*BIPM, # CNEA, BARC, $ NRC, **NIM. Abstract

Transcription

1 Update of the BIPM comparison BIPM.RI(II)-K1.Co-60 of activity measurements of the radionuclide 60 Co to include the 2011 result of the CNEA (Argentina), the 2012 results of the BARC (India) and the NRC (Canada), and the 2014 result of the NIM (China) C. Michotte*, G. Ratel*, S. Courte*, P. Arenillas #, C. Balpardo #, L. Joseph, R. Anuradha, D.B. Kulkarni, R. Galea $, K. Moore $, A. Stroak $, Ming Zhang**, Juncheng Liang** and Haoran Liu** *BIPM, # CNEA, BARC, $ NRC, **NIM Abstract Since 2010, four national metrology institutes (NMI) have each submitted a sample of known activity of 60 Co to the International Reference System (SIR) for activity comparison at the Bureau International des Poids et Mesures (BIPM), with comparison identifier BIPM.RI(II)-K1.Co-60. The values of the activity submitted were between about 175 kbq and 1600 kbq. The primary standardization results for the CNEA, Argentina and the BARC, India replace their earlier result of 2003 and 2001, respectively. There are now seventeen results in the BIPM.RI(II)-K1.Co-60 comparison. The key comparison reference value (KCRV) has been updated using the power-moderated weighted mean. The degrees of equivalence between each equivalent activity measured in the SIR and the KCRV have been calculated and the results are given in the form of a table. A graphical presentation is also given. 1. Introduction The SIR for activity measurements of -ray-emitting radionuclides was established in Each national metrology institute (NMI) may request a standard ampoule from the BIPM that is then filled with 3.6 g of the radioactive solution. For radioactive gases, a different standard ampoule is used. Each NMI completes a submission form that details the standardization method used to determine the absolute activity of the radionuclide and the full uncertainty budget for the evaluation. The ampoules are sent to the BIPM where they are compared with standard sources of 226 Ra using pressurized ionization chambers. Details of the SIR method, experimental set-up and the determination of the equivalent activity, A e, are all given in [1]. From its inception until 31 December 2014, the SIR has measured 985 ampoules to give 740 independent results for 67 different radionuclides. The SIR makes it possible for national laboratories to check the reliability of their activity measurements at any time. This is achieved by the determination of the equivalent activity of the radionuclide and by comparison of the result with the key comparison reference value determined from the results of primary standardizations. These comparisons are described as BIPM ongoing comparisons and the results form the basis of the BIPM key comparison database (KCDB) of the Comité International des Poids et Mesures Mutual Recognition Arrangement (CIPM MRA) [2]. The comparison described in this report is known as the BIPM.RI(II)-K1.Co-60 key comparison and includes results published previously [3-7]. 1/24

2 2. Participants The ampoules submitted by the CNEA in 2011 and the BARC in 2012 replace their earlier SIR submissions; the NIM, renewed their participation in the key comparison, after their 1978 result being abandoned in the 2010 final report [7]; the NRC submission is their first participation in the BIPM.RI(II)-K1 comparisons. The laboratory details are given in Table 1, with the earlier submissions being taken from [7]. In cases where the laboratory has changed its name since the original submission, both the earlier and the current acronyms are given, as it is the latter that are used in the KCDB. The AECL (Atomic Energy of Canada Ltd) is not part of the NMI in Canada but was an invited participant in various SIR comparisons, as in the early years, J.G.V. Taylor of the AECL was a personal member of the predecessor to the CCRI(II). The dates of measurement in the SIR given in Table 1 are used in the KCDB and all references in this report. Table 1. Details of the participants in the BIPM.RI(II)-K1.Co-60 NMI Original acronym BIPM Bureau International des Poids et Mesures Full name Country Regional metrology organization Date of measurement at the BIPM YYYY-MM-DD PTB ASMW* Physikalisch-Technische Bundesanstalt LNMRI /IRD IEA** IRD/IPEN** Laboratorio Nacional de Metrologia das Radiaçoes Ionizantes /Instituto de Radioproteção e Dosimetria NMIJ ETL National Metrology Institute of Japan NPL National Physical Laboratory MKEH OMH Magyar Kereskedelmi Engedélyezési Hivatal CMI- IIR UVVVR Český Metrologický Institut, Inspectorate for Ionizing Radiation IAEA International Atomic Energy Agency LNE- LNHB LMRI BNM-LNHB Laboratoire national de métrologie et d'essais - Laboratoire national Henri Becquerel NIM National Institute of Metrology Continued overleaf. Germany EURAMET * Brazil SIM ** ** Japan APMP United Kingdom EURAMET Hungary EURAMET Czech Republic EURAMET France EURAMET China APMP /24

