Irfu is part of the ScanPyramids mission aiming to "scan" the great pyramids of Egypt and in particular the pyramid of Cheops. Created in 2015 under the authority of the Egyptian Ministry of Antiquities, the project combines various non-invasive and non-destructive techniques in an attempt to reveal the presence of little-known internal structures in ancient monuments and to better understand both their design and construction. The technologies used combine infrared thermography, muon radiography and 3D reconstruction through a collaboration between the CEA (Commissariat à l'énergie atomique et aux énergies alternatives/France), Nagoya University (Japan), KEK (High Energy Accelerator Research Organization - Tsukuba Japan) and Laval University (Quebec Canada). Irfu brings to this international mission its know-how in muonic tomography, and uses gas detectors, with micro-tracks, called Micromegas.
For several years, Irfu has been developing micro-track gas detectors, called Micromegas, co-invented by CERN and CEA. Increasingly accurate, they are usually used to reconstruct traces of particles for many high-energy physics experiments. Irfu's Micromegas, which can cover large areas at a reasonable cost, have already been used in experiments carried out by global high-energy physics collaborations or have already been selected to equip the next generation of experiments:
It is therefore from these innovative detectors that CEA-Irfu has designed muonic telescopes specifically dedicated to the ScanPyramids mission. The heart of the detectors is now manufactured by the French industrial company ELVIA to whom the manufacturing process has been transferred. These detectors are then assembled, tested and integrated into the telescopes at Saclay, within the CEA laboratories.
Each telescope consists of 4 latest generation Micromegas type gas detectors called "multiplexed-resistive", an electronics managing the operation and reading of the detectors with the acquisition and transmission of events detected coincidentally in the 4 planes. The result is a compact box (1.5 meters long, 70 cm wide and about 200 kg) autonomous in terms of power supply with very low power consumption (25 W), and allowing real-time imaging.
Muonic tomography, a technology that measures cosmic particles
The muons, which fall permanently on Earth at a speed close to that of light with a flux of about 10,000 particles per m2 per minute, come from the upper layers of the atmosphere where they were created during collisions between cosmic rays from our galactic environment and the nuclei of atoms in the atmosphere.
Like the X-rays that pass through our bodies and allow us to visualize our skeleton, these elementary particles, a kind of heavy electrons, can pass through thick rocks, such as mountains.
Detectors, placed in judicious places (for example inside the pyramid, under a possible chamber not yet detected), make it possible, by accumulation in time of muons, to discern the zones of vacuum (which muons crossed without interacting) and the denser zones where some of them could be absorbed or deviated.
The art of measuring is to create extremely sensitive detectors and then accumulate enough data (for several days or months) to accentuate the contrasts. Japanese research teams use plastic scintillators to perform muon radiography of volcanoes and reactors at the Fukushima power plant. Several types of muon detectors exist. Electronic detectors (using glittery plastic-based ionizing media or gases such as Micromegas), unlike chemical emulsions, allow real-time data analysis.