Measurement of the Activity Concentration of the Radionuclide Am-241 in a Solution COOMET PROJECT 359/RU/06

Transcription

1 Measurement of the Actvty Concentraton of the Radonuclde Am-4 n a Soluton COOMET PROJECT 359/RU/06 I.A. Khartonov, A.V. Zanevsky ), V. Mlevsk, A. Ivanukovch ), P. Oropesa and Y. Moreno 3) ), ) BelGIM, 3) DMR Abstract A COOMET.RI(II)-K.Am-4comparson of the measurement of a standardzed soluton of Am-4 has enabled two natonal metrology nsttutes n the COOMET to demonstrate ther traceablty to the SI. The results of ths comparson wll be used to evaluate degrees of equvalence for these nsttutes through the measurements of the lnkng laboratory n the key comparson BIPM.RI(II)K-.Am-4. Introducton The objectve of ths project was to make a COOMET key comparson of natonal measurement standards of the actvty concentraton of a standardzed soluton of radonuclde Am-4 to enable the traceablty of the measurement results to the reference value of key comparson BIPM.RI(II)-K.Am-4. The comparson partcpants are those natonal measurement nsttutes (NMIs) of the COOMET that dd not partcpate n the CIPM comparsons. The plot laboratory and lnkng nsttute for the comparson COOMET.RI(II)- K.Am-4 to the BIPM.RI(II)-K.Am-4 s the D.I.Mendeleyev Insttute for Metrology (). The prepared an Am-4 radonuclde soluton n M ntrc acd and dspatched t to the partcpants of the COOMET.RI(II)-K.Am-4 comparson. To provde the traceablty of measurement results obtaned by the NMIs partcpatng n ths COOMET comparson to the reference value of the key comparson BIPM.RI(II)-K.Am-4, the sent a soluton alquot of mass 3.9 g n a BIPM standard ampoule to the BIPM for a comparson wthn the Internatonal Reference System (SIR).. Partcpants of the COOMET.RI(II)-K.Am-4 comparson Table gven below contans a lst of the NMIs partcpatng n the comparson and the names of the persons who carred out the measurements. In accordance wth the techncal protocol of the comparson, the partcpants had to determne the actvty concentraton of Am-4 n a soluton by the methods avalable to them. Moreover, the comparson partcpants had also to determne the actvty concentraton of any radonuclde mpurtes they determned n the soluton.

2 Table. Lst of partcpants NMI Full name of NMIs Country Persons BelGIM Belarussan State Insttute of Metrology Belarus Valer Mlevsk Alaksandr Ivanukovch DMR Centro de Isótopos. Departamento de Metrología de Radonúcldos Cuba Plar Oropesa Verdeca Yecena Moreno León D. I. Mendeleyev Insttute for Metrology Russa I.A. Khartonov A.V. Zanevsky. Results of measurng the Am-4 actvty concentraton n the soluton In accordance wth the Techncal Protocol of the comparson, each of the comparson partcpants had to submt to the a protocol of ther measurement of the Am-4 actvty concentraton n the soluton wth a complete uncertanty budget of the measurement result. The DMR Protocol of Measurements was sent to the by Mrs. Plar Oropesa Verdeca on 04 October 006 and the BelGIM Protocol was submtted by V.Mlevsk on 07 December 006. Table lsts the Am-4 standardzaton methods, as well as measurement results wth uncertanty values for a coverage factor k =, gven n accordance wth the measurement protocols whch were submtted. The detaled uncertanty budgets are gven n Table 3. Table. Methods used to measure the Am-4 actvty concentraton n the soluton and the measurement results NMI Measurement method Actvty concentraton * (kbq/g) Uncertanty (k = ) Abs. (kbq/g) Relatve 0 - BelGIM UA-GH-GR DMR 4P-LS-AP UA-GH-GR P-IC-GR P-PC-AP-NA-GR-CO * reference date = , 0:00 UTC As t s seen from the Table, two laboratores performed absolute measurements of the Am- 4 actvty concentraton n the soluton: the measured the actvty concentraton by the 4πα-γ-concedence method (4P-PC-AP-NA-GR-CO), and the DMR by the method of a lqud scntllator (4P-LS-AP ). Accordng to the current procedures, the ndcated absolute methods were dentfed n the context of the COOMET.RI(II)-K.Am-4 comparson as the prmary natonal standards of the and DMR, respectvely. The DMR used an HPGe gamma spectrometer (UA-GH-GR ) and an onzaton chamber (4P-IC-GR ) that had been calbrated wth standard 4 Am pont

