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Determination of Pb-210 and Po-210 in aqueous environmental samples [Elektronische Ressource] / von Lena Yvonne Johansson

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Determination of Pb-210 and Po-210 in aqueous environmental samples Von der Naturwissenschaftlichen Fakultät der Gottfried Wilhelm Leibniz Universität Hannover zur Erlangung des Grades Doktor der Naturwissenschaften (Dr. rer. nat.) genehmigte Dissertation von M. SC. LENA YVONNE JOHANSSON geboren am 13. Oktober 1976 in Frändefors, Schweden 2008 Referentin: Prof. Dr. Carla Vogt Korreferent: Prof. Dr. Rolf Michel Tag der Promotion: 28.07.2008II Abstract The naturally occurring radionuclides Pb-210 and Po-210, arising from the uranium-radium decay series, provide a considerable contribution to the radiation exposure to humans over mobile, aqueous systems. Since environmental compartments are generally not closed sys-tems, the individual radionuclides of a decay series may behave differently due to dissimilar chemical properties, which result in radiochemical disequilibria. Therefore, it is very impor-tant to be able to determine the activities both Pb-210 and Po-210 separately. The chemical separation of lead and polonium is performed by solid phase extraction using the Pb Resin. In order to simultaneously retain both lead and polonium, a concentra-–1tion of c(HCl) = 2 mol l is chosen for the sample load; Po-210 is selectively stripped from –1 –1the cartridge with diluted nitric acid (c = 1 mol l and c = 0.1 mol l , respectively).

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Published 01 January 2008
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Determination of Pb-210 and Po-210 in aqueous
environmental samples



Von der Naturwissenschaftlichen Fakultät der
Gottfried Wilhelm Leibniz Universität Hannover
zur Erlangung des Grades
Doktor der Naturwissenschaften (Dr. rer. nat.)
genehmigte Dissertation
von



M. SC. LENA YVONNE JOHANSSON

geboren am 13. Oktober 1976 in Frändefors, Schweden












2008




























Referentin: Prof. Dr. Carla Vogt
Korreferent: Prof. Dr. Rolf Michel
Tag der Promotion: 28.07.2008
II
Abstract

The naturally occurring radionuclides Pb-210 and Po-210, arising from the uranium-radium
decay series, provide a considerable contribution to the radiation exposure to humans over
mobile, aqueous systems. Since environmental compartments are generally not closed sys-
tems, the individual radionuclides of a decay series may behave differently due to dissimilar
chemical properties, which result in radiochemical disequilibria. Therefore, it is very impor-
tant to be able to determine the activities both Pb-210 and Po-210 separately.
The chemical separation of lead and polonium is performed by solid phase extraction
using the Pb Resin. In order to simultaneously retain both lead and polonium, a concentra-
–1tion of c(HCl) = 2 mol l is chosen for the sample load; Po-210 is selectively stripped from
–1 –1the cartridge with diluted nitric acid (c = 1 mol l and c = 0.1 mol l , respectively). More-
over, Po-210 and Pb-210 are quantitatively separated from each other; Pb-210 is completely
stripped from the cartridge with distilled water.
The activity measurement of Pb-210 in water samples is generally difficult, due to its
weak gamma radiation (E = 46.5 keV with P = 4.05 %) and its low energetic beta radiation γ γ
(E = 63 keV). The determination of Pb-210 via LSC is usually performed subsequent to βmax
chemical separation by measuring the beta activity of the daughter Bi-210, after about 30
days of ingrowth. The Pb-210 yield is determined by ICP-MS measurement of the added
stable lead carrier and yields > 90 % are reached. Po-210 is a pure alpha emitter and is meas-
ured via alpha spectrometry. The polonium fraction can directly be utilized for the making of
alpha sources by spontaneous deposition. The overall chemical yield for Po-210 is deter-
mined over Po-208 tracer and reaches 75 per cent.
–1 The detection limit for Po-210 is as low as 0.2 mBq kg , which is more than adequate for
the determination of environmental water samples as well as ground- and drinking water.
–1 –1For Pb-210, decision thresholds and detection limits of 10 mBq kg and 20 mBq kg , respec-
tively, are reached for sample volumes of 1 l and a measurement time of 24 h.
The newly developed method can be applied for the analyses of all kinds of environ-
mental water samples containing Pb-210 and Po-210; unpolluted natural waters, as well as
waters polluted by mining activities, such as the coal mining affected area near Rheinberg
(NRW) and uranium mining affected region of Mailuu Suu, Kyrgyzstan. Furthermore, the
obtained measurement results lead to a better understanding of the studied disequilibria as
well as mobilisation processes and it enable a realistic radiological dose assessment.