3 Table 1 continued NMI Original acronym Full name Country Regional metrology organization Date of measurement at the BIPM IRA IER Institut de Radiophysique Appliquée NRC AECL # National Research Council of Canada NIST NBS National Institute of Standards and Technology Switzerland EURAMET Canada # # United States SIM NMISA NAC** CSIR-NML National Metrology Institute of South Africa South Africa AFRIMETS ** ** BARC Bhabha Atomic Research Centre India APMP IFIN- HH IFIN Institutul de Fizica si Inginerie Nucleara - "Horia Hulubei" Romania EURAMET PTKMR PDS P3KRBiN Pusat Teknologi Keselamatan dan Metrologi Radiasi Indonesia APMP ENEA- INMRI Ente per le Nuove Tecnologie, l'energia e l'ambiente - Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti Italy EURAMET CNEA Comisiόn Nacional de Energia Atόmica ANSTO Australian Nuclear Science and Technology Organisation Argentina SIM Australia APMP KRISS Korea Research Institute of Standards and Science Republic of Korea APMP BEV Bundesamt für Eich- und Vermessungswesen CIEMAT Centro de Investigaciones Energéticas, Medioambientales y Tecnològicas Continued overleaf. Austria EURAMET Spain EURAMET /24

4 Table 1 continued NMI Original acronym Full name Country Regional metrology organization Date of measurement at the BIPM POLATOM RC Institute of Atomic Energy, Radioisotope Centre IRMM Institute for Reference Materials and Measurements Poland EURAMET European Union * a previous standards laboratory in the country ** another institute of the country # federal Crown corporation, not part of the NMI in Canada (see text) EURAMET NMI standardization methods Each NMI that submits ampoules to the SIR has measured the activity either by a primary standardization method or by using a secondary method, for example a calibrated ionization chamber. In the latter case, the traceability of the calibration needs to be clearly identified to ensure that appropriate correlations are taken into account. A brief description of the standardization methods used by the laboratories, the activities submitted, the relative standard uncertainties (k = 1) and the half-life used by the participants are given in Table 2. The uncertainty budgets for the four new submissions are given in Appendix 1 attached to this report; previous uncertainty budgets are given in the earlier K1 report [3-7]. The list of acronyms used to summarize the methods is given in Appendix 2. The half-life used by the BIPM since 2002 is that recommended by the IAEA, (5) d [8] 1. For the earlier SIR results, the half-life used was (1.0) d [9]. Using the recently published half-life update of (3) d [10] would not change any of the results significantly as the ampoules were all measured within 15 months of the reference date. Details regarding the solutions submitted are shown in Table 3, including any impurities, when present, as identified by the laboratories. When given, the standard uncertainties on the evaluations are shown. The BIPM standard method for evaluating the activity of impurities using a calibrated Ge(Li) spectrometer is described in [11]. The CCRI(II) agreed in 1999 [12] that this method should be followed according to the protocol described in [13] when an NMI makes such a request or when there appear to be discrepancies. However, no such impurity measurement has needed to be carried out at the BIPM for the ampoules submitted before July 2013, when the BIPM service of gamma-ray spectrometry was interrupted for technical reasons. 1 Hereafter, the last digits of the standard uncertainties are given in parenthesis. 4/24

5 Table 2. Standardization methods of the participants for 60 Co NMI or laboratory BIPM PTB LNMRI /IRD NMIJ NPL Continued overleaf Method used (see Appendix 2) Pressurized IC a 4P-IC-GR Pressurized IC calibrated on 08/06/2000 by 4 - using the same solution Pressurized IC a 4P-IC-GR (PPC)- DCC - digital 4P-PP-BP-NA-GR-CO Halflife / d Activity / kbq Reference date YYYY-MM-DD (4) Evaluation of relative standard uncertainty 100 Type A Type B method method /24

