A multimodal X-ray microscope and micro-CT
A team comprising Australian, German and Slovak researchers has combined different microscopy modalities together into a single instrument, using a lab-sized X-ray source as opposed to resorting to synchrotron radiation. Their research has been published in the journal Optics Express.
At the heart of the system is a Rigaku FRE+ rotating anode X-ray generator high-brightness X-ray source. Out of the box, the FRE+ has a focal spot size in the order of 80 to 100 µm and is not generally suited to imaging applications. However, the colleagues designed a novel optics system that magnifies the X-ray beam, causing it to act as an X-ray zoom lens and resulting in an increase in resolution. While the optic is somewhat complex, it actually adds an additional level of flexibility to the system.
The optic itself consists of two channel-cut crystals in asymmetric diffraction. This produces an X-ray beam that is magnified by 15x and highly collimated, making it suitable for high-resolution imaging. Due to the Rigaku FRE+, the system is suited to imaging weak, radiation-sensitive samples. The Bragg magnifier optic is able to generate quantitative data for analyses such as:
- microstructure determination;
- 3D computed tomography or micro-CT;
- small-angle scattering directionality.
It performs these functions due to its sensitivity to X-ray attenuation and refraction, as well as X-ray scattering. Due to the fact that the Bragg Magnifier requires an intense X-ray beam to perform, a sealed tube type X-ray source is simply not powerful enough, nor is it able to generate high enough sensitivity.
The system is also able to operate as a multimodal X-ray microscope. In this guise it can image in both bright-field and dark-field modes, which would not be possible using a sealed tube X-ray source. This imaging mode is somewhat similar to an optical microscope and is capable of revealing high levels of detail due to the large variations in contrast that it can produce.
The novel optic developed by the researchers has been able to extend the imaging capabilities of a high-intensity X-ray source like the Rigaku FRE+, with a large focal spot to create a high-resolution X-ray microscope and micro-CT. The high-flux rotating anode X-ray source is key to the system, with sealed tube X-ray sources not able to produce sufficient X-ray flux to efficiently use innovative optics to image specimens.
The new experimental set-up is said to bring synchrotron micro-imaging capabilities within the reach of laboratory researchers.
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