assumptions in NCRP 49 will meet the new standard s.