6 Table 2 continued NMI Method used or (see Appendix 2) laboratory MKEH CMI-IIR IAEA /RCC b IAEA /CMI-IIR LNE- LNHB NIM IRA Continued overleaf and anti- 4P-??-BP-??-GR-CO 4P-??-BP-??-GR-AC P-PC-BP-GL-GR-CO 4 - (Ge(Li)) 4P-PC-BP-GL-GR-CO Halflife / d 1926 (3) 1926 (3) (5) [8] Activity / kbq Reference date YYYY-MM-DD Evaluation of relative standard uncertainty 100 Type A Type B method method h UT 1925 (4) 1925 (4) h UT h UT (4) Pressurized IC c 4P-IC-GR h UT (3) [10] 0 h UT (2) /24

7 Table 2 continued NMI Method used or (see Appendix 2) laboratory NRC NIST NMISA BARC IFIN-HH PTKMR ENEA- INMRI Continued overleaf 4-4 (PP)- anti 4P-PP-BP-NA-GR-AC 4 - and anti-coinc. 4P-PC-BP-NA-GR-AC Pressurized IC d 4P-IC-GR anti 4P-PC-BP-NA-GR-AC 4 (LS)- 4P-LS-BP-NA-GR-CO 4 (LS)- [14] Halflife / d Activity / kbq Reference date YYYY-MM-DD h UT h UT (3) [10] 17 h UT h UT (3) [10] 17 h UT (2) [15] h UT P-LS-BP-NA-GR-CO h 30 UT h 30 UT h 30 UT 4 (LS)- coinc P-LS-BP-NA-GR-CO 6 h 30 UT [16] (4) 0 h UT coinc h UT Evaluation of relative standard uncertainty 100 Type A Type B method method * /24

8 Table 2 continued NMI Method used or (see Appendix 2) laboratory CNEA ANSTO KRISS BEV CIEMAT POLATOM coinc. CIEMAT/NIST 4P-LS-BP CN and PPC coinc. 4P-PP-BP-NA-GR-CO and TDCR 4P-LS-BP TD P-PP-BP-NA-GR-CO Pressurized IC e 4P-IC-GR coinc. and CIEMAT /NIST f 4P-LS-BP CN 4 (LS)- coinc. and anti-coinc. [17] 4P-LS-BP-NA-GR-CO and 4P-LS-BP-NA-GR-AC Halflife / d Activity / kbq Reference date YYYY-MM-DD Evaluation of relative standard uncertainty 100 Type A Type B method method (3) [10] h UT h UT [10] h UT g [18] IRMM 4 (PPC)-NaIwell digital coinc. (4) [19] 0 h UT P-PP-BP-NA-GR-CO a calibrated by for the nuclide considered b The Radiochemical Centre Ltd, Amersham c calibrated in 1979 by 4 - for the nuclide considered d calibrated in 1980 by 4 - and anti- for the nuclide considered e traceable to the NPL f For the CIEMAT/NIST method, a 3 H tracer from LNE-LNHB was used. g weighted mean of the results obtained by the two methods * the uncertainty of 0.08 % submitted originally has been increased to include the uncertainty of an additional correction (see Appendix 1 of [4]) 8/24

9 Table 3. Details of each solution of 60 Co submitted NMI / SIR year Chemical composition Solvent conc. / (mol dm 3 ) Carrier: conc. /( g g 1 ) Density /(g cm 3 ) Relative activity of any impurity BIPM 1976 CoCl 2 in HCl 0.1 CoCl 2 : PTB 1976 CoCl 2 in HCl 0.1 CoCl 2 : CoCl 2 : CoCl 2 : CoCl 2 : LNMRI /IRD 1976 CoCl 2 in HCl 0.1 CoCl 2 : Co in HCl 0.2 Co : NMIJ 1976 CoCl 2 in HCl 0.1 CoCl 2 : CoCl 2 : NPL 1977 CoCl 2 in HCl 0.1 CoCl 2 : CoCl 2 : 25 1 MKEH 1977 Co in HCl 0.1 Co: Co: CoCl 2 in HCl 0.1 CoCl 2 : 25 CMI-IIR 1977 CoCl 2 in HCl 0.1 CoCl 2 : 20 1 < 0.1 % CoCl 2 : 20 < 0.1 % IAEA/RCC 1978 IAEA/CMI- IIR 1978 LNE-LNHB 1978 Co in HCl 0.1 Co : 100 CoCl 2 in HCl 0.08 CoCl 2 : 20 < 0.1 % CoCl 2 in HCl 0.1 CoCl 2 : < 0.02 % 1986 < 0.01 % 1999 Co in HCl 0.1 Co ++ : NIM 1978 CoCl 2 in HCl 0.1 CoCl 2 : Co ++ in HCl 0.1 Co ++ : IRA 1979 Co ++ in HCl 0.1 Co ++ : Co ++ : (7) Continued overleaf 9/24

