Muon Imaging Techniques in Geophysical Applications

Muon imaging exploits the natural flux of high-energy cosmic-ray muons to probe the internal density structure of large geological and man-made bodies. Two principal approaches are in use: attenuation-based imaging, which measures the reduction in muon flux after passage through different materials, and scattering-based imaging, which analyses the angular deflection of muons as they traverse matter. These methods are implemented via telescopes or detector arrays comprising nuclear emulsions, gaseous trackers, scintillator panels or resistive plate chambers. Advanced reconstruction algorithms, including tomographic inversion and back-projection, convert muon flux data into two- and three-dimensional density maps. Applications range from volcano monitoring and hydrothermal reservoir dynamics to mineral prospecting, archaeological surveys and civil engineering assessments. Key advantages include non-invasiveness, deep penetration, continuous remote operation and compatibility with harsh environments. Ongoing developments focus on enhancing spatial resolution, reducing background noise, integrating dynamic imaging for time-lapse studies and optimising detector layouts through differentiable modelling and simulation tools.

Research from Nature Portfolio

Recent studies have achieved sub-metre sensitivity in archaeological and volcanic contexts by combining complementary detector technologies. A 2023 investigation of an ancient pyramid employed nuclear emulsion films alongside gaseous tracking detectors to reveal a previously uncharacterised nine-metre corridor within the monument’s core. Hybrid instrumentation yielded finely resolved density contrasts and demonstrated the feasibility of detailed non-invasive surveys in complex stone edifices. In foundational work on volcanic conduits, dynamic radiographic imaging captured the ascent and descent of magma within an active volcano. Time-sequential muographic frames provided real-time maps of density fluctuations in the conduit, offering novel insights into magmatic inflation, deflation and gas release processes that underpin eruption forecasting.

Muon Imaging Techniques in Geophysical Applications publication trend

The graph below shows the total number of articles in muon imaging techniques in geophysical applications across all publications each year (not limited to Nature Index journals).

Technical terms

Cosmic-ray muon: High-energy particle produced by interactions of primary cosmic rays with the Earth’s atmosphere, capable of penetrating hundreds of metres of rock.

Muography: Imaging technique that utilises cosmic-ray muons to infer the internal density distribution of large structures.

Attenuation-based imaging: Method that measures the decrease in muon flux after traversal through matter to map density variations.

Scattering-based imaging: Technique that analyses multiple Coulomb scattering angles of muons to reconstruct internal features.

Tomographic inversion: Computational process that converts line-integral muon flux data into cross-sectional or volumetric density images.

Nuclear emulsion detector: High-resolution film medium that records individual muon tracks for precise spatial reconstruction.

Back-projection algorithm: Reconstruction approach that projects measured muon deficits back into the object space to localise density anomalies.

References

1. Precise characterization of a corridor-shaped structure in Khufu’s Pyramid by observation of cosmic-ray muons. Nature Communications (2023).
2. Radiographic visualization of magma dynamics in an erupting volcano. Nature Communications (2014).
3. Transmission-Based Muography for Ore Bodies Prospecting: A Case Study from a Skarn Complex in Italy. Natural Resources Research (2023).
4. Monte Carlo simulation for background study of geophysical inspection with cosmic-ray muons. Geophysical Journal International (2016).
5. Towards a muon radiography of the Puy de Dôme. Geoscientific Instrumentation Methods and Data Systems (2013).