Kónyi, Júlia Kövendiné

Osváth, Szabolcs

Rell, Péter

Szabó, Gyula

Online Research Database In Technology

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Apr 10, 2018Determination of 226Ra in natural water samples by liquid scintillation countingOsváth, Szabolcs; Rell, Péter; Kónyi, Júlia Kövendiné ; Szabó, GyulaPublication date:2017Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Osváth, S., Rell, P., Kónyi, J. K., & Szabó, G. (2017). Determination of 226Ra in natural water samples by liquidscintillation counting. Poster session presented at International Conference on Advances in Liquid scintillationSpectrometry 2017, Copenhagen, Denmark.Determination of 226Ra in natural water samples by liquid scintillation counting Szabolcs Osváth 1, 2, Péter Rell 1, Júlia Kövendiné Kónyi 1, Gyula Szabó 11National Public Health Institute, Budapest, Anna utca 5., 1221, Hungary 2Current workplace: DTU Nutech, Roskilde, DTU Risø Campus, Frederiksborgvej 399, 4000, Denmark Corresponding author’s e-mail: osvath.szabolcs@osski.hu MethodFigure 1 shows the sample preparation procedure used. 0.5-1.5 L sample was taken, filtered through a 0.45 µm filter and pHwas adjusted to 4-7 using 1 M HNO3 or 1 M NaOH. After that 4 Bq 133Ba tracer and 1.25 g MnO2 Resin® were added. (AsBa/Ra divergence does not seem to be an issue using this method, 133Ba was chosen as tracer. Its activity was chosen to bemuch higher as that of β-emitter 228Ra, possibly also present in drinking and natural waters.) The sample was stirred for atleast 1 hour, and the resin was allowed to settle (preferably for a night). The supernatant was decanted, the resin wascentrifuged and the supernatant was discarded. Ba and Ra were eluted from the resin using 12 mL 6 M HCl, 1 drop 30% H2O2was added to make the solution colorless, then it was filtered through a 0.45 µm filter. (Application of MnO2 Resin® forconcentration of Ra and Ba from natural waters was developed and published by Moon et al. (2003).) 100 µL 1:1 acetic acidwas added to make complex with Pb2+. 19 mg Ba(NO3)2 and 5 mL 40% (saturated) Na2SO4-solution were added. The samplewas slightly warmed and stirred for 30 minutes to form BaSO4 precipitate, then it was centrifuged (3000 rpm, 5 min) and thesupernatant was discarded. The precipitate was suspended in 2 mL saturated K2CO3 solution and it was evaporated with3x2 mL distilled water to dryness to convert BaSO4 to BaCO3. (This is a well-known procedure, see for example Kirby andSalutsky (1964).) 30-40 mL distilled water was added, and the slurry was centrifuged. This step was repeated until the pH ofthe supernatant reached 7 (typically 3 times). The BaCO3 precipitate was dissolved in 1 mL 0.5 M HNO3, 1 drop 30% H2O2 wasadded to make it colorless. The solution was transferred into a 20 mL plastic LSC vial, 16 mL Ultima Gold LLT cocktail wasadded and LSC measurement was performed using a Tri-Carb 2900TR (Packard, USA) equipment.Sampling Addition of 133Ba tracerSorption of Ba and Ra on MnO2 Resin®Elution (6 M HCl) Co-precipitation with BaSO4Conversion into Ba(Ra)CO3using saturated K2CO3LSC source preparation LSC measurementTable 3 Activity concentration of 226Ra (mBq L-1) in some popular Hungarian (and Rumanian) bottled mineral waters (purchased from local supermarkets). The uncertainty is given using a coverage factor of 1 (k=1). AbstractA relatively fast, simple and reliable method has been developed for determination of 226Ra from natural water samples, using radiochemical separationand liquid scintillation counting (LSC). This method is based on the usage of 133Ba as tracer, sorption on MnO2 Resin® and precipitation of Ba(Ra)SO4.Ba(Ra)SO4 was converted into Ba(Ra)CO3, solubilized, and then measured by LSC. The 133Ba tracer and the 226Ra analyte were determined parallel using thesame LSC measurement. Analyzing model solutions and real samples, 60(±15)% average recovery and 10 mBq of limit of detection were observed.(Detection time was 100 min.) This method was successfully used for analysis of bottled mineral waters, medicinal thermal waters and natural surfacewaters.Highlights- A method has been developed for determination of 226Ra from natural water samples.- The method is relatively fast, simple and reliable.- The method is based on radiochemical separation and LSC measurement.- Activities of 133Ba and 226Ra were determined from the same LSC measurement.- 226Ra in natural water samples was analyzed.Keywords: Ra-226, LSC, MnO2 Resin®, natural waterIntroductionDetermination of 226Ra in drinking waters, natural waters and other environmental samples is an important task due to its high radio-toxicity. 226Ra can bedetermined directly or via its progenies (e. g. 222Rn, 214Po). According to the newest comprehensive papers (IAEA, 2010; Jia and Jia, 2012), α-spectrometry,γ-spectrometry, liquid scintillation spectrometry (LSC) and mass spectrometry are mostly used as measurement techniques for determination of 226Ra.However, in another recent comprehensive paper (Vasile et al., 2010) only α-spectrometry, γ-spectrometry and Rn emanation technique are referred, whileLSC is only mentioned as a technique for determination of 228Ra.To optimize the pulse decay discriminator setting of the LSC analyzer, 241Am standard was used as pure α-emitter (as the α-emitter 226Ra has some β-emitter progenies) and 133Ba standard was used as “pure β-emitter”. 133Ba decays by electron capture but its γ-rays, X-rays, Auger electrons and conversionelectrons can be counted by LSC as β-counts (Chylinski and Radoszewski, 1993). The crossover point was at 125 ns, but 140 ns discrimination time was usedto reduce the spillover of 133Ba counts into the α-counting region.Activity of 133Ba was calculated on the basis of the β-LSC spectrum. Counting efficiency (fβ) of 133Ba was calculated using the formula:𝑓𝑓𝛽𝛽 = 𝐼𝐼𝑐𝑐𝑐𝑐𝑐𝑐𝛽𝛽 −𝐼𝐼𝑏𝑏𝑏𝑏𝛽𝛽𝐴𝐴𝑐𝑐𝑐𝑐𝑐𝑐 (1)where 𝐼𝐼𝑐𝑐𝑐𝑐𝑐𝑐𝛽𝛽 stands for measured β-intensity of a calibration sample (containing known Acal activity of 133Ba) and𝐼𝐼𝑏𝑏𝑏𝑏𝛽𝛽 stands for measured β-intensity of a background sample of the same composition as real samples.Adding different amounts of 65% HNO3 to the calibration samples, the effect of quench was also studied. Counting efficiency of 133Ba (using channels 0-2000 of the β-LSC spectrum) was found to be 118% and independent on quench. (As not only the Auger and conversion electrons but even some γ- and X-particles are detected via their Compton electrons, counting efficiency can be higher than 100%.)Either channels 0-2000 or channels 10-250 of the β-LSC spectrum can be used for determination of recovery (R) of 133Ba. According to our results, there isno significant difference between the recoveries