10 Table 3 continued NMI Chemical Solvent Carrier: Density Relative activity / SIR year composition conc. / conc. /(g cm 3 ) of any impurity (mol dm 3) /( g g 1) NRC 1980 CoCl 2 in HCl 0.3 Co ++ : CoCl 2.6H 2 O in 0.1 CoCl 2.6H 2 O HCl CoCl 2 in HCl 0.1 CoCl 2 : (3) NIST 1980 Co in HCl 1 Co : (2) NMISA CoCl 2 in HCl 0.1 CoCl 2 : CoCl 2 : Co: 1.5(2) 10 5 CoCl 2 in HCl 1.0 CoCl 2 : CoCl 2.6H 2 O 1 Co ++ : in HCl Co ++ : BARC 1981 CoCl 2 in HCl 0.1 CoCl 2 : 55 IFIN-HH 1983 PTKMR 1984 ENEA- INMRI Co(NO 3 ) Co(NO 3 ) 2 : 1 in HNO CoCl 2 in HCl 0.1 CoCl 2 : CoCl 2 : CoCl 2 in HCl 0.1 Co : CoCl 2 : < 0.01 % CoCl 2.6H 2 O in HCl CoCl 2.6H 2 O in HCl 1 CoCl 2.6H 2 O Co ++ : (1) 137 Cs : 0.003(1) % 63 Ni : 0.026(5) % CNEA 1992 CoCl 2.6H 2 O in 0.1 CoCl 2 : < 0.1 % HCl 2003 CoCl 2.6H 2 O in HCl 1 CoCl 2.6H 2 O < 0.01 % CoCl 2.6H 2 O 1 90 ANSTO 1992 CoCl 2 in HCl 0.1 Co : KRISS 1995 CoCl 2.6H 2 O in HCl 0.5 CoCl 2.6H 2 O BEV 1998 CoCl 2 in HCl 0.1 CoCl 2 : Continued overleaf 2007 CoCl 2 in HCl 0.1 CoCl 2 : /24

11 Table 3 continued NMI / SIR year CIEMAT 1999 POLATOM 2003 IRMM 2005 Chemical composition Solvent conc. / (mol dm 3) Carrier: conc. /( g g 1) Density /(g cm 3 ) CoCl 2 in HCl 1 CoCl 2 : Relative activity of any impurity 63 Ni : % CoCl 2 in HCl 0.1 Co : < 0.1 % CoCl 2 in HCl 0.1 Co : 50 the ratio of the activity of the impurity to the activity of 60 Co at the reference date confirmed by measurements made at the BIPM. 4. Results All the submissions to the SIR since its inception in 1976 are maintained in a database known as the "master-file". The recent submissions have added four ampoules for the activity measurements for 60 Co giving rise to seventy ampoules in total. The SIR equivalent activity, A ei, for each ampoule for the previous and new results is given in Table 4 for each NMI, i. The relative standard uncertainties arising from the measurements in the SIR are also shown. This uncertainty is additional to that declared by the NMI for the activity measurement shown in Table 2. Although submitted activities are compared with a given source of 226 Ra, all the SIR results are normalized to the radium source number 5 [1]. For the CNEA and NIM agreement within standard uncertainty is observed with their previous result in the SIR. No recent submission has been identified as a pilot study so the most recent result of each NMI is normally eligible for Appendix B of the MRA. No international or regional comparison for this radionuclide has been held to date so no linking data are identified. 11/24

