BIPM comparison BIPM.RI(II)-K1.Sn-113 of activity measurements of the radionuclide 113 Sn. G. Ratel and C. Michotte BIPM

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1 Report for S /0/09 BIPM comparso BIPM.RI(II)-K1.S-113 of actvty measuremets of the radouclde 113 S G. Ratel ad C. Mchotte BIPM Abstract Sce 1975, sx atoal metrology sttutes (NMI) have submtted eght samples of kow actvty of 113 S to the Iteratoal Referece System (SIR) for actvty comparso wth comparso detfer BIPM.RI(II)-K1.S-113 at the Bureau Iteratoal des Pods et Mesures (BIPM). The actvtes raged from about 0.9 MBq to MBq. The degrees of equvalece betwee each NMI have bee calculated ad the results are gve the form of a matrx for the sx NMIs. The results of ths comparso have bee approved by Secto II of the Cosultatve Commttee for Iozg Radato (CCRI(II)). 1. Itroducto The SIR for actvty measuremets of γ-ray-emttg radoucldes was establshed Each NMI may request a stadard ampoule from the BIPM that s the flled (3.6 g) wth the radouclde lqud (or gaseous) form. The NMI completes a submsso form that detals the stadardzato method used to determe the absolute actvty of the radouclde ad the full ucertaty budget for the evaluato. The ampoules are set to the BIPM where they are compared wth stadard sources of 6 Ra usg pressurzed ozato chambers. Detals of the SIR method, expermetal set-up ad the determato of the equvalet actvty are all gve [1]. Sce ts cepto utl 31 December 003, the SIR has measured 849 ampoules to gve 615 depedet results for 6 dfferet radoucldes. The SIR makes t possble for atoal laboratores to check the relablty of ther actvty measuremets at ay tme. Ths s acheved by the determato of the equvalet actvty of the radouclde ad by comparso of the result wth the key comparso referece value determed from the results of prmary realzatos. These comparsos are descrbed as BIPM ogog comparsos ad the results form the bass of the BIPM key comparso database (KCDB) of the Mutual Recogto Arragemet (MRA) []. The comparso descrbed ths report s kow as the BIPM.RI(II)-K1.S-113 key comparso.. Partcpats Sx NMIs have submtted eght ampoules for the comparso of 113 S actvty measuremets sce The laboratory detals are gve Table 1. I cases where 1/14

2 Report for S /0/09 the laboratory has chaged ts ame sce the orgal submsso, both the earler ad the curret acroyms are gve, as t s the latter that are used the KCDB. Table 1. Detals of the partcpats the BIPM.RI(II)-K1.S-113 Orgal acroym NMI Full ame Coutry Regoal metrology orgazato Date of measuremet at the BIPM NBS NIST Natoal Isttute of Stadards ad Techology UVVVR CMI-IIR Český Metrologcký Isttut/Czech Metrologcal Isttute, Ispectorate for Iozg Radato OMH Országos Mérésügy Hvatal PTB Physkalsch- Techsche Budesastalt LPRI BNM- LNHB Bureau atoal de métrologe- Laboratore atoal Her Becquerel CNEA Comso Nacoal de Eerga Atomca Uted States SIM Czech Republc EUROMET Hugary EUROMET Germay EUROMET Frace EUROMET Argeta SIM NMI stadardzato methods Each NMI that submts ampoules to the SIR has measured the actvty ether by a prmary stadardzato method or by usg a secodary method, for example a calbrated ozato chamber. I the latter case, the traceablty of the calbrato eeds to be clearly detfed to esure that ay correlatos are take to accout. A bref descrpto of the stadardzato methods for each laboratory, the actvtes submtted ad the relatve stadard ucertates (k = 1) are gve Table. The lst of acroyms used to summarze the methods s gve Appedx 3. Full ucertaty budgets have bee requested as part of the comparso protocol oly sce Whe submtted by the NMIs, the ucertaty budgets are gve Appedx 1 /14

