Giorgio Cappuccio

X-ray propagation through hollow channel: PolyCAD – a ray tracing code

Abstract “PolyCAD”, a CAD program designed for X-ray photon tracing in polycapillary optics, is described. To understand the PolyCAD code and its results, the theoretical bases of X-ray transmission by a single cylindrical channel (monocapillary) are discussed first. Then cases of cylindrical, lens and semi-lens shaped polycapillary optics are examined. PolyCAD allows any type of X-ray source to be used: an X-ray tube of finite beam dimensions or an astrophysical object can be simulated in combination with the polycapillary optics. The radiation density distribution images formed on a screen located at various focal distances are discussed. The good agreement of the PolyCAD results with experimental and previous theoretical calculations validate the code.

On propagation of X-rays in capillary channels

In the last years several coherent phenomena associated with propagation of soft X-ray radiation through capillary optical elements (polycapillary lenses and systems of capillaries) have been observed and investigated. Unexpected effects produced by soft X-radiation traveling inside assembled capillary systems may be explained in the framework of surface wave propagation theory. In this paper theoretical analysis on dependence of the transmission characteristics on capillary wall surface is presented.

Capillary optics as an x-ray condensing lens: an alignment procedure

The procedure of capillary lens alignment is described in detail. The theoretical basis of capillary optics is given in the framework of a comparative analysis of monocapillary and polycapillary optics. The results of x-ray distribution scanning behind the capillary lens for various angle planes, together with the fitting results, are presented. A qualitative explanation is given for the discrepancy between the expected and observed divergences of x-ray beams transmitted by the capillary lens.

Alignment procedure and divergence behavior in capillary optics: first results with x-ray tubes and synchrotron radiation

Due to the low value of the critical angle, the main problem is using a polycapillary lens is to position it correctly with respect to the x-ray source. We have developed a recursive procedure for fast and precise alignment by means of a four-circle diffractometer and a Cu x-ray tube. After the alignment we observed the focusing effect on a fluorescent target and measured an increase of about 30 in the local density of the x-ray beam. During the experiments a sharp decrease in the beam divergence behind the capillary structures was also detected. This unexplained fact, already mentioned in the past by several reserachers, was explained for the first time by our group in the framework of the wave scattering theory. The same alignment procedure was successfully repeated using synchrotron radiation at the Elettra storgae ring at Trieste. The focal spot position was evaluated by a set of photo images. In the same experiment we also tested and evaluated the operating characteristics of a straight polycapillary lens.

Divergence of x-ray beams transmitted by capillary structures

The study of transmitting and focusing properties of capillary optical systems shows that a number of unexpected effects takes place during the experiments. One of those effects is a decrease of the beam divergence behind capillary structures. In this report we have considered an alignment procedure for capillary optics samples and presented the result on scattering of x rays at grazing angles. Decrease in beam divergence behind capillary systems is explained by use of the wave scattering theory for description of x-ray propagation.

2D and 3D micro-XRF based on polycapillary optics at XLab Frascati

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.

X-ray microfocusing by polycapillary optics

In this work the results on X-ray micro-imaging by means of novel polycapillary optical elements will be presented. To simulate various radiation propagation processes in both single capillary and polycapillary systems, a PolyCAD code was developed. Many experiments have recently revealed the advantage of confocal optical configuration for the fluorescence studies. Moreover, our experimental prototype layout (developped in the INFN - LNF laboratories, Frascati) enables the possibility to obtain μXRF mapping in simultaneous with X-Imaging. The recorded image of an extended sample is limited to 6 μm by the CCD pixel dimensions; the use of a second polycapillary optics in the confocal scheme followed by a SDD detector provides an additional option for elemental studies. A prototype of compact XRF spectrometer with a spatial resolution less than 100 μm has been designed.