# External Beam IBA Measurements for Cultural Heritage
## 4 Pige
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Element** & **Reaction** & **Gamma-Ray Energy (keV)** & **Isotopic Abundance** \\ \hline Li & \({}^{7}\)Li(p,p’v)\({}^{7}\)Li & 478 & 92.4\% \\ \hline Be & \({}^{9}\)Be(p,\(\alpha\)v)\({}^{6}\)Li & 3562 & 100\% \\ \hline B & \({}^{10}\)B(p,\(\alpha\)v)\({}^{7}\)Be & 429 & 19.9\% \\ \hline F & \({}^{19}\)F(p,p’v)\({}^{19}\)F & 110 & 100\% \\  & \({}^{19}\)F(p,p’v)\({}^{19}\)F & 197 & 100\% \\ \hline Na & \({}^{23}\)Na(p,p’v)\({}^{23}\)Na & 441 & 100\% \\ \hline Mg & \({}^{25}\)Mg(p,p’v)\({}^{25}\)Mg & 585 & 10.13\% \\ \hline Al & \({}^{27}\)Al(p,p’v)\({}^{27}\)Al & 843 & 100\% \\  & \({}^{27}\)Al(p,p’v)\({}^{27}\)Al & 1013 & 100\% \\ \hline Si & \({}^{28}\)Si(p,p’v)\({}^{28}\)Si & 1779 & 92.23\% \\  & \({}^{29}\)Si(p,p’v)\({}^{29}\)Si & 1273 & 4.67\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main PIGE reactions induced by protons of interest for elemental analysis in cultural heritage. Figure 4: FIGE spectrum of a topaz obtained with 3 MeV protons, showing gamma-ray lines of F, Na, Al, Mg, and Si. The spectrum is normalised by the proton beam charge accumulated during the measurement. quantification of sodium in ancient glasses [33; 34]. Lapis lazuli is a blue pigment mainly composed of lazurite (3 Na\({}_{2}\)O-3 Al\({}_{2}\)O\({}_{3}\)-6 SiO\({}_{2}\) 2 Na\({}_{2}\)S). It was used since the Middle Ages in different painting techniques, and it was considered a very precious and expensive pigment. PIGE can be used to identify lapis lazuli in pigment layers using its Na component as a tracer by simply detecting the 441 keV gamma ray from the \({}^{23}\)Na(p,p'\(\gamma\))\({}^{23}\)Na reaction. On the contrary, PIXE is severely hampered in the possibility of identifying lapis lazuli in canvas and wood paintings, since the low energy X-rays emitted by the lighter characteristic elements (not only Na, but also Al and Si) are absorbed in the protective varnish layer and within the paint layer itself, especially when lapis lazuli is mixed with another a high-Z pigment, such as lead white. Moreover, in this case, the X-rays emitted by the highest Z element of lazurite (S), less affected by the aforementioned absorption problems, might be difficult to identify due to the overlap of Pb and S X-ray lines, even with the good energy resolution of SDDs. Detection and quantification of Na is crucial also in ancient glass studies to distinguish, for instance, the natron glass of the Roman times (with high Na\({}_{2}\)O, and low K\({}_{2}\)O and MgO content) from later glass such as plant ash glass (with low Na\({}_{2}\)O and high K\({}_{2}\)O content), used since the Middle Ages. Unfortunately, a PIXE analysis could be completely blind to the presence of Na in the bulk of a sample, since the surface altered and corroded layers may strongly absorb the X-rays from the lightest elements (the 1 keV X-rays of Na are absorbed in the first few microns from the surface). A complementary use of PIXE and PIGE is particularly effective to address this problem: the PIGE analysis of Na, based on the integrated yield of the 441 keV gamma ray, refers to a much larger depth, since gamma rays are detected with negligible attenuation regardless of the depth from where they were originated. It is thus possible to immediately distinguish between surface and bulk Na composition from PIXE and PIGE measurements, respectively.