Considering differences between NCRP 49 and NCRP 147

Dr. Richard Brey
Dept. of Physics
Idaho State University

The National Council on Radiation Protection and Measurements (NCRP) issued its Report No. 147: Structural Shielding Design for Medical X-ray Imaging Facilities on November 19, 2004.  This supersedes NCRP Report No. 49: Structural Shielding Design for Medical use of X Rays and Gamma Rays of Energies up to 10 MeV which was issued September 15, 1976. A number of interesting changes have been made to the method of shielding design in medical facilities.  Changes appropriately include updated units, terminology, definitions, design goals, and assumptions on equipment application.  NCRP 147 also provides discussion of the radiological safety aspects of several different types of devices not available at the time of issuance of NCRP 49.  Although the physics of the approaches is similar, there are many subtle changes in nomenclature.  A comparison of these two documents which emphasizes improvements is given.  NCRP 147 is particularly useful for the newer types of equipment being used today. A case study using NCRP 147 to determine the shielding requirements for devices for a standard radiography unit is provided.