Gamma spectrometry for chronology of recent sediments Daniela Pittauerová Universität Bremen 2013 Fachbereich 1 (Physik und Elektrotechnik) Gamma spectrometry for chronology of recent sediments Dissertation zur Erlangung des akademischen Grades Doktor der Naturwissenschaften (Dr. rer. nat.) vorgelegt von RNDr. Mgr. Daniela Pittauerová 1. Gutachter: Dr. Helmut W. Fischer 2. Gutachter: Prof. Dr. Bernd Zolitschka Eingereicht am: 15.10.2013 Tag des Promotionskolloquiums: 17.12.2013 ii To ’nic and Timmy. iii iv Acknowledgments Completing this manuscript would not be possible without contributions from many people. My supervisor Dr. Helmut Fischer, trusting my skills and abilities, gave me the opportunity to find my place in a completely new world shortly after my arrival to Germany and made me part of his team. Later on, after my son was born, he enabled me to combine family and professional life according to my needs and preferences. I really admire his empathic attitude and careful and detailed involvement in all projects we have worked on together. My lab colleague Bernd Hettwig patiently and scholarly answered the endless stream of my ques- tions and helped me become an experienced spectrometrist. He also created a calm and friendly atmosphere in our lab and contributed to my coffee addiction. Dr. Volker Hormann helped me out on many occasions with his valuable advice and proofreading. I spent great time talking to him about Life, the Universe and Everything. He himself and Felix Rogge formed the healthy heart of our lab team, together with the girls: Susanne Ulbrich, Marievi Souti, Edda Toma and Regine Braatz that we have done lots of work and had lots of fun together. There’s been a stream of dear co-workers and students that were always eager to help out when I needed it: Dr. Ahmed Qwasmeh, Andrei Burak, Homa Ghasemifard, Dorothea Gradic, Dominic Höweling, Dr. Maarten Veevaete, Dr. Mohammed Khalil Saeed Salih, Oliver Bislich, Dr. Rolf Goedecke, Tom Bielefeld and Wissam Chehade. The PIP (Postgraduate International Programme in Physics and Electrical Engineering) sup- ported me financially by contributing to my international trips for sharing my results at confer- ences or learning new skills at workshops. My greatest THANKS go to my family. ’nic patiently made this thesis materialize and supported me by all possible and impossible means, while dragging me all around the globe or at least burning diesel with me while “conquering large parts of Europe”. Timmy was very brave when his Mom was busy. And my parents, my brother and my grandmother kept their fingers crossed far far away. v vi Abstract This thesis deals with several aspects of gamma spectrometric analysis of natural and artificial isotopes in sediments and their use as tracers for qualification and quantification of accumulation and mixing processes in different aquatic environments. Sediment cores from three distinct areas including terrigenous sediments deposited on the continental slope off NW Africa, deep sea sediments off Sumba Island and five stations from the Gulf of Eilat in the Red Sea area were measured and interpreted within this dissertation. The main concern in gamma spectrometry of voluminous environmental samples is a re- liable efficiency calibration. This is specially relevant for the analysis of low energy gamma emitters (<100 keV). 210Pb, an important isotopic tracer to cover the period of the last century, is one of them. Within this work mathematical efficiency calibration was applied using a com- mercial software package. A series of validation tests was performed and evaluated for point and voluminous samples. When using 210Pb as a tracer it is necessary to determine its excess portion, which is not supported by ingrowth from the parent nuclide 226Ra. Its analysis is mostly performed via short lived daughter isotopes that follow after the intermediate gaseous member 222Rn. Preventing the escape of radon from the sample is a critical step before analysis due to a negative effect of supported 210Pb underestimation on the chronology, which was also documented in this thesis. Time series registering ingrowth of 214Pb and 214Bi towards radioactive equilibrium with 226Ra in different containers were evaluated for analyses of 226Ra. Direct analyses of 226Ra was compared to its detection via daughter products. A method for aligning parallel radionuclide depth profiles was described and applied suc- cessfully in two case studies from the continental