T03_10

Data Reduction for Rapid, Continuous Radiocarbon Measurements by Laser Ablation

Wertnik M¹, Wacker L¹, Christl M¹, Synal H¹, Welte C¹

¹ETH Zurich, Zurich, Switzerland

The unique Laser Ablation (LA) setup coupled to a MICADAS Accelerator Mass Spectrometer (AMS) at ETH allows for the rapid measurement of continuous radiocarbon records on carbonate archives (e.g. speleothems, corals, otoliths). Using LA-AMS, ¹⁴C/¹²C ratios in such archives have been  successfully analysed at spatial resolutions of up to 100 µm.

To ensure stable measurement conditions in the AMS, a continuous carbon flow of approximately 2.5 µg/min needs to be produced by the laser. Accordingly, CaCO₃ is ablated at comparably high repetition rates of 200 Hz, which in turn requires a continuous movement of the sample relative to the laser beam through a positioning system (typical velocities: 5 – 20 µm/s). Single data points are produced at 10 sec intervals resulting in a dense dataset with well localised relative coordinates.

As LA-AMS provides a transient signal , special care needs to be taken in basic data processing and the proper assignment of the measured signal to the sampling location. Important to consider are especially signal extraction and noise reduction as well as mixing and washout effects. Here, we show the current status of data processing and report on improvements in data processing.