chemistry and analysis of...

Chemistry and Analysis of Radionuclides

Jukka Lehto and Xiaolin Hou

Laboratory Techniques and Methodology

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Chemistry and Analysis of

Radionuclides

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Chemistry and Analysis of Radionuclides

Laboratory Techniques and Methodology

The Authors

Prof. Jukka LehtoUniversity of HelsinkiLaboratory of RadiochemistryA.I.Virtasen aukio 100014 HelsinkiFinland

Dr. Xiaolin HouTechnical University of DenmarkRisö National Laboratory for Sustainable EnergyRadiation Research DivisionFrediksborgvej 3994000 RoskildeDanmark

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Contents

Preface XVIIAcknowledgments XIX

1 Radionuclides and their Radiometric Measurement 11.1 Radionuclides 11.1.1 Natural Radionuclides 11.1.2 Artificial Radionuclides 41.2 Modes of Radioactive Decay 61.2.1 Fission 61.2.2 Alpha Decay 81.2.3 Beta Decay 101.2.4 Internal Transition 121.3 Detection and Measurement of Radiation 141.3.1 Gas Ionization Detectors 141.3.2 Liquid Scintillation Counting 161.3.3 Solid Scintillation Detectors 201.3.4 Semiconductor Detectors 201.3.5 Summary of Radiometric Methods 22

2 Special Features of the Chemistry of Radionuclidesand their Separation 25

2.1 Small Quantities 252.2 Adsorption 262.3 Use of Carriers 282.4 Utilization of Radiation in the Determination of Radionuclides 312.5 Consideration of Elapsed Time 312.6 Changes in the System Caused by Radiation and Decay 312.7 The Need for Radiochemical Separations 32

V

3 Factors Affecting Chemical Forms of Radionuclidesin Aqueous Solutions 35

3.1 Solution pH 353.2 Redox Potential 383.3 Dissolved Gases 423.3.1 Oxygen 423.3.2 Carbon Dioxide 433.4 Ligands Forming Complexes

with Metals 463.5 Humic Substances 483.6 Colloidal Particles 513.7 Source and Generation of Radionuclides 523.8 Appendix: Reagents Used to Adjust Oxidation

States of Radionuclides 543.8.1 Oxidants 543.8.2 Reductants 55

4 Separation Methods 574.1 Precipitation 574.2 Solubility Product 584.2.1 Coprecipitation 594.2.2 Objectives of Precipitation 604.2.2.1 Precipitations Specific for the Investigated

Radionuclide 604.2.2.2 Group Precipitations for the Preconcentration

of the Target Radionuclide 614.2.2.3 Group Precipitations for the Removal of Interfering

Radionuclides and Stable Elements 614.3 Ion Exchange 644.3.1 Ion Exchange Resins 644.3.2 Distribution Coefficient and Selectivity 654.3.3 Cation Exchange or Anion Exchange? 664.3.4 Ion Exchange Chromatography 674.3.5 Ion Exchange in Actinide Separations 684.4 Solvent Extraction 704.4.1 Extractable Complexes 714.4.2 Distribution Constant and Distribution Ratio 724.4.3 Examples of the Use of Solvent Extraction in

Radiochemical Separations 734.5 Extraction Chromatography 744.5.1 Principles of Extraction Chromatography 744.5.2 Extraction Chromatography Resins 744.5.3 Pb and Sr Resins 754.5.4 Use of Extraction Chromatography in Actinide

Separations 76

VI Contents

5 Yield Determinations and Counting Source Preparation 815.1 The Determination of Chemical Yield in Radiochemical Analyses 815.1.1 Use of Stable Isotopic Carriers in Yield Determinations 815.1.2 Use of Radioactive Tracers in Yield Determinations 825.2 Preparation of Sources for Activity Counting 855.2.1 Preparation of Source for Gamma Emitters 855.2.2 Sample Preparation for LSC 865.2.3 Source Preparation for Alpha Spectrometry with Semiconductor

Detectors and for Beta Counting with Proportional Counters 875.2.3.1 Electrodeposition 885.2.3.2 Micro-coprecipitation 885.2.3.3 Spontaneous Deposition 895.3 Essentials in Chemical Yield Determination and in Counting

Source Preparation 895.3.1 Yield Determination 895.3.2 Counting Source Preparation 90

6 Radiochemistry of the Alkali Metals 916.1 Most Important Radionuclides of the Alkali Metals 916.2 Chemical Properties of the Alkali Metals 916.3 Separation Needs of Alkali Metal Radionuclides 926.4 Potassium – 40K 936.5 Cesium – 134Cs, 135Cs, and 137Cs 946.5.1 Sources and Nuclear Characteristics 946.5.2 Preconcentration of Cesium Nuclides from Natural Waters 956.5.3 Determination of 135Cs 966.5.3.1 Determination of 135Cs by Neutron Activation Analysis 966.5.3.2 Determination of 135Cs by Mass Spectrometry 976.6 Essentials in the Radiochemistry of the Alkali Metals 98

7 Radiochemistry of the Alkaline Earth Metals 997.1 Most Important Radionuclides of the Alkaline Earth Metals 997.2 Chemical Properties of the Alkaline Earth Metals 997.3 Beryllium – 7Be and 10Be 1027.4 Calcium – 41Ca and 45Ca 1027.4.1 Nuclear Characteristics and Measurement 1027.4.2 Determination of 45Ca and 41Ca in Concrete 1037.5 Strontium – 89Sr and 90Sr 1067.5.1 Nuclear Characteristics and Sources 1067.5.2 Measurement of Strontium Isotopes 1077.5.2.1 Measurement of 90Sr Activity 1077.5.2.2 Simultaneous Determination of 89Sr and 90Sr 1097.5.3 Radiochemical Separations of 90Sr and 89Sr 1097.5.3.1 Determination of Chemical Yield in Radiostrontium

