Broadband, monochromatic and quasi-monochromatic x-ray propagation in multi-Z media for imaging and diagnostics

With the advent of monochromatic and quasi-monochromatic x-ray sources, we explore their potential with computational and experimental studies on propagation through a combination of low and high-Z (atomic number) media for applications to imaging and detection. The multi-purpose code GEANT4 and a new code PHOTX are employed in numerical simulations, and a variety of x-ray sources are considered: conventional broadband devices with well-known spectra, quasi-monochromatic laser driven sources, and monochromatic synchrotron x-rays. Phantom samples consisting of layers of low-Z and high-Z material are utilized, with atomic-molecular species ranging from H₂O to gold. Differential and total attenuation of x-ray fluxes from the different x-ray sources are illustrated through simulated x-ray images. Main conclusions of this study are: I. It is shown that a 65 keV Gaussian quasi-monochromatic source is capable of better contrast with less radiation exposure than a common 120 kV broadband simulator. II. A quantitative measure is defined and computed as a metric to compare the efficacy of any two x-ray sources, as a function of concentration of high-Z moieties in predominantly low-Z environment and depth of penetration. III. Characteristic spectral features of $K\alpha$, $K\beta$ fluorescent emission and Compton scattering indicate pathways for accelerating x-ray photoexcitation and absorption; in particular, we model the tungsten $K\alpha$ at 59 keV alongside experimental measurements at the European synchrotron research facility to search for the signature of induced $K\alpha$ resonance fluorescence. The present study should contribute to the understanding of diagnostic potential of new x-ray sources under development, as well as the underlying fundamental physical processes and features for biomedical applications. (paper)