27.03.2015

Particle induced X-ray emission (PIXE) & Transition Edge Sensor (TES)

PIXE is the most sensitive non-destructive technique to study art objects. The University of Jyväskylä is using PIXE and TES-PIXE. TES-PIXE can be up to 10 times more sensitive than the regular PIXE due to its superior energy resolution. It can help detect elements in parts-per-million concentrations. This trace element information can be crucial in understanding where and how an object was created. The actual dating is often based on the impurities of the components.

In PIXE measurements an energetic ion beam from a small accelerator is guided to the object to be analyzed and emitted ion induced characteristic X-rays are detected. Most typically 2–4 MeV H or He ions are used in the analysis, which can be done either in vacuum or in air using external ion beam. In comparison to SEM-EDS, the bremsstrahlung induced background in the energy spectrum is orders of magnitude smaller and therefore PIXE is much more sensitive in measuring semi-heavy elements. On the other hand, PIXE is not normally suitable for measuring lighter elements than magnesium.

In Jyväskylä 1.7 MV Pelletron accelerator can be used for both conventional and high resolution PIXE measurements. The existing setups allows measurement only in vacuum but starting from mid-2014 also measurements in ambient conditions can be made.

Figure 1. Conventional PIXE energy spectrum measured in Jyväskylä from NIST SRM611 reference sample using 4.5 MeV He beam. This reference sample contains 500 ppm of several elements mixed in a glass matrix. Here silicon drifted detector (SDD) was used an energy detector.

Figure 2. High-resolution PIXE spectrum measured from stainless steel sample using the TES detector.

Analyzing a painting with the PIXE