10Be, 26Al, 36Cl, 41Ca and 129I Data Analysis at KIST
Dr John A Eliades1
1Korea Institute of Science and Technology, Seoul, South Korea
For AMS measurement, Be and Al are prepared in a form that is highly insulating (BeO and Al2O3), while AgI and AgCl compounds are volatile AMS targets. In order to increase cathode conductivity and stabilize (and in some cases increase) negative ion beam current production during sputtering, all of the materials are mixed with a second agent (ex. Ag powder) at KIST. This leads to some variability in quality, especially when end users with little or very intermittent experience prepare their own cathodes, or when sample material is very limited. Typical problems include unstable “spikey” cathodes that produce sudden bursts of large current during analysis and cathodes that do not produce current for the entirety of the analysis time. The AMS system can also experience intermittent instability during analysis, adversely affecting data quality if these data are included in the results. Considering that each cathode is analyzed for three, 10-minute “runs”, with each run divided into twenty, 30 second “block” intervals (30 min total analysis time), data can still be salvaged if poor quality blocks are excluded.
The KIST 6MV AMS system manufacturer (HVE Europa) software produces a “result file” that summarizes the “run” data for all cathodes, automatically calculating average isotope ratios and uncertainties based on all runs recorded. The software also produces individual run “result” files that provide all data from each block of the measurement. This talk describes an internal Visual Basic program that is used to analyze the raw data from each result file. It uses the block data to determine if there was a spurious period in the data acquisition. As the rare radio-isotope produces only several to several thousand counts in 30 mins, the stable isotope beam currents (typically in the range 1 μA to 10 μA) are monitored for inter-block beam stability using both the high energy beam stability and the accelerator injection current to high energy current ratio stability. Inter-run Isotope ratio stability and other system conditions are also monitored. Finally, overall cathode current during the entire 30 min period is monitored. The program calculates averages and uncertainties both for the full set of data collected and for the data less flagged points, and provides the analyst with a quick graphical interface to plot data for visual inspection. Data flagging will be discussed, along with examples of data that have been discarded based on monitoring flags.
I graduated from University of Toronto with a PhD in a joint physics and geology programme in 2012, studying at IsoTrace Laboratory. I then took a post-doctorial position with Korea Institute of Science and Technology in Korea, where I was hired as permanent research staff in 2013.