A team of researchers from Germany and Switzerland has developed a new type of X-ray detector that can achieve a magnification factor of 40 and a spatial resolution of 2.4 μm. The detector is based on capillary optics, which use hollow glass tubes to guide and focus X-rays by total external reflection. The detector can be used for full-field imaging of biological samples, materials science, and cultural heritage objects.
Capillary optics for X-rays
Capillary optics are a relatively new technology for manipulating X-ray beams. They consist of arrays of thin glass tubes with diameters ranging from a few micrometers to a few millimeters. The tubes are arranged in various shapes, such as lenses, collimators, or concentrators, depending on the desired beam profile. When X-rays enter the tubes at grazing angles, they are reflected multiple times by the inner walls until they exit at the other end. This way, the X-rays can be focused, deflected, or filtered by the capillary optics.
Capillary optics have several advantages over conventional X-ray optics, such as crystals, mirrors, or gratings. They are cheaper, easier to fabricate, more robust, and more flexible. They can also handle a wide range of X-ray energies and wavelengths, and can produce large fields of view with high flux and low divergence.
Full-field X-ray detector with capillary optics
The new X-ray detector developed by the researchers combines a capillary optic lens with a pnCCD chip, which is a type of charge-coupled device (CCD) that can detect single photons and measure their energy. The capillary optic lens consists of 19 hexagonal bundles of glass tubes with an outer diameter of 1 mm and an inner diameter of 0.8 mm. The lens has a focal length of 50 mm and a numerical aperture of 0.01. The pnCCD chip has an active area of 12.7 x 12.7 mm^2 and a pixel size of 75 x 75 μm^2.
The detector works by placing the sample at the focal plane of the capillary optic lens and illuminating it with a polychromatic X-ray source. The lens collects and magnifies the transmitted X-rays by a factor of 40 and projects them onto the pnCCD chip. The chip records the position and energy of each photon, creating an image with high spatial resolution and spectral information.
The researchers tested the performance of the detector by imaging various samples, such as a human tooth, a bee wing, a microchip, and a painting fragment. They demonstrated that the detector can resolve features as small as 2.4 μm and can distinguish different elements and materials by their characteristic X-ray absorption spectra. They also showed that the detector can operate in different modes, such as bright-field, dark-field, or phase-contrast imaging, by changing the alignment of the capillary optic lens and the pnCCD chip.
Potential applications and future developments
The researchers believe that their new X-ray detector has many potential applications in various fields that require high-resolution and high-contrast imaging of complex structures and compositions. For example, in biology and medicine, the detector could be used to study cellular structures, tissues, organs, or diseases. In materials science and engineering, the detector could be used to investigate microstructures, defects, stresses, or strains. In cultural heritage and art conservation, the detector could be used to reveal hidden details, pigments, or techniques.
The researchers also plan to further improve the performance and versatility of their detector by optimizing the design and fabrication of the capillary optic lens, increasing the size and sensitivity of the pnCCD chip, and developing software tools for image processing and analysis.
The results of their study were published in the journal X-Ray Spectrometry.
