Summary of the BIPM.RI(I)-K4 comparison for absorbed dose to water in ⁶⁰Co gamma radiation

Abstract

International comparisons of absorbed dose have been made at the Bureau International des Poids et Mesures (BIPM) since 1988. Thirteen national metrology institutes have taken part, some of which have repeated the comparison over the years. The key comparison reference value (KCRV) is taken as unity, each comparison result being the ratio of the national metrology institute's (NMI) evaluation to that of the BIPM's stable standard. The degrees of equivalence between each NMI and the KCRV, and between each pair of NMIs, are given in the form of a matrix, using the most recent result for each of eleven NMIs. 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 Mutual Recognition Arrangement (MRA).

Comparison of the standards for absorbed dose to water of the BNM-LNHB and the BIPM for 60Co γ rays

“…The measurements at the BIPM took place in October 2005. This absorbed dose to water comparison replaces the indirect comparison made between the two laboratories in 1990 [1] that was previously registered in the BIPM.RI(I)-K4 key comparison [2].…”

“…for the BIPM ionometric standard for absorbed dose to water Quantity BIPM value BIPM relative standard uncertainty (1) 100 s i 100 u i Dry air density (2) / (kg m (2)…”

“…The coherence with these figures for each type of chamber confirms the response of the chambers while at the BIPM. C summary report of the most recent comparisons, including the previous comparison with the PTB, is given in [2], and the results are available in the key comparison database (KCDB) of the CIPM MRA [12].…”

“…Indeed the only significant correlations arise from the common use of data relating to mass energy-absorption coefficients and the ratios of absorbed dose to the collision part of the kerma (β), for those NMIs using graphite calorimetry. The uncertainties are not necessarily fully correlated and this is taken into account by applying an approximate factor, f k , as indicated in [2].…”

“…The degree of equivalence of a particular NMI, i, with the key comparison reference value is expressed as the difference 1 NMI NMI − = R D (5) and the expanded uncertainty (k = 2) of this difference, , known as the equivalence uncertainty. It follows that Table 7 gives the values for D NMI and U NMI for each NMI taken from [2] and [13] and this report, using (5) and (6), and forms the basis of the entries in the KCDB of the MRA Appendix B. These data are presented graphically in Figure 1 where the black squares indicate results that date prior to 1995.…”