Geochemical dating of a Swiss freshwater limestone cave using 230 Th/ - PowerPoint PPT Presentation

PAUL SCHERRER INSTITUT Geochemical dating of a Swiss freshwater limestone cave using 230 Th/ 234 U ingrow and 226 Ra-excess decay chronometry Jost Eikenberg, Maya Jäggi Division for Radiation Protection and Safety Paul Scherrer Institute, CH-5232 Villigen Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT Overview / Topics  Presentation of a radiochemical method for simultaneous determination of 226 Ra+ 228 Ra followed by TDCR-measurement and optimized alpha/beta-separation  Application of the chronometers 230 Th/ 234 U and 226 Ra for dating sedimentary systems Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT relevant isotopes for quaternary limestone dating radionuclide analytical technique 234 U, ( 235 U), 238 U, U/TEVA separation, electro- deposition, α -spectrometry 230 Th, 232 Th 226 Ra, 228 Ra filtration (RadDisc), OptiPhase Hisafe3 cocktail, LSC 210 Po spontaneous deposition on silver disc, α -spectrometry Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT Method implementation: low level determination of 226 Ra in sediments (limestone) • Sample dissolution CaCO 3 in 1 mol/liter HCl, evaporation, dilution with distilled water • Filtration of the sample through 3 Empore RadDisc (Mn-oxide impregnated) membrane • Elution of Ra with alkaline Na-EDTA solution • Measuring via LSC with optimized α/β - discrimination Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT The triple coincidence to double coincidence ratio (TDCR) counting technique PM R SAM PLE PM PM S T Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT Pulse Length Index (PLI) discrimination with HIDEX SL 300 28 24 20 16 12 8 4 0 27 38 52 72 99 135 185 252 343 466 634 861 1169 1588 2156 2927 3973 5393 7319 9934 13481 18296 Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT α -spectrum of 226 Ra with ingrowing daughters 2 h and 8 h after separation using HIDEX 300 SL LSC Alpha 140 120 100 80 60 40 20 0 10 100 1000 10000 Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT α -spectrum of 226 Ra with ingrowing daughters obtained 6 days after separation Alpha 160 140 120 100 80 60 40 20 0 10 100 1000 10000 Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT β -spectrum of 228 Ra with ingrowing 228 Ac 1 h and 8 h after separation using HIDEX 300 SL LSC Beta 50 45 40 35 30 25 20 15 10 5 0 1 10 100 1000 Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT TDCR vs. Efficiency using high purity radionuclide standard solutions 1.0 210 Pb 0.9 226 Ra 0.8 TDCR 0.7 228 Ra TDCR = efficiency 0.6 0.5 0.4 0.4 0.5 0.6 0.7 0.8 0.9 1.0 efficiency Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT Comparison of measured 226 Ra and the progeny isotopes 222 Rn, 218 Po and 214 Po with calculated decay/ingrowth curves 4.0 3.5 3.0 relative activity 222 Rn+ 218 Po+ 214 Po ingrowth curve 2.5 226 Ra: measured data 2.0 222 Rn+ 218 Po+ 214 Po: measured data 1.5 1.0 226 Ra decay curve 0.5 0.0 0 5 10 15 20 25 30 time after separation [d] Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT 238 U-Series 235 U-Series 232 Th-Series 238 U 234 U 235 U U 4.47x10 9 y 2.45x10 5 y 7.04x10 8 y β α α α 231 Pa 234 Pa Pa 4.196 4.776 4.395 MeV MeV MeV 3.28x10 4 y 1.17min β β α 234 Th 230 Th 231 Th 227 Th 232 Th 228 Th Th 5.013 7.54x10 4 y 1.41x10 10 y 24.1d 1.06d MeV 18.7d β 1.91y β α α α α 227 Ac 228 Ac Ac 4.688 6.038 4.010 5.423 MeV MeV MeV MeV 21.8y 6.13h β 226 Ra 223 Ra 228 Ra 224 Ra Ra 1600y 11.4d 5.75y 3.66d α α α Fr 4.784 5.716 5.686 MeV MeV MeV 222 Rn 219 Rn 220 Rn Rn 3.825d 3.96s 55.6s α