FCI Frenzel Consulting & Instruments ------
TRIATHLER™: MODERN AND MOBILE LSC INSTRUMENT FOR THE DETECTION OF RADON AND OTHER RADIONUCLIDES IN WATER Dr. Eberhard Frenzel FCI Frenzel Consulting & Instruments; Steinweg 12 / 1; D-75334 Straubenhardt Phone: + 49 7082 948 290; Fax: + 49 7082 948 291;E- Mail:[email protected]
Introduction
In many european countries new regulations for radionuclides in drinking water, mineral water and foodstuff are in preparation or already in use. In addition for the first time in Germany the new radiation protection law of 2001 ( Strahlenschutzverordnung) requires workplace related estimation of radon doses for workers in the field of natural radionuclides.
Therefore the activity concentration of Rn – 222 in air and water must be known. For Rn – 222 in water LSC – technique is the best and most sensitive method.
However, the liquid scinitillation counters usually are big and heavy instruments, designed for the exclusive use in the laboratory. As an increasing number of measurements is expected for rapid in situ – detection in • water – works • dwells • the field
1 FCI Frenzel Consulting & Instruments ------the compact mobile LSC - instrument Triathler™ combined with rapid methods will be very usefull.
Instrumentation: Compact LSC Triathler™
Triathler™ is a compact LSC system, it is mobile and can be used for 1 sample. The SW foresees fixed in-stalled programms for the mainly used nuclides in LSC ( e.g.:H-3,C-14,P-32,Rn-222). All relevant parameters ( measuring times, windows, background subtraction, Quench correction, repeat mode, calibr. factors etc.) can be individually adjusted and stored. By use of 2 – D spectra optimal settings are very simple.
Due to its α-/β- separation Triathler™ enables sensitive measurements of α - emitting nuclides even in the pre-sence of β - emitting nuclides. In addition to the classical LSC tasks Triathler™ is used for measurements of :
• Rn – 222 in water • Ra – 226 in water • Ra – 228 in water • U – 238 / U – 234 in water
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Measurement of Rn – 222 in Water
Method 1 Mixed sample consisting of water and a water miscible scintillation cocktail (Cocktail: e.g.:AquaLight ) direct gros α + β measurement ( without α/β separation )
Method 2 Mixed sample consisting of water and a water miscible scintillation cocktail (Cocktail: e.g.: AquaLight ) direct α - measurement with α/β separation 7mlVial: 4,2 ml cocktail + 2,8 ml radon containing water 20mlVial: 12 ml cocktail + 8 ml radon containing water Time for sample preparation and measurement: 10 minutes
Method 3 Extraction of the sample into a water immiscible cocktail, measurement after 3 hours (Cocktail:e.g.: MaxiLight) α - measurement with α/β separation 7mlVial: 3,5 ml cocktail + 3,5 ml radon containing water 20mlVial: 10 ml cocktail + 10 ml radon containing water Time for sample preparation and measurement: 3 h
Lower Limit of Detection for Rn-222 in water The following table contains LLoD`s of the 3 methods for Triathler™ as function of different measuring times, backgound and vials sizes. T = 1 minute T = 10 minutes T = 30 minutes Bq / l Bq / l Bq / l Method 1, 20ml 30 10 4 Background:500cpm Method 2, 20ml AquaLight 2 0,7 0,3 Background: 1 cpm Method 2, 7ml AquaLight 2 0,7 0,3 Background: 0,3 cpm Method 3, 20ml MaxiLight 0,8 0,2 0,08 Background: < 0,1cpm Method 3, 7ml MaxiLight 0,8 0,2 0,08 Background: < 0,05cpm 3 FCI Frenzel Consulting & Instruments ------
Radon in water workshops:Luxembourg, September 26, 1997 Thale, May 13 - 14, 1999; Luxembourg, September 4, 2002
FCI Frenzel Consulting & Instuments participated ( 1997 and 1999 with Dres. Möbius, FZK) at international workshops for radon in water with the Triathler™. The Luxembourg workshops ( 1997 and 2002 ) were organized by Prof. Kies, University of Luxembourg, and Dr. Surbeck, Uni. Neuchatel - Switzerland. The Thale workshop ( 1999 ) was organized by Dr. Wiegand, University of Essen, and Dr. Gellermann, HGN GmbH
The overview shows the excellent performance of the Triathler™, blue for Luxembourg 1997, darkblue for Thale and darkgreen for Luxembourg 2002. The Thale values are in addition in excellent agreement with the values ( in red colour ), coming from Bundesamt für Strahlenschutz, Berlin. This group took the samples and measured it in the laboratory in Berlin, 2 days later.
