In-air PIXE, in-air PIGE, external IBA

The most used IBA technique is particle-induced X-ray emission (PIXE) analysis. PIXE analysis is considered a surface-sensitive technique that does not require prior sample preparation (except in special cases such as corrosion layer) and can be applied to a wide range of object sizes. As the PIXE analysis is carried out in very small areas and is inherently sensitive to the surface layers of thickness up to tens of microns, it is worth performing multiple measurements on the artefact. Quantitative analysis is straightforward, based on physical parameters. PIXE spectra are evaluated with the GUPIXWIN software package. PIXE can be used in parallel with particle-induced gamma-ray emission (PIGE). PIGE covers lighter elements, for example lithium, fluorine or sodium. The quantification is usually standard-based which can be refined. In our external beam set-up, the beam is delivered to the air through an ultrafine (200nm) Si3N4 window. The characteristic X-rays are collected by two detectors located on either side at 45° from the object surface. A 25 mm2 SDD X-ray detector with 8 μm Be window is used to measure low Z elements. This detector is mounted with a permanent magnet (1 T magnetic field) which protects the detector from scattered protons. A 50 mm2 Si(Li) detector, with additional filters as needed, detects medium and high Z elements. Typically, a proton beam of 3.2 MeV energy focused down to 60 × 60 μm with a current of 200–400 pA is used to irradiate the artefacts. Elemental distribution maps and summed-up X-ray spectra on, typically, 1 mm × 1 mm areas are recorded. In the case of inhomogeneity, the ‘selected raster’ mode is applied. The accumulated beam charge is monitored by the in-vacuum chopper. For PIGE, we use a portable gamma-ray spectrometer based on high-purity germanium coaxial detector, manufactured by Baltic Scientific Instruments. The analytical procedure is checked with standard reference materials.

Particle induced x-ray emission (pixe)

particle induced gamma-ray emission (PIGE)

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