COMPARISON OF EXPOSURE STANDARDS IN THE MAMMOGRAPHY X-RAY REGION

Direct comparisons of the National Institute of Standards and Technolo gy's (NIST) Ritz 20 kV to 100 kV standard free-air ionization chamber and a portable variable-length free-air ionization chamber designed by the University of Wisconsin - Madison Accredited Dosimetry Calibratio n Laboratory (UW-ADCL) were made on NISTs low-energy tungsten x-ray ra nge. As a result of this direct comparison, NIST has established a UW- ADCL designed chamber, the Attix chamber, as the national standard cha mber for the mammography energy x-ray range. The Ritz standard chamber and the Attix standard chamber have been extensively compared using t he new molybdenum and rhodium beam qualities. The results indicate tha t exposure measurements in the mammography energy x-ray region with th e two free-air chambers can be made with a discrepancy of less than 0. 35%. (C) 1997 American Association of Physicists in Medicine.