3 gamma sources certfed by the OMH (Hungary) and CIEMAT-LMRI (Span) on /5/004 and 6/0/00, respectvely. These measurng nstruments, beng part of the natonal measurement standard of Cuba, can be dentfed n these comparsons as the secondary measurement standards traceable to the prmary standards of the OMH and CIEMAT-LMRI. The BelGIM used an HPGe gamma spectrometer (UA-GH-GR ) calbrated wth standard solutons traceable to the. The BelGIM gamma spectrometer was dentfed n ths comparson as a secondary measurement standard traceable to the prmary measurement standard. Table 3. Estmated relatve values (%) of the standard uncertanty components dentfed by the partcpants for ther measurement results Effect BelGIM DMR LS Ge(HP) IC countng statstcs weghng dluton 0. 4 dead tme a background resolvng tme Gandy effect 8 countng tme b adsorpton mpurtes 0.5 c 0.05 decay-scheme parameters half lfe (T / = d; u = d ) 3 self absorpton 4 extrapolaton of effcency curve 5 calbraton other effects 0.4 d 0.7 e combned uncertanty (σ) a lnearty of the onzaton chamber b scale resoluton of the onzaton chamber equpment c quenchng d adsorpton, self-absorpton, countng tme, measurement geometry e adsorpton, sample geometry, long-term stablty, measurement tme The comparson partcpants dd not detect any radonuclde mpurtes n the soluton. 3

4 3. Results of SIR comparsons As noted n the ntroducton to ths report, the am of the COOMET.RI(II)-K.Am-4 comparson conssted n provdng the traceablty of the Am-4 soluton standardzaton results to the reference value of the BIPM.RI(II)-K.Am-4 key comparson. To enable ths, the as the lnkng NMI, performed a comparson n the SIR system by sendng to the BIPM an alquot of the same soluton that had been dspatched to the partcpants of the COOMET.RI(II)-K.Am-4 comparson. Ths result has been regstered n the SIR and s reported n []. The result of the agrees wth the KCRV wthn the stated uncertantes. Ths enables a robust lnk to be made between the COOMET.RI(II)-K.Am-4 comparson results and the results of the BIPM.RI(II)- K.Am-4 comparson. 4. Processng of the COOMET.RI(II)-K.Am-4 comparson results In accordance wth the CCRI(II)/05-0 Gudelnes for key comparsons [], each of the comparson partcpants has to submt to the plot laboratory at least one result of measurements wth an estmated uncertanty. In the present comparson the DMR used three measurement methods n the comparson. Followng tem 9 of the CCRI(II) recommendatons n [], the Protocol of measurements that the DMR submtted to the ncluded a weghted mean of two results, A = kbq/g, wth an estmated uncertanty U =. % for k =. The DMR weghted mean was calculated from the measurement results obtaned by the lqud scntllator and HP Ge spectrometer methods. Ths value s ndcated n the report as the DMR result for calculatng the degrees of equvalence of the natonal standard of Cuba for the KCDB. Table 4 shows some characterstcs of a sub-set of the measurement results where d = (A A)*00/A, and E n s a normalzed error statstc (see secton 5). Table 4. Some characterstcs of a set of the results obtaned n measurng the Am-4 actvty concentraton n the soluton A U (k = ) Insttute Method of measurement d E (kbq/g)* kbq/g % % n BelGIM UA-GH-GR DMR weghted mean of 4P-LS-AP and UA-GH-GR P-PC-AP-NA-GR-CO * reference date = 0:00 UTC of June, 006. As noted above, the natonal measurement standard of Belarus s traceable to the natonal measurement standard of Russa, and due to ths fact the measurement results of the BelGIM and are correlated. If a weghted mean calculated wthout any allowance for the correlaton of the BelGIM and s taken as the comparson result, then the estmate of the comparson result wll be based and, consequently, ncorrect. On the other hand, t s seen from the table that the uncertanty of the measurement result s consderably less than the uncertanty of the measurement results obtaned by the other two comparson partcpants, and the result wll be the nearest approach to an estmate of the measurement result for any method of weghtng. 4