Activity ( Bq / L) Activity ( Bq / L ) measured by Mean value ± variation Triathler™ Thale : mean value and max Messunsicherheit: ca 20 % /min value Luxembourg 1 10 9,4 ± 3,5 1997 2 31 30,7 ± 7,3 3 317 288 ± 54 4 857 771 ± 151 5 1214 1068 ± 128 Thale 1999 Behringer Brunnen 14 15,5 (13,4 - 24 ) 16 Bundesamt f. Strahlenschutz1 Hubertusquelle 1110 1208 (1094 - 1440) ( city ) 1110 Bundesamt f. Strahlenschutz 1130 Bundesamt f. Strahlenschutz Hubertusquelle 1172 1267 (1036 - 1614) (hill) 1200 Bundesamt f. Strahlenschutz 1230 Bundesamt f. Strahlenschutz Luxembourg 1 30 23 ± 1 ( 1 Sigma) 2002 2 280 252 ± 9 ( 1 Sigma) 3 1209 1232 ± 41 ( 1 Sigma) 4 2131 2132 ± 78 ( 1 Sigma)
1 Measurements of Dr. Bünger and Dipl.-Ing. Schkade, BfS Berlin, Germany, via LSC, estimated uncertainties: ~ 20 %; for Hubertusquelle BfS took 2 own samples. 4 FCI Frenzel Consulting & Instruments ------
The 2 – Dimensional plot of α –and β – spectra: explained with the example of a Rn-222 spectrum
Impulse 160 140 Rn-222 Alpha - Spectrum 120 Po-218 100 80 60 40 Beta - Spectrum Po-214 20 Pb - 214, Bi - 214 0
0 Channels
-20 66 132 198 264 330 396 462 528 594 660 726 792 858 924 990
Alpha – Beta separation is performed by the method of pulse length index; long alpha pulses are measured in the alpha channel, the significant shorter beta – pulses in the beta channel. The above figure ( above ) shows a typical Rn-222 spectrum, performed by Triathler™.In the 2 – d spectrum ( down) x – axis is energy, y – axis is pulse length and z – axis is intensity. The horizontal line is the pulse length index PLI, which discriminates alpha and beta pules, the vertical lines correspond with the windows settings for alphas ( top ) and beta windows settings ( down ).PLI and windows can be set individually in order to perform best alpha - beta separation settings. The tool of the 2 – d picture with Triathler™ Software is automatically created by the help of Excel –Macros.
S31 S29 S27 27-30 S25 24-27 S23 S21 21-24 S19 18-21 S17 15-18 S15 12-15 S13 9-12 S11 S9 6-9 S7 3-6 S5 0-3 S3 S1 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64
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Measurement of Ra–226 in Ground- and Drinking Water With Triathler™ via Emanation
A classical method to determine Ra–226 is the measurement by emanation, however, in this case followed by LSC counting with α-/β- separation.
• Sample Taking in accordance to H-Ra-226-TWASS-01-01 • If needed the sample is made acid • Polyethylen – container is blown by „radonfree air“ or with nitrogen, to blow out Rn-222 • Sample is stored; during this time Rn-222 is ingrowing • After 4 weeks Rn-222 is measurd by extraction and counted in a minivial • By ingrowth into a vial with cocktail even after 2 days can Rn – 222 be measured
Lower limit of detection with 14.400 sec. measuring time:
LLoD50ml = 0,04 ± 0,01 Bq / l.
LLoD600ml = 0,006 ± 0,001 Bq / l.
800 0 day 700 0 day 600 500 1 day 400 1 day 300 Counts 200 2 days 100 0 2 days 0 500 1000 3 days MCA channels 3 days 4d Rn – 222 ingrowth from Ra – 226; bold: α`s
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Bad – Brambach : Ra – 226 Determination in Triathler™ by Emanation
On april 17, 2002, in Bad Brambach ( Elstergebirge in Germany) a sample was taken at Wettinquelle2. The sample was extracted; the extraction volume was 3,5 ml, the cocktail MaxiLight Volume was 3,5 ml. The activity at april 21 was 996 Bq /l. The sample had been closed all the time – ML was kept on water all the time
Fig 1 shows the decay curve of the counts/sec ( background corrected), fig. 2 the calculated activity concentration in the sample.
