Prepared for: Nederlands Normalisatie-instituut (NEN) Vlinderweg 6 Postbus GB Delft The Netherlands

Transcription

1 Robustness validation of a method developed by CEN/TC 351/WG 3 to determine the activity concentrations of radium-226, thorium-232 and potassium-40 in construction products using gamma-ray spectrometry (doc. nr. CEN/TC 351 N 0486) Final technical implementation report for the adaptation of the examined method including proposals for the adjustment of TS on the basis of the results of the robustness validation Prepared for: Nederlands Normalisatie-instituut (NEN) Vlinderweg 6 Postbus GB Delft The Netherlands Prepared by: Bogusław Michalik Michał Bonczyk Krzysztof Samolej Główny Instytut Górnictwa (GIG) Śląskie Centrum Radiometrii Środowiskowej Plac Gwarków Katowice Poland bmichalik@gig.eu Submitted on: 1 June, 2016 page 1

2 CONTENT 1. Parameters identified for the robustness testing of draft TS standard on radioactivity in construction materials Tested construction materials product samples Spectrometers used for the execution of the tests Containers used for the execution of the tests Test results Test 1: Container volume Tested Samples Test conditions Test results Conclusion Test 2: Container geometry Tested samples Test conditions Test results Conclusion Test 3: Chemical constitution of the sample material Tested samples Test conditions Test results Conclusion Test 4: Density of the sampled material Tested samples Test conditions Test results Conclusion Test 5: Sample treatment particle size of the sample material page 2

3 Tested samples Test conditions Test results Conclusion Test 6: Method of spectrum analysis Tested samples Test conditions Test results Conclusions Test 7 and test 8: Radon tightness (Annex A test) Tested samples Test conditions Test results Conclusion Proposed alternative test for beaker radon tightness verification Tested samples Test conditions Test results Conclusion Test 9: Waiting period after test specimen preparation Tested samples Test conditions Test results Conclusion Test 10: Dry weight correction Tested samples Test conditions Test results Conclusions Test 11: Sample drying Tested samples Test conditions Test results Conclusions Test 12: Composite material page 3

4 Tested samples Test conditions Test results Conclusions Test 13: Thorium-232 approximation on 228 Ra and 228 Th Tested samples Test conditions Test results Conclusions Test 14: Room temperature Test 15: Background level protection Tested samples Test conditions Test results Conclusions Test 16: Type of detector Test samples Test conditions Test results Conclusions Repeatability and material homogeneity test Repeatability Homogenity Final conclusions and recommendations page 4

5 Silesian Centre for Environmental Radioactivity re po rt 1. Parameters identified for the robustness testing of draft TS standard on radioactivity in construction materials The determining of the active concentration of natural radionuclides in construction materials is based on the principles of gamma-spectrometry. Therefore the measurement circumstances influencing the results obtained from this method must be tested and the effect on the final results must be assessed. Important phenomena that should be considered, when gamma spectrometry is applied, are: self-attenuation in an analyzed sample, radon exhalation from measurement beakers, a temporary lack of secular equilibrium inside uranium, actual (long term) lack of secular equilibrium inside uranium and/or thorium decay series Sample self-attenuation depends on the intrinsic properties of the tested material in terms of density and chemical composition. Density is a primordial property of a material but during the pretreatment of a laboratory sample, tested material is usually transferred into a measurement beaker and this is why its original form, the form which a material is intended to be used, must be C destroyed. A laboratory sample is crushed or crumbled and finally the bulk density of a test specimen may differ from the apparent density of the sampled material. This is one of the most important facts /T that must be considered in order to get measurement results reflecting radionuclides activity concentration as a specific property of the tested material- and not a function of the physical form of EN a test specimen prepared. The chemical composition of the tested material is important when the contribution of the photoelectric effect to the total material s attenuation may be significant. The probability of photoelectric absorption depends on gamma-ray energy (E), electron binding energy, and the atomic C number of the element (Z) and is approximately shown by the equation 1-1: Z5 E3 1-1 where µ photoelectric mass attenuation coefficient. page 5

6 Equation 1-1 shows that this kind of ionizing radiation s interaction with matter is more important for heavy atoms like lead or uranium and low-energy gamma rays. Therefore, this phenomenon should not have a significant influence on the measurement of radionuclide activity concentration in construction materials. Moisture content, if significant, can change as well as the density of a tested material as can its chemical composition. All of the parameters influencing sample self-attenuation and particular stages of the measurement analysis, should be especially considered at particular times and this is presented in Fig Fig Parameters influencing measurement results obtained by high gamma spectrometry. Radon exhalation from a tested material is important during sample pre-treatment (crushing and drying) and when a tested material portion is already in the measurement beaker. The radon exhalation from the material results in temporary disequilibrium between 226 Ra and its progeny when the test portion has just been enclosed in the measurement beaker. According to the decay law the secular equilibrium between 226 Ra and its progeny is achieved after about four weeks. Depending on the material s internal structure radon exhalation can be limited and equilibrium may be achieved earlier but usually a test specimen is retained for four weeks after preparation and then measured. However, the equilibrium state inside a measurement beaker can be achieved only when a beaker is page 6