3 Report for S /0/09 attached to ths report. Cosequetly, o ucertaty budgets were provded for ths comparso. The half-lfe used by the BIPM s (1) days [3]. The data could be revsed usg the half-lfe recommeded by the IAEA [4], (4) d. However, the updated degrees of equvalece would ot dffer sgfcatly as most of the SIR measuremets were performed wth less tha two moths followg the referece date. I the extreme case of 70 days, for the PTB, the relatve chage A e s about Table. Stadardzato methods of the partcpats for 113 S NMI Method used ad acroym (see Appedx 3) NIST Pressurzed IC * 4P-IC-GR CMI- IIR OMH 4πe c -x cocdece 4P-PC-CE-NA-XR-CO ad 4πe c coutg 4P-PC-CE Ge(L) γ coutg UA-GL-GR PTB Pressurzed IC ** BNM- LNHB CNEA 4P-IC-GR HP-Ge spectrometry # UA-GH-GR HP-Ge spectrometry UA-GH-GR Half-lfe / d Actvty A / kbq Referece date YY-MM-DD [3] h UT h UT h UT (3) [5] h UT h UT (3) [5] h UT h UT Relatve stadard ucertaty 100 by method of evaluato A B correspodg to a 39 kev γ-ray emsso rate of s 1 two ampoules submtted * calbrated for 113 S by NaI ad Ge(L) photopeak coutg UA-NA-GR ad UA-GL-GR ** calbrated 1980 by effcecy calculato ad Ge spectrometry UA-GL-GR # calbrated 1990 usg about 80 eergy pots ot cludg those of 113 S gamma trastos. Detals regardg the soluto submtted are show Table 3, cludg ay mpurtes, whe preset, as detfed by the laboratores. Whe gve, the stadard ucertates o the evaluatos are show. Recetly the BIPM has developed a stadard method for evaluatg the actvty of mpurtes usg a calbrated Ge(L) spectrometer [6]. The CCRI(II) agreed 1999 [7] that ths method should be 3/14

4 Report for S /0/09 followed accordg to the protocol descrbed [8] whe a NMI makes such a request or whe there appear to be dscrepaces. Table 3. Detals of the soluto of 113 S submtted NMI Chemcal composto Solvet coc. / (mol dm 3 ) Carrer: coc. /(µg g 1 ) Desty /(g cm 3 ) NIST SCl 4 HCl S HCl 4 S : ()* CMI- IIR OMH Hexachlorostaate HCl S + I HCl PTB SCl HCl BNM- LNHB SCl 4 HCl Relatve actvty of mpurty () 6 6 S : 8 I : 17 3 SCl : 50 SCl 4 : I m : 3.6 (7) % 15 Sb : 0.1 () % 114 I m : 0.90 (5) % 15 Sb : (5) % 114 I m : (5) % 14 Sb : (3) % Sb : 0.06 (1) % 60 Co : 0.00 (1) % CNEA SCl S : the rato of the actvty of the mpurty to the actvty of 113 S at the referece date * at.8 C. 4. Results All the submssos to the SIR sce ts cepto 1976 are mataed a database kow as the "mother-fle". The actvty measuremets for 113 S arse from sx ampoules ad the SIR equvalet actvty for each ampoule, A e, s gve Table 4 for each NMI,. The assumpto s made that the daughter radouclde 113 I m (T 1/ of (5) h [5]) was equlbrum wth the paret at the SIR measuremet dates. The dates of measuremet the SIR are gve Table 1 ad are used the KCDB ad all refereces ths report. The relatve stadard ucertates arsg from the measuremets the SIR are also show. Ths ucertaty s addtoal to that declared by the NMI for the actvty measuremet show Table. Although actvtes submtted are compared wth a gve source of 6 Ra, all the SIR results are ormalzed to the radum source umber 5 [1]. The sgfcat SIR correctos for mpurtes are ad for the NIST (1980) ad CMI-IIR respectvely. 4/14

5 Report for S /0/09 I prcple, the chemcal composto of the solutos could have a fluece o the SIR measuremets owg to the tese x-ray emsso from 113 S. However, usg the effcecy curve of the SIR [9], the cotrbuto of the x-rays to the ozato curret s estmated to be eglgble. I cosequece, the fluece of the chemcal composto o the SIR measuremets ca also probably be eglected ths case although a more detaled study could be performed. No recet submsso has bee detfed as a plot study so the most recet result of each NMI s ormally elgble for Appedx B of the MRA. No teratoal or regoal comparso for ths radouclde has bee held to date so o lkg data are detfed. Table 4. Results of SIR measuremets of 113 S NMI Mass of soluto m / g Actvty submtted A / kbq N of Ra source used SIR A e / kbq Relatve ucertaty from SIR Combed ucertaty u c, / kbq NIST * 640 CMI- IIR OMH PTB BNM LNHB CNEA after trasfer ad weghg at the BIPM of part of the NIST soluto the mea of the two A e values show for the same measuremet date s used wth a averaged ucertaty, as attrbuted to a dvdual etry [10] * maly due to the ucertaty of the mpurty actvtes as gve by the NIST. 5/14

