# The Role of PIXE and XRF in Heritage Science:
## 4 Technological Advance: The Micro-PIXE Technique at the INFN-LABEC
The magnetic deflector coils allowed, in principle, a maximum scanned area of several mm\({}^{2}\) for 3 MeV protons but was, however, limited by the exit window aperture (2 \(\times\) 2 mm\({}^{2}\), typically). Furthermore, the facility was developed for exploiting and combining the advantages of the two scanning modes, magnetic and mechanical. The magnetic scanning allowed for collecting elemental maps in times faster than the mechanical scanning but within an area limited to \(\sim\)1 \(\times\) 1 mm\({}^{2}\) by the beam exit window size, whereas the travel range of the motorised stages permitted the possibility to analyse an area on the sample surface up to 25 \(\times\) 25 mm\({}^{2}\). Depending on the case study and on the query, one or both systems could be used. The number of the beam particles impinging in each point was indirectly measured by counting the number of Si X-rays produced by the beam in the exit window and was used to normalise X-ray yield during measurements. As results from an extensive series of tests, for a given window, the emitted X-rays from the exit window to the collected charge ratio kept constant within 1%, varying the current of two orders of magnitude, from about 10 nA down to about 100 pA.  
A summary of the results of the beam profile characteristics, in air or in a helium atmosphere, is shown in Table 1. The effect of the width of the grid bar (10 \(\upmu\)m), used for the measurements, on the profiles is already taken into account [42]. Among the different applications, this beamline was used to analyse lapis lazuli [43; 44], a blue semi-precious stone used for more than 7000 years for carved jewels, decorative objects, as well for pigments. This study, besides increasing the knowledge on this blue rock, could shed light on many unresolved questions, especially regarding the trade routes exploited in ancient times. For those measurements, both \(\mu\)-PIXE and \(\mu\)-IBIL (micro-Ion Beam Luminescence) techniques were performed. They allow for analysing single crystals of different mineral phases, a fundamental aspect in a heterogeneous material as lapis lazuli, and they are non-invasive, a necessary feature since it is impossible to take samples from artworks. In this study, different markers were found and proposed to distinguish among the four possible provenances: Afghanistan (Badakhshan), Tajikistan (Pamir Mountains), Siberia (near Lake Baikal), and Chile (Ovalle) [45]. For example, the presence of diopside (CaMgSi\({}_{2}\)O\({}_{6}\)) or wollastonite (CaSiO\({}_{3}\)) was studied as a potential marker for the Chilean provenance. The presence of wollastonite, due to the double band at 560 and 620 nm, is a clear indication of the Chilean provenance, quickly distinguishable even only by means of luminescence with this set-up. Instead, diopside shows its main IBIL signal band at 585 nm. As an example of application, six objects of the _Collezione Medicea_ carved in lapis lazuli were studied in order to obtain some indications about the provenance of the raw material used for their execution [45]. The absence of wollastonite allowed excluding the Chilean provenance for all the lapis lazuli in these artworks, whereas diopside was detected. Moreover, \(\mu\)-PIXE results obtained for diopside crystals of these samples show that the titanium, vanadium, and chromium amount are comparable with that in the Afghan rock samples of certain provenance [46]. Further information about the micro-beam line at INFN-LABEC and additional results can be found in [47; 48].