α α At 5.490 6.819 6.288 MeV MeV MeV 218 Po 214 Po 210 Po 215 Po 216 Po 212 Po Po 66.3% 1.6x10 -4 s 1.8x10 -3 s 3x10 -7 s 3.11min β β 138.4d β 0.15s α α α α α α 214 Bi 210 Bi 211 Bi 212 Bi Bi 6.003 7.687 5.304 7.386 6.779 8.784 MeV 19.9min MeV MeV MeV β MeV β 1.01h MeV 5.01d 2.14min β β α 33.7% 214 Pb 210 Pb 206 Pb 211 Pb 207 Pb 212 Pb 208 Pb α Pb 6.623 6.051 MeV 10.6h 26.8min 22.3y stable 36.1min stable stable MeV β β 207 Tl 208 Tl Tl 4.77min 3.05min Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT Challange for the isotope geochemist: closing the gap between the established 210 Pb and 230 Th/ 234 U chronometers ( ) ( ) → → → → 238 234 230 226 222 210 210 U U Th Ra Rn Pb Po 2.0 230 Th/ 234 U 226 Ra/ 230 Th 1.5 210 Pb/ 226 Ra daughter / parent 210 Po/ 210 Pb 1.0 210 Po/ 210 Pb 0.5 210 Pb/ 226 Ra 226 Ra/ 230 Th 230 Th/ 234 U 0.0 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 time after formation [y] Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT Principles of U series dating: 1. 230 Th/ 234 U/ 238 U − λ − λ − λ t = ⋅ + ⋅ − 230 230 234 t t 230 234 230 Th ( t ) Th ( 0 ) e U ( 0 ) ( e e ) − λ − λ = ⋅ t − t 230 234 ( ) ( 0 ) ( 234 230 ) Th t U e e − λ t = ⋅ 234 234 238 U ( t ) U ( 0 ) e ( ) − λ = ⋅ − 230 234 t Th ( t ) U ( 0 ) 1 e 230 Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT Principles of U series dating: 1. 230 Th/ 234 U/ 238 U ( ) − λ = ⋅ − 230 234 t = = Th ( t ) U ( 0 ) 1 e 234 238 238 230 U ( 0 ) U ( 0 ) U relative activity (not to scale) 1.0 238 U, 234 U 0.8 0.6 0.4 230 Th 0.2 0.0 0 50 100 150 200 250 300 time after separation [ky] Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT Problem 1: inherited 230 Th, wrong age calculation ( ) − λ − λ = ⋅ − + ⋅ t t 230 234 230 Th ( t ) U ( 0 ) 1 e Th ( 0 ) e 230 230 234 U activity ratio 1.0 230 Th/ 234 U = 1 0.8 0.6 0.4 230 Th(t)/ 230 Th ingrowth, without inherited 230 Th 230 Th ingrowth + decay, with initial 230 Th(0)/ 234 U = 0.1 0.2 230 Th ingrowth + decay, with initial 230 Th(0)/ 234 U = 0.2 0.0 0 50 100 150 200 250 300 time after formation [ky] U-Th-evolution Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT U-series application with U-Th isochrones in sedimentology Sedimentary Systems 3.0 230 Th 232 Th activity ratio (relative scale) mixed (authigenic + detritus) phases: ingrowth dating U/Th ratio of detritus component 2.5 equiline: T > 0.3 My T 1 equipoint = 2.0 isochrone 1.5 T 0 1.0 U/Th mixing line at T 0 : 230 Th / authigenic phases with detritus contamination 0.5 0.5 1.0 1.5 2.0 2.5 3.0 234 U / 232 Th activity ratio (relative scale) Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT Geological section of the aquifer / recharge area of hell grottoes springs Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT Travertine dating via 226 Ra ex / 234 U and 230 Th/ 234 U Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT View into the cave system Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT Travertine precipitation: thermodynamic background + → +   H CO O CO H O 2 2 2 2 + + − + → → CO H O H CO H HCO 2 2 2 3 3 + − + − + + ↔ + 2 CaCO H HCO Ca 2 HCO 3 3 3 − − ↔ + HCO CO OH 3 2 − − + ↔ + 2 HCO CO H 3 3 + − + ↔ 2 2 Ca CO CaCO 3 3 − + + ↔ ↓ + ↑ + 2 2 HCO Ca CaCO CO H O 3 3 2 2 Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT Ingrowth of 230 Th without an inherited component, why that ? 1E-4 uraninite solubility (mildly reducing: Eh = 0.5 - 0.059pH) 1E-6 concentration [mol/l] 1E-8 1E-10 1E-12 232 Th, 230 Th and 228 Th detection limit for 1E-14 thorianite solubility 1E-16 3 4 5 6 7 8 9 pH Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017