Muon Imaging Team at Lanzhou University has long been engaged in developing muon detectors, forward and inverse imaging algorithms, and data analysis and visualization platforms. The team has successfully validated three-dimensional imaging using muon imaging technology in both cultural heritage preservation and mineral exploration, thereby promoting its application across a broader range of disciplines. In 2023, the team conducted muon imaging surveys over selected areas of the Zaozigou Gold Mine in Gannan City, Gansu Province. The study addressed the challenges of reconstructing gold deposits, which typically exhibit only subtle density contrasts relative to surrounding host rocks, and evaluated the effects of high-altitude muon energy spectra on imaging performance. The team reconstructed high-density gold-bearing ore veins above the tunnels, along with low-density slate layers and mined-out zones. This achievement represents an important milestone in the application of muon imaging technology to mineral exploration in China. The upper figure shows the muon detectors deployed at the Zaizigou Gold Mine prior to installation. The lower figure shows the 3D muon inversion results of the Zaizigou Gold Mine (colored blocks represent inversion results, and closed surfaces represent geological survey data).

(Photograph & Explanation: Zhiyi LIU)

 Muometric complimentary positioning, navigation, and timing (muometric CPNT) utilizes muonic signals which are capable of penetrating through any type/density of material straightforwardly to reach regions inaccessible to microwaves and other established PNT signals such as sound; hence, muometric CPNT techniques offer a seamless connection between outdoor and indoor-underground-underwater regions. This paper is intended to outline the background and current status of muometric CPNT among other PNT techniques.

 In this work, we present the status of the ongoing scientific collaboration between INRIM (Istituto Nazionale di Ricerca Metrologica) and VMI (International Virtual Muography Institute) on the possibility of synchronizing atomic clocks and disseminating reference atomic time scales using relativistic charged particles, muons, from cosmic rays induced Extended Air Showers (EAS), through an approach called CTS (Cosmic Time Synchronizer), ideated by the University of Tokyo. Based on muons, this system aims to grant timing services within the EAS shower disc with improved robustness and reliability against consolidated time synchronization systems. The CTS approach is, in principle, not affected by malicious or intentional jamming and spoofing actions, typically undermining time synchronization techniques based on the use of RF (Radio Frequency) signals, like those emitted by GPS (Global Positioning System) and other GNSS (Global Navigation Satellite Systems) satellites. This reliability makes CTS a good candidate for providing secure synchronization and dissemination of reference time in critical applications. In addition, it could complement GNSS in areas/environments not covered by its RF signals, such as indoors, underground, and underwater.

 Muography is a technique that employs muons in cosmic rays to facilitate visualization of the Earth's crust and underlying large-scale architectural structures. As a novel application of muography, we are investigating the interior of Kofun, ancient burial mounds in Japan. This report presents the preliminary results of muographic imaging of an unexcavated Kofun, which is believed to contain artifacts. A high-sensitivity Multi-Wire-Proportional-Chamber (MWPC) detector was employed as the measurement device, and 128 × 64 pixel muon transmission images were acquired. The images were compared with muon transmission simulations assuming the presence of a stone chamber inside. As a result, it was indicated that there was a possibility of an uneven area around the projected image of the virtual stone chamber. Although the lack of resolution did not allow the identification of artefacts with a high degree of confidence, it demonstrated the potential for using muography to explore the interior of the Kofun.

 Muography is a novel green nuclear imaging technology that has rapidly advanced in recent years. This technique utilizes natural muon rays to achieve non-destructive, high-precision three-dimensional imaging of objects. Several universities and research institutes in China have engaged in research related to muography, including system development, application scenarios, and some imaging algorithm studies. This paper provides an overview of research progress in China on two different principles of muography and, through the introduction of several typical cases, demonstrates the significant economic, cultural, and social value and potential of this technology. Given China's vast territory and comprehensive industrial system, muography has a wide range of applications in various fields. With the advancement of related research, this technology is expected to continue developing and find broad applications in cultural relics protection and excavation, mineral exploration, infrastructure monitoring, and natural disaster early warning.

 Ophiolites provide useful information about the evolution of oceanic lithosphere that has not yet been assessed by drilling experiments to date. In spite of the relevance of ophiolites, geophysical explorations provided sparse data about the internal structure of these natural formations. We propose a novel geophysical technique, called muography, that allows scanning of the internal density structure of ophiolites by measuring the yield of naturally occurring cosmic-ray muon particles which penetrate across the ophiolites. We report on the first muographic experiment that is in progress to image the mass density structure of an ophiolite segment at Wadi Fizh in the Samail ophiolite, Sultanate of Oman. The installation and commissioning of the experimental setup, the operational performance of the muographic observation system and the preliminary results are presented. The structure of lower crust can be distinguished from the upper mantle and Moho transition zone in a preliminary mass density image. Data collection will be continued at the current position and at additional measurement sites around the ophiolite segment to resolve its density structure in three dimensions with sufficient spatial and density resolution for studying the Moho transition zone.

 Muography, a method utilizing cosmic ray muons, can obtain high-resolution density information and has been investigated for its applicability to CCS (Carbon Dioxide Capture and Storage) monitoring through numerical simulations. These studies suggest that muography can be effective when employing a large muon detector (e.g., 1000 m²). However, deploying such a large detector underground is impractical. To address this limitation, this review introduces a methodological combination of muography and seismic exploration. This approach enables the decomposition of seismic wave velocities, which are composite parameters, into two elastic constants and density. This facilitates the estimation of CO₂ saturation and geomechanical properties, which were previously difficult to evaluate. This review also discusses the systematic organization and current state of performance evaluations of muography, focusing on spatial, density, and temporal resolutions. The necessity for advancements in interpretation techniques related to anomaly detection is emphasized. While performance evaluations based on numerical simulations and applicability assessments of new measurement and analysis methods are needed, laboratory-scale verification remains scarce. Establishing reliable laboratory experimental methods is essential for validating these techniques. Considering current CCS projects, monitoring should initially target depths shallower than approximately 1000 m, given the density of CO₂ and the penetration depth of muons. In particular, such shallow-depth applications may contribute to assessing the integrity of caprock formations, which is a critical aspect of ensuring long-term storage safety. Developing new measurement and analysis methods under these conditions is a critical first step.