calculated using the different regions. In some cases, recoveries were checked and confirmed bydetermining the activity of 133Ba by γ-spectrometry. When analyzing samples whose activity of 228Ra is commensurate with that of 133Ba tracer, channels40-250 can be used as well (as the β-endpoint of 228Ra is 40 keV), but this increases the uncertainty of recovery too much – this is why in such cases it isadvisable to use another method.Recovery of 226Ra was assumed to be the same as that of 133Ba. Activity of 226Ra (Asample) was calculated using channels 90-500 of the α-LSC spectrumsubtracting spillover of 133Ba counts into the α-counting region ( ⁄𝐼𝐼𝑐𝑐𝑐𝑐𝑐𝑐𝛼𝛼 𝐼𝐼𝑐𝑐𝑐𝑐𝑐𝑐𝛽𝛽 ; typically 0.2%-0.5%) by the formula:𝐴𝐴𝑠𝑠𝑐𝑐𝑠𝑠𝑠𝑠𝑐𝑐𝑠𝑠 = 𝐼𝐼𝑠𝑠𝑐𝑐𝑠𝑠𝑠𝑠𝑐𝑐𝑠𝑠𝛼𝛼 −𝐼𝐼𝑐𝑐𝑐𝑐𝑐𝑐𝛼𝛼𝐼𝐼𝑐𝑐𝑐𝑐𝑐𝑐𝛽𝛽 𝐼𝐼𝑠𝑠𝑐𝑐𝑠𝑠𝑠𝑠𝑐𝑐𝑠𝑠𝛽𝛽𝑓𝑓𝛼𝛼 (2)where 𝐼𝐼𝑠𝑠𝑐𝑐𝑠𝑠𝑠𝑠𝑐𝑐𝑠𝑠𝛼𝛼 is α-intensity of the sample,𝐼𝐼𝑐𝑐𝑐𝑐𝑐𝑐𝛼𝛼 is α-intensity of the calibration sample,𝐼𝐼𝑠𝑠𝑐𝑐𝑠𝑠𝑠𝑠𝑐𝑐𝑠𝑠𝛽𝛽 is β-intensity of the sample andfα is detection efficiency of α-particles (95%).In the region mentioned above, peaks of all α-emitter progenies of 226Ra (namely 222Rn, 218Po and 214Po) are present (as shown in Figure 3). Their in-growthwas taken into account using a calibration curve based on the results and equations described by Fons et al. (2013):𝐴𝐴𝑠𝑠𝑐𝑐𝑠𝑠𝑠𝑠𝑐𝑐𝑠𝑠𝛼𝛼 (𝑡𝑡) = 1 + 3 � 1 − 𝑒𝑒𝑒𝑒𝑒𝑒 − ln 2 �𝑡𝑡91.68 ℎ𝑜𝑜𝑜𝑜𝑜𝑜𝑠𝑠 � 𝐴𝐴𝑠𝑠𝑐𝑐𝑠𝑠𝑠𝑠𝑐𝑐𝑠𝑠(𝑡𝑡 = 0) (3)where 𝐴𝐴𝑠𝑠𝑐𝑐𝑠𝑠𝑠𝑠𝑐𝑐𝑠𝑠(𝑡𝑡 = 0) is the 226Ra-activity of sample at separation,𝐴𝐴𝑠𝑠𝑐𝑐𝑠𝑠𝑠𝑠𝑐𝑐𝑠𝑠𝛼𝛼 (𝑡𝑡) is the α activity of sample at t hours after separation and91.68 hours is half-life of 222Rn.ConclusionsA relatively fast, simple and reliable method has been developed for determination of 226Ra from natural water samples, using radiochemical separationand LSC measurement. Activities of 133Ba (for determination of the chemical yield of the procedure) and 226Ra were determined from the same LSCmeasurement.As no extra gamma-spectrometry was used for measurement of 133Ba, the overall time consumption of this method (about 20 hours) is comparable withthat of methods based on α-spectrometry and more convenient than that of methods based on 222Rn in-growth. (However, presence of 228Ra increases theuncertainty of recovery.)This method was successfully applied for analysis of bottled mineral waters, medicinal thermal waters and natural surface waters.Figure 1 Flowchart of the procedure Discussion 1: Evaluation of LSC measurementsFocal point of this method is that the same LSC measurement was used for determination of activity of 133Ba tracer as well as that of 226Ra analyte (seeFigure 2), as proposed by Tinker and Smith (1996).0501001502002500 100 200 300 400 500 600CountsChannelsAlphaBetaFigure 2 LSC spectrum of 226Ra and 133Ba. The peak in the α-spectrum correspond to 226Ra (4784 keV). The β-spectrum consists of counts from 133Ba tracer and spillover of α counts of 226Ra. As these spectra were acquired right after separation, progenies of 226Ra are not present. 