A portable EDXRF apparatus for the analysis of sulphur and chlorine in frescoes and stony monuments

We describe a simple, portable apparatus, meant for the EDXRF analysis of sulphur and chlorine in frescoes and monuments. This instrument, which can be held in a small bag and is not more than a few kg in total weight, is composed of a small, dedicated X-ray tube, a thermoelectrically cooled Si-PIN detector and a pocket multi-channel analyser. The X-ray tube has a Ca or Pd anode. The Ca-K or Pd-L-lines are induced when the tube works at 10 or at 3-5 kV, respectively. Elements with higher atomic numbers may also be excited when the tube works at 30 kV. The apparatus was tested for determining the counts/concentration relationship and the minimum detection limit using calibration samples. Then it was employed to analyse sulphur and chlorine in various churches and monuments. Sulphur was found to be present in the frescoes of all churches. This was caused by pollution and was responsible for blackening of the frescoes surface. Our apparatus was also employed for checking the various types of restoration processes which have been employed to remove this pollution layer. The presence of chlorine was detected in the church of San Croce (Lecce).