Claudia Caliri

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.

Real-time elemental imaging of large dimension paintings with a novel mobile macro X-ray fluorescence (MA-XRF) scanning technique

A novel mobile macro-XRF (MA-XRF) scanning technique allowing real-time elemental imaging is presented for the investigation of macroscopic paintings. The instrument is based on a microfocus X-ray tube focused with a polycapillary and two SDD detectors operated simultaneously in a time-list event mode. The scanner is based on a three-axis system covering a dimension of 110 × 70 × 20 cm3. MA-XRF scanning is generally performed by positioning samples out of the polycapillary focus with the primary X-ray beam presenting a spot size in the range of hundreds of microns. However, a lateral resolution of up to 25 μm can be achieved at the focus position, allowing complementary use of the scanner for both micro-XRF and macro-XRF mapping. Scanning of artworks is performed with a maximum continuous speed of 100 mm s−1. The full area is covered in 4.3 h in the case of final images presenting a 500 μm pixel size (i.e., corresponding to a dwell time per pixel of 5 ms). The system is controlled with a custom developed control unit (CU) including a graphical user interface (GUI) programmed in Labview for real-time control of all sensors in the scanner and for real-time elaboration of X-ray data. X-ray spectra are processed during the scanning by the least square fast fitting procedure developed in PyMCa and integrated in the system. Up to 7000 fitted spectra per second are possible. A number of editing, processing and mathematical tools are available to users in the GUI and can be applied in a live mode to the forming elemental images. The sum spectrum and maximum pixel spectrum are continuously updated. Final images are available at the end of the scanning and, in most of the cases, they are ready for the interpretation.

X-ray spectroscopy of warm and hot electron components in the CAPRICE source plasma at EIS testbench at GSI.

An experimental campaign aiming to detect X radiation emitted by the plasma of the CAPRICE source - operating at GSI, Darmstadt - has been carried out. Two different detectors (a SDD - Silicon Drift Detector and a HpGe - hyper-pure Germanium detector) have been used to characterize the warm (2-30 keV) and hot (30-500 keV) electrons in the plasma, collecting the emission intensity and the energy spectra for different pumping wave frequencies and then correlating them with the CSD of the extracted beam measured by means of a bending magnet. A plasma emissivity model has been used to extract the plasma density along the cone of sight of the SDD and HpGe detectors, which have been placed beyond specific collimators developed on purpose. Results show that the tuning of the pumping frequency considerably modifies the plasma density especially in the warm electron population domain, which is the component responsible for ionization processes: a strong variation of the plasma density near axis region has been detected. Potential correlations with the charge state distribution in the plasma are explored.

X-ray pinhole camera setups used in the Atomki ECR Laboratory for plasma diagnostics

Imaging of the electron cyclotron resonance (ECR) plasmas by using CCD camera in combination with a pinhole is a non-destructive diagnostics method to record the strongly inhomogeneous spatial density distribution of the X-ray emitted by the plasma and by the chamber walls. This method can provide information on the location of the collisions between warm electrons and multiple charged ions/atoms, opening the possibility to investigate the direct effect of the ion source tuning parameters to the plasma structure. The first successful experiment with a pinhole X-ray camera was carried out in the Atomki ECR Laboratory more than 10 years ago. The goal of that experiment was to make the first ECR X-ray photos and to carry out simple studies on the effect of some setting parameters (magnetic field, extraction, disc voltage, gas mixing, etc.). Recently, intensive efforts were taken to investigate now the effect of different RF resonant modes to the plasma structure. Comparing to the 2002 experiment, this campaign used wider instrumental stock: CCD camera with a lead pinhole was placed at the injection side allowing X-ray imaging and beam extraction simultaneously. Additionally, Silicon Drift Detector (SDD) and High Purity Germanium (HPGe) detectors were installed to characterize the volumetric X-ray emission rate caused by the warm and hot electron domains. In this paper, detailed comparison study on the two X-ray camera and detector setups and also on the technical and scientific goals of the experiments is presented.

FF-XRF, XRD, and PIXE for the Nondestructive Investigation of Archaeological Pigments

This chapter discusses the integration of particle-induced X-ray emission (PIXE), full-field X-ray fluorescence (FF-XRF), and X-ray diffraction (XRD) for the analysis of archaeological pigments. It summarizes the research activity performed for developing these innovative, custom-built, and portable instruments. A novel analytical protocol has been developed by combining these techniques with the aim of performing an in situ quantitative characterization of painted materials. The potentiality of using this approach is demonstrated for manganese black used in archaeological pottery manufactured over time by different cultures.

EXPERIMENTAL CHARACTERIZATION OF AN OVERDENSE PLASMA IN A COMPACT ION SOURCE

Electron Cyclotron Resonance Ion Sources (ECRIS) are compact plasma-based machines able to feed particle accelerators with high intensity beams of multi-charged ions. ECRIS plasmas are density-limited, since they are sustained by E.M. wave propagation up to a cut-off density value. In the past, the only way to improve ECRIS performance was to increase the microwave frequency and the magnetic field strength to satisfy the ECR condition. A different plasma heating mechanism is being applied at INFN-LNS. It is based on Electron Bernstein Waves (EBW), i.e., electrostatic waves which do not suffer any density cut-off. Highlights concerning preliminary signatures of EBW formation and subsequent absorption are given here.