Separations 110

Contents VII

7.5.3.2 Separation of Radiostrontium by the Nitrate PrecipitationMethod 110

7.5.3.3 Separation of Radiostrontium by a Ca(OH)2 PrecipitationMethod 113

7.5.3.4 Separation of Radiostrontium by Extraction Chromatography 1147.6 Radium – 226Ra and 228Ra 1177.6.1 Nuclear Characteristics of Radium Isotopes 1177.6.2 Measurement of the Activity of Radium Isotopes 1177.6.3 Need for Determining the Activity of Radium Isotopes 1197.6.4 Radiochemical Separations of Radium 1197.6.4.1 Separation of 226Ra in Rock Samples with Use of Ion

Exchange 1207.6.4.2 Determination of 226Ra and 228Ra in Water by Extraction

Chromatography 1217.7 Essentials in the Radiochemistry of the Alkaline Earth Metals 122

8 Radiochemistry of the 3d-Transition Metals 1238.1 The Most Important Radionuclides of the 3d-Transition Metals 1238.2 Chemical Properties of the 3d-Transition Metals 1248.3 Iron – 55Fe 1258.3.1 Nuclear Characteristics and Measurement of 55Fe 1258.3.2 Chemistry of Iron 1258.3.3 Separation of 55Fe 1288.3.3.1 Separation of 55Fe by Solvent Extraction 1288.3.3.2 Separation of 55Fe by Extraction Chromatography 1298.4 Nickel – 59Ni and 63Ni 1308.4.1 Nuclear Characteristics and Measurement of 59Ni and 63Ni 1308.4.2 Chemistry of Nickel 1318.4.3 Separation of 59Ni and 63Ni 1328.4.3.1 Separation of Nickel by the DMG Precipitation Method 1328.4.3.2 Separation of 63Ni by Ni Resin 1348.4.3.3 Separation of Nickel for the Measurement of Nickel Isotopes

with AMS 1358.4.3.4 Simultaneous Determination of 55Fe and 63Ni 1358.5 Essentials in 3-d Transition Metals Radiochemistry 137

9 Radiochemistry of the 4d-Transition Metals 1399.1 Important Radionuclides of the 4d-Transition Metals 1399.2 Chemistry of the 4d-Transition Metals 1409.3 Technetium – 99Tc 1409.3.1 Chemistry of Technetium 1419.3.2 Nuclear Characteristics and Measurement of 99Tc 1419.3.3 Separation of 99Tc 1439.3.3.1 Yield Determination in 99Tc Analyses 1439.3.3.2 Enrichment of 99Tc for Water Analyzes 144

VIII Contents

9.3.3.3 Separation of 99Tc from Water by Precipitation and SolventExtraction 144

9.3.3.4 Separation of 99Tc by Extraction Chromatography 1459.3.3.5 Separation of 99Tc by Distillation 1469.4 Zirconium – 93Zr 1469.4.1 Chemistry of Zirconium 1479.4.2 Nuclear Characteristics and Measurement of 93Zr 1489.4.3 Separation of 93Zr 1489.4.3.1 Determination of 93Zr by TTA Extraction and Measurement

by LSC 1499.4.3.2 Separation of 93Zr by Coprecipitation and Solvent Extraction

for the Zr Measurement by ICP-MS 1499.5 Molybdenum – 93Mo 1519.5.1 Chemistry of Molybdenum 1519.5.2 Nuclear Characteristics and Measurement of 93Mo 1539.5.3 Separation of 93Mo 1549.5.3.1 Separation of Radioactive Molybdenum by Aluminum Oxide 1549.5.3.2 Separation of 93Mo by Solvent Extraction 1549.6 Niobium – 94Nb 1569.6.1 Chemistry of Niobium 1569.6.2 Nuclear Characteristics and Measurement of Niobium

Radionuclides 1579.6.3 Separation of 94Nb 1579.6.3.1 Separation of 94Nb by Precipitation as Nb2O5 1589.6.3.2 Separation of 94Nb by Precipitation as Nb2O5 and by

Anion Exchange 1589.6.3.3 Separation of 94Nb by Solvent Extraction 1599.7 Essentials in the Radiochemistry of 4-d Transition Metals 159

10 Radiochemistry of the Lanthanides 16310.1 Important Lanthanide Radionuclides 16310.2 Chemical Properties of the Lanthanides 16310.3 Separation of Lanthanides from Actinides 16510.4 Lanthanides as Actinide Analogs 16510.5 147Pm and 151Sm 16710.5.1 Nuclear Characteristics and Measurement of 147Pm

and 151Sm 16710.5.2 Separation of 147Pm and 151Sm 16810.5.2.1 Separation with Ln Resin 16810.5.2.2 Determination of 147Pm from Urine Using Ion Exchange

Chromatography 17010.5.2.3 Separation of 147Pm from Irradiated Fuel by Ion Exchange

Chromatography 17010.5.2.4 Determination of 147Pm and 151Sm in Rocks 17110.6 Essentials of Lanthanide Radiochemistry 173