12 Table 4. Results of SIR measurements of 60 Co NMI / SIR year Mass of solution m i / g Activity submitted A i / kbq N of Ra source used SIR A e,i / kbq Relative uncertainty from SIR Combined standard uncertainty u i / kbq BIPM PTB LNMRI/IRD a / (9) a NMIJ NPL MKEH CMI-IIR 1977 IAEA/RCC 1978 IAEA/CMI- IIR 1978 LNE-LNHB NIM Continued overleaf

13 Table 4 continued. NMI Mass of / SIR year solution m i / g Activity submitted A i / kbq N of Ra source used SIR A e,i / kbq Relative uncertainty from SIR Combined standard uncertainty u i / kbq IRA a NRC b b NIST NMISA c d a e * BARC IFIN-HH 1983 PTKMR 1984 ENEA- INMRI a CNEA ANSTO 1992 Continued overleaf f h /24

14 Table 4 continued. NMI Mass of / SIR year solution m i / g Activity submitted A i / kbq N of Ra source used SIR A e,i / kbq Relative uncertainty from SIR KRISS Combined standard uncertainty u i / kbq BEV CIEMAT 1999 POLATOM g IRMM a b c d e f g h * the mean of the two A e values shown for the same measurement date is used with an averaged uncertainty, as attributed to an individual entry [22] mass of solution before dilution mass of solution before dilution. Masses after dilution are g and g respectively. mass of solution before dilution. Masses after dilution are g and g respectively. mass of solution before dilution. Mass after dilution is g. solution contained in a CNEA-type ampoule (see paragraph 4 of [4]). the weighted mean value of the activity standardizations obtained from two methods is used. the arithmetic mean value of the comparison results based on the two methods is used, i.e. 7070(26) kbq. not representative of the activity presently disseminated by NMISA (see [4]). 4.1 The key comparison reference value In May 2013 the CCRI(II) decided to no longer calculate the key comparison reference value (KCRV) by using an unweighted mean but rather by using the power-moderated weighted mean [20]. This type of weighted mean is similar to a Mandel-Paule mean in that the NMIs uncertainties may be increased until the reduced chi-squared value is one. In addition, it allows for a power smaller than two in the weighting factor. Therefore, all SIR key comparison results can be selected for the KCRV with the following provisions: a) only results for solutions standardized by primary techniques are accepted, with the exception of radioactive gas standards (for which results from transfer instrument measurements that are directly traceable to a primary measurement in the laboratory may be included); b) each NMI or other laboratory has only one result (normally the most recent result or the mean if more than one ampoule is submitted); c) possible outliers can be identified on a mathematical basis and excluded from the KCRV using the normalized error test with a test value of 2.5 and using the modified uncertainties; d) results can also be excluded for technical reasons; and e) the CCRI(II) is always the final arbiter regarding excluding any data from the calculation of the KCRV. 14/24