Decay Curve Ra - 226 Activity Concentration 7 15 6 5 12,5 4 10 3 7,5 2 5 log cpm net
1 c in Bq / m3 2,5 0 0 0204060 25 35 45 55 65 Time ( days ) Time ( days )
Fig.1: background corrected decay curve Fig. 2: activity concentration
Alpha - Spectrum R31 R28 27-30 R25 24-27 30 R22 21-24 R19 18-21 20 R16 15-18 12-15 R13 9-12 R10 10 6-9 R7 3-6 0 R4 0-3 R1
0 200 400 600 800 1000 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64
Fig.3: alpha spectrum of june 21; Fig.4: 2 D – spectrum of june 21; 3244 counts in 99.999 seconds; n0=0,5cpm 3244 counts in 99.999 seconds
After 65 days the Rn – 222 activity – concentration should be < 0,1 Bq/l; however, as seen from fig. 2 the measured acticivity concentration on june 24 is 2,5 Bq /l. The difference can only be explained by Ra-226, which is now in equilibrium with ist daughters ( see fig. 3 and fig. 4). Hence, the activity concentration is:
CRn - 226 = 2,5 Bq /l ± 0,3 Bq /l
2 Wettinquelle: Strongest Rn-spring in central europe with ~26 kBq/l activity conc. of Rn-222; selected data: 176l/h; 8,8 °C; pH 5,8 7 FCI Frenzel Consulting & Instruments ------
U – 238/ U - 234 Extraction From 250 ml Water and Measurement in Triathler™
U-238 can be extracted from water with modified MaxiLight added with a few per cent ( 6 % ) of a complexing agent, such as e.g. bis(2-ethylhexyl)-phosphate (HDEHP), trioctylphos-phine oxide (TOPO) or tributyl phosphate (TBP). Before extraction, water is thoroughly bubbled to remove Rn-222 and made acidic with nitric acid. According to literature, these agents are rather effective so that a few milliliters of the modified cocktail can extract over 90 % of U from one liter of water.
LLoD in 1 hour: 1 µg/l or 0,01 Bq ( U -238) / l
45 40 35 U-238 U-234 30 25 ALPHA 20 BETA counts 15 10 5 0 200 400 600 800 1000 MCA channels
Activity of the sample: 3,36 mg/l or 42 Bq/l, measured with Triathler™ in an Eppendorf Vial
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New Rapid Methods for:Ra – 226 und Ra – 228 in Water with 3M Radium Rad Disk Since some time selective filters of 3M Empore™ are available for the „Rapid Analysis of Ra – 226, Ra – 228”. Most of these methods have been developped by US – Research centres (e.g. Argonne National Laboratories ) in cooperataion with 3M. The 3M Empore™ Rad Disks are availalble as Radium Rad Disks, Strontium Rad Disks, Technetium Rad Disks and Cesium Rad Disks. 3M Empore™ Rad Disks are thin membranes, loaded with elementselective particles ( AnaLig™) and crown - ether, embedded in a stable, inert matrix of PTFE. Up to 5 liters of water are filtered through the filter ( diameter: 47mm ), after this procedure depending on the measuring method evaluation takes place ( e.g. Triathler™ ), or via α- / β- Low Level Counter, α - spectrometry or γ - spectrometrie. It is possible to achieve the following LLoD`s:
Nuclide L L o D in Bq / l Ra-226 <0,001 Ra-228 <0,01 Sr 0,04 Cs < 0,4 TC 0,04
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Determination of Ra- 226 and Ra – 228 with 3M Radium RadDiscs in Triathler™ according to Dr. Möbius, FZ Karlsruhe
A method for the measurement of Ra-226 and Ra-228 with 3M filters was published of Dr. Möbius, Forschungszentrum Karlsruhe, et. al. at the occasion of the „LSC 2001 Conference“. The paper describes the methods in details including excellent tips for the procedure. Extract:
EXTRACTIVE METHODS FOR FAST RADIUM ANALYSIS S. MÖBIUS;Forschungszentrum Karlsruhe GmbH, P.O. Box 3640, D-76021 Karlsruhe, Germany K. KAMOLCHOTE;Silpakorn University, Faculty of Science, Nakorn Pathom 73000, Thailand T. RAKOTOARISOA :Institut National des Sciences et Techniques Nucléaires, BP 4279, 101 Antananarivo, Madagascar
ABSTRACT. Extractive methods for Radium analysis in combination with PeralsTM α-spectrometry or proportional counting have been applied in the past using either an extractive scintillator RADAEXTM (Method A) or a selective 3M Empore Rad DiskTM (Method B). Crown-21-ether is reported to act as selective organic extractant. Additional chemical procedures or enhanced storage time according to the original procedure prevent both methods from their use in rapid field analysis. We have investigated these techniques for fast Ra analysis using α/β-LS Spectrometry and mobile instruments.
