Characterization of short-pulse laser-produced bremsstrahlung spectrum using x-ray radiograph images of mm-diameter metal rods

Determination of an object density via bremsstrahlung x-ray radiography requires understanding of accurate broadband x-ray spectrum. To characterize laser-produced bremsstrahlung and demonstrate bremsstrahlung x-ray radiography of mm-diameter Al rods, we carried out an experiment using a 50TW Leopard laser at the UNR's Nevada Terawatt Facility. Angularly resolved bremsstrahlung was determined by comparing measured x-ray signals from a silver foil with hybrid particle-in-cell simulations. Transmission of the Al rods from the radiograph images is further simulated with a Monte Carlo code. The measured transmission profiles with three different diameters agree with calculations when a simulated x-ray spectrum composed of line emissions and bremsstrahlung is used with a source size of 600 \textpm 200 $\mu $m. Transmission calculations with only 22 keV Ag K$\alpha $ or an exponential x-ray spectrum do not reproduce the measurement. This work suggests that the accurate modeling of the x-ray source spectrum as well as the photon sensitivity of the detector is critical in transmission calculation to infer the density of an object.