15 The data set used for the evaluation of the KCRVs is known as the KCRV file and is a reduced data set from the SIR master-file. Although the KCRV may be modified when other NMIs participate, on the advice of the Key Comparison Working Group of the CCRI(II), such modifications are made only by the CCRI(II) during one of its biennial meetings as for the case of 60 Co in March 2015, or by consensus through electronic means (e.g., ) as discussed at the CCRI(II) meeting in The BARC (2012) result is considered as an outlier so that only their earlier result in 2001 is eligible to be kept in the KCRV. Consequently, the KCRV for 60 Co has been calculated as (2.7) kbq on the basis of the SIR results of the BIPM, ASMW (1976), PTB (2001), LNMRI/IRD (1984), NMIJ (2004), NPL (2000), MKEH (1999), CMI-IIR (1978), LNE-LNHB (1999), NIM (2014), IRA (1979), AECL (1993), NRC (2012), NIST (2007), NMISA (1992), BARC (2001), IFIN-HH (2007), PTKMR, ENEA-INMRI, CNEA (2011), ANSTO, KRISS, CIEMAT, POLATOM and the IRMM. This can be compared with the previous KCRV values of (3.8) kbq, (3.5) kbq and (4.0) kbq as published in 2003, 2006 and 2010, respectively [3, 6, 7]. As expected, 60 Co is the radionuclide with the smallest relative standard uncertainty of the KCRV. 4.2 Degrees of equivalence Every participant in a comparison is entitled to have one result included in the KCDB as long as the NMI is a signatory or designated institute listed in the CIPM MRA, and the result is valid (i.e., not older than 20 years). Normally, the most recent result is the one included. An NMI may withdraw its result only if all other participants agree. The degree of equivalence of a given measurement standard is the degree to which this standard is consistent with the KCRV [2]. The degree of equivalence is expressed quantitatively in terms of the deviation from the key comparison reference value and the expanded uncertainty of this deviation (k = 2). The degree of equivalence between any pair of national measurement standards is expressed in terms of their difference and the expanded uncertainty of this difference and is independent of the choice of key comparison reference value Comparison of a given NMI result with the KCRV The degree of equivalence of the result of a particular NMI, i, with the key comparison reference value is expressed as the difference D i between the values D i Ae KCRV (1) i and the expanded uncertainty (k = 2) of this difference, U i, known as the equivalence uncertainty; hence U u( D ). (2) i 2 i When the result of the NMI i is included in the KCRV with a weight w i, then u 2 (D i ) = (1-2w i ) u i 2 + u 2 (KCRV). (3) However, when the result of the NMI i is not included in the KCRV, then u 2 (D i ) = u i 2 + u 2 (KCRV). (4) 15/24

16 4.2.2 Comparison between pairs of NMI results The degree of equivalence between the results of any pair of NMIs, i and j, is expressed as the difference D ij in the values D ij D D A A (5) i j and the expanded uncertainty (k = 2) of this difference, U ij = 2u(D ij ), where ei e j u 2 Dij 2 i 2 j - ei ej u u 2u( A, A ) (6) where any obvious correlations between the NMIs (such as a traceable calibration, or correlations normally coming from the SIR or from the linking factor in the case of linked comparison) are subtracted using the covariance u(a ei, A ej ) (see [21] for more detail). However, the CCRI decided in 2011 that these pair-wise degrees of equivalence no longer need to be published as long as the methodology is explained. Table 5 shows the matrix of all the degrees of equivalence as they will appear in the KCDB. It should be noted that for consistency within the KCDB, a simplified level of nomenclature is used with A ei replaced by x i. The introductory text is that agreed for the comparison. The graph of the results in Table 5, corresponding to the degrees of equivalence with respect to the KCRV (identified as x R in the KCDB), is shown in Figure 1. This graphical representation indicates in part the degree of equivalence between the NMIs but obviously does not take into account the correlations between the different NMIs. It should be noted that the final data in this paper, while correct at the time of publication, will become out-of-date as NMIs make new comparisons. The formal results under the CIPM MRA [2] are those available in the KCDB. Conclusion The BIPM ongoing key comparison for 60 Co, BIPM.RI(II)-K1.Co-60 currently comprises seventeen results, including the four new results that replace two earlier results in the KCDB. The results have been analysed with respect to the KCRV now re-evaluated for this radionuclide. The degrees of equivalence have been approved by the CCRI(II) and are published in the BIPM key comparison database. Other results may be added when other NMIs contribute 60 Co activity measurements to this comparison or take part in other linked comparisons. Acknowledgements The authors would like to thank the NMIs for their participation in this comparison, and Dr J.M. Los Arcos of the BIPM for editorial assistance. 16/24