7 made from radon-tight material and radon cannot escape from it. Due to radon having the properties of a noble gas, many materials are more or less transparent for it. Hence beakers used for measurement must be tested against radon exhalation. For that, quality of raw material which a beaker is made of should be considered and all possible leaks related to a container s construction must be identified and sealed. Sometimes even when a radon-tight measurement beaker is used and a sample has been retained for the proper amount of time, a lack of secular equilibrium between 226 Ra and its long living progeny, or, more importantly, between 228 Ra and 228 Th, can be observed. Such situations often occur in NORM residues where the equilibrium between particular radionuclides occurring in thorium and uranium decay series was fractured due to a technological process. The most spectacular differentiation of particular decay products activity concentration is observed in a mixture of fractured decay series, with 226 Ra in the uranium decay series and 228 Ra in the thorium decay series (Fig. 1-2) (Michalik B., Brown J., Krajewski P. The fate and behaviour of enhanced natural radioactivity with respect to environmental protection. Environmental Impact Assessment Review 38 (2013) ). Both of these situations must be taken into account during the analysis of the sample spectrum (see Fig. 1-2 last row). Fig Activity concentration changes in sub-series started from pure 226 Ra and 228 Ra page 7

8 All of the identified phenomena mentioned above were tested individually and the possible effects on the measurement results according to the standard draft of concern were evaluated. All tests have been carried out according to the revised work program for the robustness validation of draft TS (doc. nr. CEN/TC 351 N 0487). 2. Tested construction materials product samples Materials for tests were collected from the local market and represent typical building materials used for construction work. Materials have been chosen in order to cover the existing variety of available construction products considering their final form in which they are intended to be used, density and chemical composition (Fig. 2-1). The list of the collected materials (product samples) and their basic properties are presented in Table 2-1 andtable 2-2. Fig Product samples of building materials collected from the local market. page 8

9 Material Table 2-1. Construction materials sampled Density of end-product [g/cm 3 ] Dry matter content [%] ready - mixed concrete B cavity clinker brick light concrete chipboard plaster finish (gypsum) glazed tiles fly ash fly ash Table 2-2 The activity concentration of tested materials 226 Ra Number Energy line [kev] of material measure ments Activity concentration [Bq/kg] St. St. St. St. St. Aver Aver Aver Aver Aver dev. dev. dev. dev. dev. ready - mixed concrete B cavity clinker brick light concrete chipboard 1 < 4.0 < 2.1 < 1.8 < plaster finish (gypsum) < 2.1 < glazed tiles fly ash (1) fly ash (2) The dry matter content of the collected product samples was measured according to Test portion for determination of the dry matter content and Determination of the dry matter content as described in the standard. All of the results of the measurements presented in this report were calculated using the mass of a test specimen adjusted to match the dry mass content in tested material. One exception is test No. 12 which was focused on the impact of different samples relative humidity on the measurements results. 232 Th 40 K page 9

10 3. Spectrometers used for the execution of the tests The Silesian Centre for Environmental Radioactivity applies gamma-ray spectrometry in order to analyze environmental samples such as soil, sediment, vegetation, water, etc. The gamma spectrometry laboratory is located in an underground part of the Centre s building. The walls are made of 50 cm thick barite concrete (natural radionuclides content < 10 Bq/kg), which allows for the reduction of the influence of surrounding soils and rocks on indoor radiation background. A ventilation system exchanges all of the air in the laboratory room 4 times per hour. An overview of the laboratory is presented in Fig Fig An overview of gamma spectrometers applied for tests The spectrometers are equipped with germanium detectors (HPGe) with different configurations. Technical details of the spectrometers applied for particular tests are listed in Table 3-1. Data processing software GENNIE 2000 ver. 3.1., CANBERA was used for analysing complex spectra on a number of radionuclides. ROI (region of interest) identification and its area calculation procedures were adapted to the requirements of the tested standard. of the applicable. Energy and efficiency calibration were performed based on a set of standard samples applied in routine laboratory activity. page 10

