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Radiocarbon dating

Radiocarbon dating. Student presentation for Analytical Strategy Autumn semester 2018. Possible source of cosmic rays. Supernova remnant, Fermi particle acceleration Particles travel through galactic magnetic field Nuclear reactions induced by cosmic rays. ~ 2 atoms/cm 2 min

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Radiocarbon dating

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  1. Radiocarbon dating Student presentation for Analytical Strategy Autumn semester 2018 Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  2. Possible source of cosmic rays • Supernova remnant, Fermi particle acceleration • Particles travel through galactic magnetic field • Nuclear reactions induced by cosmic rays • ~2 atoms/cm2min • Production is greater in high levels of atmosphere • 14C remains in the atmosphere long enough to be mixed with stable carbon in the form of 14CO2 Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  3. Production of radiocarbon • Particle shower • Thermal neutrons 14N + n  14C + p 14C + O2  14CO2 6CO2+ 6H2O  C6H12O6 + 6O2 • Radioactive decay 14C  14N + e- + ṽ󠇯e • Exponential rate law A = A0e-(t/Ʈ) Ʈ = t1/2/ln2 t1/2 = 5730 ± 30 y (?) Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  4. Is radiocarbon age convertible to real age? Assumptions: • Production rate of 14C in the atmosphere was constant over time • 14C is distributed homogenuously in the environment • Every living organism takes up the same ratio of 14C over 12C (and distributes it equally in its tissues) • After death, the system is closed, there is no contamination and no “fresh” carbon intake • Humanspecies didn’t mess up anything Underlying problems: • Production variations • Reservoir effect • Isotope fractionation • Contamination of samples • Human influence Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  5. Variations in the isotope production Solar magnetic field fluctuations: • Schwabe cycles – 11 years • Weaker magnetic field of the Sun: •  Low sunspot number AND higher GCR flux towards Earth • Maunder Minimum : 100-year periods with no sunspots • Earth’s magnetic field deflects the charged particles • Highly energetic particles are less deflected • Deflection is smaller at magnetic poles • Geomagnetic field varied over time • Areas around poles are much more vulnerable Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler D. Güttler et al. NuclearInstrumentsand Methods in Physics Research B 294, 459–463, 2013

  6. Carbon circulation and Reservoir effect • Global inventory of 14C ~70 tons • 90% in the oceans, • 8% in biosphere, soils, • 2% in the atmosphere • Ratio 14C/12C ~ 1.2·10-12 *(Normalized to 1.00 in the figure) Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  7. Ocean radiocarbon heterogeneity • Long mixing time • “Old” water from the bottom depletes surface water layers in 14C during mixing • Mixing patterns depend on climate • Surface water ~ 400 years “old” • Surface – bottom difference 100-2000 y • Apparent age of +40 years for southern hemisphere • Reason?  Water surface Matsumoto, K., J. Geophys. Res., 112, C09004, 2007 Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  8. Isotope fractionation • Kinetic isotope effect: Heavier isotope  higher reduced mass  lower zero point energy  stronger bonds  lower uptake by living organisms • Organisms with limited sources of carbon intake slightly more 13C and 14C isotopes • Biochemical processes vary among species • When dating a given sample, better to determine δ13C directly than to rely on published results • Better solubility of heavier CO2 affects water 14C content (still it’s <1.00) Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  9. Antropogenic influence on radiocarbon ratio • Suess effect: fossil fuels • Nuclear bomb testing Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler Stuiver M. et al. Earth and Planetary Science Letters, 53 (1981) 349-362 www.cdiac.ess-dive.lbl.gov

  10. Other effects on 14C/12C ratio Contamination of samples • Volcanic eruptions • Hard water effect: Limestone mineral and humus dissolving affect the age • Island effect – proposed • Artificially or naturally caused • Preservation of archeological materials • Contamination of very old samples by contemporary carbon: e.g. 100,000-year old sample: • 0.01% – 76,000 years • 0.1 % – 57,000 • 1% – 38,000 Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler Caughley, G,; J. RoyalSoc.ofNew Zealand, 18 (3), 215-270, 1988

