The generation of x-ray beams in the energy range from keV to MeV is an active research area, essential to the study of high-energy-density matter, to improve the understanding of inertial confinement fusion and astrophysical systems. An ultrabroad-band x-ray source, with photon energies from 10 keV to >1 MeV, based on a picosecond laser-driven plasma accelerator, is characterized and used to radiograph a gold half hohlraum with a high-density sphere inside with relevant characteristics for high-energy-density science and inertial confinement fusion.