11 Table 3-1. Technical details of the gamma-ray spectrometry system Detector number Detector type Coaxial BEGe XtRa BEGe Relative efficiency [%] Energy range [kev] Background [cps] Additional info. n-type p-type ISOCS & LabSOCS ISOCS & absocs HV power supply 3106D 3106D InSpector D Preamplifier - integrated with detector RFP CLS 2002CLS 2002CLS Amplifier Canberra 2026 Canberra 2026 InSpector 2000 Canberra 2026 MCA Multiport II Multiport II InSpector 2000 AccuSpec Due to a lack of any criterion of measurement time or an appropriate detection limit in the teted standard, the tested samples were measured until sufficient statistics were reached (eg. less than 5 % for 186 kev). Hence, measurement time varies from s to s depending on the actual activity concentration level in a sample. 4. Containers used for the execution of the tests The containers used for the execution of the tests meet general requirements as outlined in section (Test specimen container) of the tested TS. Technical details of the beakers applied in this study are listed in Table 4-1. Cross sections and specific dimensions are presented in Fig. 4-1, Fig. 4-2 and Table 4-2 and Table 4-3 for marinelli type beakers and cylindrical beakers, respectively. Beaker type Volume [ml] Marinelli 250 Marinelli 600 Table 4-1. Technical details of the used beakers. Material Manufacturer Model polyvinyl chloride (PVC) polyvinyl chloride (PVC) Central Laboratory for Radiological Protection (CLOR) Central Laboratory for Radiological Protection (CLOR) Marinelli 700 polypropylene (PP) GA-MA AND ASSOCIATES, INC Marinelli 1000 polypropylene (PP) GA-MA AND ASSOCIATES, INC G-E Analysis Container With Lid 190G-E Analysis Container With Lid page 11

12 Beaker type Volume [ml] Polipack 130 polyethylene (PE) Polipack 280 polyethylene (PE) petri dish 80 polystyrene (PS) Material Manufacturer Model POLIPACK P.P.H.U. POLIPACK s.j. POLIPACK P.P.H.U. POLIPACK s.j. FALCON TM Thermo Fisher Scientific Brand Fig Cross section and specific measurements of the marinelli beakers used Table 4-2. Specific dimensions of the marinelli beakers used. pp100 pp250 Beaker type Model A [cm] B [cm] C [cm] D [cm] E [cm] Marinelli Marinelli Marinelli Marinelli 590G-E Analysis Container With Lid 190G-E Analysis Container With Lid page 12

13 Fig Cross section and specific dimensions of the cylindrical beakers used Table 4-3. Specific dimensions of the cylindrical beakers used. Beaker type Model A [cm] B [cm] Polipack 130 pp Polipack 280 pp petri dish Test results All tests have been carried out according to the suggestion developed in Revised work programme for the robustness validation of draft TS (doc. nr. CEN/TC 351 N 0487). Necessary changes implied by existing objective circumstances were discussed and then accepted by members of TG-31. In tables presenting data obtained during tests execution column A contain a radionuclide activity concentration and column AU - measurement uncertainty. Measurements uncertainty was calculated at k=2 level (95 %), if no additional comments present Test 1: Container volume The objective of the tests was to identify the effect of the volume of the measurement containers (beakers) used on the measurement results. The containers volumes in ml were: 250, 500, 750 and Tested Samples Three kind of construction materials with a significant range of density were chosen for the test performance: ready- mixed concrete, cavity clinker brick, fly ash. page 13

14 Test specimens were prepared in four Marinelli beakers (Fig. 5-1): 250 ml, 600 ml, 700 ml (Model 590G-E Analysis Container With Lid), 1000 ml (Model 190G-E Analysis Container With Lid) and two cylindrical beakers ( Fig. 5-2): Polipack 130 ml, Polipack 280 ml. Fig Test specimen containers applied for container volume test: marinelli geometry Fig Test specimen containers applied for container volume test: cylindrical geometry Identification and physical properties of test specimens are listed in Table 5-1 and Table 5-2. page 14

15 Table 5-1. Density of tested materials and test specimens: marinelli beakers Density of Bulk Sample Sample Material Geometry end-product density code [g/cm 3 ] [g/cm 3 mass [kg] ] 1.5 Marinelli Marinelli ready-mixed concrete B Marinelli Marinelli Marinelli Marinelli Fly ash Marinelli Marinelli Table 5-2. Density of tested materials and test specimens: cylindrical beakers Density of Bulk Sample Sample Material Geometry end-product density code [g/cm 3 ] [g/cm 3 mass [kg] ] 3.4 Polipack cavity clinker brick (< 2 mm) Polipack Polipack ready-mixed concrete B Polipack Polipack Fly ash Polipack Test conditions detector: 2 (see Table 3-1) software: GENIE 2000 temperature: ᵒC RH%: % Test results The results obtained for the three pairs of test specimens prepared from different construction materials measured in two cylindrical beaker and four test specimens of ready-mixed concrete B-20 and fly ash in different volume marinelli beakers are presented in Table 5-3. For each kind of measurement beaker (measurement geometry), a dedicated efficiency calibration curve was prepared based on the calibration standards used. Measurement uncertainty was calculated at a level of 2 using a standard GENIE 2000 procedure. In addition, the results obtained by the direct measurement of 226 Ra kev energy line were included. Fluctuations of the results are presented in Fig. 5-3 to Fig page 15

16 Table 5-3. Results of measurement test specimens in containers varying in volume 226 Ra 232 Th Sample code Energy line [kev] Activity concentration [Bq/kg] AC U AC U AC U AC U AC U Cylindrical Marinelli Fig Measurement volume impact (marinelli) on the results of activity concentration in readymixed concrete B K page 16

