Characteristics and parameter optimization of electron beam radiography

Abstract

The electron beam produced by an ultra-short, high-intensity laser pulse is of properties of small source size, short duration, and quasi-monoenergetic energy, and will play a unique role in radiographic diagnostics. By analyzing the scattering processes of electrons in materials and performing Monte-Carlo simulations, electron radiography for probing target surface non-uniformities or material interfaces is studied for electron energy ranging from 100 keV to several hundreds of MeV, and the results are compared with those of proton radiography and X-ray radiography, respectively. Features and parameter optimization of electron radiography are obtained, and some applications are suggested. By taking advantage of inelastic scattering or energy loss of charged particles, target surface nonuniformities could be diagnosed by a charged-particle beam whose range is close to the target thickness. Such a diagnosis would produce a higher detection contrast than that by absorption-type X-ray radiography. For a proton beam, a target thickness variation as small as 0.1% could be detected due to a more evident Bragg peak of the stopping power near its range. Nevertheless, the energy of laser-accelerated proton beams being up to 100 MeV would limit the applications. For an electron beam, since a thickness variation of 0.3% could be detected, its energy over 1 GeV has been realized by laser acceleration, the electron radiography could be extended to diagnose thicker targets. When using an electron beam to radiograph a thin or a foil target, for example, of thickness on the order of 100 μm, a spatial resolution of 11 μm or better could be achieved due to the reduced elastic scattering and angular deflection. By taking advantage of elastic scattering of electrons, an electron beam whose range is much greater than the target thickness could be used to diagnose a target interface composed of different materials or even a multilayered capsule, and a higher contrast of the electron fluence modulation at interfaces would be realized than that by absorption-type X-ray radiography, which is caused by stronger scattering of electrons as the electron scattering cross section is several orders of magnitude greater than that of X-ray scattering such as the Thomson scattering. As a laser-produced electron beam is prone to have an ultrafast pulse duration of 100’s of femtoseconds or less, it is anticipated that the electron radiography will produce an ultrasfast temporal resolution. These results and conclusions would be helpful to the applications and parameter optimization of electron radiography.