  11. Intcal04 Tree-ring data contain 7 different data set Reservoir effects are corrected by subtracting factor «R» or «𝛥R» Calibration curve from 0 to 26kyrs BP (before present) Separate calibration curves for marine and terrestrial samples. Separate curves for northern and southern hemisphere. (Newest is INTCAL13 and MARINE13 going from 0 to 50kyrs BP) Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  12. Calibration curve (BP means actually before 1950) IntCal98 (light grey) and IntCal04 (dark grey) showing 95% Cal age ranges Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  13. Probability determination with OxCal OxCal can be downloaded for free OxCal gives the probabilities for each time range OxCal is based in Bayesian statistics Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  14. Compensating the fractionation effect Measured for 13C because it is easier to measure Listed for different species The fractionation effect of 14C is just two times the effect for 13C The 13C can also be measured with AMS directly Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  15. Accelerator Mass Spectroscopy Very high sensitivity Only mg of sample needed Carbon is transformed into graphite before measuring Today also CO2 can be used for AMS Use 1200°C and 10’000 bar to form graphite from organic carbon Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  16. AMS setup No negative ions generated for Nitrogen The «Stripper» operates in the MV area. 13C can be measured from the Faraday cups collecting 13C and 12C Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  17. Gas ionization counter as AMS detector The incoming particles hit the gas and cause ionization The signal is proportional to charge and kinetic energy 14C4+ and 7Li2+ can be distinguished Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  18. Beta counting techniques Geiger counter • Completely non invasive • No protection against background radiation • Low sensitivity Liquid Scintillation Counter • Carbon ins converted to benzene • A fluorophore is added • Emitted electrons cause photoreaction which is detected • 10g of sample needed Yanick Fleischmann, Olivera Zivojinovic, Gabriela Stadler

  19. Applications - Archaeology Dating possible back to ~50’000 yrs Sediments Wood Corals Shroud of Turin (dated to 14th century) Dead Sea Scrolls Animal and plant remains (Archaeobiology) Egyptian mummies Olivera Zivojinovic, Yanick Fleischmann, Gabriela Stadler

  20. Newer applications Rock surface exposure e.g. for glacial dynamics Linking tree rings to solar flares: explaining fluctuations in calibration curves Meteorites: Residence time on earth Olivera Zivojinovic, Yanick Fleischmann, Gabriela Stadler

  21. Sample preparations • Contaminations: • Natural contaminations, exchange with environment • Collection and preservation of archaeological artefacts (wax, glue, labels) • Wood (charcoal, peat, textiles): • Physically remove invading rootlets and sediments • Acid-alkali-acid wash (hot HCl/NaOH) to remove contaminating carbonates and humic acids • Cellulose extraction: Treatment with sodium chlorite (NaClO2) at pH 3, 70°C • Bone: • Wash, scrap of exterior layers, crush • Wash with cold HCl to remove carbonates and extract collagen • Optional: wash extract with NaOH to remove secondary organic acids Olivera Zivojinovic, Yanick Fleischmann, Gabriela Stadler

  22. Ötzi – The Iceman • Discovered in 1991 in the Ötztal Alps • Archaeological sensation: First complete body ever recovered from stone age Olivera Zivojinovic, Yanick Fleischmann, Gabriela Stadler

  23. Ötzi • 14C measurements from Zurich and Oxford • Radiocarbon age 4550 ± 19 yrs BP(error 68.2% (1σ)) • Calibration by INTCAL98 tree-ring calibration curve and OxCal computer program • “Wiggling of curve leads to three peaks for calendar age • Distribution of the 68.2% (1σ) confidence ranges into three sections of 3360–3300 BC (29.3%), 3210–3190 BC (19.8%) and 3160–3130 BC (19.1%). • Distribution of 95.4% (2σ) confidence ranges of 3370–3320 BC (34.3%) and 3230–3100 BC(61.1%). Olivera Zivojinovic, Yanick Fleischmann, Gabriela Stadler W. Kutschera, W. Müller / Nucl. Instr. and Meth. in Phys. Res. B 204 (2003) 705–719.

  24. Ötzi Olivera Zivojinovic, Yanick Fleischmann, Gabriela Stadler W. Kutschera, W. Müller / Nucl. Instr. and Meth. in Phys. Res. B 204 (2003) 705–719.

  25. Reservoir effect & calibration: Marine diet • Mixed marine and atmospheric calibration • 19th century global surface reservoir correction R of ~ 400 years • Local reservoir correction for British coastal waters ΔR is 1±8 yrs • Using the fractionation effect: Percentage of marine carbon can be estimated from a linear interpolation between the δ13C endpoints for 100% terrestrial and 100% marine diets • New dating up to 200 yrs younger Barrett, J., Beukens, R., & Brothwell, D. (2000). Antiquity,74(285), 537-543. Olivera Zivojinovic, Yanick Fleischmann, Gabriela Stadler

  26. Case study: African mask • Take a few mg of wood sample • try to get untreated, uncoloured parts • Acid-alkali-acid wash • Extract cellulose • Carbonize sample • Measure AMS • Use calibration curve for wood with expected origin • Correct for reservoir effect and fractionation effect(if applicable) Olivera Zivojinovic, Yanick Fleischmann, Gabriela Stadler

  27. Applications - Conclusion • Widely used technology with diverse applications • Powerful tool do date archaeological artefacts, • However, exact historical embedding might still be difficult • Calibration, reservoir effects, fractionation and contaminations need to be considered Olivera Zivojinovic, Yanick Fleischmann, Gabriela Stadler

  28. Thank you! https://www.cartoonstock.com/directory/w/white_diamond.asp Olivera Zivojinovic, Yanick Fleischmann, Gabriela Stadler

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