Imaging by using proton-induced quasi-monochromatic X-ray emission

Abstract

Quasi-monochromatic X-ray emission induced by MeV-proton bombardment onto metallic targets was applied to radiography of small samples. The X-ray energy was adjusted in the range of z4-23 keV by changing the target material. The radiograms were recorded on an imaging plate. A small phantom made of Lucite was prepared for the test of photography using a contrast medium (RuCl 3 $H 2 O; ruthenium chloride). To clearly observe the image of the contrast agent, the photon energy was chosen to be 23.17 keV (Cd Ka) which is slightly above the K-absorption edge of Ru at 22.12 keV. Only the image of the contrast agent was successfully extracted by subtracting the image taken by 21.18-keV X-rays (Pd Ka) from that obtained by the 23.17-keV photons. Also images of a small fish sample were taken using a point-like X-ray source excited by a proton microbeam with a diameter of z10 mm. In this experiment, the X-ray energy was adjusted to 4.51 keV (Ti Ka) to obtain a strong attenuation by Ca in the bones. A fine structure of the bones in the thin caudal fin (!100 mm) was highly contrasted by this method. The spatial resolution of the picture was z20 mm. Performance of the above technique based on the proton-induced quasimonochromatic X-ray emission is discussed in comparison to conventional methods. q