JTomo-MV tomograph
The JTomo-MV is a unique in-house built megavoltage computed tomography (MVCT) system. It uses Varian Clinac® medical accelerator as an X-ray source. The acceleration voltage is either 6000 keV or 15000 keV and the maximum intensity of the X-ray spectrum is around 1 MeV or 2 MeV, respectively. The detector is a Varian flat panel and the device works in cone-beam geometry. The maximum resolution is less than 0.3 mm, and the maximum sample diameter is approximately 30 cm.
The JTomo-MV device is currently in an experimental development state and the specifications above resemble the current status, not the final performance of the device. The system has been successfully employed, e.g., in the imaging of large rock samples to digitalize fracture networks, analysis of heavy metals, and dynamic radiography of samples changing shape in high temperatures inside thick-walled environmental chambers.
The device is built thanks to collaboration with the RADiation EFfects facility in the Accelerator Laboratory.
In low-porosity crystalline rocks such as those occurring in the Fennoscandian shield, the primary means of groundwater transport is provided by networks of mechanical discontinuities, e.g., fault-induced fracture systems. Characterization of these systems is challenging due to them consisting of structures spanning over several orders of magnitude in length. Here, the JTomo-MV device was used to acquire images of fracture networks in dm-scale natural samples obtained from outcrops by our collaborators (University of Turku, GTK, Ã…bo Akademi). The images are then used to determine the geometrical properties of the fractures and their connectivity.
