Activity measurements of the radionuclide 111 In for the LNE-LNHB, France in the ongoing comparison BIPM.RI(II)-K1.In-111

Size: px

Start display at page:

Download "Activity measurements of the radionuclide 111 In for the LNE-LNHB, France in the ongoing comparison BIPM.RI(II)-K1.In-111"

Asher Floyd
5 years ago
Views:

1 Activity measurements of the radionuclide 111 In for the LNE-LNHB, France in the ongoing comparison BIPM.RI(II)-K1.In-111 C. Michotte*, G. Ratel*, S. Courte*, E. Verdeau, M.-N. Amiot *BIPM, LNE-LNHB, France Abstract In 2006, the Laboratoire national de métrologie et d essais - Laboratoire national Henri Becquerel (LNE-LNHB) submitted a sample of known activity of 111 In to the International Reference System (SIR). The value of the activity submitted was about 14 MBq. This provides a new result for France in the matrix of degrees of equivalence in the key comparison database that enables them to maintain their degrees of equivalence for this radionuclide. The key comparison reference value has been re-evaluated and the comparison, identifier BIPM.RI(II)-K1.In-111, now contains five valid results. 1. Introduction The SIR for activity measurements of γ-ray-emitting radionuclides was established in Each NMI may request a standard ampoule from the BIPM that is then filled (3.6 g) with the radionuclide in liquid form. For radioactive gases, a different standard ampoule is used. The 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]. Since its inception, the SIR has measured over 931 ampoules to give 686 independent results for 64 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 realizations. These comparisons are described as BIPM ongoing comparisons and the results form the basis of the BIPM key comparison database (KCDB) that was set up under the CIPM Mutual Recognition Arrangement (CIPM MRA) [2]. The comparison described in this report is known as the BIPM.RI(II)- K1.In-111 key comparison and the earlier results have been published in [3, 4]. 1/13

2 2. Participants The LNE-LNHB, five other NMIs and two other laboratories, have now submitted thirteen ampoules for the comparison of 111 In activity measurements since The NMI details are given in Table 1. Note that the AECL 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). Table 1. Details of the participants in the BIPM.RI(II)-K1.In-111 Original acronym NMI Full name Country Regional metrology organization Date of measurement at the BIPM NBS NIST National Institute of Standards and Technology NPL National Physical Laboratory AECL Atomic Energy of Canada Ltd LMRI BNM- LNHB LNE- LNHB Laboratoire national de métrologie et d essais - Laboratoire national Henri Becquerel NIRH National Institute of Radiation Hygiene UVVVR CMI-IIR Český Metrologický Institut/Czech Metrological Institute, Inspectorate for Ionizing Radiation NMIJ National Metrology Institute of Japan PTB Physikalisch- Technische Bundesanstalt United States United Kingdom SIM EUROMET Canada France EURAMET Denmark EURAMET Czech Republic EURAMET Japan APMP Germany EUROMET /13

3 3. 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 any correlations are taken into account. A brief description of the standardization methods for the laboratory, the activities submitted and the relative standard uncertainties (k = 1) are given in Table 2. The recent uncertainty budget for the LNE-LNHB is given in Appendix 1. The uncertainty budgets for previous submissions, when available, are included in the earlier reports [3, 4]. The acronyms used for the measurement methods are given in Appendix 2. The half-life used by the BIPM is (1) d [5] which compares well with the value of (4) d in the BIPM Monographie 5 [6]. A change to the latter half-life would have a negligible effect on the SIR results. Details regarding the solution submitted are shown in Table 3, including any impurities, when present, as identified by the laboratory. The BIPM has a standard method for evaluating the activity of impurities using a calibrated Ge(Li) spectrometer [7]. The CCRI(II) agreed in 1999 [8] that this method should be followed according to the protocol described in [9] when an NMI makes such a request or when there appear to be discrepancies. No impurity measurement was carried out for this latter submission. 3/13