6 Report for S /0/ The key comparso referece value The key comparso referece value s derved from the uweghted mea of all the results submtted to the SIR wth the followg provsos: a) oly prmary stadardzed solutos are accepted, or ozato chamber measuremets that are drectly traceable to a prmary measuremet the laboratory; b) each NMI or other laboratory has oly oe result (ormally the most recet result or the mea f more tha oe ampoule s submtted); c) ay outlers are detfed usg a reduced ch-squared test ad, f ecessary, excluded from the KCRV usg the ormalzed error test wth a test value of four; d) exclusos must be approved by the CCRI(II). The reduced data set used for the evaluato of the KCRVs s kow as the KCRV fle ad s the reduced data set from the SIR mother-fle. Although the KCRV may be modfed whe other NMIs partcpate, o the advce of the Key Comparso Workg Group of the CCRI(II), such modfcatos are oly made by the CCRI(II), ormally durg oe of ts beal meetgs. As oly oe NMI has submtted a result for ths comparso that comes from a prmary stadardzato, o KCRV ca be determed at preset. However, the detals of how the KCRV s ormally determed are gve the followg secto for completeess. 4. Degrees of equvalece Every NMI that has submtted ampoules to the SIR s ettled to have oe result cluded Appedx B of the KCDB as log as the NMI s a sgatory or desgated sttute lsted the MRA. Normally, the most recet result s the oe cluded. Ay NMI may wthdraw ts result oly f all the partcpats agree. The degree of equvalece of a gve measuremet stadard s the degree to whch ths stadard s cosstet wth the key comparso referece value []. The degree of equvalece s expressed quattatvely terms of the devato from the key comparso referece value ad the expaded ucertaty of ths devato (k = ). The degree of equvalece betwee ay par of atoal measuremet stadards s expressed terms of ther dfferece ad the expaded ucertaty of ths dfferece ad s depedet of the choce of key comparso referece value Comparso of a gve NMI wth the KCRV The degree of equvalece of a partcular NMI,, wth the key comparso referece value s expressed as the dfferece betwee the results D = A e KCRV (1) ad the expaded ucertaty (k = ) of ths dfferece, U, kow as the equvalece ucertaty, hece U = u D, () takg correlatos to accout as approprate (see Appedx ). 6/14

7 Report for S /0/ Comparso of ay two NMIs wth each other The degree of equvalece, D, betwee ay par of NMIs, ad, s expressed as the dfferece ther results D = D D = A A (3) ad the expaded ucertaty of ths dfferece U where u D = u + u e e ( f k ucorr, ) ( f k u ) k corr, k k ad ay obvous correlatos the stadard ucertates for a gve compoet, u corr,k,, betwee the NMIs (such as a traceable calbrato) are subtracted usg a approprate correlato coeffcet, f k, as are ormally those correlatos comg from the SIR. The ucertates of the dffereces betwee the values assged by dvdual NMIs ad the key comparso referece value (KCRV) are ot ecessarly the same ucertates that eter to the calculato of the ucertates the degrees of equvalece betwee a par of partcpats. Cosequetly, the ucertates the table of degrees of equvalece caot be geerated from the colum the table that gves the ucertaty of each partcpat wth respect to the KCRV. However, the effects of correlatos have bee treated a smplfed way, as the degree of cofdece the ucertates themselves does ot warrat a more rgorous approach. Table 5 shows the matrx of all the degrees of equvalece as they wll appear Appedx B of the KCDB. It should be oted that for cosstecy wth the KCDB, a smplfed level of omeclature s used wth A e replaced by x. The troductory text s that agreed for the comparso. The matrx of degrees of equvalece show yellow Table 5 takes ay kow correlatos to accout. Cocluso The BIPM ogog key comparso for 113 S, BIPM.RI(II)-K1.S-113 curretly comprses sx results. These have bee aalysed for degrees of equvalece wth respect to each other. The matrx of degrees of equvalece has bee approved by the CCRI(II) ad s publshed the BIPM key comparso database. Other results may be added as ad whe other NMIs cotrbute 113 S actvty measuremets to ths comparso. If prmary measuremet methods are submtted, a KCRV wll the be determed. k (4) Ackowledgemets The authors would lke to thak the NMIs for ther partcpato ths comparso, Mr Chrsta Colas of the BIPM for hs dedcated work matag the SIR sce ts cepto ad for the thousads of measuremets he has made over the years, ad Dr P.J. Allsy-Roberts of the BIPM for edtoral assstace. 7/14