020040060080010001200140016000 100 200 300 400 500 600CountsChannelsAlphaBetaResultsSome results of 38 analyzed water samples (bottled mineral waters, medicinal thermal waters and natural surface waters) can be seen in Tables 1 and 2.Our experiments have showed that the average chemical recovery was 60(±15)%, and we could not find correlation between recovery and samplecomposition (alkaline earth content).According to 2.2 cpm background between channels 90-500 of the α-LSC spectrum and applying 100 min detection time, typically 10 mBq of minimaldetectable activity (MDA) was achieved. Therefore, analyzing a sample of 0.5-1.5 L, the limit of detection described in the Council Directive2013/51/Euratom [3] (namely 40 mBq/L for drinking water) is easily achievable. Typical relative uncertainty of results (in cases they were over MDA) was8%, calculated using a coverage factor of 1 (k=1).Discussion 2: Method reliabilityTo check the reliability of the method, 2 water samples of a proficiency test (Determination of activity concentration of 3H, 226Ra, 241Am, 239Pu in food andenvironmental samples; Institute of Nuclear Chemistry and Technology (INCT), Warsaw, Poland 2014-14) were analyzed. The results show acceptableagreement with the reference values (see Table 1).The well-known medicinal thermal waters of Spa Rudas were also analyzed, results are reported in Table 2. The result of sample ‘Hungária” was checkedand confirmed by γ-spectrometry. A 20 L aliquot was evaporated and the residue was ashed. According to the γ-spectrum of the ash, activity concentrationof 226Ra in the original sample was 447±17 mBq L–1. Earlier results are also presented in Table 2, taking into account their high variability, the resultsreported in this paper are acceptable.Results of analysis of some popular bottled mineral waters (selected randomly) are reported in Table 3. Differences between older and newer values can beexplained by changes in exploitation or processing technology (e. g. changing of the spring).Table 2 Activity concentration of 226Ra (mBq L-1) in medicinal thermal waters of Spa Rudas. The uncertainty is given using a coverage factor of 1 (k=1). Name of spring Measured value Earlier results Hungária 452 ± 45 993 ± 96 (Baradács, 1999) 699 ± 69 (Baradács, 2002) 532 (Baradács, 2002) Attila 729 ± 57 2150 (Szerbin, 1996) 1650 ± 30 (Kasztovszky et al., 1996) 912 ± 89 (Baradács, 1999) 834 ± 81 (Baradács, 2002) 500 (Baradács, 2002) Juventus 708 ± 61 710 ± 67 (Baradács, 1999) 646 ± 64 (Baradács, 2002) 522 (Baradács, 2002) Brand name Measured value Earlier results Balfi < 10 85 (Baradács et al., 2001) < 200 (Ugron, 2010) Borsec[sparkling; Romania]343 ± 38 Borsec[still; Romania]41 ± 9 Fonyódi < 10 Kereki Theodora < 10 Kékkúti Theodora < 10 270 (Szerbin and Köteles, 1999) 77 (Baradács et al., 2001) < 170 (Ugron, 2010) Mizse < 10 Natur Aqua < 10 Óbudai Gyémánt 100 ± 9 110 (Baradács et al., 2001) 68 ± 29 (Guczi, 2005) 128 ± 17 (Guczi, 2005) 92 ± 33 (Ugron, 2010) Szentkirályi < 10 Visegrádi 159 ± 14 204 (Baradács et al., 2001) < 129 (Guczi, 2005) < 180 (Ugron, 2010) Sample code Measured value Reference value R1/13. < 24 50 ± 10R2/13. 432 ± 37 440 ± 60Table 1 Activity concentration of 226Ra (mBq L-1) in two intercomparison samples. The uncertainty is given using a coverage factor of 1 (k=1). Figure 3 LSC spectrum of 226Ra and its progenies (without 133Ba tracer). The peaks in the α-spectrum correspond (from left to right) to 226Ra (4784 keV), 222Rn (5490 keV), 218Po (6002 keV) and 214Po (7687 keV). As no 133Ba tracer is present, the β-spectrum consists of β counts from β-emitter progenies of 226Ra (214Pb and 214Bi) as well as of spillover of α counts. References• Baradács, E., Hunyadi, I., Dezső, Z., Mócsy, I., Csige, I., Szerbin, P., Vaupotic, J., 