Scientists have developed and field-tested portable, gas-tight glass particle detectors that track cosmic-ray muons with over 95% efficiency, paving the way for non-invasive imaging of volcanoes, tunnels, and ancient monuments.
What to know about A new portable cosmic ray muon detector can
An international team of researchers from India and Belgium has engineered a new generation of portable muon tracking systems that could revolutionise how we peer inside massive, dense structures without ever touching them. Muography is a cutting-edge imaging technique that uses naturally occurring cosmic rays called muons to map the internal structures of large objects like volcanoes, mineral deposits, and monuments. However, the technique has traditionally relied on bulky, delicate, or energy-intensive equipment.
The team, including researchers from the National Institute of Science Education and Research (NISER) Bhubaneswar, Homi Bhabha National Institute, Université catholique de Louvain, Belgium, and the Inter-University Institute for High Energies (IIHE), Belgium, has successfully shrunk the muon detector. They developed robust, gas-tight Resistive Plate Chambers (RPCs) to create a portable detector that overcame major hurdles in portability and environmental stability, delivering a field-ready instrument that operates with high precision under challenging conditions.
When high-energy particles from deep space collide with gases in our upper atmosphere, they trigger a shower of secondary particles, notably including muons. Muons are heavy, high-energy cousins of electrons that pass easily through hundreds of meters of rock, concrete, or metal, though they lose energy and can be absorbed or deflected depending on the material’s density. By counting how many muons successfully pass through a target from various angles, scientists can reconstruct a density map of the interior, much like an X-ray machine images human bones.
RPCs consist of two parallel, high-resistivity flat plates enclosed in a gas-filled chamber. When a charged particle, such as a muon, passes through the gas gap, it ionises gas atoms, triggering an electron avalanche that can be used to track the muon. The team achieved this size reduction through clever design optimisation, allowing these particle detectors to operate autonomously while maintaining exceptional tracking accuracy. The glass RPCs developed in this study capture passing muons by using an avalanche mode in a specialised, environmentally friendly gas mixture. When a muon zips through the narrow gas gap, it ionises the gas molecules, triggering a tiny electrical avalanche. Intersecting rows of copper strips on printed circuit boards above and below the gas gap capture this signal, giving researchers precise two-dimensional coordinates for the muon’s trajectory.
Key context and latest developments
The team built and tested three distinct glass RPC prototypes, Prototypes A, B, and C, through collaborative efforts at NISER in India and universities in Belgium. Each prototype uses thin glass electrodes, 1.1-3 mm thick, coated with semi-resistive paint and separated by uniform gas gaps. To validate their system’s real-world capabilities, the researchers conducted a proof-of-principle absorption study using Prototype A. They placed a heavy lead block between two plastic scintillator triggers and two orthogonal glass RPC layers and measured how the dense material blocked or slowed cosmic-ray muons. An initial open-sky measurement recorded nearly 55,000 muon tracks, but when the lead absorber was introduced, the recorded count dropped sharply to 30,894. The results clearly mapped this attenuation, showing that the compact telescope has the high sensitivity needed for detailed radiographic imaging of heavy materials.
Earlier devices were also frequently restricted to laboratory settings or required cumbersome infrastructure to operate in remote locations like the slopes of active volcanoes. In contrast, the new glass RPCs are engineered for sealed-mode operation, meaning they can trap their gas mixture inside a hermetically sealed, modular aluminium or acrylic casing to minimise gas consumption drastically. Furthermore, by utilising front-end application-specific integrated circuits and field-programmable gate arrays, the team managed to process signals with remarkable efficiency, achieving a cosmic-ray detection efficiency of 95% or higher, exceptional timing resolution of around 1.8 nanoseconds, and very low strip multiplicity where electrical signals remain cleanly confined to just one or two readout strips.
The researchers, however, have outlined several limitations and necessary future upgrades to push the technology even further. Currently, some prototypes still rely on continuous gas-flow operation or heavy aluminium casings, and certain configurations lack the broad directional coverage needed for sweeping architectural or geological scans. To address this, the team’s upcoming upgrades include replacing heavy metal frames with lightweight 3D-printed carbon fibre or high-strength polymer structures featuring integrated gas channels. They also plan to transition Prototype B into a four-layer configuration mounted on an alt-azimuthal platform to achieve wide, hemispherical sky coverage, and to scale up Prototype C to a larger active area with high-granularity readout chips to drastically improve signal-to-background ratios.
Nonetheless, the study provides a portable, rugged, and highly accurate tool for non-destructive imaging. The technology could help geologists monitor active volcanoes well before they erupt, assist engineers in inspecting the structural integrity of ageing bridges, tunnels, and dams, and allow archaeologists to inspect historical monuments without damaging precious cultural heritage.
