A portable apparatus for energy-dispersive X-ray fluorescence analysis of sulfur and chlorine in frescoes and stone monuments

A simple and portable equipment was constructed, based on the energy dispersive X-ray fluorescence. It is composed of a small size X-ray tube, a thermoelectrically cooled Si-PIN detector, and a multi channel analyzer. The tube has a Pd anode, and works at 3-30 kV, 0.1 mA. At 3-5 kV, it emits Pd-L lines and bremsstrahlung radiation, and therefore is suited to the analysis of low atomic number elements, such as P, S, Cl. Working at 30 kV the tube emits Pd-K lines and bremsstrahlung radiation, and is able to excite medium atomic number elements up to tin (K-lines) and high atomic number elements (L-lines). The Si-PIN detector has a 25 mu m Be-window and energy resolution of about 190 eV at 5.9 keV. It has a thickness of about 300 mu m and thus an efficiency rapidly decreases at energies larger than about 20 keV. The equipment is completed by a portable multi channel analyzer. The described system was first tested in Laboratory and then employed to analyze mainly sulfur and chlorine in the follwoing frescoes and monuments: frescoes of Piero della Francesca (church of S. Francesco, Arezzo) frescoes of Domenichino (cathedral of Fano) Roman frescoes (church of S. Clemente, Rome) lapideous altars (church of S. Croce, Lecce).