Trace Element Quantification in High-Resolution Rutherford Backscattering Spectrometry

Full text: Rutherford backscattering spectrometry (RBS) is a versatile tool for analysis of composition and thickness of nm-films. Low concentrations of heavy elements in light matrices, e.g. transition metals in C, can easily be detected. In the present work a multi-element organic compound, i.e. human blood was investigated to show the potential of high-resolution RBS for quantification of trace elements. This is of special interest also for other ion beam based techniques (e.g. SIMS, PIXE) have been successfully applied for organic materials. The experiments were performed employing the AN-700 accelerator at the Johannes Kepler University of Linz, which can provide monoenergetic beams of H,D and He ions with up to 700 keV primary energy. A high resolution LN2 cooled surface barrier detector was used to record the spectra of backscattered projectiles. The blood sample was prepared in the following way: a droplet of human blood was deposited on a graphite sample, dried in air and subsequently transferred to the target chamber together with a graphite reference target. RBS spectra were recorded for 250 keV D+ ions scattered from the blood film and the reference sample. Simulations of the RBS spectra were performed using the program SIMNRA. For the graphite reference target elements other than C were below a concentration of 1.5 at%. From the shape of the RBS spectrum of the organic sample it can be ascertained that the substrate signal is not visible. It was possible to identify at least 10 chemical elements with high accuracy. For instance, the concentration of Fe was determined to 350 +/- 10 ppm equivalent to 400 mg/L in perfect agreement with standard blood test values. The detection limit for elements with atomic number higher than Fe is found to be below 20 ppm. Note that it would be possible to resolve a concentration gradient within the film by high-resolution RBS. (author)