Borehole muon tomograph for search and evaluation of ore deposits

This work presents the development and testing of the borehole muon tomograph to search for ore by measuring the attenuation of the cosmic ray muon flux in the rock. The borehole muon tomograph is designed to carry out measurements at depths up to 1500 m.w.e., with the capacity to be placed in water-filled boreholes, with an effective radius of surface research being no less than 400 m. The borehole muon tomograph consists of four detector modules, each having a length of 2.4 m and an outer diameter of 89 mm. The modules are connected consecutively, and the overall length of the tomograph is about 9 m. The borehole muon tomograph contains more than 600 signal acquisition channels coming from scintillating optical fibers that are placed on three cylindrical layers nested inside each other. On the outer layer, the optical fiber is placed parallel to the cylinder axis, while on the inner and middle layers, it is placed spirally in opposite directions. The borehole muon tomograph detector allows for the measurement of angular parameters with a precision of ∼17 mrad on the azimuth angle in the range from 0° to 360° and ∼19 mrad on the zenith angle in the range from 10° to 90°. A method for reconstructing the average rock density by measuring the attenuation of the muon flux has been developed. To reconstruct and visualize a three-dimensional density distribution of the studied area, a program and algorithm were developed based on the Simultaneous Iterative Reconstruction Technique method. Tests of the borehole muon tomograph performed on a test site have shown its full operational capability, and based on the results, a 3D density reconstruction of a test object has been made with an accuracy of determining the average areal density in a solid angle within 5%. Such a level of accuracy is achievable after accumulating sufficient muon statistics (at least 5 × 105 muons).