High resolution radiography of ambers with pixel detectors

Radiography serves as a powerful non-destructive technique for studying inner structure of biological samples and materials. In the last years X-ray imaging has taken advantage of the developments in instrumentation such as table-top micro-focus X-ray tubes and quantum counting pixel detectors. The imaging setups used for our measurements allow for the observation of tiny samples including fossils in amber. The main goal of the study was to apply microradiography as representative of non-destructive and non-invasive methods for imaging fossils in amber. Those fossils are generally not easy to visualize, especially their internal structures. We investigated a combination of sources and detectors: (a) an X-ray unit for mammography with tungsten anode, emissive spot of 100 μm and an amorphous selenium imager; (b) a micro-focus X-ray tube with tungsten anode, emissive spot of 5 μm and a flat panel imager; (c) a nano-focus X-ray tube with tungsten anode, with gauge of emissive spot of 1 μm and as imager the pixel semiconductor detector Medipix2. The study of fossils in amber can be for example not well visible because of the presence of organic detritus from various sources. The amber preserves various ancient biological objects which are fully or partly saturated with amber resin. These samples attenuate X-rays similarly, but the use of pixel detectors enables capturing these differences, without permanent destruction of the samples (cracking, slicing, etc.). Microradiographic studies are completed by the observation of amber fossils in scanning and transmission electron microscopes.