Production of quasimonochromatic X-ray microbeams using MeV-protons and a polycapillary X-ray half lens

In this paper, we have proposed monochromatic X-ray microbeams, produced by a proton-induced X-ray technique and a polycapillary X-ray half lens, as a tool for micro-X-ray fluorescence (XRF) analysis. A 30 μm thick planar Cu target was irradiated by a 2.5 MeV proton beam to produce Cu Kα X-rays (8.0 keV), and a polycapillary X-ray half lens was utilized to focus the X-rays emitted behind the Cu target. The focal spot size of the focused X-ray beam was 250 μm at full width at half maximum, which was verified using a knife-edge scanning method. The output focal distance and the depth of focus of the optics were measured to be 47 mm and 1 mm, respectively. A square grid pattern of Co thin films, formed on a thick Cu substrate by thermal evaporation, was used as a test sample for evaluation of the analytical performance of the micro-XRF setup. Two-dimensional mapping of the Co distribution on the Cu substrate was successful, and the spatial resolution was consistent with the beam spot size. For this Co layer, a minimum detection limit of 2.3 ng was achieved.