Keywords

Pb-210, Po-210, disequilibria
III
IV
Kurzzusammenfassung

Beim Transport über wässrige Systeme liefern die natürlich vorkommenden Radionuklide
Pb-210 und Po-210 aus der Uran-Radium-Zerfallsreihe einen erheblichen Beitrag zur Strah-
lenexposition des Menschen. Da es sich in der Umwelt oft um nicht abgeschlossene Systeme
handelt, können sich die einzelnen Radionuklide einer Zerfallskette wegen ihrer unterschied-
lichen chemischen Eigenschaften deutlich uneinheitlich verhalten, wodurch radioaktive Un-
gleichgewichte entstehen. Daher müssen die Pb-210- und Po-210-Aktivitäten separat gemes-
sen werden.
Die chemische Trennung von Blei und Polonium wird mittels Festphasenextraktion
unter Verwendung vom Pb-Resin durchgeführt. Die Probenaufgabe erfolgt in salzsaurer Lö-
–1sung (c = 2 mol l ), um Blei und Polonium simultan zu extrahieren. Polonium lässt sich
–1 –1selektiv mit Salpetersäure (c = 1 mol l bzw. c = 0,1 mol l ) eluieren. Polonium und Blei
werden quantitativ voneinander getrennt; das Blei wird mit wenig Wasser von der Säule aus-
gewaschen.
Die Bestimmung von Pb-210 in Umweltproben ist wegen der schwachen Gamma-
Strahlung (E = 46,5 keV mit P = 4,0 %) und der niedrigen Energie der Betastrahlung γ γ
(E = 63 keV) schwierig. Die Bestimmung von Pb-210 per LSC erfolgt üblicherweise nach βmax
chemischer Trennung über die Messung der Beta-Aktivität des Tochternuklids Bi-210 nach
etwa 30 Tagen Einwachszeit. Die chemische Ausbeute von Pb-210 lässt sich mittels ICP-MS
anhand der Ausbeute des stabilen Bleis bestimmen und liegt bei > 90 %. Po-210 ist ein reiner
Alphastrahler und wird per Alphaspektrometrie gemessen. Die Polonium-Fraktion kann zur
Herstellung von Messpräparaten mittels Autodeposition direkt eingesetzt werden. Die ge-
samte Ausbeute von Po-210 wird über einen Po-208-Tracer bestimmt und liegt bei 75 %.
–1 Die Nachweisgrenze von Po-210 beträgt 0,2 mBq kg , niedrig genug für die Bestimmung
von sowohl wässrigen Umweltproben, als auch Grund- und Trinkwasserproben. Für Pb-210
–1liegen die Erkennungsgrenze und die Nachweisgrenze bei 10 bzw. 20 mBq kg , bei einem
Probenvolumen von 1 Liter und einer Messzeit von 24 h.
Die neu entwickelte Methode kann im Bereich der Radioökologie bei allen Arten von
wässrigen Umweltproben zur Anwendung kommen; auf nicht belastete, natürliche Gewässer,
sowie bergbaulich belastete Wasserproben, wie z.B. aus der durch Kohlebergbau beeinflusste
Region in Rheinberg (NRW) oder der durch Uranbergbau belasteten Gebiet in Mailuu-Suu,
Kirgisistan. Die dabei gewonnenen Messergebnisse sollen zu einem besseren Verständnis der
betrachteten Ungleichgewichte und Transportvorgänge beitragen und eine Festlegung von
realistischen radioökologischen Modellparametern ermöglichen.



