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Introduction: X-ray computed tomography (CT) is now used in the cultural heritage field because it is non-invasive and it can give a large amount of information on the inner structure of the object under study. Until recently mainly medical CT scanners or micro-CT setups have been used, limiting the analysis to relatively small artworks or requiring multiple acquisition and difficult image-joining for objects larger than detector dimensions.

X-ray fluorescence (XRF) analysis is one of the most widely used techniques for material analysis in the field of cultural heritage, thanks to its non-destructive and multi-elemental character and also to the possibility of using portable instrumentations. The need of compact systems for in situ analyses results generally in a worse, more limited performance: the detection of low-Z elements is the most affected aspect. In this article, we present a custom-realised portable XRF spectrometer developed in Florence at the LABEC laboratory of Istituto Nazionale di Fisica Nucleare (INFN), in collaboration with ICVBC of Consiglio Nazionale delle Ricerche (CNR). The system features a high efficiency for a wide range of elements, even at low Z (down to sodium), thanks to the use of two tubes with different anodes and to the presence of a continuous helium flow in front of the tubes and the detector, in order to enhance transmission of both primary and characteristic X-rays. After a detailed description of the spectrometer, the experimental characterisation of its performance is presented: efficiency curves obtained from the analysis of thin standards are reported, together with minimum detection limits for some elements in a thick target of medium-low density matrix. Examples of measurements, which demonstrate the capability and effectiveness of this spectrometer, are also reported.

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A multifrequency electron paramagnetic resonance, EPR, study has been carried out on TiO 2 nanocrystals (NCs) capped by organic moieties prepared according to both a nonhydrolytic and a hydrolytic procedure, respectively, with spherical or rodlike shape. In particular, EPR measurements have been performed in the 9-95 GHz range, at various temperatures, and with and without UV irradiation. The behavior of the electrons promoted in the conduction band by UV irradiation and of the holes in the valence band has been monitored by means of the generated paramagnetic species that are detectable by EPR, thus enabling the identification of the different sites at which the charges are trapped. In particular, an EPR signal which can be considered a mark of the localization of the photoinduced charge on a carbon of the capping molecule is observed. The presence of paramagnetic species on the surfaces of TiO 2 NCs has been used to account for the catalytic performance of such a class of nanostructured material which has been recently proven to present a high catalytic efficiency. The observed carbon radical is suggested to be responsible for the higher catalytic activity of organic capped nanosized catalysts. Indeed, upon irradiation, the intensity of this signal with respect to the bulk Ti 3+ signal is larger in the NCs characterized by higher photocatalytic activity; namely, those prepared with a hydrolytic procedure.

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