PET scans can be used to observe brain function through prior injection of a positron-emitting tracer combined with a molecule of biological interest. This tracer is then detected from outside the brain, providing an image of the brain "in action". "Scintillating" crystals do not directly record the positron, but the gamma photons emitted in pairs at 180 ° from each other, which are a result of its annihilation.

The physicists at IRFU proposed to replace the crystal scintillator with an ionization chamber filled with liquid tri-methylbismuth (TMBi). The interaction of a gamma photon with this liquid releases a primary photoelectron which generates a quasi-instantaneous flash of a few tens of "blue" photons by the Cherenkov effect, this ionizes the liquid, producing thousands of pairs of charges. The key of the project is the simultaneous detection of blue photons and charges, which will lead to significant improvements in both space and time resolution.

TMBi, however, is very chemically reactive and must be thoroughly purified. The scientists developed a process using molecular sieves, which they tested on a product that had been more documented than TMBi in the literature. The ultra-purification obtained was successfully controlled by chemists from the Nuclear Energy Division (DEN). To be continued!