Macro and micro full field x-ray fluorescence with an X-ray pinhole camera presenting high energy and high spatial resolution.

This work describes a tabletop (50 cm × 25 cm × 25 cm) full field X-ray pinhole camera (FF-XPC) presenting high energy- and high spatial-resolution. The FF-XPC consists of a conventional charge-coupled device (CCD) detector coupled, in a coaxial geometry, to a pinhole collimator of small diameter. The X-ray fluorescence (XRF) is induced on the samples with an external low-power X-ray tube. The use of the CCD as an energy dispersive X-ray detector was obtained by adopting a multi-image acquisition in single photon counting and by developing a processing algorithm to be applied in real-time to each of the acquired image-frames. This approach allowed the measurement of X-ray spectra with an energy resolution down to 133 eV at the reference value of 5.9 keV. The detection of the X-ray fluorescence through the pinhole-collimator allowed the two-dimensional elemental mapping of the irradiated samples. Two magnifications (M), determined by the relative sample-pinhole-CCD distances, are used in the present setup. A low value of M (equal to 0.35×) allows the macro-FF-XRF of large area samples (up to 4 × 4 cm(2)) with a spatial resolution down to 140 µm; a large magnification (M equal to 6×) is used for the micro-FF-XRF of small area samples (2.5 × 2.5 mm(2)) with a spatial resolution down to 30 µm.

In-air broad beam ionoluminescence microscopy as a tool for rocks and stone artworks characterisation.

Broad beam ionoluminescence (IL) microscopy is a promising technique for the non-destructive characterisation of rocks and stone objects. Luminescence imaging by means of broad ion beams has been sporadically used by other authors but, to our knowledge, its potential has not yet been fully investigated, neither in geological science nor in other fields. The in-air broad beam IL microscope was developed and installed at the INFN-LABEC external microbeam in Florence. Similar to the cathodoluminescence (CL) microscope, the apparatus exploits a CCD colour camera collecting images (few square millimetres wide, with ~10-µm spatial resolution) of the luminescence emitted by the sample hit by a defocused megaelectron volt (MeV) proton beam. The main differences with the well-established and widespread CL are the possibility of working in air (no sampling or conductive coatings required) and the possibility of combining the analysis with microbeam analysis, such as, for example, µ-IL and µ-PIXE (particle-induced X-ray emission). To show the potential of the technique, IL images of thin sections of lapis lazuli are compared with those obtained by means of an in-vacuum cold CL. An application to the study of stone artworks is also reported. This technique and apparatus will provide a valuable help for interdisciplinary applications, e.g. in geological sciences and in the cultural heritage field.

Multitechnique characterization of lapis lazuli for provenance study.

Lapis lazuli is one of the oldest precious stone, being used for glyptic as early as 7,000 years ago: jewels, amulets, seals, and inlays are examples of objects produced using this material. Only a few sources of lapis lazuli exist in the world due to the low probability of geological conditions in which it can form, so that the possibility to associate the raw material to man-made objects helps to reconstruct trade routes. Since art objects produced using lapis lazuli are valuable, only nondestructive investigations can be carried out to identify the provenance of the raw materials. Ionoluminescence (IL) is a good candidate for this task. Similar to cathodoluminescence (CL), IL consists in the collection of luminescence spectra induced by megaelectronvolt ion (usually protons) irradiation. The main advantage of IL consists in the possibility of working in air while measuring simultaneously the composition of major and trace elements by means of complementary ion beam analysis techniques like particle-induced X-ray emission (PIXE) or particle-induced gamma-ray emission (PIGE). In the present work, a systematic study of the luminescence properties of lapis lazuli under charged particle irradiation is reported. In the first phase, a multitechnique approach was adopted (CL, scanning electron microscopy with microanalysis, micro-Raman) to characterize luminescent minerals. This characterization was propaedeutic for IL/PIXE/PIGE measurements carried out on significant areas selected on the basis of results obtained previously. Criteria to identify provenance of lapis lazuli from four of the main sources (Afghanistan, Pamir Mountains in Tajikistan, Chile, and Siberia) were proposed.