The ITRAX™ Core scanner was developed by Cox Analytical Systems. The principle of operation is based on the simultaneous acquisition of microdensity (radiography) and microcompositional variations (XRF) using two separate X-ray detection systems. Moreover, colour information and magnetic susceptibility are provided through respectively a high resolution digital line-scanning camera and a magnetic susceptibility sensor incorporated in the system. The analysis is performed without touching the sample surface and is completely non-destructive.
EXCITATION SOURCE AND DETECTION SYSTEMS
An intense source of X-rays is provided using a Molybdenum X-ray tube anode (maximum power load is 3 kW at 50 mA). These X-rays are squeezed through a flat-beam capillary optic (developed by Cox Analytical Systems) that generates a beam with a rectangular cross-section of nominally 22 mm x 100 microns. Two other tubes are also available to improve the detection of light elements from Al to Ti (Cr anode), and for Mo and Nb (Rh anode).
Micro X-ray fluorescence analysis:
Chemical profiles along sediment samples are recorded for a broad range of elements. The concentrations of elements (from Si to U, for the Molybdenum tube) can be determined simultaneously, based on X-ray fluorescence. Most of these elements can be determined in concentrations down to 20 ppm depending on the element, analysis time and matrix composition. The fluorescent X-rays are measured at 45º to the incident X-ray beam using a Si drift X-ray detector. Digital signal processing provides energy-dispersive spectrometry. The XRF geometric resolution is high and offers good sensitivity due to the high X-ray flux and well defined measuring spot. The analytical resolution is down to 100 microns step-size, the effective XRF spot size is 0.1 x ~ 4 millimeters.
Detection limits depend on the atomic number of the chemical element, the x-ray exposure time and the x-ray anode too.
Detection limits of elements (in ppm) for micro x-ray fluorescence analysis using a Mo x-ray tube anode with different exposition times.
The transmitted X-rays are recorded with an array of 1024 diodes, each 25 microns wide, providing a digital radiographic image. Highly resolved and distorsion free images are digitally recorded by scanning along sediment cores (pixel size is 0.1 X 0.025 millimeters, 0.1 millimeters in scan direction). The radiogram shows density changes below the % level and have a very large dynamic range with 16bit image format. Successive radiographic lines are acquired strictly perpendicular to the core, therefore minimizing the blur and distortion that usually occur in the corner of image in classic radiography. The recorded density image thereby gets very high quality. The system will record the radiographic information line by line as the sample moves through the beam. By selection of an appropriate tube voltage and current, exposure time (up to 1 s) and step-size, the image quality and resolution can be controlled.
Optical line camera :
The new high resolution line camera system consists of a RGB colour camera operating in line mode synchronized with the stepper motor movement. The light source uses polarizing filters to produce an image which is essentially free from effects of glare from water on the sample surface. The image resolution is 50 µm pixel size.
Magnetic susceptibility sensor :
The magnetic suceptibility sensor device automatically moves down for measurement and up when the sample is moved.The active region of sensing surface (i.e. the area receiving 50% maximum response) is a 3,8 X 10,5 mm rectangle allowing very fine resolution surface measurements.
The maximum measurable core length is 1.8 meters. The sample thickness for XRF analysis is from 20 to 80 millimeters. The maximum sample thickness for density analysis is 50 millimeters. Note that these values refer to the sample thickness and not the complete core diameter. Split cores, slabs, U-channels, rocks or soil samples and drill cuttings can be analyzed.