X-ray computed tomography (XCT) is an established technique to investigate the 3D structure of materials and EESA scientists have used ALS µ-XCT beamline 8.3.2 to image Earth materials including rock cores from the subsurface, and soil (below) or roots from the critical zone. The development and validation of predictive models for subsurface science requires dynamic (time-lapse) observations under realistic conditions such as elevated stress and pressure. EGD researchers, Dr. Marco Voltolini and colleagues, have an international reputation for the design and construction of novel sample cells for geoscience, including triaxial compression cells capable of reaching 40 MPa and 400˚C.
Recently, EGD researchers in two DOE-funded programs (BES Geosciences and Nuclear Waste — Used Fuel Disposition) initiated a collaboration with the Advanced Light Source and with the University of Utah to construct a hard-X-ray microscope on ALS beamline 11.3.1 for time-lapse nanotomography studies of geologic and materials science samples under controlled stress, temperature and pressure. This instrument has recently been commissioned and is operational. First tests achieved 2D imaging to <30 nm resolution suggesting that 3D tomography with 50-nm resolution will be possible (limited by the mechanical stability of the rotation stage). This instrument will be operated separately from the ALS User Program and will enable an unprecedented opportunity to perform ambitious long-term studies of rock deformation and failure with full pore and grain resolution. A miniaturized uniaxial compression cell that permits fluid flow has been constructed and additional in situ cells are under development. A virtual view of the 11.3.1 beamline is given below.
Recently, EGD researchers in two DOE-funded programs (BES Geosciences and Nuclear Waste — Used Fuel Disposition) initiated a collaboration with the Advanced Light Source and with the University of Utah to construct a hard-X-ray microscope on ALS beamline 11.3.1 for time-lapse nanotomography studies of geologic and materials science samples under controlled stress, temperature and pressure. This instrument has recently been commissioned and is operational. First tests achieved 2D imaging to <30 nm resolution suggesting that 3D tomography with 50-nm resolution will be possible (limited by the mechanical stability of the rotation stage). This instrument will be operated separately from the ALS User Program and will enable an unprecedented opportunity to perform ambitious long-term studies of rock deformation and failure with full pore and grain resolution. A miniaturized uniaxial compression cell that permits fluid flow has been constructed and additional in situ cells are under development. A virtual view of the 11.3.1 beamline is given below.
An annotated view of the X-ray microscope is given below
The measurement consists of placing a ~100 micron sample on a rotating stage. The energy of the X-ray beam generated by the insertion device in the ALS synchrotron storage ring is selected through a monochromator and enters the experimental hutch through a Be window. Mirrors further shape the X-ray beam illuminating the sample, which attenuates the X-rays depending on the material present along the path. After the sample, the beam is magnified through a diffractive lens (“zone plate”), and the resulting image is recorded via a system composed by a scintillator (converting X-ray into visible light), followed by a microscope objective + camera detector. Different images (“radiographs”) are collected while rotating the sample.From the stack of angular images, a 3D volume representing the local X-ray attenuation of the sample is finally reconstructed via filtered back-projection, or other tomographic algorithms. The resulting dataset is a 3D image of the microstructure of the sample that can be visualized through 3D rendering or virtual cuts. Image processing techniques can be applied to obtain quantitative information, such as sample porosity, pore size distribution, pores connectivity, etc.
The measurement consists of placing a ~100 micron sample on a rotating stage. The energy of the X-ray beam generated by the insertion device in the ALS synchrotron storage ring is selected through a monochromator and enters the experimental hutch through a Be window. Mirrors further shape the X-ray beam illuminating the sample, which attenuates the X-rays depending on the material present along the path. After the sample, the beam is magnified through a diffractive lens (“zone plate”), and the resulting image is recorded via a system composed by a scintillator (converting X-ray into visible light), followed by a microscope objective + camera detector. Different images (“radiographs”) are collected while rotating the sample.From the stack of angular images, a 3D volume representing the local X-ray attenuation of the sample is finally reconstructed via filtered back-projection, or other tomographic algorithms. The resulting dataset is a 3D image of the microstructure of the sample that can be visualized through 3D rendering or virtual cuts. Image processing techniques can be applied to obtain quantitative information, such as sample porosity, pore size distribution, pores connectivity, etc.