Contents IX

11 Radiochemistry of the Halogens 17511.1 Important Halogen Radionuclides 17511.2 Physical and Chemical Properties of the Halogens 17611.3 Chlorine – 36Cl 17811.3.1 Sources and Nuclear Characteristics of 36Cl 17811.3.2 Determination of 36Cl 17811.3.2.1 Determination of 36Cl from Steel, Graphite, and Concrete

by Solvent Extraction and Ion Exchange 17911.4 Iodine – 129I 18111.4.1 Sources and Nuclear Characteristics of 129I 18111.4.2 Measurement of 129I 18211.4.2.1 Determination of 129I by Neutron Activation Analysis 18211.4.2.2 Determination of 129I by Accelerator Mass Spectrometry 18411.4.3 Radiochemical Separations of 129I 18511.4.3.1 Separation of 129I by Solvent Extraction 18511.4.3.2 Pretreatment of Samples for 129I Analyses 18811.4.3.3 Speciation of Iodine Species in Water 18811.5 Essentials of Halogen Radiochemistry 190

12 Radiochemistry of the Noble Gases 19312.1 Important Radionuclides of the Noble Gases 19312.2 Physical and Chemical Characteristics of the Noble Gases 19312.3 Measurement of Xe Isotopes in Air 19412.4 Determination of 85Kr in Air 19412.5 Radon and its Determination 19612.5.1 Determination of Radon in Outdoor Air and Soil Pore Spaces 19712.5.2 Determination of Radon in Indoor Air 19712.5.3 Determination of Radon in Water 19712.6 Essentials of Noble Gas Radiochemistry 198

13 Radiochemistry of Tritium and Radiocarbon 20113.1 Tritium – 3H 20113.1.1 Nuclear Properties of Tritium 20113.1.2 Environmental Sources of Tritium 20213.1.3 Determination of Tritium in Water 20313.1.4 Electrolytic Enrichment of Tritium 20313.1.5 Determination of Tritium in Organic Material 20413.1.6 Determination of Tritium from Urine 20413.1.7 Determination of Tritium after Conversion into Benzene 20513.1.8 Determination of Tritium using Mass Spectrometry 20513.1.9 Determination of Tritium in Nuclear Waste Samples 20613.2 Radiocarbon – 14C 20713.2.1 Nuclear Properties of Radiocarbon 20713.2.2 Sources of Radiocarbon 20713.2.3 Chemistry of Inorganic Carbon 209

X Contents

13.2.4 Carbon Dating of Carbonaceous Samples 20913.2.5 Separation and Determination of 14C 21013.2.5.1 Removal of Carbon from Samples by Combustion for

the Determination of 14C 21113.2.5.2 Determination of 14C as Calcium Carbonate by Liquid Scintillation

Counting 21113.2.5.3 Determination of 14C by Liquid Scintillation Counting

with Carbon Bound to Amine 21313.2.5.4 14C Determination by LSC in Benzene 21313.2.5.5 14C Determination in Graphite form by AMS 21313.2.5.6 Determination of 14C in Nuclear Waste 21413.3 Essentials of Tritium and Radiocarbon Radiochemistry 215

14 Radiochemistry of Lead, Polonium, Tin, and Selenium 21714.1 Polonium – 210Po 21814.1.1 Nuclear Characteristics of 210Po 21814.1.2 Chemistry of Polonium 21914.1.3 Determination of 210Po 22014.2 Lead – 210Pb 22114.2.1 Nuclear Characteristics and Measurement of 210Pb 22114.2.2 Chemistry of Lead 22314.2.3 Determination of 210Pb 22414.2.3.1 Determination of 210Pb from the Ingrowth of 210Po 22514.2.3.2 Separation of 210Pb by Precipitation 22614.2.3.3 Separation of 210Pb by Extraction Chromatography 22614.3 Tin – 126Sn 22814.3.1 Nuclear Characteristics and Measurement of 126Sn 22814.3.2 Chemistry of Tin 22914.3.3 Determination of 126Sn 23014.4 Selenium – 79Se 23314.4.1 Nuclear Characteristics and Measurement of 79Se 23314.4.2 Chemistry of Selenium 23314.4.3 Determination of 79Se 23514.5 Essentials of Polonium, Lead, Tin, and Selenium

Radiochemistry 236

15 Radiochemistry of the Actinides 23915.1 Important Actinide Isotopes 23915.2 Generation and Origin of the Actinides 23915.3 Electronic Structures of the Actinides 24415.4 Oxidation States of the Actinides 24515.5 Ionic Radii of the Actinides 24615.6 Major Chemical Forms of the Actinides 24715.7 Disproportionation 24715.8 Hydrolysis and Polymerization of the Actinides 249

Contents XI

15.9 Complex Formation of the Actinides 25015.10 Oxides of the Actinides 25015.11 Actinium 25115.11.1 Isotopes of Actinium 25115.11.2 Chemistry of Actinium 25215.11.3 Separation of Actinium 25315.11.4 Essentials of Actinium Radiochemistry 25415.12 Thorium 25515.12.1 Occurrence of Thorium 25515.12.2 Thorium Isotopes and their Measurement 25515.12.3 Chemistry of Thorium 25615.12.4 Separation of Thorium 25815.12.4.1 Separation of Thorium by Precipitation 25815.12.4.2 Separation of Thorium by Anion Exchange 25815.12.4.3 Separation of Thorium by Solvent Extraction 25915.12.4.4 Separation of Thorium by Extraction Chromatography 25915.12.5 Essentials of Thorium Radiochemistry 25915.13 Protactinium 26015.13.1 Isotopes of Protactinium 26015.13.2 Chemistry of Protactinium 26115.13.3 Separation of Protactinium 26215.13.4 Essentials of Protactinium Radiochemistry 26315.14 Uranium 26415.14.1 The Most Important Uranium Isotopes 26415.14.2 Occurrence of Uranium 26615.14.3 Chemistry of Uranium 26715.14.4 Hydrolysis of Uranium 26915.14.5 Formation of Uranium Complexes 26915.14.6 Uranium Oxides 27115.14.7 From Ore to Uranium Fuel 27115.14.8 Measurement of Uranium 27215.14.9 Reasons for Determining Uranium Isotopes 27315.14.10 Separation of Uranium 27415.14.10.1 Separation of Uranium from Other Naturally Occurring