5 In connecton wth ths, as well as takng nto account the fact that the result wll be used as the lnkng value of the COOMET.RI(II)-K.Am-4 and BIPM.RI(II)-K.Am-4 comparsons, the result of the actvty concentraton measurement presented by the s taken as the result of the comparson. Statstcal consstency of the comparson data set was verfed wth a normal statstcal test usng the followng formula: A - A E n= () U + U cov A, A For the BelGIM value, effectvely ( ) ( ) cov A, A = u, therefore formula () s transformed nto: A - A E n= () U U - For the Cuban value, cov (, A) = 0 A, therefore formula () s transformed nto: A - A E n= (3) U + U Where A s the result of a comparson partcpant, except for the A s the result U s the value of expanded uncertanty of a partcpant measurement result, except for the, and U s the expanded uncertanty value of the result, as gven n Table 4 The values of E n are also gven n Table 4 and as each s <, the data are deemed to be consstent. 5. Prelmnary evaluaton of the COOMET.RI(II)-K.Am-4 comparson results For the convenence of comparson, the expanded uncertanty values and the values of devaton, d from the results are gven n Table 4 n terms of relatve unts. Table 4 shows that all the data of the comparson comply wth a normal statstcal test, and the devatons of the results d from the value of actvty concentraton (A = kbq/g, u = 0.63 kbq/g, u/a = 0.9%) are all wthn 0.4 %. As an llustraton, Fgure shows the results lsted n Table wth ther standard devatons (k = ). The horzontal lne represents the weghted mean of the results of all the A partcpants A = u u = kbq/g and ts uncertanty u A = u = 0.6 kbq/g. 5

6 BelGIM (HPGe) Actvty concentraton / (kbq/g) DMR (LS) DMR (IC) DMR (HPGe) DMR 480 BelGIM HPGe DMR LS DMR HPGe DMR IC DMR LS + HPGe 4πα-γ- Fg. Results of the COOMET.RI(II)-K.Am-4 comparson wth standard uncertanty bars (k = ) Concluson The results of three NMI partcpants n the COOMET.RI(II)-K.Am-4 comparson are consstent wth each other and ndcate agreement n the dssemnaton of actvty measurements for solutons of 4 Am. In accordance wth the Gudelnes for CCRI(II) key comparsons [], the results of the COOMET.RI(II)-K.Am-4 comparson, havng been approved by the comparson partcpants, have been sent to the BIPM to establsh a lnk of the results obtaned wth the reference value of the BIPM.RI(II)-K.Am-4 key comparsons. The degrees of equvalence for these partcpants wll be publshed subsequently. Acknowledgements The as the plot laboratory thanks all partcpants of ths comparson, as well as the BIPM for the efforts n mantanng the SIR system. References [] Ratel G., Mchotte C., Khartonov I.A, Update of the BIPM comparson BIPM.RI(II)- K.Am-4 of actvty measurements of the radonuclde 4 Am to nclude the 006 result and lnks for the 006 regonal comparson COOMET.RI(II)-K.Am-4, (007) Metrologa Techncal Supplement, n preparaton. [] CCRI(II), Gudelnes for CCRI(II) key comparsons, 005, CCRI(II)/