Itrax XRF Core Scanner
The Itrax XRF Core Scanner is the latest development in non-destructive analytical instrumentation aimed at paleoclimate research. Scanning of a core produces an optical RBG and a micro-radiographic image as well as micro-X-ray fluorescence spectrometry (XRF) elemental profiles, all at high resolution. The generated digital images can be overlaid and compared to changes in chemical composition using special post-processing software.
The Itrax can accommodate a variety of sample types including sediment and rock cores as well as drop stones, corals and wood (providing they are the right shape). The instrument can analyse split cores, slabs or U-channel samples up to 1800 mm in length with a diameters up to 120 mm and with a minimum thickness of 1 cm.
Samples are loaded into the left-hand ‘wing’ of the instrument and fed into the central tower where the cameras and XRF instrumentation sits. First, a surface scan is initiated which records the surface topography. This ensures that the XRF detector does not collide with the sample on subsequent scans and that the sample-detector distance is constant, which is important for reliable XRF analysis. During this scan the optical image is acquired. The user must then set the radiographic parameters including the tube voltage and current and the exposure time. The aim here is to generate a radiograph with suitable contrast and brightness. The next step is to set the XRF parameters. The user selects elements of interest likely to be found in the sample (some prior knowledge of the sample is thus an asset) and optimises the peak fitting parameters. If some elements are missed in this initial selection, these can be recovered later by reprocessing the spectral data generated during the scan. A primary signal is then recorded; this is akin to a ‘blank’ reading. The final step for the user is to specify the core name and file destination and the XRF step-size and exposure time. It is possible at this stage to set-up multiple analyses of the same core. Once all this information is entered the Itrax starts scanning for first the radiograph, and then the XRF elemental profiles.
Something to consider prior to analysis is the resolution and elemental sensitivity you are interested in. The step size for XRF analyses range from 200 µm up to 1 cm and each point in the scanning process can be measured for as little as 1 second up to 1000 seconds. Major elements that are found in high concentrations within the sample (e.g., Si, K, Ca, Ti, Sr) can be measured with confidence with lower time spent per point. If however you are interested in trace elements for instance, the spent at each point must be long enough to detect them. Essentially the time it takes to measure a core is dependant on the number of points and how long is spent measuring each point. A good grasp of the core stratigraphy helps as it can highlight areas where higher resolution measurements should be made.
Two types of X-ray tubes are available at the CPL. The molybdenum tube is suitable for both transition and heavy elements. The chromium tube is however best for the analysis of lighter elements only (K, Ca, Sc, Ti, V).
For each point measured a single spectra is produced. The data output is as an intensity (counts sec-1) rather than as a concentration. With the use of standard reference materials or matrix matched standards with pre-determined concentrations it is possible to acquire absolute concentrations (CPL does not offer the elemental analysis of such standards however).
For more information about using the Itrax core scanner please contact:
Barbara Wohlfarth +46 (0)8 16 48 83
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