Alpha-Emitting Radionuclides 27415.14.10.2 Determination of Chemical forms of Uranium in Groundwater 27415.14.10.3 Separation of Uranium from Transuranium Elements by Anion

Exchange or by Extraction Chromatography 27515.14.10.4 Separation of Uranium by Solvent Extraction with

Tributylphosphate (TBP) 27515.14.11 Essentials of Uranium Radiochemistry 27515.15 Neptunium 27715.15.1 Sources of Neptunium 27715.15.2 Nuclear Characteristics and Measurement of 237Np 27815.15.3 Chemistry of Neptunium 278

XII Contents

15.15.4 Separation of 237Np 28015.15.4.1 Neptunium Tracers for Yield Determinations 28015.15.4.2 Preconcentration of Neptunium from Large Water Volumes 28215.15.4.3 Separation of 237Np by Extraction Chromatography 28215.15.4.4 Separation of 237Np by Anion Exchange Chromatography 28315.15.4.5 Separation of 237Np by Solvent Extraction 28315.15.5 Essentials of Neptunium Radiochemistry 28315.16 Plutonium 28415.16.1 Isotopes of Plutonium 28415.16.2 Sources of Plutonium 28615.16.3 Measurement of Plutonium Isotopes 28715.16.4 The Chemistry of Plutonium 28915.16.4.1 Oxidation States and Plutonium 28915.16.4.2 Disproportionation 29015.16.4.3 Hydrolysis 29115.16.4.4 Redox Behavior 29115.16.4.5 Complex Formation 29315.16.5 Separation of Plutonium 29315.16.6 Tracers Used in the Determination of Pu Isotopes 29415.16.7 Separation by Solvent Extraction 29515.16.8 Separation of Pu by Anion Exchange Chromatography 29615.16.9 Separation of Pu by Extraction Chromatography 29715.16.10 Separation of Pu from Large Volumes of Water 29815.16.11 Automated and Rapid Separation Methods for Pu Determination 30015.16.12 Essentials of Plutonium Radiochemistry 30115.17 Americium and Curium 30215.17.1 Sources of Americium and Curium 30215.17.2 Nuclear Characteristics and Measurement of 241Am, 242Cm,

243Cm, and 244Cm 30315.17.3 Chemistry of Americium and Curium 30415.17.4 Separation of Americium and Curium 30615.17.4.1 Separation of Am and Cm by Ion Exchange 30715.17.4.2 Separation of Am and Cm by Extraction Chromatography 30715.17.4.3 Separation of Am and Cm by Solvent Extraction 30715.17.4.4 Separation of Lanthanides from Am and Cm 30815.17.5 Essentials of Americium and Curium Radiochemistry 309

16 Speciation Analysis 31116.1 Considerations Relevant to Speciation 31116.2 Significance of Speciation 31216.3 Categorization of Speciation Analyzes 31316.4 Fractionation Techniques for Environmental Samples 31416.4.1 Particle Fractionation in Water 31416.4.2 Fractionation of Aerosol Particles 31616.4.3 Fractionation of Soil and Sediments 317

Contents XIII

16.5 Analysis of Radionuclide and Isotope Compositions 31716.6 Spectroscopic Speciation Methods 31816.7 Wet Chemical Methods 32116.7.1 Coprecipitation 32116.7.2 Solvent Extraction 32216.7.3 Ion Exchange Chromatography 32316.8 Sequential Extractions 32416.9 Computational Speciation Methods 32616.10 Characterization of Radioactive Particles 32916.10.1 Identification and Isolation of the Particles 33016.10.2 Scanning Electron Microscopic Analysis of the Particles 33016.10.3 Gamma and X-ray Analysis of the Particles 33116.10.4 Secondary Ion Mass Spectrometry Analysis of Radioactive

Particles 33216.10.5 Synchrotron-Based X-ray Microanalyses 33216.10.6 Post-Dissolution Analysis of Particles 334

Further Reading 335

17 Measurement of Radionuclides by Mass Spectrometry 33717.1 Introduction 33717.2 Inductively Coupled Plasma Mass Spectrometry (ICP-MS) 33817.2.1 Components and Operation Principles of ICP-MS Systems 33917.2.2 Resolution and Abundance Sensitivity 34217.2.3 Dynamic Collision/Reaction Cells 34317.2.4 Detectors 34417.2.5 Detection Limits 34517.2.6 90Sr Measurement by ICP-MS 34617.2.7 99Tc Measurement by ICP-MS 34817.2.8 Measurement of Uranium and Thorium Isotopes by ICP-MS 34817.2.9 237Np Measurement by ICP-MS 34917.2.10 Measurement of Plutonium Isotopes by ICP-MS 34917.3 Accelerator Mass Spectrometry (AMS) 35017.3.1 Components and Operation of AMS 35017.3.2 14C Measurement by AMS 35217.3.3 36Cl Measurement by AMS 35317.3.4 41Ca Measurement by AMS 35317.3.5 63Ni and 59Ni Measurement by AMS 35317.3.6 99Tc Measurement by AMS 35417.3.7 129I Measurement by AMS 35517.3.8 Measurement of Plutonium Isotopes by AMS 35517.4 Thermal Ionization Mass Spectrometry (TIMS) 35617.5 Resonance Ionization Mass Spectrometry (RIMS) 35817.6 Essentials of the Measurement of Radionuclides by Mass