8 Report for S /0/09 Refereces [1] Ratel G. The teratoal referece system for actvty measuremets of γ- emttg radoucldes (SIR), 003, BIPM Moograph XX, ( preparato). [] MRA: Mutual recogto of atoal measuremet stadards ad of calbrato ad measuremet certfcates ssued by atoal metrology sttutes, Iteratoal Commttee for Weghts ad Measures, 1999, 45 pp. [3] Murray J. Mart, Nuclear Data Proect, ORNL, prvate commucato, [4] IAEA-TECDOC-619, X-ray ad gamma-ray stadards for detector calbrato, 1991, Vea, IAEA. [5] BNM-CEA, Table de Radouclédes, Verso : 1984, BNM-LNHB, Gf-sur- Yvette. [6] Mchotte C., Effcecy calbrato of the Ge(L) detector of the BIPM for SIRtype ampoules, 1999, Rapport BIPM-1999/03, 15 pp. [7] Comté Cosultatf pour les Étalos de Mesures des Rayoemets Iosats 16th meetg (1999), 001, CCRI(II) [8] Mchotte C., Protocol o the use of the calbrated spectrometer of the BIPM for the measuremet of mpurtes ampoules submtted to the SIR, 001, CCRI(II)/01-01, pp. [9] Mchotte C., Effcecy curve of the ozato chamber of the SIR, 00, Appl. Rad. Isot. 56, [10] Woods M.J., Reher D.F.G., Ratel G., Equvalece radouclde metrology, 000, Appl. Radat. Isotop., 5, /14

9 Table 5. Table of degrees of equvalece ad troductory text for 113 S Key comparso BIPM.RI(II)-K1.S-113 MEASURAND : Equvalet actvty of 113 S There s curretly o key comparso referece value. The value x s take as the equvalet actvty for laboratory. The degree of equvalece betwee two laboratores s gve by a par of umbers: D = D - D = (x - x ) ad U, ts expaded ucertaty (k = ), both expressed MBq. The approxmato U ~ (u + u ) s used the followg table. Lab Lab NIST CMI-IIR OMH PTB BNM-LNHB CNEA D U D U D U D U D U D U / MBq / MBq / MBq / MBq / MBq / MBq NIST CMI-IIR OMH PTB BNM-LNHB CNEA /14

10 Report for S /0/09 Appedx 1. Ucertaty budgets for the actvty of 113 S submtted to the SIR No detaled ucertaty budgets have bee submtted for ths comparso. 10/14

11 Report for S /0/09 Appedx. Evaluato of the ucertaty of the degree of equvalece Table 5 dcates for each laboratory the degree of equvalece D wth ts assocated ucertaty U. Ths appedx presets the procedure used to evaluate these ucertates. The degree of equvalece of oe laboratory s defed as the dfferece betwee the dvdual value of the equvalet actvty A e for a NMI ad a sutable referece value whch has bee evaluated by the KCDB Workg Group ad the expaded ucertaty of ths dfferece. Curretly, the referece value, KCRV, for a gve radouclde s calculated as the arthmetc mea value of the SIR expermetal etres for ths radouclde. Brefly at least four stuatos ca occur depedg o the cosstecy of the expermetal SIR data sets : 1. All data are cosstet ad cotrbute to the referece value; ths s the geeral case;. The value obtaed by a laboratory that o loger exsts, s used as log as t fts the usual qualty crtera; t s take to accout whe evaluatg the referece value but does ot appear the matrces of results; 3. A value, that has bee detfed for example as a outler, s ot take to accout for the evaluato of the referece value but, evertheless, the correspodg laboratory appears the matrces of results. The stuato where a laboratory that o loger exsts but cotrbutes to the referece value ad where a outler has bee detfed the data set ca occur. Ths s a combato of both stuato ) ad stuato 3). The results, deduced from these two precedg cases, are also preseted here, case 4. I the followg, the expresso of the ucertaty for these four cases s cosdered o the assumpto that the ucertates of the dfferet equvalet actvtes A e are ot correlated. For the sake of coherece wth the defto of the varables used the text, the followg otato s used : x = A e ad u = u Ae ts ucertaty. 11/14

