Simultaneous In-Air PIXE and XRF
Particle Induced X-ray Emission (PIXE) and X-ray Fluorescence (XRF) are techniques based on Energy dispersive X-ray Emission Spectrometry (ED-XES). They offer high analytical potential for non-destructive and non-invasive material characterization and imaging.
In PIXE, when a material is exposed to a proton beam, atomic interactions occur that give off X-ray radiation of wavelengths specific to each element. PIXE can be performed both in a vacuum as well as outside of a vacuum. Similarly, in XRF the material is excited by bombarding with high-energy X-rays which results in the emission of characteristic secondary (fluorescent) X-rays of wavelengths specific to each element.
Although both PIXE and XRF measure the energy of characteristic X-ray radiation from samples, they can provide complementary information about the sample under investigation due to different excitation mechanisms and depth sensitivities. Generally, PIXE has higher sensitivity for lighter elements and XRF is more sensitive to the elements whose characteristic radiation is closer to the energy of the primary X-ray beam. They also have different in-sample depth sensitivities. PIXE yield is restricted to the ion beam range, which is usually at the levels of 100 μm, while XRF excitation can penetrate several mm in depth.
The setup uses proton beam of 2 MeV energy obtained from 1 MV Tandetron accelerator for PIXE. The proton beam is extracted in air through 8 µm thin Al foil and directed to a sample positioned at the distance of about 8.5 mm from the exit foil. The resulting proton beam energy on target is about 1580 keV. Portable lightweight (500 g) Moxtek Magnum transmission anode X-ray tube has also been incorporated at the in-air external beam end-station. The tube is equipped with Rh anode and 0.25 mm thick Be exit window. The tube has been positioned to irradiate the same spot on the sample as the ion beam used for PIXE measurements. Home-made acquisition software SPECTOR is used to acquire both XRF and PIXE spectra.
In-air setup offers a possibility to do 2D mapping of samples with various geometries at the macro scale, therefore being of great benefit to fields such as cultural heritage, forensics etc. A sample configuration is controlled with the XYZ translation stage integrated into SPECTOR system to enable control of the movement and positioning. The sample holder can accept relatively large objects and lateral scans of up to about 40 x 40 cm2 are possible.
Contact person: Stjepko Fazinić