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With the Avaatech optical system the length and the width of the X-ray beam can be determined independently. The length (in down core direction) of the irradiated sample area can be varied from 10 to 0.1mm. The width can be varied from 15 to 2mm. This allows to measure with the highest resolution and largest analyzed sample surface for all types of sediment. Namely, if the signal in the sediment is vague due to e.g. bioturbation, then a large irradiated length and width can be applied providing for a high count rate. If the signal in the sediment is clear however, e.g. with laminations, a small irradiated length with in combination with a large width can be chosen. The count rate will now be much lower. However, since the signal in the sediment with laminated sediments is clearly present, the relatively low count rates from XRF analysis will be sufficient for a proper analysis. Applying a small X-ray spot, as obtained with poly-capillaries having irradiated sample diameters of 100um down to 20um, only one or a few grains are analyzed per sample position, which is far from a homogeneous sample. This will give strongly fluctuating count rates, seen as scatter that obscures the detection of actual processes in the sediment. Moreover, diffraction effects can give then spurious peaks in the XRF spectra. So, even at a high resolution scan the irradiated surface of the sample must be kept as large as possible. Applying the Avaatech variable optical system this can be set to optimum measuring conditions to minimize the above mentioned effects.
After penetration of the sample by the incident X-ray beam primary fluorescence of the elements in the sample will occur. However, inter-element effects (secondary fluorescence) will generate X-ray fluorescence outside the irradiated sample volume thus providing for detection of X-rays beyond the irradiated sample area. This results in an unwanted decrease of resolution. This effect is prevented with the Avaatech optical system due to a slit system in this device.
The entire optical system is He-flushed for good light element detection. During measurement the device makes contact with the sediment. The sediment is covered with a thin foil highly transparent to X-rays to prevent the device being soiled and to prevent drying of the sample during long measurement times.
The direct radiation from an X-ray tube with an Rh-anode is used for excitation of elements in the sample. This provides for an excellent excitation of the elements from Mg to U.
The digital Canberra X-ray detector is equipped with a unique 1.5mm thick Si-crystal. This provides for an increased detection of the elements >As (10keV). As an example, with this detector Ba gives 2.5 times more counts than with a 0.5mm thick Si-crystal.
The digital Color Line Scan Camera is a tool for recording images of samples and of measuring variations of color intensities along a transect. These color intensities can be compared with the chemical data from the XRF analysis. If a certain color represents a component of the sediment, this will give extra high resolution information. It is also possible to make UV luminescence images with this tool. Color variations then provide information about mineralogy. This promising new methodology is currently being developed.
After penetration of the sample by the incident X-ray beam primary fluorescence of the elements in the sample will occur. However, inter-element effects (secondary fluorescence) will generate X-ray fluorescence outside the irradiated sample volume thus providing for detection of X-rays beyond the irradiated sample area. This results in an unwanted decrease of resolution. This effect is prevented with the Avaatech optical system due to a slit system in this device.
The entire optical system is He-flushed for good light element detection. During measurement the device makes contact with the sediment. The sediment is covered with a thin foil highly transparent to X-rays to prevent the device being soiled and to prevent drying of the sample during long measurement times.
The direct radiation from an X-ray tube with an Rh-anode is used for excitation of elements in the sample. This provides for an excellent excitation of the elements from Mg to U.
The digital Canberra X-ray detector is equipped with a unique 1.5mm thick Si-crystal. This provides for an increased detection of the elements >As (10keV). As an example, with this detector Ba gives 2.5 times more counts than with a 0.5mm thick Si-crystal.
The digital Color Line Scan Camera is a tool for recording images of samples and of measuring variations of color intensities along a transect. These color intensities can be compared with the chemical data from the XRF analysis. If a certain color represents a component of the sediment, this will give extra high resolution information. It is also possible to make UV luminescence images with this tool. Color variations then provide information about mineralogy. This promising new methodology is currently being developed.
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Latest website update: 21st June 2008
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