1. Different potential systematic uncertainties involved in 210 Pb dating method Begy R.-Cs. 1,2, Reizer E. 1, Forray F.-L. 3, Simon H. 1, Gabor A.-I. 1,2, This work is financially supported by PN-II-RU-TE-2012-3-0351 project 1 Babeş-Bolyai University, Faculty of Environmental Science and Engineering, 30 Fântânele Street, 400294, Cluj-Napoca, Romania; 2 INCDO-INOE 2000, Research Institute for Analytical Instrumentation, ICIA Cluj-Napoca, Romania 3 Babeş-Bolyai University, Faculty of Geology, M. Koganiceanu Street nr.1, Cluj-Napoca, Romania;

2. About us Nuclear spectrometry laboratory from “Babes- Bolyai” University (Faculty of Environmental Science and Engineering) Team: Begy R.-Cs.(Phd. head), Simon H. (Phd stud.), Reizer E.(Msc. Stud.), Vasilache D. (Phd stud.), Kelemen Sz. (Res. asist) Facilities: two HpGe gamma spectrometer (GEM and GMX type) 8 alpha chamber with 900 mm 2 PIPS detector, scintillations cell for Rn and Ra measurements etc. Task: Pb-210 dating(Starts in 2005 for first time in Romania (in our laboratory) ) and Monitoring of Environmental radioactivity (NORM, TENORM)

3. Aims of this study For Pb-210 dating Determination of Pb-210 Alpha spectrometry (chemical preparation) Gamma spectrometry To analyze the effect of the undisolved (insoluble) materials especially for silicates found in the sediments Estimate the uncertainty caused by the silicates Improved the chemical separation process To analyze the variation of the mass attenuation in sediment layers (compared with IAEA reference material) Establish a correction for the self attenuation effect

4. Study Area NameLocationType 1.Buh ă escu 47°35’18,52″N 24°38’ 35,56″E GLACIAL 2.Știol 47°35’ 08,97″N 24°48’ 59,50″E GLACIAL 3.Muced 47°34’26,63″N 24°32’41,64″E GLACIAL 4.Saint Anna 46°07’66″É 25°53’14,52″K VOLCANIC 5.Iacob 45° 07' 49,30'' N 29° 23' 38.80'' DELTAIC

5. Alpha spectrometry The total 210 Pb can be determine by measuring its daughter isotope 210 Po ( one of the most precise method) is generally based on various acids leachings procedures. EPA -David N.Edgington, 1975 without HF Leaching with mineral acids, partial digestion without HF Wojciech Tylmann, 2013 Rolf Aalto, 2012 Begy et al. 2015 digestion totality of sediment samples using HF Negative effect their difficult decontaminations their costly prices Most time consuming (1 week) quick contamination of teflon disches Negative effect Positive effect Lose of Po-210 Less time consuming (max 1 day) Getting the total amount of Po from sample 1. 2. Just HCl and H 2 O 2

6. () Materials and Methods 1 (EPA -David N.Edgington, 1975) Application of the first method, and the residual was digested in Teflon dishes in presents of HF, HNO 3 until total dissolution. Total activity represent the activity measured in first and second step together Chemical processes was yielded by adding Po- 209 as tracer Measurements with PIPS detector alpha- spectrometric system Total time consumption is 1 day

7. Control of measurements

8. without HF 1.Results of Leaching with mineral acids, partial digestion without HF ȘtiolBuhăescuMucedIacobSt Anne Total Activity of sed. (Bq/kg) 572  602727  400330  29200  30161  20 Activity of silicate content (Bq/kg) 91  5 (16%) 226  18 (9%) - 60  9 (30%) 78  7 (45%) Undissolved silicate content (mass) 25%36%-48%22% The uncertainty of the value are represented in 2σ confidence interval Activity of 226 Ra 55  4 60% 76  5 33% - 20  2 33% 50  4 64%