slope off NW Africa and off Sumba Island, Indonesia. This is primarily important when combined profiles obtained from short multicorer cores and long gravity cores (with topmost parts not being preserved) need to be studied. Another useful strategy involving summing up spectra was suggested for the Indonesian sediments, which lead to reducing detection limits and allowed quantifying artificial radionuclides activity concentrations, ratios and inventories. Finally, an approach of using 232Th series additionally to 210Pb and 137Cs gamma emitters for interpretation of depth profiles in order to quantify accumulation and mixing rates was applied within a study of phosphorous contribution to eutrophication in the Gulf of Eilat. The three upper mentioned approaches lead to easier and more complete interpretation of radionuclide data and their practical use within interdisciplinary studies of climate of the past and environmental pollution. Sediment chronology, Gamma spectrometry, Excess 210Pb, Excess 228Th, 137Cs, 241Am ii Contents 1 Introduction and overview 1 2 Chronology in the Holocene 5 2.1 Radionuclide dating methods . 5 2.2 Non-radionuclide dating methods . 13 3 Chronology using excess Pb-210 17 3.1 Principle . 17 3.2 Radionuclide profiles modelling . 19 3.3 Radionuclide inventories and fluxes . 25 4 Gamma spectrometry 27 4.1 Radioactivity . 27 4.2 Gamma radiation . 34 4.3 Detection of gamma radiation . 38 4.4 Characteristics of gamma spectra . 40 4.5 Analysis of gamma spectra . 42 4.6 Statistics . 47 4.7 Quality control . 49 5 Background in gamma-spectrometry 51 5.1 Methods . 51 5.2 Results and discussion . 51 5.3 Conclusions . 57 6 Gamma emitters in sediments 61 6.1 Uranium-238 series . 63 6.2 Thorium-232 series . 66 6.3 Potassium-40 . 67 6.4 Beryllium-7 . 67 6.5 Artificial isotopes . 67 iii 7 Efficiency calibration 69 7.1 Experimental efficiency calibration . 69 7.2 Density and elemental composition effects . 69 7.3 Mathematical efficiency calibration . 71 7.4 Efficiency calibration with LabSOCS . 72 7.5 LabSOCS efficiency calibration problems . 74 7.6 Validation of LabSOCs efficiency calibration in the Laboratory . 75 7.7 Conclusions . 84 8 Supported lead in Pb-210 chronology 87 8.1 Motivation and introduction . 87 8.2 Effects of supported Pb-210 underestimation on excess Pb-210 sediment depth profiles . 87 8.3 Possible consequences of supported Pb-210 underestimation for chronologies . 89 8.4 Materials and methods . 89 8.5 Results and discussion . 91 8.6 Conclusions . 94 9 Depth aligning of paired core samples based on naturally occurring and arti- ficial radionuclides: A case study from off NW Africa 97 9.1 Introduction . 97 9.2 Materials and methods . 98 9.3 Results and discussion . 102 9.4 Conclusions . 110 10 Artificial radionuclides in deep-sea sediments from Indonesia 111 10.1 Introduction . 111 10.2 Regional setting . 111 10.3 Artificial radionuclides in the central Indo-Pacific region . 112 10.4 Methods . 115 10.5 Results . 118 10.6 Discussion . 126 10.7 Conclusions . 127 11 Radionuclides and recent sedimentation rates in Northern Gulf of Eilat/Aqaba, Red Sea 129 11.1 Introduction . 129 11.2 Material and methods . 132 11.3 Results and discussion . 135 iv 11.4 Conclusions . 153 12 Summary and outlook 155 12.1 Technical aspects of gamma spectrometry of sediments . 155 12.2 Site specific results . 156 12.3 Outlook . 156 Publications connected to this thesis 157 Publications not included in the thesis 158 A Measured data 161 B Others 189 Bibliography 195 v vi List of Figures 1.1 An overview . 3 2.1 Radionuclide dating methods in the Holocene . 6 2.2 137Cs transport in the atmosphere . 10 2.3 137Cs deposition in N and S hemispheres . 11 2.4 Ingrowth of 241Am from 241Pu ............................ 13 3.1 Sources of 210Pb to sediment . 18 3.2 Latitudal distribution of 210Pb in the air . 19 3.3 Example of application of CF-CS model . 21 3.4 Example of application of CRS model . 22 4.1 Radioactive decay . 28 4.2 Transient radioactive equilibrium . 31 4.3 Secular radioactive equilibrium . 31 4.4 No radioactive equilibrium . 32 4.5 Radioactive decay scheme . 32 4.6 Decay scheme of 137Cs................................. 35 4.7 Photoelectric effect . 36 4.8 Compton effect . 37 4.9 Energy of a photon and an electron after Compton scattering . 37 4.10 Pair production . 38 4.11 Photon cross sections in Ge . 39 4.12 HPGe vs NaI(Tl) detector spectra comparison . 40 4.13 Gamma spectrum features . 41 4.14 FWHM calibration . ..