Mountain muon tomography using a liquid scintillator detector

Abstract

Muon tomography (MT), based on atmospheric cosmic rays, is a promising technique suitable for nondestructive imaging of the internal structures of mountains. This method uses the measured flux distribution after attenuation, combined with the known muon angular and energy distributions and a 3D satellite map, to perform tomographic imaging of the density distribution inside a probed volume. A muon tomography station (MTS) requires direction-sensitive detectors with a high resolution for optimal tracking of incident cosmic-ray muons. The spherical liquid scintillator detector is one of the best candidates for this application due to its uniform detection efficiency for the whole $4\pi$ solid angle and its excellent ability to distinguish muon signals from the radioactive background via the difference in the energy deposit. This type of detector, with a 1.3~m diameter, was used in the Jinping Neutrino Experiment~(JNE). Its angular resolution is 4.9~degrees. Following the application of imaging for structures of Jinping Mountain with JNE published results based on the detector, we apply it to geological prospecting. For mountains below 1~km in height and 2.8~${\rm g}/{\rm cm}^3$ in the reference rock, we demonstrate that this kind of detector can image internal regions with densities of $\leq$ 2.1~${\rm g}/{\rm cm}^3$ or $\geq$ 3.5~${\rm g}/{\rm cm}^3$ and hundreds of meters in size.