NIST and BIPM Complete Key Comparisons for Air Kerma Standards
The National Institute of Standards and Technology (NIST) and the Bureau International des Poids et Mesures (BIPM) have completed two key comparisons for air kerma standards, supporting the CIPM MRA. The comparisons involved therapy level and radiation protection gamma-ray beams.
NIST’s therapy level comparison was conducted at their 60Co gamma-ray beam facility, providing traceability for nationwide hospital measurements critical for patient safety during cancer treatment. The radiation protection level comparisons used NIST’s 137Cs and 60Co facilities, disseminating air kerma standards nationwide for various applications.
Five ionization chambers were calibrated for air kerma and shipped to BIPM for measurements. The comparison results showed ratios of 1.0039 (therapy), 1.0023 (60Co protection), and 0.9990 (137Cs protection) with combined standard uncertainties of 3.4 x 10-3 to 3.3 x 10-3. The results were published in Metrologia technical supplements.
Keywords: air kerma, gamma-ray beams, radiation protection
