3D density imaging of muography with variable angular resolutions and its application in the detection of fracture zones in mountains

Fracture zones in mountains are hazardous for the infrastructure constructions like tunnels. In order to prevent collapses triggered by constructions and ensure the safety of infrastructures, it is necessary to accurately locate fracture zones before and during the construction. Muography is a novel density imaging technology, suitable for complex field construction environments with vibrations and electromagnetic noises. Attenuation of cosmic-ray muon flux is associated with the density distribution along muon ray paths. The density of the target can be imaged by converting attenuated fluxes into opacity and then inverting the opacity to recover the density model. Therefore, muography can be applied to mountainous areas covered by dense vegetation, and the instruments do not need to be placed close to the geological object. In this feasibility study, we propose a new muon detector with variable angular resolutions for a more efficient reception of muon particles in engineering applications. Different from the traditional muon detector that fixes the separation of detecting plates, our instrument can increase the count of muon events by adjusting the separation between detectors, effectively saving the time of field observation at the cost of angular resolution. We design a mountain model containing a low-density fracture zone using a realistic topography. In the forward part, the three detectors are set with four detection unit separations. Considering the influence of the effective receiving area and solid angle of the instrument on muon rays from different directions, the total opacity is calculated by weighted summation. The result shows that the visual range of the instrument is wide under the condition of small spacing, and it is easier to perceive the existence of fracture zone in a short time. The detection area with large spacing shows highly directional rays. Only when the rays pass through the abnormal body can there be abnormal data reflection, but the determination of the abnormal body position is more accurate. In the inversion part, we increase the number of detectors around the mountain and change the angle of detectors facing the mountain. The recovered 3D density model can delineate the low-density fracture zone well under the condition of sufficient data and good coverage of muon ray paths.