Friday, 15 April 2016

Small but powerful XRF-device

Figure 1: Adam Martin is using the 
hand-held XRF in the field. This method 
has the advantage of giving a result
straight away and helps deciding which
samples should be send to a Laboratory to
 get a more precise answer.
Adam Martin is a Research Geologist based at GNS Science’s Dunedin office. In Figure 1 he is using a state of the art hand-held X-ray fluorescent (XRF) device to obtain in-situ geochemical information for elements between Magnesium and Uranium in the Periodic Table. This device can determine elemental compositions for bedrock (outcrop), rock pieces (hand specimen), sliced and polished rock (thin sections), cylindrical depth sections (drill cores), rock chips, soil, fluid and liquid samples.

Figure 2: Diagram showing the principle of the XRF device.
 The XRF device sends out a continuous x-ray which hits an atom and ejects an electron from the atom’s orbital shell. This gap gets filled by an electron dropping from a higher energy orbital shell to a lower energy orbital shell releasing a fluorescent x-ray (Figure 2). It is used to analyse a substance to determine the chemical composition of the sample of interest. Nearly every element has a unique fluorescent x-ray energy signature.

Figure 3: Lead (Pb) versus arsenic (As) plot for hand-held and lab XRF.

This instrument was used to analyse soil compositions at various locations around Dunedin City as part of an urban geochemical baseline survey to help assess the state of the environment in our cities. This provides a chemical snapshot that can be used to assess human and geological influences. The measurements so far of lead (Pb) and arsenic (As) concentration by hand-held XRF are comparable to Pb and As concentrations measured by lab XRF (taken from a more regional soil study as shown in the graphic opposite in Figure 3). These results show that Dunedin City soil has safe levels of Pb and As and that hand-held XRF results can be used to supplement laboratory XRF data for certain elements.