17 References [1] Ratel G., The Système International de Référence and its application in key comparisons, Metrologia, 2007, 44(4), S7-S16 [2] CIPM MRA: Mutual recognition of national measurement standards and of calibration and measurement certificates issued by national metrology institutes, International Committee for Weights and Measures, 1999, 45 pp. [3] Ratel G., Michotte C., BIPM comparison BIPM.RI(II)-K1.Co-60 of the activity measurements of the radionuclide 60 Co, Metrologia, 2003, 40, Tech. Suppl., [4] Ratel G., Michotte C., Simpson B.R.S., Iglicki A., Activity measurements of the radionuclide 60 Co for the CSIR-NML and the CNEA in the BIPM comparison BIPM.RI(II)-K1.Co-60, Metrologia, 2003, 40, Tech. Suppl., [5] Ratel G., Michotte C., Broda R., Listkowska A., Activity measurements of the radionuclide 60 Co for the RC, Poland in the ongoing comparison BIPM.RI(II)-K1.Co-60, Metrologia, 2003, 40, Tech. Suppl., [6] Ratel G., Michotte C., Hino Y., Keightley J., Wätjen U., Update of the ongoing comparison BIPM.RI(II)-K1.Co-60 including activity measurements of the radionuclide 60 Co for the NMIJ, Japan and the IRMM (Geel), Metrologia, 2006, 43, Tech. Suppl., [7] Michotte C., Courte S., Ratel G., Sahagia M., Wätjen A.C., Fitzgerald R., Maringer F.-J., Update of the ongoing comparison BIPM.RI(II)-K1.Co-60 including activity measurements of the radionuclide 60 Co for the IFIN-HH (Romania), NIST (USA) and the BEV (Austria), Metrologia, 2010, 47, Tech. Suppl., [8] IAEA-TECDOC-619, X-ray and gamma-ray standards for detector calibration, (1991), Vienna, IAEA. [9] Rytz A., Mesures de périodes radioactives, Procès-Verbaux des Séances du Comité international des poids et mesures, 1973, 41, 68 (Paris : Off. Lib.). [10] Bé M.-M., Chisté V., Dulieu C., Browne E., Baglin C., Chechev V., Kuzmenko N., Helmer R., Kondev F., MacMahon D., Lee K.B., 2006, Table of Radionuclides, Monographie 5 Vol pp. [11] Michotte C., Efficiency calibration of the Ge(Li) detector of the BIPM for SIR-type ampoules, 1999, Rapport BIPM-1999/03, 15 pp. [12] Comité Consultatif pour les Étalons de Mesures des Rayonnements Ionisants 16th meeting (1999), 2001, CCRI(II) [13] Michotte C., Protocol on the use of the calibrated spectrometer of the BIPM for the measurement of impurities in ampoules submitted to the SIR, 2001, CCRI(II)/01-01, 2pp. [14] Simpson B.R.S. and Meyer B.R. Standardization of 60 Co by the 4π(LS)β-γ method, NAC Report NAC/93-05 (1993). [15] BNM-CEA/DTA/DAMRI/LPRI, Nucléide, Nuclear and Atomic Decay Data Version : /12/98 CD ROM, BNM-LNHB, Gif-sur-Yvette. [16] I. Asavinei, E. L. Grigorescu, C. Lazarovici, M. Oncescu, Mesure absolue de l'activité des radionucléides par la méthode des s 4π beta-gamma. Corrections de schéma de désintegration, Congrès MESUCORA-Paris, 1963, Tome 1, Séance 8. 17/24

18 [17] Chyliński A., Radoszewski T., Terlikowska-Droździel T., Jęczmieniowski A., A multimethodic and multiparametric system for standardisation of radionuclides, Appl. Radiat. Isot., 2000, 52, [18] Schötzig U. and Schrader H., Halbwertszeiten und Photonen- Emissionwahrscheinlichkeiten von häufig verwendeten Radionukliden, PTB-Bericht, PTB-Ra-16/5, Braunschweig, September [19] BNM-LNHB/CEA, Nucléide 2000, Nuclear and Atomic Decay Data Version : 30 June 2004 CD ROM, BNM-LNHB, Gif-sur-Yvette. [20] Pommé S, Keightley, J., Determination of a reference value and its uncertainty through a power-moderated mean, Metrologia, 52, 2015, S200-S212. [21] Michotte C. and Ratel G., Correlations taken into account in the KCDB, CCRI(II) working document, 2003, CCRI(II)/ [22] Woods M.J., Reher D.F.G. and Ratel G. Equivalence in radionuclide metrology, Applied Radiation and Isotopes, 52, 2000, /24

