Imaging X-Ray Fluorescence Using Microchannel Plate (MCP) Optics

X-ray fluorescence imaging is a widely used, nondestructive method for determining the distribution and relative concentration of metals within a sample. To create a two-dimensional map of an image, x-rays are usually sent through a 25-250 μm wide aperture, then point by point an image is scanned. Microchannel plates contain an array of tiny holes that can be used to collimate x-rays fluorescing off a sample. When a microchannel plate is used as a collimator between a sample and detector, the sample can be uniformly illuminated and imaged onto a detector. This method allows many different metals to be detected within a sample and it reduces scan time from hours to minutes. The transmissions through a circular channel plate and square channel plate have been found to be 48% and 64% respectively. The transmission percentages are nearly equal to the open-air percentages. The square channel microchannel plate was able to resolve two copper wires fluorescing at 8.046 keV. In this image, the three component cruxiform predicted for an ideal square channel plate is seen. An image created from a 0.66 mm copper wire had a FWHM that was 20% larger than the theoretical value. The extra width is believed to be due to smearing through the channel walls. This experiment demonstrates that microchannel plates are capable of resolving images for x-ray fluorescence at energies as high as 8 keV.