# The Role of PIXE and XRF in Heritage Science:
## 5 XRF: From Point Analysis to Elemental Maps with Portable Equipment  
The main limit of the PIXE and the other IBA techniques is the lack of portability, a feature that is a severe limitation when a work of art cannot be moved to a laboratory. The XRF technique preserves non-invasive, non-destructive, and multi-elemental characteristics; moreover, it exploits portable instrumentation. For this reason, it is one of the most widely used techniques for material analysis in the field of cultural heritage. Its main drawback is a much lower sensitivity than PIXE to light elements [49] and the limited possibility of a quantitative analysis in HS [26]. At INFN-LABEC, a portable XRF spectrometer was designed and assembled, exploiting the experience acquired over the years with X-ray spectroscopy using ion beams. In this device, different tubes (Mo, Ti and W anodes available) were used for maximising the efficiency of the production of X-rays over a wide range of energies, as it depends on the main emission lines of the anode material. In addition, since any source emits its own X-rays, and they can hide X-rays emitted by the sample in spectra, the combination of more tubes with different materials limits this effect. For example, the M-lines of Molybdenum at 2.3 keV overlap with the sulphur, whereas the K-lines of Ti (4.5 keV and 4.9 keV) overlap with the L-lines of Barium; therefore, for detecting sulphur, the Ti anode is preferable to Mo, and vice-versa for detecting titanium. The detector installed was an SDD by Ketek GmbH with an energy resolution of 139 eV at the Mn K\(\alpha\) line. The electronic chain was also supplied by Ketek GmbH and was \begin{table}
\begin{tabular}{c c} \hline \hline
**Atmosphere** & **FWHM X \(\times\) Y (\(\mu\)m \(\times\)\(\mu\)m)** \\ \hline Vacuum & \(\sim\)7 \(\times\) 5 \\ Helium & \(\sim\)9 \(\times\) 8 \\ Air & \(\sim\)15 \(\times\) 15 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimental FWHM of lateral microbeam profiles measured after traversing 2 mm in different atmospheres. assembled on the top of the detector case. The entrance window (8 \(\upmu\)m thick in beryllium) was located at about 20 mm from the measuring point. Despite the collimation and the quite large distance between tubes and target, the X-ray rate on the detector was satisfactory with current values around 0.3 mA, thanks to the limited target-detector distance. Furthermore, a continuous helium flow in front of the tubes and the detector enhanced the production and detection of low-energy X-rays. The angle between the tubes was reduced as much as possible, to minimise the difference of the two irradiated volumes. During the measurements, the positioning of the measuring head was obtained through the superposition, on the target surface, of the spots of two appropriately aimed lasers. The measuring area was continuously monitored through a camera. The instrument is presented in Figure 4.  
Among the many applications, see for example [50; 51]. This instrument was also successfully employed for the discrimination between polishing methods of Japanese swords, or \"katanas\". Katanas have the high features of hardness and elasticity of steel and require a long polishing process traditionally carried out with a layer of clay mixed with charcoal after forging. Polishing of the blade can be repeated for maintenance during their life. A fast method to visually imitate a traditional polishing process is to use an acid bath to mimic the aspect of the undamaged blade but, in spite of a good appearance, the martensitic structure of the sword becomes severely damaged. It is worth noting that on the market their price can vary from a few k\(\epsilon\) for a damaged blade to tens of k\(\epsilon\) for a well-preserved one. Thus, a doable way to analytically distinguish the two methods is to detect silicon traces left by the stone-based traditional polishing method. For the study, a set of katanas, both damaged and well-conserved, from the Stibbert Museum of Florence, were analysed, exploiting the XRF spectrometer.