Opaque Scintillation

Summary of the state-of-the-art developments in Opaque Scintillation today. Most of the developments known today have happened — and are still happening to my knowledge — within the LiquidO collaboration, including a broad range of scintillation experts from (alphabetically) Canada, France, Germany, Japan, Portugal, the UK and the US, with a growing fraction of specialised photo-chemical expertise. The concept and utility of Opaque Scintillation were pioneered upon the LiquidO conception (before the collaboration existed) since opacity, via extremely high scattering, was necessary. Some of the elements for the opaque scintillators were already there, while they were typically regarded as impractical (or even useless) for particle detection. Using scintillation in LiquidO is essential for MeV sub-atomic particle detection. Still, LiquidO has been demonstrated to work without scintillation in other contexts, such as events at higher energies (GeV).

Nonetheless, today, much effort is devoted to exploring LiquidO’s ability to adapt to many types of opaque scintillators. In fact, several options are being considered in parallel as part of today’s explorations. Some developments I am aware of remain confidential; hence, this is only hinted at to illustrate the level of ongoing R&D activity. Given this presentation's time limitations and broad audience, only a general description is provided, including some images to illustrate the options. However, I provided a simplified comparison (not free of caveats) between transparent and opaque scintillator options that may help as a rough guideline. Opaque scintillators do offer clear advantages regarding topology and particle imaging, for which they have been designed and optimised so far, i.e. LiquidO. It is clear that, as opposed to the transparent technology (tuned to excel over many decades), there is much to be done in terms of new explorations (i.e. new chemistry, etc.) and the optimisation of today’s performance (light yield, etc.). The opaque medium solution nonetheless opens a revolution potential for doping (a scattering element), but this needs far more work. Transparent solutions remain the optimal choice in some experimental scenarios. As of today, though, there is a strong synergy between opaque and transparent scintillator solutions since there are ways to opacify transparent solutions. However, this may change in the near future with natively opaque specialised formulations, which will generally remain impractical for the transparent detection paradigm.