Aplicación de la técnica PIXE (Particle Induced X-Ray Emision) a la caracterización no destructiva de una pieza de ajuar funerario (s. I d.C.) procedente de una excavación arqueológica (antiguo Hospital de las Cinco Llagas, Sevilla)

Abstract

In this work, a non-destructive characterization of a burial-sample object dated S.I. a.C. (ring with an incrusted material) coming from an archaeological excavation (former Hospital de las Cinco Llagas, Sevilla) has been carried out. The glass or ceramic nature of this sample was unknown. Several non-destructive techniques have been applied: optical microscopy, SEM-EDX, XRD and XRE In this particular case, the technique Particle Induced X-ray Emision (PIXE) has been also applied. PIXE allows to obtain a fast information concerning chemical composition of trace elements using the object directly. The study of this interesting object indicates the extreme quality and accurance of the engrave observed on its surface, for instance a long-legged bird and a palm leaf despite their reduced size. Relief effects have been observed in the engrave using the own constitution of this particular material. The XRD phase analysis demonstrates that crystalline quartz as single phase constitutes the incrusted material of the ring considered as a gem: blue quartz. The chemical composition obtained from XRF analysis confirm the XRD result, with Si and O as main elements, although there are minoritary elements such as Ca and Fe (< 1,5 %), Na and Al (ca. 0,3 %). Other elements, such as CI, K and P were detected in similar percentages (0.2-0,25 %), besides Mg and S (less than 0,08 %). However, the application of the PIXE technique based on ion beam analysis to this material allowed to demonstrate the presence of Ti and V, probably as ions in the quartz crystal structure which constitutes the gem. This experimental fact would then explain the blue colour observed in the gem. Consequently, PIXE as a non-destructive technique allows to find an important chemical difference between zones of the same object. There are some advantages, first of all that these chemical differences can not be accurately observed using other conventional techniques and secondly, the analysis is performed directly on the object, which is very interesting in studies on glass and ceramics samples of the Cultural Heritage.