Spectrometry 359Further Reading 360

XIV Contents

18 Sampling and Sample Pretreatment for the Determinationof Radionuclides 361

18.1 Introduction 36118.2 Air Sampling and Pretreatment 36218.2.1 Sampling Aerosol Particles 36218.2.1.1 Radioactive Aerosol Particles 36318.2.1.2 Integral Aerosol Particle Sampling 36318.2.1.3 Size-Selective Aerosol Particle Sampling 36518.2.1.4 Passive Aerosol Particle Sampling 36618.3 Sampling Gaseous Components 36618.4 Atmospheric Deposition Sampling 36918.4.1 Dry/Wet Deposition Sampling 36918.4.2 Ion Exchange Collector 37018.5 Water Sampling 37118.5.1 Surface Water Sampling 37118.5.2 Water Core (Depth Profile) 37218.5.3 Preconcentration of Radionuclides from Natural Waters 37518.5.3.1 Preconcentration of Radiocesium (137Cs and 134Cs) 37518.5.3.2 Preconcentration of Pu, Am, Np, and 99Tc 37618.6 Sediment Sampling and Pretreatment 37718.6.1 Surface Sediment Sampling 37718.6.2 Sediment Core Sampling 37918.6.3 Sediment Pore Water Sampling 38118.6.4 Pretreatment of Sediments – Storage, Drying, Homogenizing 38318.7 Soil Sampling and Pretreatment 38418.7.1 Planning the Sampling 38418.7.2 Soil Core Sampling 38518.7.3 Template Method 38718.7.4 Trench Method 38718.7.5 Pretreatment of Soil Samples 38818.8 Essentials in Sampling and Sample Pretreatment

for Radionuclides 388

19 Chemical Changes Induced by Radioactive Decay 39119.1 Autoradiolysis 39119.1.1 Dissolved Gases 39219.1.2 Water Solutions 39219.1.3 Organic Compounds Labeled with Radionuclides 39219.1.4 Solid Compounds 39319.2 Transmutation and Subsequent Chemical Changes 39319.3 Recoil – Hot Atom Chemistry 394

Index 397

Contents XV

Preface

I started to give a lecture course on radionuclide analysis to students of radio-chemistry in 2001. Two problems quickly became apparent. The first was that Icould not properly lecture on this subject if the basic chemistry underlying thebehavior of radionuclides in separation procedures was not understood. Thereseemed to be no sense in talking about precipitation of hydrolyzable metals withferric hydroxide, for example, if the hydrolysis of metals was not understood. I had togo back to basics and teach the chemistry of the elements. This was a good choice –not least for myself – since I had to refresh my understanding of basic chemicalphenomena. The second problem was that there was no adequate textbook on thechemistry of radionuclides. I had a handout from my predecessor to give to thestudents, but it had been written in the 1970s: it was good but outdated and short.Most books on radiochemistry available at that time, though comprehensiveenough, contained little actual chemistry of the radionuclides and concentrated ontheir radioactive decay processes and the detection and measurement of radiation.In 2005 I began to write a text ofmy own, in Finnish. Then, seeing a broader need forsuch a text, I decided to write in English.

After working on the book for three years, I realized that analytical methodscannot be properly described if one has not done the analysis oneself, as was true inmy case. I therefore askedDr. XiaolinHou, of Risö National Laboratory, Denmark, tojoin me in the project. I knew him as a most experienced analytical radiochemistwho had personally analyzed a great number of radionuclides in environmental andnuclear waste samples and developed new separation methods. During the past twoyears we have collaborated in writing this book, and I have learned a host of newthings, not just from reading papers but also from extensive discussions withDr. Hou.

Our book describes the basic chemistry needed to understand the behavior andanalysis of radionuclides of most groups of elements, and the analytical methodsrequired to separate the most important alpha- and beta- decaying radionuclidesfrom environmental and nuclear waste samples (e.g., 90Sr and plutonium isotopes).Many new radionuclides have become important in radiochemistry in the past ten tofifteen years. Most of these are very long-lived, appearing in spent nuclear fuel and

XVII

nuclear reactor structures and are relevant to safety analysis of the final disposal ofthe nuclear fuel and decommissioning waste. Mass spectrometric techniques arewell suited for the measurement of these radionuclides (135Cs, 129I, etc.) because oftheir low specific activities. Traditionally, radiometric methods have been used tomeasure radionuclides, but the development of mass spectrometric techniques hasopened up new avenues for the analysis of radionuclides, in particular for theiranalysis in much lower concentrations. Mass spectrometric measurements alsocreate new requirements for radionuclide analyses, because the interfering radio-nuclides and other elements which need to be separated before measurement aremostly not the same ones that affect radiometric measurements.My first intention was to write a book for undergraduate and post-graduate

students, but now that the book is finished I see that it could also serve as a handbookfor more experienced radiochemists – at least I hope so.

November 1, 2010 Jukka LehtoProfessor in RadiochemistryUniversity of HelsinkiDepartment of ChemistryFinland

XVIII Preface

Acknowledgments

The authors thank Dr. Kathleen Ahonen for translating part of the book fromFinnish and Dr. Shannon Kuismanen, Mr. Howard McKee, and Mr. StewartMakkonen-Craig for language revision. The comments of Professor Markku Leskeläand Mr. Martti Hakanen from the University of Helsinki, Dr. Sven P. Nielsen andDr. Jussi Jernstöm from Risø-DTU, Denmark, and Dr. Iisa Outola from STUK,Finland, have led to many improvements in the text, and we warmly thank them fortheir help. We are grateful to Mr. Lalli Jokelainen for careful preparation of figuresand also to Dr. Steffen Happel from Triskem International, France, for providingsome of the figures. Finally, we thank Wiley-VCH and Dr. Eva-Stina Riihimäki forpublishing the book.

