A re-evaluation of the BIPM standard for air kerma in 60 Co radiation has been made. The changes to the air-kerma rate determination arise from four sources: (i) the results of Monte Carlo calculations of correction factors for the standard; (ii) a re-evaluation of the correction factor for saturation; (iii) a new evaluation of the air volume of the standard using an experimental chamber of variable volume; (iv) the adoption of a new reference beam at the BIPM. The combined effect of these changes is an increase in the BIPM determination of air-kerma rate by the factor 1.0054 and a reduction of the relative standard uncertainty of this determination to 1.
An overview of the international framework that supports the dissemination of the dosimetry quantities for ionizing radiation is presented. The aim of international traceability is for confidence in such measurements around the world, which is particularly important for the equivalence of patient treatment regimes as required in international clinical trials for radiotherapy but also for fields as diverse as industrial processing, diagnostic medicine and radiation protection. This paper gives some explanation of the comparison system for national primary standards in the field of dosimetry and shows how these can support the claims for the calibration and measurement capabilities of national metrology institutes represented in the BIPM key comparison database.
A re-evaluation of the BIPM standards for air kerma in low- and medium-energy x-rays has been made. The changes to the air-kerma rate determination arise from three sources: (i) the results of Monte Carlo calculations of diaphragm correction factors for the standards, (ii) a measurement of the effect of scatter from the diaphragm support and (iii) a re-evaluation of the electron-loss corrections for the medium-energy standard. Scatter from the diaphragm support explains a long-standing trend observed in the results of international comparisons for medium-energy x-rays. The new standards were implemented on 1 September 2009.
Following the change to the BIPM standard for air kerma in 60Co adopted in November 2007, a re-evaluation of the BIPM standard for air kerma in 137Cs radiation has been made. The changes to the air-kerma rate determination arise from three sources: (i) the results of Monte Carlo calculations of correction factors for the standard; (ii) a re-evaluation of the correction factor for saturation; (iii) a new evaluation of the air volume of the standard using an experimental chamber of variable volume. The combined effect of these changes is an increase in the BIPM determination of the air-kerma rate by the factor 1.0030 and a reduction in the relative standard uncertainty of this determination to 1.9 parts in 103. A full uncertainty budget is presented.
A comparison of the standards for absorbed dose to water of the Physikalisch-Technische Bundesanstalt (PTB), Germany and of the Bureau International des Poids et Mesures (BIPM) has been made in 60Co gamma radiation under the auspices of the key comparison BIPM.RI(I)-K4. The comparison result, based on the calibration coefficients for three transfer standards and expressed as a ratio of the PTB and the BIPM standards for absorbed dose to water, is 0.9961 (0.0037). This result replaces the earlier PTB value in this key comparison. The degrees of equivalence between the PTB and the other participants in this comparison have been calculated and the results are given in the form of a matrix for the twelve national metrology institutes (NMIs) that have taken part in the ongoing comparison for absorbed dose to water. A graphical presentation is also given.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by Section I of the Consultative Committee for Ionizing Radiation (CCRI(I)), according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
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