Fast Electron Transport in Multilayer Targets

Here we briefly show how this novel imaging technique can be used to perform multi-energy X-ray imaging with a comparable spatial resolution. To this purpose, we will show some results obtained from laser irradiation of a target consisting of three metallic layers obtained from galvanic deposition of Cr and Ni on a Fe substrate. The first layer (laser side) was 1.2 pm thick Cr, the middle layer was a 10.9 pm thick Ni, and a third layer (on the rear side) was a 10 pm thick Fe. 

From the width of the lines we find that the spectral resolution ranges from about 3.5% at 5keV down to 2.5% at 8keV. This value of the resolution 

These plots show the projections on the (y, E) and (x, E) planes of the distribution of all the X-ray photons identified according to their position in the (x, y, E) space, that is, the energy resolved image of the source. Clearly visible in the plots are the contributions of the main fluorescence lines of each target layer. In most cases, the emission is centered at a common position (corresponding to the expected position of the source). In contrast, the emission around 900 ADC levels (corresponding approximately to 22.IkeV) 

Additional information concerning the fast electron distribution can be obtained in such experiments by direct measurement of forward escaping electrons using a calibrated stack of radiochromic films [52] that can provide information of the angular and energy distribution of fast electrons. These measurements were performed in the same experiment described above [31] and the summary of those measurements is reported in Fig. 7.10 and reveal a distribution that is consistent with a relativistic Maxwellian distribution with a characteristic temperature of 160keV. 

Such an experimental characterization is a necessary step to carry out a detailed comparison of emission properties as measured experimentally with the corresponding quantities as calculated by numerical models capable of describing transport and energy deposition of fast electrons in matter and consequent emission of characteristic X-ray emission. A possible modeling approach of fast electron transport experiments is given here, where the above results on Ka imaging were interpreted using the hybrid code PETRA [53] to 

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