Comparison of exposure standards in the mammography x-ray region

Direct comparisons of the National Institute of Standards and Technology'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 Calibration Laboratory (UW-ADCL) were made on NISTs low-energy tungsten x-ray range. As a result of this direct comparison, NIST has established a UW-ADCL designed chamber, the Attix chamber, as the national standard chamber for the mammography energy x-ray range. The Ritz standard chamber and the Attix standard chamber have been extensively compared using the new molybdenum and rhodium beam qualities. The results indicate that exposure measurements in the mammography energy x-ray region with the two free-air chambers can be made with a discrepancy of less than 0.35%. (C) 1997 American Association of Physicists in Medicine.