XRF imaging spectrometry is a powerful tool for materials characterization. A high spatial resolution is often required, in order to appreciate very tiny details of the studied object. With respect to simple pinholes, polycapillary optics allows much more intense fluxes to be achieved. This is fundamental to detect elements in trace and to strongly reduce the global acquisition time that is actually among the main reasons, in addition to radioprotection issues, affecting the competitiveness of XRF imaging with respect to other faster imaging techniques such as multispectral imaging. Unlike other well-known X-ray optics, principally employed for high brilliant radiation source such as synchrotron facilities, polyCO can be efficiently coupled also with conventional X-ray tubes. All these aspects make them the most suitable choice to realize portable, safe and high performing μXRF spectrometers.
In this work preliminary results achieved with a novel 2D and 3D XRF facility, called Rainbow X-Ray (RXR), are reported, with particular attention to the spatial resolution achieved. RXR is based on the confocal arrangement of three polycapillary lenses, one focusing the primary beam and the other two capturing the fluorescence signal. The detection system is split in two couples of lens-detector in order to cover a wider energy range. The entire device is a laboratory user-friendly facility and, though it allows measurements on medium-size objects, its dimensions do not preclude it to be transported for in situ analysis on request, thanks also to a properly shielded cabinet.
Polycapillary lenses are well known optical devices for radiation and charged particles. These lenses consist of thousands channels through which the signal is transmitted by total external reflection phenomenon. Their application have made possible technical improvements in different fields such as imaging, fluorescence analysis, channeling studies etc. In particular, the application of this optics coupled with conventional sources such as X-ray tubes has opened a new season for potential applications of desktop instrumentations. For instance, the usage of such lenses has enhanced the spatial coherence and the brilliance over the sample allowing better resolution and contrast for imaging purposes. In addiction, improved focusing power and confocal configuration of other lenses has improved the resolution, from both the energy and the spatial points of view, in fluorescence mapping.
A recent work has addressed the behavior of the transmitted radiation through a single capillary in vibrating regime. In this work a test of using a vibrating capillary for stroboscopic imaging is presented. A sample characterized by a known periodic event is studied with a synchronized vibrating capillary.
The study of transient high pressure fuel sprays by X-ray based techniques is worldwide diffused. Synchrotron radiation is successfully exploited for this aim because of its high intensity and pulsed nature. However top-table application are unusual. This work reports the structure of a gasoline spray from an automotive GDI injection system obtained by X-ray Tomography desktop experiments using an 8 keV Cu Kα X-ray. Polycapillary semilens shaped the divergent X-ray beam into quasi-parallel one allowing to focus the radiation on the investigated spray region. High contrast focus images were collected by a CCD detector for X-radiation. A 6-hole GDI injector has been coupled to the high pressure pump by a specially designed rotating device able to work up to 25MPa. X-ray absorption measurements have been performed with angular steps Δθ = 1° at the injection pressure of 12.0 MPa. The sinogram reconstruction of the jets by slices permitted to get information about the inner structure of the fuel spray downstream the nozzle tip, where conventional optical techniques are inhibited. A 3D spatial distribution of the fuel emerging from the injector has been obtained. The data have been used to perform spray density measurements. The results concerning the absorption profile along the fuel jets axis and the cross section distribution at different distances from the nozzle have been reported.