XIX

1Radionuclides and their Radiometric Measurement

1.1Radionuclides

The first radioactive elements – radium and polonium – were discovered by MarieCurie at the end of the nineteenth century. During the first decades of the twentiethcentury, tens of natural radioactive elements and their various isotopes in theuranium and thorium decay chains were identified. The first artificial radionuclide,30P, was produced by Fr�ed�eric and Ir�ene Joliot-Curie in an accelerator by bombardingaluminumwith protons. Today,more than two thousand artificial radionuclides havebeen produced and identified, especially after the discovery and use of nuclear fissionof uranium and plutonium. This book focuses on radionuclides found in theenvironment and in nuclear waste. This chapter presents an overview of radio-nuclides, radioactive decay processes, and the radiometric measurement of radio-nuclides, which are categorized according to their sources and ways of formation; inlater chapters they are classified based on their chemical nature and are discussed inmore detail. Radionuclides can be primarily categorized into natural and artificialradionuclides.

1.1.1Natural Radionuclides

In nature there are three types of radionuclides: those belonging to the decay chainsof uranium and thorium, single very long-lived radionuclides, and cosmogenicradionuclides.

The decay chains of uranium and thorium start with two isotopes of uranium andone of thorium, 235U, 238U, and 232Th,whichwere formed at the birth of theUniversesome 13.7 billion years ago, and, since they are so long-lived, they have survived in theearth since its birth 4.5 billion years ago. These three primordial radionuclides eachinitiate a decay chain leading to the stable lead isotopes 207Pb, 206Pb, and 208Pb,respectively. In between, there are altogether 42 radionuclides of 13 elements, ofwhich nine elements, those heavier than bismuth, have no stable isotopes at all. Thethree decay chains are depicted in Tables 1.1–1.3. The determination of radionuclides

j1

Table 1.1 Uranium decay chain.

Nuclide Decay mode Half-life Decay energy (MeV) Decay product

238U a 4.4� 109 y 4.270 234Th234Th b� 24 d 0.273 234Pa234Pa b� 6.7 h 2.197 234U234U a 245 500 y 4.859 230Th230Th a 75 380 y 4.770 226Ra226Ra a 1602 y 4.871 222Rn222Rn a 3.8 d 5.590 218Po218Po a 99.98% 3.1min 6.874 214Pb

b� 0.02% 2.883 218At218At a 99.90% 1.5 s 6.874 214Bi

b� 0.10% 2.883 218Rn218Rn a 35ms 7.263 214Po214Pb b� 27min 1.024 214Bi214Bi b� 99.98% 20min 3.272 214Po

a 0.02% 5.617 210Tl214Po a 0.16ms 7.883 210Pb210Tl b� 1.3min 5.484 210Pb210Pb b� 22.3 y 0.064 210Bi210Bi b� 99.99987% 5.0 d 1.426 210Po

a 0.00013% 5.982 206Tl210Po a 138 d 5.407 206Pb206Tl b� 4.2min 1.533 206Pb206Pb stable

Table 1.2 Actinium decay chain.


235U a 7.1� 108 y 4.678 231Th231Th b� 26 h 0.391 231Pa231Pa a 32,760 y 5.150 227Ac227Ac b� 98.62% 22 y 0.045 227Th

a 1.38% 5.042 223Fr227Th a 19 d 6.147 223Ra223Fr b� 22min 1.149 223Ra223Ra a 11 d 5.979 219Rn219Rn a 4.0 s 6.946 215Po215Po a 99.99977% 1.8ms 7.527 211Pb

b� 0.00023% 0.715 215At215At a 0.1ms 8.178 211Bi211Pb b� 36min 1.367 211Bi211Bi a 99.724% 2.1min 6.751 207Tl

b� 0.276% 0.575 211Po211Po a 516ms 7.595 207Pb207Tl b� 4.8min 1.418 207Pb207Pb stable

2j 1 Radionuclides and their Radiometric Measurement

in the decay chains has been, and still is, a major topic in analytical radiochemistry.They are alpha and beta emitters, most of which do not emit detectable gamma rays,and thus their determination requires radiochemical separations. This book exam-ines the separations of the following radionuclides: U isotopes, 231Pa, Th isotopes,227Ac, 226;228Ra, 222Rn, 210Po, and 210Pb.

In addition to 235U, 238U, and 232Th, there are several single very long-livedprimordial radionuclides (Table 1.4) which were formed in the same cosmicprocesses as those that formed uranium and thorium. The most important of these,with respect to the radiation dose to humans, is 40K. However, as this emits readilydetectable gamma rays and does not require radiochemical separations, neither thisnor the others are discussed further in this book.

The third class of natural radionuclides comprises cosmogenic radionuclides,which are formed in the atmosphere in nuclear reactions due to cosmic radiation(Table 1.5). These radionuclides are isotopes of lighter elements, and their half-livesvary greatly. The primary components of cosmic radiation are high-energy alphaparticles and protons,which induce nuclear reactionswhen they impact on the nucleiof the atmospheric atoms. Most of the cosmogenic radionuclides are attached toaerosol particles and are deposited on the ground. Some, however, are gaseous, suchas 14C (as carbon dioxide) and 39Ar (a noble gas), and thus stay in the atmosphere. In

Table 1.3 Thorium decay chain.