In Method B Ra-isotopes are extracted from up to 3 L water volume into a filter disk. Successive elution into 0.25 M alkaline EDTA and α/β-LS counting in properly adjusted energy windows allows 226Ra quantification without storage time. 228Ra can be quantified either directly in a low energetic β-window or through 228Ac ingrowth after 6 to 12 hours but β-emitting daughters from 224Ra interfere slightly in both cases, if present. Pb, Tl and partly Ba are coextracted, Bi, Po, Th and U are not. Interferences due to 210,212,214Pb may be minimized when previously stripped from the filter with 5 mL 0.2 M diammonium hydrogen citrate (DHC). A derived procedure for in field application is presented. Summarized the Ra – 226 is measured in Triathler™ via α/β separation in the α - channel directly after filtering and sample preparation. Ra – 228 can be measured by method 1, which is the β- measurement of the 39 keV β`s. According to method 2 the filter is stored for appr. 3 weeks, to have the Ra-224 and its daughters to decay; after this the period Ac-228 is eluted and the sample can be measured via Ac-228 and its β-energy of 1,17 MeV. LLoD of Triathler™ for 5 liters water is shown in the table ( yield and quench are taken into account), in red α-LLoD for Ra-226, in blue β-LLoD for Ra-228 and Ra-228/Ac-228 resp.
Backgr. I Backgr. II with LLoD for I LLoD for II LLoD with lead additional lead k=3,T=48h k=3,T=48h k=3,T=6h Ra – 226 < 1 cpm < 0,4 mBq/l Ra – 228 60 cpm 30 10 mBq/l 7 mBq/l calculated : € = 20% Ra – 228/Ac-228 80 cpm 45 6 mBq/l 5 mBq/l Calculated : € =40% 10 FCI Frenzel Consulting & Instruments ------
New drinking water regulation and Triathler™
• Implemenation of the European Drinking Water Directive in 1998 • Limit of uptake: ”total indicative dose” of 0.1 mSv per year • Problem: cannot be measured directly • Recommendation: screening-methods • Parameters of choice: the gross-α and gross-β activity concentration excluding 3H, 40K, radon and radon decay products ) • Gross-α activity concentration < 0,1 Bq/l ⇒ annual total indicative dose of adults < 0.1 mSv/yr • Gross- β activity concentration < 1 Bq/l ⇒ annual total indicative dose of adults < 0.1 mSv/yr
• Salonen & Hukkanen 1997: new method for the determination gross-α and gross-β activity concentration utilizing a freeze-drying of the liquid samples • volatile radon degasses during the entire process • Adopting of the method for Triathler™ by ESWE institut, Wiesbaden/Germany by Wisser & Koch • freeze-drying of ~150ml tap water by -22C° • Dissolving with a weak hydrochloric acid of residue and filling up with AquaLight cocktail; best ratio: 14ml cocktail:4 ml acid
LLoD for Triathler™
LLoDα for 1 hour measuring time: 70 mBq/l LLoDα for 4 hours measuring time: 40 mBq/l LLoDα for 12 hours: measuring time: 20 mBq/l LLoDβ are by a factor 12 higher 11 FCI Frenzel Consulting & Instruments ------
Summary
For the detection of natural radionuclides in water (ground and drinking water ) mobile Liquid Scintillation Counting combined with modern direct and extraction technique are essential for rapid in situ detection.
Radionuclide LLoD
Rn-222 non-extractive methods ~ 5 Bq/l in minutes extractive methods < 1 Bq/l after 3 hours
U-234 / U 238 extractive methods < 10 Bq/l after 3 hours
Ra – 226 emanation and extraction < 0,03 Bq/l after 2 days, 600 ml Ra – 226 filtering 3M RadDisks < 0,001 Bq/l in 1 day
Ra – 228 filtering 3M RadDisks < 0,01 Bq/l in 1 day
α-Gross counting: < 20 mBq/l in 12 hours
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Literature
Venso E.A. et al., in Liquid Scintillation Spectrometry 1992, ed. Noakes J.E., Schönhofer F. and Polach H.A. RADIOCARBON 1993, 425-430
L. Salonen,H Hukanen: Advantages of low background liquid scintillation alpha-spectroscopy and pulse shape analysis in measuring Rn-222, uranium and Ra-226 in groundwater Samples Journal of Radioanalytical and Chemical Nuclear Chemistry ; Vol. 226; 1997
S. Möbius et al.:Extractive methods for fast radium analysis; published at “LSC 2001”
S. Wisser,E.Frenzel, M. Dittmer: Innovative Procedure for the Determination of Gross-Alpha/Beta Activities in Drinking Water ( to be published)
Preusse, Schwokowski: Urandetermination with Triathler™; private Mitteilung; UBG, 2. Landesmessstelle für Umweltradioaktivität Sachsen, D – 09131 Chemnitz. June 2000
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