4 Table 2. Standardization methods of the participants for 111 In NMI NIST NPL AECL LNE- LNHB NIRH CMI- IIR NMIJ Method used and acronym (see Appendix 2) Pressurized IC calibrated in 1977 by 4π(e A,x)-γ coinc. 4P-PP-MX-NA-GR-CO Pressurized IC calibrated by primary meas. of 111 In 4P-PC-MX-NA-GR-CO 4π(PC)-γ coincidence 4P-PC-MX-NA-GR-CO 4πγ 4P-NA-GR HE Pressurized IC calibrated in Oct by 4πγ 4P-NA-GR HE Pressurized IC* 4π(e,x)-γ coinc. 4P-PC-MX-NA-GR-CO Pressurized IC calibrated in 2001 by 4π(e,x)-γ coinc. 4P-PC-MX-NA-GR-CO PTB Pressurized ionization chamber calibrated in April/May 2005 by 4πPPC e c -γ coinc. 4P-PP-MX-NA-GR-CO * traceable to the NPL Half-life / d Activity A i / kbq Reference date YY-MM-DD h UT (1) (1) 12 h UT h UT (4) [6] 0 h UT h UT h UT h UT h UT h UT (5) [10] 12 h UT h UTC Relative standard uncertainty 100 by method of evaluation A B /13

5 4. Results All the submissions to the SIR since its inception in 1976 are maintained in a database known as the "master-file". The activity measurements for 111 In arise from thirteen ampoules and the SIR equivalent activity for each ampoule, A ei, is given in Table 4 for each NMI, i. The dates of measurement in the SIR are given in Table 1 and reproduced in Tables 3 and 4. 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 activities submitted are compared with a given source of 226 Ra, all the SIR results are normalized to the radium source number 5 [1]. Table 3. Details of the solution of 111 In submitted NMI NIST Chemical composition Solvent conc. / (mol dm 3 ) Carrier or salt conc. /(μg g 1 ) Density /(g cm 3 ) Relative activity of 114 In m impurity InCl 3 in (1) (33) % HCl 3.19 InCl 3 : (4) % NPL InCl 3 in HCl 0.1 InCl 3 : In in HCl 0.1 In: AECL In in HCl < 0.1 % LNE- LNHB InCl 3 in HCl 0.1 InCl 3 : (1) % InCl 3.4H 2 O 0.1 InCl 3.4H 2 O : in HCl 41 NIRH 111 In Ca- NaHCO 3 and DTPA in NaHCO 3 and NaCl NaCl : CMI-IIR In in HCl NMIJ InCl 3 and NaCl in HCl 0.1 InCl 3 : 100 NaCl : PTB In(NO 3 ) 2 5 H 2 O in HCl 0.1 In(NO 3 ) 2 5 H 2 O: the ratio of the activity of the impurity to the activity of 111 In at the reference date In m : 1.58 (4) /13

6 Measurements repeated at the BIPM for the LNE-LNHB 2006 ampoule over a period of two half-lives give results in agreement within the SIR standard uncertainty. No submission has been identified as a pilot study so the most recent result, dating post 1984, of each NMI is eligible for Appendix B of the CIPM MRA. Note that the AECL and the NIRH no longer provide activity measurement services under the CIPM MRA. No international or regional comparison for this radionuclide has been held to date so no linking data are identified. Table 4. Results of SIR measurements of 111 In NMI NIST Mass of solution m i / g Activity submitted A i / kbq N of Ra source used SIR A e / kbq Relative uncertainty from SIR Combined uncertainty u c,i / kbq NPL AECL * LNE- LNHB (6) NIRH CMI-IIR NMIJ PTB (9) * the mass given is that before dilution the mean of the two A e values is used with an averaged uncertainty, as attributed to an individual entry [11] 6/13