232Th a 1.41� 1010 y 4.081 228Ra228Ra b� 5.8 y 0.046 228Ac228Ac b� 6.3 h 2.124 228Th228Th a 1.9 y 5.520 224Ra224Ra a 3.6 d 5.789 220Rn220Rn a 56 s 6.404 216Po216Po a 0.15 s 6.906 212Pb212Pb b� 10.6 h 0.570 212Bi212Bi b� 64.06% 61min 2.252 212Po

a 35.94% 6.208 208Tl212Po a 299 ns 8.955 208Pb208Tl b� 3.1min 4.999 208Pb208Pb stable

Table 1.4 Some single primordial radionuclides.

Nuclide Isotopic abundance (%) Decay mode Half-life (y)

40K 0.0117 b� 1.26� 10987Rb 27.83 b� 4.88� 1010123Te 0.905 EC 1.3� 1013144Nd 23.80 a 2.1� 1015174Hf 0.162 a 2� 1015

1.1 Radionuclides j3

primary nuclear reactions, neutrons are also produced, and these induce furthernuclear reactions. Two important radionuclides are produced in these neutron-induced reactions: 3H and 14C (reactions 1.1 and 1.2), whose chemistry andradiochemical separations are described inChapter 13. These radionuclides – tritiumand radiocarbon – are generated not only by cosmic radiation but also in otherneutron activation processes in nuclear explosions and in matter surroundingnuclear reactors.

14Nþn! 14Cþ p ð1:1Þ

14Nþn! 12Cþ 3H ð1:2Þ

1.1.2Artificial Radionuclides

Artificial radionuclides form the largest group of radionuclides, comprising morethan two thousand nuclides produced since the 1930s. The sources of artificialradionuclides are:

. nuclear weapons production and explosions;

. nuclear energy production;

. radionuclide production by reactors and accelerators.

Awide range of radionuclides are produced in nuclear weapons production, whereplutonium is produced by the irradiation of uranium in reactors and innuclear powerreactors.Most arefission products, and are generated by theneutron-inducedfission of235U and 239Pu. In nuclear power reactors, they are practically all retained in thenuclear fuel; however, in nuclear explosions they end up in the environment – on theground in atmospheric explosions or in the geosphere in underground explosions.The spent nuclear fuel from power reactors is stored in disposal repositories deepunderground. The radionuclide composition of nuclear explosions and the spent fuelfrom nuclear power reactors differ somewhat for several reasons. Firstly, the fissionsin a reactor aremostly caused by thermal neutrons, while in a bomb fast neutrons are

Table 1.5 Some important cosmogenic radionuclides.

Nuclide Half-life (y) Decay mode Nuclide Half-life (y) Decay mode

3H 12.3 beta 7Be 0.15 EC10Be 2.5� 106 beta 14C 5730 beta22Na 2.62 EC 26Al 7.4� 105 EC32Si 710 beta 32P 0.038 beta33P 0.067 beta 35S 0.24 beta36Cl 3.1� 105 beta/EC 39Ar 269 beta41Ca 3.8� 106 EC 129I 1.57� 107 beta


mostly responsible for the fission events, and this results in differences in theradionuclide composition. Secondly, fission is instantaneous in a bomb, while in areactor the fuel is irradiated for some years. This allows the ingrowth of someactivation products, such as 134Cs, that do not exist in weapons fallout. 90Sr and 137Csare themost important fission products because of their relatively long half-lives andhigh fission yields. In addition to these, there is range of long-lived fission products,such as 79Se, 99Tc, 126Sn, 129I, 135Cs, and 151Sm, the radiochemistry of which isdiscussed in this book.

Along with fission products, activation products are also formed in side reactionsaccompanying the neutron irradiation. The intensive neutron flux generated in thefission induces activation reactions both in the fuel or weapons material and in thesurrounding material. These can be divided into two categories, the first comprisingthe transuranium elements – a very important class of radionuclides in radiochem-istry. These are created by successive neutron activation and beta decay processesstarting from 238U or 239Pu (Figure 1.1). Of these, the most important and the mostradiotoxic nuclides are 237Np, 238;239;240;241Pu, 241;243Am, and 243;244;245Cm, which arediscussed further in this book. In addition to transuraniumelements, a newuraniumisotope 236U is also formed in neutron activation reactions.

Another activation product group comprises radioisotopes of various lighterelements. In addition to tritium and radiocarbon, a wide range of these activationproducts are formed in nuclear explosions and especially in nuclear reactors.Elements of the reactors construction materials, especially the cladding and othermetal parts surrounding the nuclear fuel, the steel of the pressure vessel and theshielding concrete structures are activated in the neutron flux from the fuel. Part ofthese activation products, such as elements released from the steel by corrosion, endup in the nuclear waste disposed of during the use of the reactor. A larger part,

Figure 1.1 Formation of transuranium elements in nuclear fuel and nuclear weapons material(Holm, E., Rioseco, J., and Petterson, H. (1992) Fallout of transuranium elements following theChernobyl accident. J. Radioanal. Nucl. Chem. Articles, 156, 183).

1.1 Radionuclides j5

however, remains in the steel and concrete and ends up in the waste when the reactoris decommissioned. This category has many important radionuclides, such as 14C,36Cl, 41Ca, 55Fe, 59Ni, and 63Ni, which are discussed later in the book. These areall purely beta-decaying radionuclides that require radiochemical separations. Inaddition to these, there is a range of activation products, such as 60Co, 54Mn, 65Zn,which emit gamma rays and are thus readily detectable and measurable. In additionto the reactor steel and shielding concrete, the spent fuel, itsmetal cladding, and othermetal parts surrounding the fuel and ending up in the final disposal, contain largeamounts of the long-lived beta decaying activation products 93Zr, 94Nb, and 93Mo(together with 14C, 36Cl, 59Ni, 63Ni), which are also discussed in this book.

