Accelerator Mass Spectrometry at VERA – Status and new developments

Dr. Oliver Forstner, VERA-Laboratory, Faculty of Physics, University of Vienna

Accelerator Mass Spectrometry (AMS) is a highly precise tool to measure minute concentrations of trace elements (mainly radioisotopes) on the ultra-trace level. Typical isotope ratios detected with AMS range from 10^-12 down to 10^-16. The challenge in measuring such low abundances is to eliminate all disturbing interferences by a combination of various highly selective filters. The first part of my talk will be an introduction into AMS which I will describe using the example of VERA. The Vienna Environmental Research Accelerator (VERA) is a dedicated AMS facility at the University of Vienna based on a 3 MV pelletron tandem accelerator built by NEC. Originally designed as device for radiocarbon measurements it was continuously upgraded to be a versatile machine for “all” isotopes. Radioisotopes measured at VERA range from the “standard” AMS isotopes ¹⁴C, ¹⁰Be, ²⁶Al, ¹²⁶I up to heaviest isotopes including ²³⁶U and ²⁴⁴Pu.

However, being a mass spectrometric technique AMS is limited by the presence of isobars. Except for some fortunate cases like ¹⁴C, ²⁶Al or ¹²⁶I even more effort has to be taken to detect the radioisotope hidden under a background of a stable isobar. In the second part of the talk I will give an introduction into the new developments at VERA with the aim of extending the range of radioisotopes available to AMS. Special focus will be given on a current research project funded by the Austrian Science Fund (FWF) in which the feasibility of using laser photodetachment of negative ions as a possible solution to the isobar problem will be studied.