The Role of Reference Materials in the Measurement of Terrestrial Radionuclides

Transcription

1 Terrestrial Radionuclides in Environment International Conference on Environmental Protection May 2012, Veszprém (Hungary) The Role of Reference Materials in the Measurement of Terrestrial Radionuclides S. Tarjan National Food-chain Safety Office, Hungary Collaboration Centre of the IAEA

2 Topics What is the reference material Proper use of the reference material Reference material production Experiences of the world-wide PT with Moss-Soil What is the accreditation?

3 The REFERENCE MATERIAL s I. VIM (International Vocabulary of Metrology) JGCM 200:2012 Reference material RM material, sufficiently homogeneous and stable with reference to specified properties, which has been established to be fit for its intended use in measurement or in examination of nominal properties NOTE 1 Examination of a nominal property provides a nominal property value and associated uncertainty. This uncertainty is not a measurement uncertainty. NOTE 2 Reference materials with or without assigned quantity values can be used for measurement precision control whereas only reference materials with assigned quantity values can be used for calibration or measurement trueness control.

4 The REFERENCE MATERIAL s II. certified reference material CRM reference material, accompanied by documentation issued by an authoritative body and providing one or more specified property values with associated uncertainties and traceabilities, using valid procedures EXAMPLE Human serum with assigned quantity value for the concentration of cholesterol and associated measurement uncertainty stated in an accompanying certificate, used as a calibrator or measurement trueness control material.

5 The REFERENCE MATERIAL s III. RM CRM CRM may be use as calibrant

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7 Proper use of the RMs (because of the accreditation) Method validation With RM at least two different materials are required With CRM one is enough Method verification To demonstrate the selected methods fulfill the requirements against the validation at given laboratory conditions Internal QC Control chart (regularly) Control of the calibration (occasionaly) Training material Proficiency test material

8 Terrestrial origin radionuclides in reference matrerial Natural-series RGU-1 (standard uranium ore diluted with quarc) characterised for the uranium content RGTh-1 (thorium ore diluted with quarc) characterised for thorium content Soil type materials Soil (IAEA Soil 6, IAEA ) Sediment (Irish Sea Sediment) Industrial waste (phosphogypsum) Characterisation for individual progeny of the decay series

9 IAEA-447 alias Moss-Soil The site is an old red marble mine area closed in 1962 Colledted: 240 kg Treated: 180 kg

10 After Before sampling

11 Be-7 Pb-210 I-125 Cs-137 Air flow: m 3 /week, counting time s, with ULB detector system

12 210 Pb activity in fall-out, (Budapest Fogoly u ) 40 A, Bq/m Month

13 Milling Sieving Homogenising Homogeneity test Final result: 1200 packing units 13

14 The bulk material (180 kg)

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16 IAEA-447 high organic content soil (moss-soil) 30% rel. eff. ULB detector with carbon-epoxi window

17 Bulk homogeneity test ANNOVA comparative method by decomposing of uncertainty budget (only for gammaspectrometry) Sources of uncertaity Estimated value Longterm stability sd(ls) Less than 1% Geometry sd(g) 0.5-1% Counting stat. sd(cs) Depend on Heterogeneity sd(ht) It should be less than 1% sd ( ht) sdmeas sdls sdg sdcs

18 Energies of gamma-ray peaks used for determination of the activity concentrations of the studied radionuclides Series U- series Nuclide 234 Th Energy, kev Yield, % Interfering lines Nuclide energy in kev (Yield,%) Corrections / Remarks Not used 214 Bi 62.5 (0.011) 227 Th (0.007) Pa 62.7 (1.5) 234m Pa 62.7 (0.001) 227 Th (0.025) Ra Pb Bi Self absorption correction is required. The intensity of the overlapping lines are negligible or the branching ratio is low ( 234 Pa 0.17%) Disturbed by X- rays Not used Disturbed by X- rays Not used 235 U (57.0) The disturbing effect of the 235 U is strong 212 Pb (43.6) The disturbing effect is strong, not Ra recommended line (4.12) 234 Pa (3) 210 Tl (79) 231 Pa (0.007) 234 Pa (0.41) 228 Ac (0.023) 234 Pa (0.389) 234 Pa (0.25) 234m Pa (0.008) Branching ratio is low (0.17%) Branching ratio is low (0.021%) The intensity is negligible Branching ratio is low (0.17%) The intensity is negligible Branching ratio is low (0.17%) Branching ratio is low (0.17%) The intensity is negligible True coincidence factor is 1.00 for the applied geometry Free from true coincidence effect True coincidence correction is required True coincidence factor is for the applied geometry

19 Series Thseries Others Nuclide Energy, kev Yield, % Interfering lines Nuclide energy in kev (Yield,%) 214 Pb Corrections / Remarks 212 (7.268) The disturbing effect is strong but there is no Pb Ra other possibility (4.12) 228 Ac None Free from true coincidence effect 228 Ac The intensity is negligible 208 (0.111) Tl Pa Branching ratio is low (0.17%) (0.18) 40 K Ac Free from true coincidence effect (0.83) 137 Cs Bi The intensity is Free from true (0.054) negligible coincidence effect 241 Am Pa 58.2 Branching ratio is low The self absorption

20 IAEA-447 high organic content soil (moss-soil) Bulk homogeneity test of Pu content 6 samples (10g of each) same process for digestion separation dilution into 25cm 3 volumetric flask preparatum making with Nd co-precipitation preparatum making with electrodeposition- Results in relative values Nd, co-pr. Electro dep. Min Max Average sd

21 Feasibility study Reported results of 40 K-isotope (relative values, moss soil) a Lab code

22 Reported results of 137 Cs-isotope (relative values, moss soil) a Lab code

23 Characterisation for individual progeny of radioactive decay series

24 World-wide PT 69 countries 300 lab. Am-241 was 140 reported by laboratories

25 Application field (an example only) Cross validation using the same material with one reference value and associated uncertainty 210 Pb by gamma-sp 210 Pb+ 210 Bi by LSC 210 Po by alpha sp. Soil erosion study Long term effects by gamma-sp. 137 Cs and 210 Pb Short term effects based on the 210 Pb(ex) and 210 Po equilibrium

26 What is the accreditation? A strong administration? Any process optimalisation? Any evolution of the laboratory work?

27 Thank you for your attention!