Large-scale cultural relics share common characteristics such as immovability, indestructibility, and extreme fragility due to prolonged exposure to natural conditions. Traditional detection methods are constrained by inherent physical limitations, making non-destructive detection a persistent challenge in cultural heritage conservation.The application of natural muon imaging technology in archaeology primarily serves two purposes. First, it enables in-depth exploration of the internal structure distribution of ancient sites without damaging the relics, providing archaeologists with multidimensional information to facilitate subsequent excavation efforts. Second, it helps identify potential safety hazards within the internal structures of historical sites, delivering precise imaging maps and target coordinates for conservation and restoration. Additionally, this technology allows for real-time monitoring of key cultural relics, employing artificial intelligence to predict potential risks, thereby achieving digital and intelligent health monitoring of heritage artifacts.

Xi'an City Wall

The Xi'an City Wall is one of the largest and best-preserved ancient city walls in China, designated as a National Key Cultural Relics Protection Unit. The existing wall, built during the Ming Dynasty, stretches 13.7 kilometers and was constructed in 1370 (the third year of Emperor Hongwu's reign), making it 655 years old. Due to its age, a major restoration was conducted in the 1980s, focusing on wall reinforcement and ancient architectural repairs.

The main structure of the Xi'an City Wall consists of rammed earth encased in gray bricks. Long-term erosion from rainwater and groundwater can cause internal subsidence of the rammed earth, leading to structural instability, cracks, and settlement. Therefore, non-destructive detection technology is needed to identify internal defects, analyze the wall's structural integrity, and provide technical support for targeted restoration.

In 2021, the team conducted China's first technical verification of muon imaging in cultural heritage conservation. They selected No. 58 "Horse Face" (a protruding defensive structure) as the detection target, setting up six measurement points to collect muon flux data from multiple angles. After over a month of data acquisition and inversion analysis, the team discovered a hollow structure between the northern wall bricks and rammed earth. Additionally, a low-density area in the imaging results was confirmed to be an electrical distribution room (not disclosed beforehand)—demonstrating the technology's ability to precisely reveal the location, shape, and size of hidden structures in a blind test.

The findings were published as a Featured and Cover article titled "High-precision muography in archaeogeophysics: A case study on Xi'an defensive walls" in the renowned applied physics journal Journal of Applied Physics.

DOI: https://doi.org/10.1063/5.0123337