17 Fig Measurement volume impact (marinelli) on the results of activity concentration in readymixed concrete B-20. Fig Measurement volume impact (marinelli) on the results of activity concentration in fly ash. page 17

18 Fig Measurement volume impact (marinelli) on the results of activity concentration in fly ash. Fig Measurement volume impact (polipack) on the results of activity concentration in readymixed concrete B-20. page 18

19 Fig Measurement volume impact (polipack) on the results of activity concentration in readymixed concrete B-20. Fig Measurement volume impact (polipack) on the results of activity concentration in fly ash. page 19

20 Fig Measurement volume impact (polipack) on the results of activity concentration in fly ash. Fig Measurement volume impact (polipack) on the results of activity concentration in cavity clinker brick. page 20

21 Fig Measurement volume impact (polipack) on the results of activity concentration in cavity clinker brick Conclusion In spite of the different total volume of the marinelli beakers, the thickness of the space between the beaker side walls is comparable (Table 4-2). Therefore, the total volume of a beaker does not significantly influence the sample self-attenuation and results obtained for different marinelli beakers are comparable, as can be observed in Table 5-4. The standard deviation of the average values calculated for all of the results is lower than the uncertainty of each individual result. Moreover, no significant effect caused by sample density is present. Table 5-4. Results of measurement test specimens in marinelli beakers varying in volume 226 Ra 232 Th Energy line [kev] Sample code Activity concentration [Bq/kg] AC U AC U AC U AC U AC U Average Std. deviation K page 21

22 Sample code 226 Ra 232 Th Energy line [kev] Activity concentration [Bq/kg] AC U AC U AC U AC U AC U Average Std. deviation In contrast, in the case of cylindrical beakers, the thickness of the sample layer in the 250 ml beaker is over two times greater than in the 100 ml beaker. This results in greater sample self-attenuation. This effect is clearly noticeable in Fig. 5-7 to Fig and is proportional not only to the sample density (the correction for sample density has been applied). The effect is significant in the case of cavity clinker brick. The most probable reason is the differences in the chemical composition between a calibration standard and a sample (even if they have similar density). In general, bigger container volumes lead to a better counting rate but they requires additional correction related to the sample self-attenuation phenomenon. Optimization for each particular case of beakers and detector types used is required Test 2: Container geometry The test objective was to identify the effect of the shape (geometry) of measurement beakers used on measurement results. Five measurement beakers including marinelli and cylindrical shapes were studied. The geometries and test specimen containers used were: cylindrical: petri dish 80 ml, polipack 130 ml, polipack 280 ml, Fig. 5-13, marinelli beaker: 700 ml (Model 590G-E Analysis Container With Lid) and 1000 ml (Model 190G-E Analysis Container With Lid), Fig K page 22

23 Tested samples Fig Test specimen containers applied for container geometry test Fig Test specimens in different geometries Two types of construction materials differing in density were tested: ready- mixed concrete, fly ash. The properties of the tested construction materials and the test specimens are presented in Table 5-5. Table 5-5. Density of tested materials and test specimens Density of Bulk Sample Sample Material Geometry end-product density mass [kg] code [g/cm 3 ] [g/cm 3 ] 1.1 Petri dish Polipack ready-mixed concrete B Polipack Marinelli page 23

24 Density of Bulk Sample Sample Material Geometry end-product density mass [kg] code [g/cm 3 ] [g/cm 3 ] 1.5 Marinelli Petri dish Polipack Fly ash 1 Polipack Marinelli Marinelli Test conditions detector: 4 (see Table 3-1) software: Genie 2000 temperature: ᵒC RH%: % Test results The results are presented in Table 5-6 and Table 5-7. In addition, results obtained by direct measurement of the 226 Ra kev energy line were included. The average value was calculated for all five of the geometries tested. In pictures Fig Fig. 5-24, simple analysis of the obtained results is presented. The upper and lower limits depicted in the pictures were calculated based on the standard deviation of all 5 results. For each measurement beaker type (geometry), individually calculated calibration coefficients were applied (using standards RGU-1, RGTh-1 and RGK-1 from IAEA). No correction for sample density was applied. Measurement uncertainty was calculated at a level of 2 using a standard GENIE 2000 procedure. page 24

25 Table 5-6. Results of the measurement of test specimens in different geometries: ready- mixed concrete 226 Ra 232 Th Sample code Energy line [kev] Activity concentration [Bq/kg] AC U AC U AC U AC U AC U Cylindrical Marinelli average std. Deviation Fig Measurement geometry impact on results direct 226 Ra measurement 40 K page 25

26 Fig Measurement geometry impact on results 226 Ra measurement by progeny Fig Measurement geometry impact on results 232 Th measurement by 208 Tl page 26

27 Fig Measurement geometry impact on results 232 Th measurement by 228 Ra Fig Measurement geometry impact on results direct 40 K measurement page 27