1999: 226Ra in geothermal waters of the Carpathian Basin. IRPA RegionalCongress on Radiation Protection in Central Europe, Budapest, 23-27 August 1999• Baradács, E., Hunyadi, I., Dezső, Z., Csige, I., Szerbin, P., 2001: 226Ra in geothermal and bottled mineral waters of Hungary. Radiat Meas 34, 385-390.Baradács E., 2002: Radon and radium content of thermal and mineral waters (in Hungarian). PhD thesis, University of Debrecen, Hungary• Chylinski, A., Radoszewski, T., 1993: Liquid scintillation standardization of 133Ba. In: Noakes, J. E., Schönhofer, F., Polach, H. A. (eds.): Liquid ScintillationSpectrometry 1992, Radiocarbon, 269-274• Council of the European Union, 2013: Council Directive 2013/51/Euratom of 22 October 2013 laying down requirements for the protection of the healthof the general public with regard to radioactive substances in water intended for human consumption• Fons, J., Zapata-García, D., Tent, J., Llauradó, M., 2013: Simultaneous determination of gross alpha, gross beta and 226Ra in natural water by liquidscintillation counting. J Environ Radioact 125, 56-60.• Guczi J., 2005: Unpublished results. “Frédéric Joliot-Curie” National Research Institute for Radiobiology and Radiohygiene, Hungary• IAEA, 2010: Analytical Methodology for the Determination of Radium Isotopes in Environmental Samples. International Atomic Energy Agency AnalyticalQuality in Nuclear Applications Series No. 19• Jia, G., Jia, J., 2012: Determination of radium isotopes in environmental samples by gamma spectrometry, liquid scintillation counting and alphaspectrometry: a review of analytical methodology. J Environ Radioact 106, 98-119.• Kasztovszky, Zs., Kuczi, R., Szerbin, P., 1996: On the natural radioactivity of waters in Hungary. Centr Europ J Occup Env Med 2 (4), 335-347• Kirby, H. W., Salutsky, M. L., 1964: The Radiochemistry of Radium. National Research Council, USA• Moon, D. S., Burnett, W. C., Nour, S., Horwitz, P., Bond, A., 2003: Preconcentration of radium isotopes from natural waters using MnO2 resin. Appl RadiatIsot 59, 255-262.• Szerbin P., 1996: Natural radioactivity of certain spas and caves in Hungary. Environ Int, 22 (1), 389-398• Szerbin P., Köteles Gy., 1999: Survey of natural radioactivity in drinking water (in Hungarian). Egészségtudomány 43, 287-296• Tinker, R. A., Smith, J. D., 1996: Simultaneous measurement of 226Ra and 133Ba using liquid scintillation counting with pulse shape discrimination. AnalChim Acta 332, 291-297.• Ugron Á., 2010: Unpublished results. “Frédéric Joliot-Curie” National Research Institute for Radiobiology and Radiohygiene, Hungary• Vasile, M., Benedik, L., Altzitzoglou, T., Spasova, Y., Watjen, U., González de Orduna, R., Hult, M., Beyermann, M., Mihalcea, I., 2010: 226Ra and 228Radetermination in mineral waters — Comparison of methods. Appl Radiat Isot 68, 1236–1239.LSC 2017 An International Conference on Advances in Liquid Scintillation Spectrometry1-5th May, 2017, Copenhagen, Denmarkhttp://lsc2017.nutech.dtu.dkPoster ID = 282 

Determination of <sup>226</sup>Ra in natural water samples by liquid scintillation counting

http://orbit.dtu.dk/ws/files/142126767/226Ra_LSC2017_v10_3_.pdf

Determination of <sup>226</sup>Ra in natural water samples by liquid scintillation counting

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology