The external PIXE setup for the analysis of manuscripts at the Florence University

Abstract

The external beam PIXE setup of the 3 MV Van de Graaff accelerator in Florence is extensively used for the analysis of parchments, rulings, inks and miniature temperas of Medieval and Renaissance manuscripts. The beam is collimated to about 200 μm and exits from the vacuum environment through a 8 μm Kapton window. Beam currents from 200 to 500 pA are used; they have been found to produce no visible damage to the examined materials. Two Si(Li) detectors are simultaneously used with different geometries in order to cover the widest possible Z-range of the detected elements: even Na is detected with good sensitivity. A robust and versatile support has been constructed for safe and easy handling of the manuscripts. A laser alignment system allows accurate aiming at the detail of interest. A rotating chopper samples the beam at a frequency of the order of 1 Hz; X-rays produced on a Ni layer evaporated on the graphite vane of the chopper are used for charge normalization, since the weak current pulses would be unreliably measured in air due, in particular, to space-charge effects. An application is shortly presented, concerning the materials used for the “colour” rulings which are found, starting from the 11th century, to delimit the writing field for the copyist.