12 Report for S /0/09 Case 1. All laboratores cotrbute to the referece value, ad appear Table 5. I ths case obvously we have = 1 x xref = x= (A 1) D x xref = (A ) x x = 1 1 D = x = x 1 (A 3) At ths stage the ucertaty of D has to be calculated. Applyg the method of Gauß for the propagato of the ucertates t s ecessary to calculate the partal dervatves of D wth respect to the x. D 1 So = 1,ad x (A 4) D 1 =,( ). x (A 5) The the total combed ucertaty becomes D D c u = u + u (A 6) x x 1 ( 1 ) 1 = u + (A 7) u or, after recombato 1 = 1 u +. (A 8) u 1 = Whe a coverage factor of s used (A-8) becomes 1 U = 1. (A 9) u + u = 1 Case. A laboratory was used to evaluate the referece value but does ot appear Table 5. Let us assg the subscrpt to the addtoal laboratory that cotrbutes to the referece value. The ucertaty of ths laboratory wll appear oly the secod part of equato (A-9). Accordgly, equato (A-9) becomes 1/14

13 Report for S /0/09 U 1 = 1 + ( ),for = 1, 1. (A 10) u u = 1 Case 3. The referece value was evaluated wth all reported values except oe. For the sake of smplcty let us assg the subscrpt + 1 to the elgble laboratory so that the subscrpt for the other laboratores wll ru from 1 to. Uder ths assumpto the treatmet of the elgble laboratory wll be slghtly dfferet ad two formulae are deduced. The elgble laboratory does ot cotrbute to the referece value, so the term (1 /) (A-9) reduces to 1 ad the ucertaty s smply gve by 1 = +. (A 11) U + 1 u + 1 u = 1 I the evaluato of the ucertaty related to the other laboratores the cotrbuto from laboratory + 1 dsappears totally ad the ucertaty remas gve by the expresso (A-10) wthout restrcto over the subscrpt rage. e. U 1 = 1 +. (A 1) u u = 1 Case 4. A laboratory that o loger exsts cotrbutes to the referece value ad a outler has bee detfed for aother laboratory. Let us assg the subscrpt to the defuct exstg laboratory so that the expresso for the mea (A-1) remas applcable. I addto the outler wll be labelled by + 1. For the ( 1) frst laboratores whch cotrbute to the mea value ad appear Table 5 the ucertaty of D s gve by U 1 = 1 +,for = 1, 1. (A 13) u u = 1 For the laboratory + 1 that s elgble for the KCRV, ts coeffcet (1 /) (A- 13) reduces to 1 ad the expresso of the ucertaty Table 5 becomes 1 = +, (A 14) U + 1 u + 1 u = 1 smlar to (A-11). 13/14

14 Report for S /0/09 Appedx 3. Acroyms used to detfy dfferet measuremet methods Each acroym has sx compoets, geometry-detector (1)-radato (1)-detector ()-radato ()-mode. Whe a compoet s ukow,?? s used ad whe t s ot applcable 00 s used. Geometry acroym Detector acroym 4π 4P proportoal couter PC defed sold agle SA press. prop couter PP π P lqud sctllato coutg LS udefed sold agle UA NaI(Tl) NA Ge(HP) Ge-L S-L CsI ozato chamber grd ozato chamber bolometer calormeter PIPS detector Radato acroym Mode acroym postro PO effcecy tracg ET beta partcle BP teral gas coutg IG Auger electro AE CIEMAT/NIST CN coverso electro CE sum coutg SC bremsstrahlug BS cocdece CO gamma ray GR at-cocdece AC X - rays XR cocdece coutg wth effcecy tracg alpha - partcle AP at-cocdece coutg wth effcecy tracg mxture of varous radato e.g. X ad gamma MX trple-to-double cocdece rato coutg selectve samplg GH GL SL CS IC GC BO CA PS CT AT TD SS Examples method acroym 4π(PC)β γ-cocdece coutg 4P-PC-BP-NA-GR-CO 4π(PPC)β γ-cocdece coutg eff. trac. 4P-PP-MX-NA-GR-CT defed sold agle α-partcle coutg wth a PIPS detector SA-PS-AP π(PPC)AX-γ(GeHP)-atcocdece coutg 4P-PP-MX-GH-GR-AC 4π CsI-β,AX,γ coutg 4P-CS-MX calbrated IC 4P-IC-GR teral gas coutg 4P-PC-BP IG 14/14