Schlagworte

Pb-210, Po-210, Ungleichgewichte

V






VI
Contents

1 INTRODUCTION AND SCIENTIFIC AIM ...................................................1
1.1 Aim of study...........................................................................................................................3
2 RADIOACTIVITY IN THE ENVIRONMENT ...............................................5
2.1 Natural radioactivity in the environment.........................................................................5
2.1.1 Radiation exposure...............................................................................................................6
2.1.2 Natural deposits ....................................................................................................................6
2.1.3 Uranium-radium decay chain.............................................................................................7
2.1.3.1 Lead ....................................................................................................................................9
2.1.3.2 Polonium .........................................................................................................................11
2.1.4 Carrier-free radionuclides.................................................................................................13
2.1.5 Age determination from radioactive decay....................................................................14
2.2 Radioactive equilibria and disequilibria.........................................................................17
2.2.1 Radioactive disequilibria in waters..................................................................................19
2.2.2 Disequilibria of Pb-210 and Po-210 in water and sediments ......................................20
2.3 Technically enhanced natural radioactivity ...................................................................21
2.3.1 Mining and processing of ores, minerals, and coal.......................................................21
2.3.2 Energy production by combustion25
2.3.3 Other energy production...................................................................................................26
2.3.4 Phosphate processing and fertilizers ...............................................................................26
2.4 Other anthropogenic sources............................................................................................27
3 AQUATIC RADIOCHEMISTRY....................................................................29
3.1 Mobility of radionuclides ..................................................................................................29
3.2 Radionuclide reactions in natural waters .......................................................................30
3.2.1 General aspects of aquatic radiochemistry ....................................................................30
3.2.2 Redox potential and pH.....................................................................................................31
3.2.3 Inorganic salts .....................................................................................................................34
3.2.4 Organic compounds ...........................................................................................................36
3.2.5 Radiocolloids.......................................................................................................................37
3.2.6 Precipitation and co-precipitation...................................................................................38
VII
3.3 Biological availability.........................................................................................................39
3.3.1 Radionuclide uptake by plants .........................................................................................40
3.3.2 Radionuclide uptake by fresh water fish.........................................................................41
3.3.3 Radionuclide uptake by humans......................................................................................42
4 MEASUREMENT INSTRUMENTATION..................................................... 47
4.1 Alpha spectrometry............................................................................................................47
4.1.1 Alpha decay .........................................................................................................................47
4.1.2 Alpha spectrometer48
4.1.2.1 Background radiation ...................................................................................................52
4.1.2.2 Prevention of contamination .......................................................................................53
4.1.3 Calibrations56
4.1.3.1 Energy calibration .........................................................................................................56
4.1.3.2 Efficiency calibration ....................................................................................................57
4.2 Beta spectrometry ..............................................................................................................59
4.2.1 Beta decay ............................................................................................................................59
4.2.2 Liquid Scintillation Counting ..........................................................................................60
4.2.2.1 Comparison of beta spectrometry methods .............................................................60
4.2.2.2 LSC counting vials61
4.2.2.3 Scintillation solutions ...................................................................................................62
4.2.2.4 Surfactants ......................................................................................................................65
4.2.2.5 Principle of liquid scintillation counting...................................................................65
4.2.3 Background radiation........................................................................................................67
4.2.4 Quench effects.....................................................................................................................69
4.2.5 Quench corrections ............................................................................................................70
4.2.6 Pulse Shape Analysis..........................................................................................................72
4.2.7 The Liquid Scintillation Counter.....................................................................................74
5 METHOD DEVELOPMENT.......................................................................... 77
5.1 Overview ..............................................................................................................................77
5.1.1 Direct counting by gamma spectrometry.......................................................................77
5.1.2 Beta spectrometry measurements ...................................................................................78
5.1.3 Indirect measurement of Po-210 by alpha spectrometry ............................................79
5.1.4 Mass spectrometry .............................................................................................................80
5.2 Sampling procedure and sample preparation................................................................80
5.3 Chemical separation ..........................................................................................................82
5.3.1 Resin distribution coefficients for lead and polonium ................................................84
5.3.1.1 Experimental performance ..........................................................................................85
VIII
5.3.1.2 Results ..............................................................................................................................87
5.3.2 Chemical separation using the Pb Resin .........................................................................90
5.3.2.1 Reuse of extraction columns ........................................................................................94
5.3.2.2 Effect of high ion concentrations ................................................................................94
5.4 Measurement of Po-210 via alpha spectrometry ...........................................................96
5.4.1 Source preparation for the alpha spectrometry.............................................................96
5.4.1.1 Summary of source preparation ................................................................................102
5.4.2 Evaluation of the alpha spectra.......................................................................................102
5.5 Measurement of Pb-210 via Liquid Scintillation Counting.......................................107
5.5.1 Ingrowth of Bi-210............................................................................................................108
5.5.2 Pulse shape setting............................................................................................................109
5.5.3 Quench calibration ...........................................................................................................110
5.5.4 Efficiency calibration .......................................................................................................110
5.5.5 Determination of the chemical yield .............................................................................110
5.5.6 Evaluation of the LSC spectra.........................................................................................111
5.6 Determination of Pb-210 by measuring Po-210 after ingrowth ...............................114
5.6.1 Ingrowth of Po-210...........................................................................................................115
5.6.2 Determination of the Pb-210 activity............................................................................116
5.7 Va l i d a t i o n ...........................................................................................................................116
5.7.1 IAEA Proficiency test .......................................................................................................116
5.7.2 CEA Proficiency test in water .........................................................................................118
6 METHOD APPLICATION ...........................................................................121
6.1 Coal mining at Rheinberg (Nordrhein-Westfalen).....................................................121
6.1.1 Measurement results and discussion .............................................................................123
6.1.2 Summary ............................................................................................................................126
6.2 Uranium mining in Mailuu Suu, Kyrgyzstan...............................................................127
6.2.1 Measurement results and discussion .............................................................................131
6.2.2 Summary ............................................................................................................................137
7 DOSE ASSESSMENT ....................................................................................139
7.1 Coal mining area of Rheinberg (NRW) ........................................................................141
7.1.1 Conclusions........................................................................................................................143
7.2 Uranium mining district of Mailuu Suu, Kyrgyzstan .................................................143
7.2.1 Conclusions........................................................................................................................146
IX
8 SUMMARY AND OUTLOOK...................................................................... 149
8.1 Summary............................................................................................................................149
8.2 Conclusion.........................................................................................................................151
8.3 Outlook ..............................................................................................................................152
9 ACKNOWLEDGEMENTS ........................................................................... 153
10 APPENDICES ............................................................................................... 155
10.1 Abbreviation......................................................................................................................156
10.2 List of Tables158
10.3 List of Figures....................................................................................................................161
10.4 Method: Step-by-step .......................................................................................................164
10.5 Measurement evaluations................................................................................................167
10.5.1 Evaluation of the Po-210 alpha measurements ......................................................167
10.5.2 Evaluation of the Pb-210 LSC measurements.........................................................175
10.6 Changeable parameters ...................................................................................................180
10.6.1 Rheinberg......................................................................................................................180
10.6.2 Mailuu Suu181
11 BIBLIOGRAPHY .......................................................................................... 183

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