28 Table 5-7. Results of the measurement of test specimens in different geometries: fly ash 226 Ra 232 Th Energy line [kev] Sample code Activity concentration [Bq/kg] AC U AC U AC U AC U AC U Cylindrical Marinelli average std. deviation Fig Measurement geometry impact on results direct 226 Ra measurement 40 K page 28

29 Fig Measurement geometry impact on results 226 Ra measurement by progeny Fig Measurement geometry impact on results 232 Th measurement by 208 Tl page 29

30 Fig Measurement geometry impact on results 232 Th measurement by 228 Ra Conclusion Fig Measurement geometry impact on results direct 40 K measurement No statistically significant differences between the different geometries were observed. However, the results confirm the conclusion from the previous test that correction for sample density may be insufficient in the case of thick cylindrical containers when the chemical composition of the sample differs too greatly from the calibration standard. page 30

31 5.3. Test 3: Chemical constitution of the sample material The test objective was to identify the effect of the chemical composition of the construction material on the measurement results. As described in section 1, chemical composition influences the selfabsorption of gamma rays in matter due to the photoelectric effect. The lower the energy of the penetrating gamma-ray, the stronger the expected effect. What is more, the higher the effective atomic number (Z) of matter constituting the sample measured, the greater the absorption expected Tested samples It is impossible to distinguish between the influence of density and chemical composition in routine measurements. Usually, different construction materials have different bulk density and chemical composition simultaneously. At least two samples with the same bulk density, different chemical composition and known activity concentration are required to perform this test. In order to solve this problem, two samples with similar bulk density and a significantly different chemical constitution (chipboard and light concrete) have been spiked with the known activity of natural radionuclides - RGU-1 and RGTh-1 IAEA reference materials were applied (see Table 5-8). Table 5-8. Density of the construction materials used for this test Material Bulk density [g/cm 3 ] Calibration standard (RGU-1, RGTh-1 mix) 0.49 chipboard 0.44 light concrete 0.45 Chemical composition of the calibration standard: SiO %, other elements (Ca, Mg, K) 0.04 %. The chemical composition of the samples was assumed to be typical either for wood or light concrete respectively. The linear mass attenuation coefficient for the materials was calculated theoretically using the XCOM model. The results are shown in Table 5-9 and Fig page 31

32 Silesian Centre for Environmental Radioactivity re po rt Table 5-9. Linear mass attenuation coefficient µ Linear mass attenuation coefficient µ [cm2/g] Material 351 kev 583 kev 911 kev 1461 kev light concrete chipboard Calibration standard (RGU-1, EN /T C 35 1 RGTh-1 mix) Fig Linear mass attenuation coefficient µ as a gamma-ray energy function C Test conditions detector: 2 (see Table 3-1) software: Genie 2000, Canberra temperature: ᵒC RH%: % page 32

33 Test results Radionuclides activity concentration in the samples prepared was determined by direct measurements according to the standard of concern. The spectrometer was calibrated using the calibration standard sample which is a mixture of RGU-1 and RGTh-1 reference materials (Table 5-8). The results were compared with nominal values calculated based on the reference material certificate (Table 5-10). Table Comparison of nominal activity and measurements results 226 Ra 232 Th Results Energy line [kev] Activity concentration [Bq/kg] AC U AC U AC U AC U Chipboard nominal experimental light concrete nominal experimental Conclusion In contrary to expectations, the test results obtained underline a considerable influence of chemical composition on the measurement outcome. The biggest difference is observed for chipboard whose chemical composition is significantly different from the applied calibration standard. In the second tested case light concrete existing chemical differences between the calibration standard and tested sample are negligible. Above is a result of the self-absorption in a sample that is not directly related to sample density, as both tested samples are characterized by similar density (Table 5-8). The chemical composition of light concrete is similar to the applied calibration standard. Hence, similar self-absorption is expected. In the case of chipboard, self-absorption is significantly lower than in the calibration standard. This finally results in significant overestimation of activity concentration measured. Correction for samples with a significantly different chemical composition from those used in the calibration of the spectrometer must be considered. page 33

34 5.4. Test 4: Density of the sampled material The test objective was to identify the effect of the density of construction material on measurement results. Density is a primordial property of a material and influences sample self-attenuation. Taking into consideration the fact that existing construction materials cover a wide range of density values it must be assumed that appropriate correction is necessary regardless of a measurement beaker s shape or volume Tested samples Assumed test conditions in terms of density in kg/m 3 : 500, 1000, 1500, Number of samples: 1. Tested material: Cavity clinker brick (Table 5-11) Test conditions Table Construction materials used for this test Material detectors: 1,2 (see Table 3-1) software: Genie 2000 temperature: ᵒC RH%: % Test results Density of end-product [g/cm 3 ] cavity clinker brick 2.10 It is difficult to collect a set of samples which are of the same material (e.g. cavity clinker brick) but with different density. Analysis of four different materials is not appropriate in the case of this test due to the self-attenuation caused by chemical composition, which was shown in the previous section. A possible solution is to prepare a few samples of the same material but mixed with different portions of other material which reduces the final bulk density but again the effect of the changes of the chemical composition of the mixtures is unknown. That is why, in practice, the test was performed in a slightly different way. Four efficiency calibration curves were obtained based on the measurement of calibration standards (the chemical constitution of the reference materials corresponds to the tested sample) with different bulk density (reference materials were mixed with page 34

