Radiocarbon dating

Jonas Metzger and Samuel Krieg

Num

bers

of C

-14

Atom

s

0 5'000 10'000 Time in ages15'000

C-14 Dating

C-14C-14

C-14C-14

C-14C-14 C-14C-14

C-14

100%

50%

25%12.5%

Blend

C-14

Cosmic radiation

C-14

Stratosphere

unstable atom ‚radiation'

Atom changed to an other

Radioactive decay

Examples:- Radon changed to Polonium- Carbon changed to Nitrogen

Sample preparationCleaning of sample-> Remove contaminants

Graphitisation-> Minimised sample contamination-> No cross-contamination-> Reproducible and reliable

Particle accelerator2. Mass spectrometer

Ion source

1. Mass spectrometer

C-14

Detector

otherAtoms

The sample is fragemented into

atoms

The accelerator is a huge filter

6 MV EN-Tandem 600 kV PSI/ETH system 200 kV system for 14C

Multi isotope system

Evolution of AMS over the last 10 years

High precision 14C dating

15 m 2.5 m 1 m

Biomedical 14C applications

TANDY MICADAS BioMICADAS

Dimensions of the new accelerator14C

13C12C

2.5 m

3.0 m

Overview

3. filterstripping processmolecule destruction

2. filtermass analysis(low-energy end)

5. filterparticle identification

4. filtermass analysis(high-energy end)

1. filternegative ion formation

13C / 12C14C / 12C

12C13C

Conclusions

MICADAS...

- runs very stable over time

- runs unattended with low maintenance

- dates samples back to 45 000 years

- allows high-precision measurements

Requirements for high-precision

- Reproducible sample preparation-> Sample composition

(procedure blank, contamination)-> Quantity-> Sample geometry

- Stability of the measuring system-> Changes in sample geometry-> Instrumental drifts-> Cross contamination-> Linearity

Golden Handfeste of Berne

Sample   Radiocarbon age   δ13CNumber Type (BP) +- (‰)ETH36716.1 parchment 888 20 -22.6ETH36716.2 parchment 878 19 -20.7ETH36716.3 parchment 882 19 -23.9ETH36716.4 parchment 875 19 -22.3ETH36716 parchment 881 10 -22.4

Blank variation: < 0.5 ‰

Statistical uncertainty: 1.0 - 3.0 ‰

Reproducibility of samples: 0.5 - 3.0 ‰

Standard normalisation: 0.5 - 1.5 ‰

Over all uncertainty: 1.5 - 5.0 ‰

age depended

relative

Summary

Thank you for your attention!