19 Table 5. Introductory text for 60 Co and table of degrees of equivalence Key comparison BIPM.RI(II)-K1.Co-60 MEASURAND : Equivalent activity of 60 Co Key comparison reference value: the SIR reference value for this radionuclide is x R = kbq with a standard uncertainty, u R = 2.7 kbq (see Section 4.1 of the Final Report). The value x i is the equivalent activity for laboratory i. The degree of equivalence of each laboratory with respect to the reference value is given by a pair of terms: D i = (x i - x R) and U i, its expanded uncertainty (k = 2), both expressed in kbq, and U i = 2((1-2w i)u i 2 + u R 2 ) 1/2, where w i is the weight of laboratory i contributing to the calculation of x R. Lab i D i / kbq MKEH LNE-LNHB -3 9 CIEMAT NPL IRA PTB NMISA POLATOM NMIJ IRMM IFIN-HH NIST BEV CNEA 7 52 BARC NRC 2 18 NIM U i 19/24

20 Figure 1. Graph of degrees of equivalence with the KCRV for 60 Co (as it appears in Appendix B of the MRA) N.B. Right-hand axis shows approximate values only 20/24

21 Appendix 1. Uncertainty budgets for the activity of 60 Co submitted to the SIR CNEA (2011) Relative standard uncertainties u rel,i 10 4 evaluated by method Contributions due to A B counting statistics 38 weighing 37 dead time 0.2 background resolution time 0.2 half-life extrapolation 1.6 Quadratic summation Relative combined standard uncertainty, u c 54 CNEA (2011) 4P-LS-BP TD Relative standard uncertainties u rel,i 10 4 evaluated by method Contributions due to A B counting statistics 32 weighing 32 dead time < 1 background < 1 counting time < 1 input parameters and statistical model 8 half-life < 1 Quadratic summation Relative combined standard uncertainty, u c 46 21/24

22 BARC (2012) Relative standard uncertainties u rel,i 10 4 evaluated by method Contributions due to A B counting statistics 20 weighing 5 dead time 26 background 2 resolving time 24 half-life < 1 extrapolation 21 Quadratic summation Relative combined standard uncertainty, u c 46 NRC (2012) Relative standard uncertainties u rel,i 10 4 evaluated by method Comments Contributions due to A B counting statistics 3 Weighted average of 10 sources 2 2 = 1/ i weighing < 2 Balance calibration live time < 0.1 background 1 ma 1 (N γ Y) N γ N β u(b γ ) N γ * extrapolation 10 Maximum standard error on N 0 Quadratic summation 3 10 Relative combined standard uncertainty, u c 10 * a 1 fit coefficient Y, N count rates in, anti- channels N count rate in monitor channel u(b ) uncertainty in background rate 22/24

23 NIM (2014) Relative standard uncertainties u rel,i 10 4 evaluated by method Contributions due to A B counting statistics 21 weighing 10 dead time 5 background 5 resolving time 5 extrapolation 8 impurities < 1 Quadratic summation Relative combined standard uncertainty, u c 26 23/24

24 Appendix 2. Acronyms used to identify different measurement methods Each acronym has six components, geometry-detector (1)-radiation (1)-detector (2)-radiation (2)-mode. When a component is unknown,?? is used and when it is not applicable 00 is used. Geometry acronym Detector acronym 4 4P proportional counter PC defined solid angle SA press. prop counter PP 2 2P liquid scintillation counting LS undefined solid angle UA NaI(Tl) NA Ge(HP) Ge(Li) Si(Li) CsI(Tl) ionization chamber grid ionization chamber Cerenkov light detector calorimeter solid plastic scintillator PIPS detector Radiation acronym Mode acronym positron PO efficiency tracing ET beta particle BP internal gas counting IG Auger electron AE CIEMAT/NIST CN conversion electron CE sum counting SC mixed electrons ME CO bremsstrahlung BS anti- AC gamma rays GR counting with efficiency tracing X - rays XR anti- counting with efficiency tracing photons (x + ) PH triple-to-double ratio counting alpha - particle AP selective sampling SS mixture of various radiation GH GL SL CS IC GC LC CA SP PS CT AT TD MX high efficiency HE Examples method 4 (PC) - counting 4 (PPC) - counting eff. trac. defined solid angle -particle counting with a PIPS detector 4 (PPC)AX- (GeHP)-anti counting 4 CsI-,AX, counting calibrated IC internal gas counting acronym 4P-PP-MX-NA-GR-CT SA-PS-AP P-PP-MX-GH-GR-AC 4P-CS-MX HE 4P-IC-GR P-PC-BP IG 24/24