9. Total digestion of sediment samples using HF ( 2. Total digestion of sediment samples using HF ( Wojciech Tylmann, 2013 Rolf Aalto, 2012 Begy et al. 2015) Activity in residuals (Bq/kg) UDL - Teflon dish contamination % 2046-3522 Improvement for avoid the using of Teflon : The sample is place first in a single use plastic glass with 2.5 ml HF and 3 ml of HNO 3 for two days. After, 2 ml of 0.8 mol boric acid is added and replaced in Erlenmeyer glasses with 10 ml of HNO 3 and placed on a hot plate at 90 ˚C. Evaporation at almost dryness 10ml HNO 3 Evaporation 10 ml HCl Evaporation 10 ml HCl Evaporation Adding H2O2 and three times distilled Water Deposition on a Stainless Steel disc at 0.4-0.9 pH fixed with HCl on 82 ˚C UDL – Under Detection Limit that in our case is 3 mBq

10. Mineralogy of the residuals 1 The samples mineral composition were identified using powder X-ray diffraction (XRD) analysis with a Bruker D8 Advance powder diffractometer using Bragg-Brentano geometry. The samples from Muced, Buh ă escu and Știol Lakes contain quartz with undulatory extinction typical for metamorphic rocks. Besides quartz, muscovite and feldspar where identified by x-ray diffraction Other minerals identified by polarised optical microscopy, besides those identified by x-ray diffraction, are amphiboles and chlorite. Sediments accumulated in St. Anna Lake consist of minerals originated for the alteration of volcanic rocks (dacite). The dominant minerals identified by X-ray diffraction are feldspar and quartz The quartz is of non- undulatory type, typical for magmatic rocks. Small quantities of amphibole, pyroxene, biotite where identified by polarised optical microscopy. Jacob lake samples have predominantly quartz with undulatory extinction, muscovite, and rare feldspars, pyroxene and amphiboles.

11. Mineralogy of the residuals 2 Power X-ray diffraction patterns for sediments from Buhaiescu Lake, St. Anna Lake. Identified minerals are: MS- muscovite, Pl-plagioclase and Qtz-quartz

12. Resulted Uncertainties Lakes ȘtiolBuhăescuMucedIacobSt Anne Effect of silicates to 210 Pb dating method Difference in Ages(y) % 2,05 (max 8,6) -1,03 (max 8,3) - -5,9 (max 21) -11 (max 17) Difference in Dates % 0,78 (max 4,5) 0,54 (max 3,4) - 0,2 (max 3,11) 0,45 (max 1,3) uncertainties in 210 Pb dating method (%) 712-519 uncertainties in 210 Pb dating method with silicates effect 19%20%-26%36%

13. Gamma spectrometry The main problem is regarding to the matrix effect, the self attenuation in the sample Three possibilities: – Computing software for self attenuation corrections (monte-carlo simulation) – Analytical techniques for density correction (empirical equations) – Simple determination of the self attenuation coefficient and recalculate the peak intensity (very important in relative method ) Unfortunately it must to be apply for each analyzed sediment layer

14. Self attenuation coefficient in sediment column

15.  Empirical approach

17. Correction by recalculation the peak intensity trough mass attenuation correction Before CorrectionAfter Correction

18. Conclusions Leaching with just mineral acids (HCl and H 2 O 2 ) can result residue of 22-48% depending on the origin of the sediments The remaining activity of 210 Pb( 210 Po) in the undisolved material can vary in the range of 9-45% The remaining residual activity found in sediments which have predominantly quartz or are originating from volcanic rocks Second digestion procedure was developed, in this case the residue was negligible and the remaining activity was under the detection limit The highest uncertainty is produced in case of volcanic rocks, total error can reach 30% In gamma spectrometric measurements the matrix effect is very important to correct, the simplest way being with the determination of the mass attenuation coefficient for each sediment layer

19. Thank you for attention This work is financially supported by PN-II-RU-TE-2012-3-0351 project, Radionuclides as tracers of the anthropic influence on the Danube Delta sedimentary processes National project, initiated by the Romanian Guverment