There are also a number of radionuclides produced by neutron and proton irradiationsin reactors and in cyclotrons. Their properties are later described only if they are used astracers in radionuclide analysis. An example is a fairly short-lived gamma-emittingstrontium isotope, 85Sr, which is used as a tracer in model experiments for studyingthe behavior of the beta-emittingfission product 90Sr or as a yield-determinant in 90Srdeterminations.

1.2Modes of Radioactive Decay

This book describes the chemistry and analysis of radionuclides – nuclei which areunstable, that is, radioactive. The instability comes from the fact that the mass of thenucleus is either too high or its neutron to proton ratio is inappropriate for stability.By radioactive decay, the nucleus disposes of themass excess or adjusts the neutron toproton ratio more closely to what is required for stability. The four main radioactivedecay modes – fission, alpha decay, beta decay and internal transition – are brieflydescribed below.

1.2.1Fission

Spontaneous fission is a characteristic radioactive decay mode only for the heaviestelements. In fission, the heavy nucleus divides into two nuclei of lighter elementswhicharecalledfissionproducts.Of thenaturally occurring isotopes,only 238U decaysby spontaneous fission. Only a very minor fraction, 0.005%, of 238U decays by thismode, therestdecayingbyalphamode.Spontaneousfissionbecomesmoreprevailingwith the heaviest elements, and for some, such as 260No, it is the only way of decay.Considering the production and amounts of fission products, a more importantprocess thanspontaneousfissionis inducedfission:aheavynucleusabsorbsaparticle,most usually a neutron, which results in the excitation and further fission of thenucleus (Figure 1.2). There are several fissionable isotopes, of which 235U and 239Puare the most important from the point of view of the amounts of fission productsgenerated. These two nuclides are not only fissionable but also fissile, that is, theyundergo fission in the presence of thermal neutrons, which enables their use as


nuclear fuel in nuclear reactors. 235U is obtained by isotopic enrichment fromnaturaluranium and 239Pu by the irradiation of 238U in a nuclear reactor and subsequentchemical separation of plutonium from the irradiated uranium.

A large number of fission products are generated in fission processes. Figure 1.3gives, as an example, the distribution of fission products for 235U from thermal

Figure 1.2 An example of a neutron-induced fission of 235U. The reaction is235U þ n ! 236U ! 141Ba þ 92Kr þ 3n (http://en.wikipedia.org/wiki/Nuclear_fission).

Figure 1.3 Fission yield distribution of 235U as a function of the mass number of the fissionproduct.

1.2 Modes of Radioactive Decay j7

neutron-induced fission. As can be seen, the fission is extremely seldom symmetric,that is, the twofission products of onefission event are not of the samemass. Instead,the maxima of fission products are found at the mass numbers 90–100 and at135–145. At these ranges, the fission yields are between 5% and 7%. This applies tothermal neutron-induced fission; fissions induced by high energy particles becomemore symmetric with the energy of the bombarding particle.

Mostfission products are radioactive since they have an excess of neutrons. In both235U and 239Pu, the neutron to proton ratio is around 1.6, which is too high for thelighter elements to be stable. For example, for the stable elements in the uppermaximum of the fission yield at the mass numbers 135–145, the highest neutron-to-proton ratio is around 1.4, and, through the radioactive decay, by betaminus decay inthis case, thenucleus transforms the ratio intoanappropriate one.Anexampleof sucha decay chain of neutron-rich fission products leading to stable 137Ba is as follows:

137 Teðt1=2 ¼ 3:5 s;n=p ratio 1:63Þ! 137Iðt1=2 ¼ 24:5 s;n=p ratio 1:58Þþ b� !137Xeðt1=2 ¼ 3:82min; n=p ratio 1:54Þþ b� !

137Csðt1=2 ¼ 30 y;n=p ratio 1:49Þþ b� ! 137Baðstable; n=p ratio 1:45Þþ b�

1.2.2Alpha Decay

Alpha decay is also a typical decay mode for the heavier radionuclides. Most actinideisotopes and radionuclides in the uranium and thorium decay chains decay by thismode. A few exceptions among the radionuclides discussed in this book are 210Pb,228Ra, and 241Pu, which decay solely by beta emission. 227Ac also decays mostly(98.8%) by beta decay. As can be seen fromTables 1.1–1.3, beta decay is a decaymodecompeting with alpha decay for many radionuclides in the decay chains. In an alphadecay, the heavy nucleus gets rid of excessmass by emitting a helium nucleus, whichis called an alpha particle (a). An example is

226Ra! 222Rnþ 4HeðaÞ ð1:3Þ

where 226Ra turns into 222Rn by emitting an alphaparticle. Thus, in an alphadecay, theatomic number decreases by two units and themass number by four. The energies ofthe emitted alpha particles are always high, typically between 4 and 7MeV. Since themass of the alpha particle is relatively high, the daughter nuclide receives considerablekinetic energy due to recoil. For example, when 238U decays to 234Th by alphaemission, the daughter nuclide 234Th gets 0.074MeV of the 4.274MeV decay energyand the alphaparticle the rest, 4.202MeV. Even though the fraction of the recoil energyis only 1.7%, this energy is some ten thousand times higher than that of a chemicalbond, and thus recoil results in the breaking of the chemical bond by which thedaughter nuclide is bound to thematrix. The transformations from parent nuclides todaughter nuclides take place between defined energy levels corresponding to defined


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