Schnellmethoden Für Die Analytik Von Natürlichen Radionukliden in Wasser

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 2 FCI Frenzel Consulting & Instruments ------------------------------------------------------------------------------------------------------- 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 5 FCI Frenzel Consulting & Instruments ------------------------------------------------------------------------------------------------------- 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 6 FCI Frenzel Consulting & Instruments ------------------------------------------------------------------------------------------------------- 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.

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