Penelope J. Allisy

International framework of traceability for radiation dosimetry quantities

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.

Re-evaluation of the BIPM international standard for air kerma in 60Co gamma radiation

A re-evaluation of the BIPM standard for air kerma in 60Co 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 1.5 parts in 103. A full uncertainty budget is presented. The new standard is effective from 1 November 2007.

Re-evaluation of the BIPM international standards for air kerma in x-rays

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.

Re-evaluation of the BIPM standard for air kerma in 137Cs gamma radiation

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.

Comparison of the standards for absorbed dose to water of the NPL, United Kingdom and the BIPM for60Co γ rays

A comparison of the standards for absorbed dose to water of the National Physical Laboratory (NPL), United Kingdom 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 two transfer standards and expressed as a ratio of the NPL and the BIPM standards for absorbed dose to water, is 0.9980 (0.0064). The degrees of equivalence for the NPL and the other participants in this comparison have been calculated and the results are given in the form of a table for the eleven 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 the CCRI Section I, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Linking the results of the regional key comparison APMP.AUV.V-K1 to those of the CIPM key comparison CCAUV.V-K1

During 1996 and 1997, eight national metrology institutes (NMI) took part in a vibration accelerometer comparison, identifier APMP.AUV.V-K1. Two NMIs ultimately withdrew from the comparison and the results of the remaining six NMIs have been approved by the CCAUV. Four NMIs subsequently took part in the 2001 CIPM key comparison for the same quantity, identifier CCAUV.V-K1. The results of these four CIPM participants have been used to link the results of the remaining two NMIs to the results in the CIPM key comparison using the reference frequency of 160 Hz. The CCAUV nominated the PTB to propose the methodology for the link and subsequently approved the linked results as presented in this report. The degrees of equivalence between each result and the key comparison reference value (KCRV), and between each NMI have been calculated and the results are given in the form of a matrix and graph for six NMIs. As two results from the APMP can now be linked to the published CCAUV.V-K1 comparison, the updated graph for the key comparison database is also given.

Comparison of the standards for air kerma of the NPL and the BIPM for60Co γ rays

An indirect comparison of the standards for air kerma of the National Physical Laboratory (NPL), United Kingdom and of the Bureau International des Poids et Mesures (BIPM) was made in 60Co gamma radiation in September 2007. The comparison result, based on the calibration coefficients for two transfer chambers and expressed as a ratio of the NPL and the BIPM standards for air kerma, is 1.0011 (0.0038). The degrees of equivalence between the NPL and the other participants in the key comparison have been calculated and the results are presented in the form of a matrix. 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 the CCRI Section I, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).