On the human radiation exposure as derived from the analysis of natural and man-made radionuclides in soils Vom Fachbereich Physik der Universität Hannover zur Erlangung des Grades Doktor der Naturwissenschaften Dr. rer. nat. genehmigte Dissertation von (M.Sc. Phys.) Shaban Ramadan Mohamed Harb geboren am 10.01.1966 in Qena, Ägypten 2004 Referent: Prof. Dr. Rolf Michel Korreferent: PD. Dr. Ingo Leya Tag der Promotion: 11.02.2004 Content I Content Content ...........................................................................................................................I List of Tables..............................................................................................................IV List of Figures .......................................................................................................... VII Summary ......................................................................................................................X Zusammenfassung..................................................................................................... XII Acknowledgements ..................................................................................................XIII 1 Introduction ........................................................................................................ 1 1.1 Radioactivity in the environment ................................................................................1 1.1.1 Natural Radionuclides in the environment..................................................................1 1.1.1.1 Cosmogenic radionuclides..........................................................................................2 Tritium (3H )........................................................................................................3 Beryllium-7, 10...................................................................................................3 Carbon-14............................................................................................................3 Krypton................................................................................................................4 1.1.1.2 Terrestrials sources of radiation ..................................................................................5 1.1.1.2.1 Potassium-40 ...............................................................................................................5 1.1.1.2.2 Rubidium-87................................................................................................................6 1.1.1.2.3 Uranium-238 series.....................................................................................................6 Uranium-238 subseries (238 U, 234Th, 234mPa,234U)..............................................7 Radium-226.........................................................................................................8 Radon-222 and its short-lived products (218Po, 214Pb, 214Bi, 214Po) ....................8 Long-lived decay products of Radon-222 (210Pb, 210Bi, 210Po).........................10 1.1.1.2.4 Thorium-232 series...................................................................................................10 Thorium-232......................................................................................................11 Radium-228 subseries (228Ra, 228Ac, 228Th, 224Ra).........................................11 Randon-220 and its decay products (215Po, 212Pb,212Bi, 212Po,208Tl).................12 1.1.1.2.5 The actinium series....................................................................................................12 1.1.1.2.6 The neptunium series ................................................................................................13 1.1.1.2.7 Decay Relationships Series .......................................................................................13 1.1.2 Man-made Radionuclides in the environment ..........................................................20 1.1.2.1 Strontium-90..............................................................................................................21 1.1.2.2 Iodine-131 .................................................................................................................22 1.1.2.3 Cesium-134 and 137..................................................................................................22 1.2 The human radiation exposure ..................................................................................23 1.2.1 External exposure......................................................................................................25 1.2.2 Internal exposures.....................................................................................................27 1.2.2.1 Ingestion....................................................................................................................27 1.2.2.2 Inhalation...................................................................................................................28 1.2.3 Mean values and variability of the natural radiation exposure .................................28 2 Experimental..................................................................................................... 32 2.1 Soil sampling.............................................................................................................32 2.1.1 The trench method.....................................................................................................32 2.1.2 Template method.......................................................................................................32 2.1.3 The bore core method................................................................................................34 2.2 Sample preparation....................................................................................................35 2.3 Experimental methods, measurements and evaluations............................................36 2.3.1 Gamma spectrometry ................................................................................................36 2.3.2 HPGe detector...........................................................................................................40 2.3.3 Gamma spectrometry System (HPGe) ......................................................................41 Content II 2.3.4 Energy calibration.....................................................................................................42 2.4 Calibration and efficiency determination of detectors for different measuring geometries and sample containers............................................................................43 2.4.1 Preparation of reference standard solution (Calibration source QCY48) ...............44 2.4.2 Preparation of standard soil sample procedure ........................................................45 2.4.3 Efficiency calibration................................................................................................45 2.4.4 Analytical efficiency expressions..............................................................................45 2.5 Natural Background .................................................................................................58 2.6 Calculation of elemental concentrations ...................................................................60 2.7 Experimental uncertainties........................................................................................62 2.8 Quality assurance including Ringversuch.................................................................67 2.9 Characteristic limits...................................................................................................69 3 Analysis of radionuclides in soils..................................................................... 72 3.1 Concentration of artificial radionuclides in depth profile and surface......................72 3.1.1 137Cs concentration in depth profile soil samples from Lower Saxony, North Germany...................................................................................................................73 3.1.1.1 137Cs deposition densities in soil samples from Lower Saxony, North Germany...79 3.1.1.2 Activity concentration of 137Cs and 40K [Bq kg-1] in surface soil samples from different sites in Lower Saxony, North Germany. ...................................................81 3.1.2 137Cs in depth profile soil samples from Lippe, North Rhine-Westphalia, Germany. ..................................................................................................................................83 3.1.2.1 137Cs deposition densities in soil samples from Lippe, (North Rhine-Westphalia), Germany...................................................................................................................83 3.1.2.2 Activity concentration of 137Cs and 40K [Bq kg-1] in surface soil samples from Lippe (North Rhine-Westphalia, NRW), Germany............................................................84 3.1.3 137Cs concentrations in depth profile soil samples from Ukraine. ...........................85 3.1.3.1 Highly contaminated (Zone II)..................................................................................87 3.1.3.2 Medium contaminated (ZoneIII)...............................................................................89 3.1.3.3 Not contaminated ......................................................................................................90 3.1.3.4 137Cs and 134Cs deposition densities [Bq