35 Thixotropic Gel Powder CAB-O-SIL to reduce bulk density). The relationship was interpolated between measurement points Fig Fig Experimentally determined relationship between measurement efficiency and sample density for chosen gamma line The spectrum obtained by the measurement of a cavity clinker brick test specimen (2.1 g/cm 3 ) has been analyzed through the use of four efficiency calibration curves. The results are shown below (Fig Fig. 5-29). Diagrams shows possible differences in obtained results when a correction for density is not applied. page 35

36 Fig Relationship between observed activity and density of sample Fig Relationship between observed activity and density of sample page 36

37 Conclusion Fig Relationship between observed activity and density of sample An appropriate correction for sample density is required in order to get accurate results of activity concentration determination. In other cases, both under- and over-estimation are possible. It is important to use a calibration standard with a similar chemical composition to the sample. In other cases, only corrections for density, regardless sample chemical composition are not sufficient (see the previous section). Previous tests (beaker volume and geometry) proved that correction for sample density plays an important role. In summary, the general conclusion from the four tests above is that measurement beaker geometry and/or volume do not significantly affect the results when appropriate corrections (density and chemical composition) are applied. The optimal shape (thickness, volume) of a container exists when the influence of the above parameter is as low as possible and count rate is the highest. This optimal shape depends on the detector and the tested material. Technical note: it is difficult to collect an appropriate reference material whose chemical composition strictly corresponds to all available construction materials. In some cases, efficiency transfer and computer modeling is an easier and faster way to calibrate a spectrometer than preparing a set of calibration standards in a wide ranging chemical matrix. This fact should be considered as an option in standard of concern in the section dealing with spectrometer calibration. page 37

38 Silesian Centre for Environmental Radioactivity 5.5. Test 5: Sample treatment particle size of the sample material re po rt Tested samples The test objective was to identify the effect of pretreatment and preparation of the sample and test specimen on measurement results. For this test, construction materials that significantly differ in density in the state in which they are intended to be used were chosen: light concrete cavity clinker brick Particle size tested (mm): x < 2, 2 < x < 5, 5 < x < 10 (Fig and Fig. 5-31). Test specimens were EN /T C 35 1 prepared in cylindrical geometry, type pp 250 (Fig and Fig. 5-33). C Fig Light concrete crushed into different grain sizes, > 10 mm, < 10 mm, < 5 mm and < 2 mm page 38

39 Fig Cavity clinker brick crushed into different grain sizes, > 10 mm, < 10 mm, < 5 mm and < 2 mm Fig Test specimens - cavity clinker brick different grain sizes Fig Test specimens - light concrete different grain sizes page 39

40 Table Density of tested materials and test specimens Density of Sample Grain size Bulk density Sample Material Geometry end-product code [mm] [g/cm 3 [g/cm 3 ] mass [kg] ] light concrete < Polipack cavity clinker brick < Test conditions detector: 1,2,4 (see Table 3-1) software: GENIE 2000 temperature: ᵒC RH%: % Test results For each measurement the same efficiency calibration curve was obtained from a standard sample prepared from the application of base reference materials RGU-1, RGTh-1 and RGK-1 from IAEA. Measurement uncertainty was calculated at a level of 2 using the standard GENIE 2000 procedure. Results are presented in Table 5-13 and Table page 40

41 Table Results of test specimens with different particle sizes: light concrete 226 Ra 232 Th Sample code Energy line [kev] Activity concentration [Bq/kg] AC U AC U AC U AC U AC U polipack Table Results of test specimens with different particle sizes: cavity clinker brick 226 Ra 232 Th Sample Energy line [kev] code Activity concentration [Bq/kg] AC U AC U AC U AC U AC U polipack In pictures below (Fig Fig. 5-36) a simple analysis of the results is presented. 40 K 40 K page 41

42 Fig Results for different grain sizes 226 Ra Fig Results for different grain sizes 232 Th page 42

43 Conclusion Fig Results for different grain sizes 40 K The specimens prepared with different grain sizes differ significantly in density from the apparent density of the tested materials. Moreover, the bulk density of particular test specimens differs significantly from each other. As a test portion prepared by sieving contains a different grain size it is important to sieve the whole test portion in order to avoid material fractionation in the test specimen afterward prepared. Depending on the particular construction material being tested, different fraction used for test specimen preparation reflects correctly the apparent density of the material, see Table The biggest differences were for the fractions of <2 mm. A possible reason is that a test specimen prepared in this way is actually a mixture of grains from ~ 0 to 2 mm and is not homogenous, additionally sample self-attenuation can unintentionally vary among the test specimens prepared. The most uniform results were obtained for fractions of 2-5 mm; these are more homogenous than those of <2mm and fit better to the beaker used than fractions of 5-10 mm. The best solution is to prepare the most uniform sample possible e.g. 4-5 mm, when the material measured must be crushed Test 6: Method of spectrum analysis The test objective was to identify effect of the method of spectrum analysis applied on the measurement results. As some radionuclides of interest emit gamma rays with different energy, the page 43

