Angle resolved-XRF: analysis of layers in cultural heritage related samples

The field of Cultural Heritage (CH) comprises many rare, valuable, and fragile samples and for this very reason non-invasive and non-destructive techniques are the most preferred to their analysis. Among these techniques, XRF allows to perform a fast elemental characterization of the artifacts, detecting a high range of elements (from Al to U in air). XRF allows also to perform quantitative analysis, which is more feasible and reliable if the samples are of infinite thickness for the considered radiation, homogenous and flat. Unfortunately, many samples related to the field of CH are inhomogeneous, and they often present a layered structured. Indeed, they may have been created as a series of layer (like painting, surface-decorated ceramics, or gilded metals) or their surface may have been alteredby crust or patinas formation over the surface. In these cases, it can be useful to characterize the composition and the thickness of each layer, as to support inferences on the materials and technology employed to produce the layers, or on the alteration process behind the presence of the crusts. The characterization of the layered structure can be performed by means of data analysis, like the calculation Ka/Kb La/Lb ratio, or the use of Monte Carlo simulations; by employing lenses to select the volume of analysis (Confocal XRF); or by developing a proper experimental set-up: for nanolayers it is possible to use grazing emission or grazing incident XRF, while for thicker layer angle resolved XRF (AR-XRF) can be performed. AR-XRF is an experimental set-up in which the sample is analyzed at different angles (of irradiation or detection or both); the intensity of the elements’ characteristic lines changes accordingly the pathlength crossed by the source radiation and by the fluorescence radiation, which is changed during the experiment. The presence of different elements in different layers can be inferred by the intensity profiles obtained from the angular scanning. In this work we have applied AR-XRF to the analysis of different layered samples related to the field of CH. The analyses have been performed with the multipurpose XRF spectrometer of the Nuclear Science and Instrumentation Laboratories (NSIL) laboratories of the International Atomic Energy Agency (IAEA), (Seibersdorf, Austria) rotating the sample (thus changing the angle of irradiation and detection) within a range from -5° to 45°. The study involved two types of samples: in a first attempt we tested the method on gilded samples prepared for this purpose in the laboratory; in a second attempt, instead, we analyzed Mexican and Italian glazed ceramic samples, made with different technologies.