Particle Induced X-ray Emission (PIXE) is an ion beam analysis technique. In PIXE, atoms in the sample are excited when the sample is bombarded with protons, alpha particles, or heavy ions. X-rays are emitted when atoms in the sample de-excite. Each element has unique characteristic x-rays. In the spectrum, area of each peak is proportional to the elemental concentration in the sample.
The existing PIXE set-up in the accelerator laboratory was upgraded to external beam PIXE to do in air measurements, because of need to analyse large amounts of archaeological samples. Different exit window set-ups were constructed and tested. The goal was to get maximum beam spot area with minimum beam energy loss in the exit window. The set-up enables the use of 100 nm thick Si3N4 exit window membranes and 4-mm-diameter beam spot area. For the measurements in the current work, a 500 nm thick Si3N4 membrane was used due to its higher durability.
Current measurement can be difficult when doing PIXE in air because of ionization of air molecules in the beam's path and charge collection differences at sample surface. The set-up utilizes a beam profile monitor (BPM), which measures the current in vacuum prior to the exit window, and therefore is not affected by the current measurement difficulties in air. Along with the BPM, a current integrator was also used in the current measurements. Current integrator was used to collect the charge from the sample holder. These two methods together provided reliable way of current measurement.
With the developed set-up, 166 pottery pieces from the neolithic stone age from different parts of Finland, Sweden and Estonia, were measured to determine their elemental concentrations for provenance research. AXIL software was used to analyse the spectra.