44 possibility exists to use them separately in order to quantify their activity concentration. In the test results obtained using different methods of radionuclide activity concentration analysis were compared Tested samples Tested materials: cavity clinker brick (3.5.5) and glazed tiles (12.3). Description of test specimens used is presented in Table Table Density of tested materials and test specimens Density of Bulk Sample Sample Material Geometry end-product density [g/cm 3 ] [g/cm 3 mass [kg] ] cavity clinker brick (< 5 mm) Polipack glazed tiles ( < 5 mm) Test conditions detector: 2 (see Table 3-1) software: GENIE 2000 temperature: ᵒC RH%: % Test results All of the spectra were analyzed according to the standard of concern, based on lines from Annex D and according to the standard GENIE 2K procedure using the radionuclide library containing all significant energy lines ( 226 Ra: 186, 295, 351, 609, 1120, 1765 kev; 228 Ra: 338, 911, 969 kev; 228 Th: 239, 583, 861 kev) for each particular natural radionuclide. The weighted average of activity concentration was calculated for the radionuclides proportionally to energy line efficiency (ε γ ). Results are presented in Table Table Comparison of results gained by two methods of spectrum analysis 226 Ra 232 Th Method Energy line [kev] Activity concentration [Bq/kg] AC U AC U AC U AC U Standard TS Genie 2K K page 44

45 The comparison of results obtained by analysis of basic (in bold) and complementary lines, which are listed in the Annex D, for these two samples is shown in Table Table Comparison of results gained by two methods of spectrum analysis Radionuclide Intermediate radionuclide 226 Ra Th Conclusions 228 Th 228 Ra Measured radionuclide Energy line [kev] Sample Activity concentration [Bq/kg] AC U AC U 214 Pb Ra Pb Bi < Tl Ac Ra Pb Tl 861 < Ac It is not possible to use lines kev from 224 Ra and kev from 214 Pb as recommended in Annex D. A similar situation occurs in the case of 615 kev 208 Tl which can interfere with 609 kev 214 Bi. Other gamma lines are valuable and can be used for the verification of the basic line (Table 1 of Standard; in bold in Table 5-17). The use of the weighted average of activity concentration calculated based on the most efficient energy lines of a particular radionuclide, allow lower uncertainty to be achieved and minimize the possibility of accidental mistakes. In a spectrum of 208 Tl which reflects the activity concentration of 228 Th, an efficient energy peak occurs at energy 2614 kev. This peak is not taken into consideration in the standard of concern at all. page 45

46 But, the use of this peak can improve the quality and efficiency of this radionuclide activity concentration measurement. Comments: When gamma spectrometry is applied, there is no reason to use only one energy line for nuclide activity concentration evaluation, aside from potassium Test 7 and test 8: Radon tightness (Annex A test) The test objective was to identify the effect of the escape of radon from measurement beakers on measurement results. As the measurement of radium 226 activity concentration is based on the direct measurement of radon progeny ( 214 Bi 352 kev), radon exhalation from the sample and from a measurement beaker is crucial for the quality of the final measurement results Tested samples Marinelli beaker, Model 590G-E, made from polypropylene and a polipack made from polyethylene meet the assumed test conditions and they were used for the execution of the test. Three 700 ml marinelli beakers and three polipack 250 were filled with radon (Table 5-18). The first was covered by using a lid (not sealed). The second was sealed with adhesive tape. The third was sealed with two-component epoxy adhesive (Fig. 5-37). Sample code Table Samples used for radon tightness assessment Sample Material which a beaker is made from 11.1 radon in marinelli (not sealed) polypropylene 11.3 radon in marinelli (sealed with tape) polypropylene 11.5 radon in marinelli (sealed with epoxy adhesive) polypropylene 11.2 radon in polipack (not sealed) polyethylene 11.4 radon in polipack (sealed with tape) polyethylene 11.6 radon in polipack (sealed with epoxy adhesive) polyethylene page 46

47 Test conditions Fig The containers sealed with epoxy adhesive. Empty, open beakers were placed in a radon chamber with an open source of 222 Rn inside. They were closed inside a radon chamber for 72 hours and then sealed as described in the section above. Radon activity concentration measurements inside every beaker used were repeated every hour during 3 days (7 hours in every day) under the conditions listed below: detector : 1, 2, 3, 4 (see Table 3-1) software : GENIE 2000 temperature : ᵒC RH%: % Test results Experimental data was processed as described in Annex A of the draft standard. An example of the radon concentration as a function of time in a test beaker is presented in Fig page 47

