Muon Laser Photographed Object Through 6 Feet Of Concrete

European researchers report the first demonstration of imaging dominated by an artificial, laser-driven muon beam. Conducted at Romania’s Extreme Light Infrastructure–Nuclear Physics facility, the experiment used laser-accelerated electrons to generate high-energy muons, characterize their spatial distribution, and image a dense lead object. The results establish a proof of concept for controlled muography, a non-invasive technique that exploits muons’ ability to penetrate substantial thicknesses of matter.

Conventional muography relies on naturally occurring cosmic-ray muons to investigate structures such as volcanoes, archaeological sites, tunnels, and nuclear materials. However, their limited flux, predominantly downward arrival directions, and uncontrolled energy distribution constrain imaging speed and geometry. Artificial sources could provide greater control over these parameters. Previous experiments had demonstrated laser-driven muon production; this study advances that work by measuring beam profiles and demonstrating transmission imaging.

The researchers employed the facility’s 10-petawatt laser system, capable of delivering 230-joule pulses lasting 23 femtoseconds. Laser wakefield acceleration produced electrons reaching approximately 8 GeV, which struck a thick lead converter. Inside the target, energetic bremsstrahlung photons generated muon–antimuon pairs through the Bethe–Heitler process. Extensive polyethylene, paraffin, lead, and concrete shielding suppressed accompanying radiation while allowing sufficiently energetic muons to reach downstream detectors. The experimental campaign comprised 230 laser shots.

Three scintillator-based detector systems measured the emerging radiation. Two remained stationary 12 meters from the converter, while a vehicle-mounted muon telescope sampled positions as far as 42 meters away. GEANT4 Monte Carlo simulations reproduced the experimental geometry and incorporated measured electron spectra, enabling comparisons between observations and predicted contributions from muons, gamma rays, and neutrons. The researchers also modeled optical collection and the electronics’ nonlinear time-over-threshold response to translate simulated energy deposition into detector signals.

Measured beam profiles were strongly forward-peaked, with full widths at half maximum of 4.51 meters at a distance of 20 meters and 6.35 meters at 29 meters. Simulated widths closely matched these observations. Although background particles were more numerous, muons deposited substantially more energy in the scintillators: simulations attributed approximately 87% of deposited energy at 20 meters to muons. Transport calculations indicated that muons needed initial energies exceeding roughly 1.5 GeV to reach the detectors, supporting a few-GeV interpretation rather than a direct energy measurement.

For imaging, the team placed a 20-by-25-by-100-centimeter lead object immediately ahead of the telescope, 23 meters from the source, and recorded 30 consecutive pulses. The resulting transmission image reproduced the object’s approximately 25-centimeter width, with detector segmentation providing an intrinsic resolution of 2.5 centimeters. Signal reductions of roughly 26% appeared in the relevant detector layers. Simulations reproduced the image, whereas calculations excluding muons did not, strengthening the attribution to muon transmission.

The study demonstrates feasibility, not a deployment-ready scanner. Beam spreading, source variability, background radiation, and incompletely characterized detector behavior remain limitations. Future work will pursue higher electron energies and detectors optimized for intense particle bursts and particle discrimination, aiming to improve characterization of laser-driven muon sources for controlled imaging applications involving dense or inaccessible materials.