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 ≈4–23 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 (RuCl₃$H₂O; ruthenium chloride). To clearly observe the image of the contrast agent, the photon energy was chosen to be 23.17 keV (Cd Kα) 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 Kα) 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 ≈10 mm. In this experiment, the X-ray energy was adjusted to 4.51 keV (Ti Kα) 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 ≈20 mm. Performance of the above technique based on the proton-induced quasi-monochromatic X-ray emission is discussed in comparison to conventional methods.

Key words:

• Radiography
• K-absorption edge
• Particle-induced X-ray emission
• Characteristic X-ray
• Proton microbeam
• Electrostatic accelerator