48 Fig Activity concentration of 214 Pb progeny of 222 Rn closed in sealed polipack The total counting rate can be described using formula: where: R cor,w total counting rate in a spectrum that is determined from the total number of pulses that is collected for the chosen photopeak [s -1 ], a, b, c free parameters Radon tightness was calculated using: where: a free parameter [s -1 ] λ I radon tightness [s -1 ] λ Rn-222 = s -1 decay constant of Rn-222. A tested beaker is considered to be radon tight when the condition set by the equation below is met: where s a is the uncertainty of the free parameter a in [s -1 ]. page 48

49 Silesian Centre for Environmental Radioactivity Obtained λi radon tightness parameters are listed in Table Changes of actual radon concentration in comparison to changes caused by radon decay alone, in all of the measured beakers re po rt are presented in Fig to Fig Full color lines in these figures reflect radon decay (without any leakage). A final comparison of the tested beakers and the used sealant is presented in Fig Table Radon tightness test (a and λi parameters) Geometry Seal none Tape Epoxy adhesive none Tape Epoxy adhesive Marinelli 700 Polipack 280 a [s-1] λi [s-1] λi +2sa [s-1] /T C 35 1 Sample code C EN Fig Measured relationship between the corrected counting rate and the time at which the spectrum was recorded in an unsealed marinelli beaker. page 49

50 Fig Measured relationship between the corrected counting rate and the time of counting in a sealed (with tape) marinelli beaker. Fig Measured relationship between the corrected counting rate and the time of counting in a sealed (with epoxy adhesive) marinelli beaker. page 50

51 Fig Measured relationship between the corrected counting rate and the time at which the spectrum was recorded in an unsealed polipack. Fig Measured relationship between the corrected counting rate and the time at which the spectrum was recorded in a sealed (with tape) polipack. page 51

52 Fig Measured relationship between the corrected counting rate and the time at which the spectrum was recorded in a sealed (with epoxy adhesive) polipack Conclusion Fig Radon tightness in different seals. The general conclusion is that none of the tested beakers met the condition set in the standard of concern. However, the effect of applying different sealants is noticeable. The most effective sealant was the two-component epoxy adhesive. However, marinelli beakers are made from polypropylene (PP) and polipacks are made from polyethylene (PE). These materials belong to polyolefins. This page 52

53 group of materials is very difficult to stick to using an epoxy adhesive and that is why it is necessary to use an activator (Multiband 77) and a two-component epoxy adhesive (Multiband 15) to seal such beakers. Glue and activator are very expensive and using them requires a lot of efforts to ensure the beakers are tight. When analyzing the results, it can be assumed that the application of a sealant effectively limits the leakiness existing at a lid-container abutment that is why the remaining lack of tightness is likely to be caused by radon diffusion. At first sight it seems that polyethylene (polipack) is better than polypropylene (marinelli) - see Fig But it must be underlined that, in the case of marinelli beakers, the total surface of the walls compared to the total volume of the container ratio is higher than in polipacks with a cylindrical shape (Marinelli S/V = 1,05 and Polipack S/V = 0,81). This could be another reason for lower radon tightness for marinelli beakers than polipacks when the same sealant is applied. Moreover, the lid construction, different in both of the beakers, can also influence total radon tightness. Unfortunately, there was no possibility to test identical beakers made from different materials. The proposed method and criterion for the verification of measurement beakers radon tightness does not represent normal conditions under which construction materials are measured, i.e. none of the construction products are gases. So the presence of solid material, which is characterized by specific radon emanation and exhalation, in a beaker influences final radon escape during a measurement. Moreover, the proposed methods need additional equipment and a radon source that are usually not available in typical laboratories involved in the measurement of construction materials Proposed alternative test for beaker radon tightness verification This test is focused on assessing the properties of measurement beakers and the applied seals according to Annex A based on the available NORM (Naturally Occurring Radioactive Material) characterized with specific parameters, mainly high radon exhalation. page 53

54 Tested samples As marinelli beakers, Model 590G-E, are made from polypropylene (PP) and polipack containers are made from polyethylene (PE) they meet the assumed test conditions and were used for the test execution, as before. Two 700 ml marinelli beakers and three polipack 280 were filled with the NORM. In this case it was a mixture of charcoal and sand from spent filters that had been used for ground water purification. One of these samples for each beaker type was sealed with adhesive aluminum tape (Fig. 5-46). The main parameters of the test specimens are listed in Table Samples used for radon tightness assessment are in Table Fig Test specimens prepared for the assessment of the properties of different containers and seals Sample code Table Samples used for radon tightness assessment Sample Material which the beaker is made from Sample mass [kg] Expected 226 Ra activity concentration [Bq/kg] 5.1 NORM in marinelli sealed polypropylene ~ NORM in marinelli not sealed polypropylene ~ NORM in polipack sealed polyethylene ~ NORM in polipack not sealed polyethylene ~ NORM in polipack sealed polyethylene ~4000 page 54