7 4.1 The key comparison reference value The key comparison reference value is derived from the unweighted mean of all the results submitted to the SIR with the following provisions: The key comparison reference value is derived from the unweighted mean of all the results submitted to the SIR with the following provisions: a) only primary standardized solutions 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 more recent or the mean if more than one ampoule is submitted at the same time); c) any outliers are identified using a reduced chi-squared test and, if necessary, excluded from the KCRV using the normalized error test with a test value of four; d) exclusions must be approved by the CCRI(II). The reduced data set used for the evaluation of the KCRVs is known as the KCRV file and is the 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 only made by the CCRI(II), normally during one of its biennial meetings. This was the case in 2007 when the CCRI approved the inclusion of the PTB result in the KCRV. Consequently, the KCRV for 111 In has been re-evaluated from (120) kbq [3] to (130) kbq using the results from the AECL, LNE-LNHB (1981), NPL (1982), CMI-IIR, NIST (1998), NMIJ and the PTB. 4.2 Degrees of equivalence Every NMI that has submitted ampoules to the SIR 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, that is, not older than 20 years. Normally, the most recent result is the one included. Any NMI may withdraw its result only if all the participants agree. The degree of equivalence of a given measurement standard is the degree to which this standard is consistent with the key comparison reference value [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 with the KCRV The degree of equivalence of a particular NMI, i, with the key comparison reference value is expressed as the difference between the results D i = A e KCRV (1) i 7/13

8 and the expanded uncertainty (k = 2) of this difference, U i, known as the equivalence uncertainty, hence U = 2, (2) i u Di taking correlations into account as appropriate [12] Comparison of any two NMIs with each other The degree of equivalence, D ij, between any pair of NMIs, i and j, is expressed as the difference in their results D = D D = A A (3) and the expanded uncertainty of this difference U ij where ij i j ei e j u u + u - 2u( A, A ) (4) D ij = i j e, i e, j where any obvious correlations between the NMIs (such as a traceable calibration) are subtracted using the covariance u(a ei, A ej ), as are normally those correlations coming from the SIR. The uncertainties of the differences between the values assigned by individual NMIs and the key comparison reference value (KCRV) are not necessarily the same uncertainties that enter into the calculation of the uncertainties in the degrees of equivalence between a pair of participants. Consequently, the uncertainties in the table of degrees of equivalence cannot be generated from the column in the table that gives the uncertainty of each participant with respect to the KCRV. However, the effects of correlations have been treated in a simplified way as the degree of confidence in the uncertainties themselves does not warrant a more rigorous approach. Table 5 shows the matrix of all the degrees of equivalence as they 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 first column of 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. The graphical representation indicates in part the degree of equivalence between the NMIs but does not take into account the correlations between the different NMIs. However, the matrix of degrees of equivalence shown in yellow in Table 5 does take the known correlations into account. Conclusion The new result for the LNE-LNHB is now included in the key comparison database. This 2006 result agrees well with the previous result of 1981 which demonstrates the consistency of the measurements at the LNE-LNHB over this period. The BIPM ongoing key comparison for 111 In, BIPM.RI(II)-K1.In-111 currently comprises five results. These have been analysed with respect to the KCRV determined for this radionuclide, and with respect to each other. The matrix of degrees 8/13

9 of equivalence has been approved by the CCRI(II) and is published in the BIPM key comparison database. Other results may be added as and when NMIs contribute 111 In activity measurements to this comparison or take part in linked comparisons. Acknowledgements The authors would like to thank Dr P.J. Allisy-Roberts of the BIPM for editorial assistance. References [1] R 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, 14 October 1999, 45 pp. Available from the BIPM website: [3] Ratel G., Michotte C., BIPM comparison BIPM.RI(II)-K1.In-111 of activity measurements of the radionuclide 111 In, Metrologia, 2003, 40, Tech. Suppl., [4] Ratel G., Michotte C., Kossert K., Janßen H., Activity measurements of the radionuclide 111 In for the PTB, Germany in the ongoing comparison BIPM.RI(II)-K1.In-111,, Metrologia, 2006, 43, Tech. Suppl., [5] Firestone R. B., Table of isotopes, 1996, Eighth edition, volume 1, New York, Wiley and sons. [6] 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, BIPM Monographie 5 Vol [7] [8] [9] [10] [11] [12] Michotte C., Efficiency calibration of the Ge(Li) detector of the BIPM for SIRtype ampoules, Rapport BIPM-1999/03, 1999, 15 pp. Comité Consultatif pour les Étalons de Mesures des Rayonnements Ionisants 16th meeting (1999), 2001, CCRI(II) Michotte C., Protocol on the use of the calibrated spectrometer of the BIPM for the measurement of impurities in ampoules submitted to the SIR, CCRI(II)/01-01, 2001, 2p. IAEA-TECDOC-619, X-ray and gamma-ray standards for detector calibration, (1991), Vienna, IAEA. Woods M.J., Reher D.F.G. and Ratel G., Equivalence in radionuclide metrology, Applied Radiation and Isotopes, 2000, 52, Ratel G., Evaluation of the uncertainty of the degree of equivalence, 2005, Metrologia 42, /13

10 Table 5. Table of degrees of equivalence and introductory text for 111 In Key comparison BIPM.RI(II)-K1.In-111 MEASURAND : Equivalent activity of 111 In Key comparison reference value: the SIR reference value x R for this radionuclide is MBq, with a standard uncertainty of 0.13 MBq (see Section 4.1 of the Report), the value x i is taken as 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 MBq, and U i = 2((1-2/n )u 2 i + (1/n 2 )Σu 2 i ) 1/2 when each laboratory has contributed to the calculation of x R, with n the number of laboratories. The degree of equivalence between two laboratories is given by a pair of numbers: D ij = D i - D j = (x i - x j ) and U ij, its expanded uncertainty (k = 2), both expressed in MBq. The approximation U ij ~ 2(u i 2 + u j 2 ) 1/2 is used in the following table. Lab j Lab i CMI-IIR NIST NMIJ PTB LNE-LNHB D i U i D ij U ij D ij U ij D ij U ij D ij U ij D ij U ij / MBq / MBq / MBq / MBq / MBq / MBq CMI-IIR NIST NMIJ PTB LNE-LNHB /13

11 Figure 1. Graph of degrees of equivalence with the KCRV for 111 In (as it appears in Appendix B of the MRA) BIPM.RI(II)-K1.In-111 Degrees of equivalence for equivalent activity of 111In [Di = (xi - xr)] / (MBq)) [Di / xr] / (kbq / MBq) -1.5 CMI-IIR NIST NMIJ PTB LNE-LNHB -30 N.B. Right-hand axis shows approximate values only 11/13

12 Appendix 1. Uncertainty budget for the activity of 111 In submitted to the SIR Uncertainty budget for the LNE-LNHB measurement (2006) Relative standard uncertainties u i 10 4 evaluated by method Contributions due to A B Ionization current ( 111 In) including background 9 and geometry uncertainties Radium reference source 5.6 Linearity < 1 Calibration factor 11 Weighing 1.2 Impurities Decay corrections < 0.1 Quadratic summation Relative combined standard uncertainty, u c /13

13 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 4π 4P proportional counter PC defined solid angle SA press. prop. counter PP 2π 2P liquid scintillation counting LS undefined solid angle UA NaI(Tl) NA Ge(HP) GH Ge(Li) GL Si(Li) SL CsI(Tl) CS ionization chamber IC grid ionization chamber GC bolometer BO calorimeter CA PIPS detector PS 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 coincidence CO bremsstrahlung BS anti-coincidence AC gamma rays GR coincidence counting with CT efficiency tracing X - rays XR anti-coincidence counting with efficiency tracing AT photons (x + γ) PH triple-to-double coincidence TD ratio counting photons + electrons PE selective sampling SS alpha - particle AP high efficiency HE mixture of various radiations MX digital coincidence counting DC Examples method acronym 4π(PC)β γ-coincidence counting 4P-PC-BP-NA-GR-CO 4π(PPC)β γ-coincidence counting eff. trac. 4P-PP-MX-NA-GR-CT defined solid angle α-particle counting with a PIPS detector SA-PS-AP π(PPC)AX-γ(Ge(HP))-anticoincidence counting 4P-PP-MX-GH-GR-AC 4π CsI-β,AX,γ counting 4P-CS-MX HE calibrated IC internal gas counting 4P-PC-BP IG 13/13

Activity measurements of the radionuclide 153 Sm for the ANSTO, Australia in the ongoing comparison BIPM.RI(II)-K1.Sm-153

Activity measurements of the radionuclide 153 Sm for the ANSTO, Australia in the ongoing comparison BIPM.RI(II)-K1.Sm-153 G. Ratel*, C. Michotte*, M. Reinhard, D. Alexiev, L. Mo *BIPM, ANSTO, Australia