Enhanced electromagnetic radiation in oriented scintillating crystals at the 100-MeV and sub-GeV scales

Nowadays, it is well known that the electromagnetic interaction between high-energy particles and matter experiences substantial modifications when the latter consists of a crystalline medium and its lattice axes are almost parallel to the input beam direction. In particular, a strong boost to the cross section of bremsstrahlung by electrons and positrons in high-density oriented crystals has been observed in the $10$-to-$100~\mathrm{GeV}$ regime. This effect proves particularly appealing when it comes to inorganic scintillators, given the possibility to exploit it for the development of high-performance, ultra-compact electromagnetic calorimeters. This work provides a detailed discussion of the results obtained by probing a PWO (lead tungstate) oriented sample with $120~\mathrm{GeV}/c$ electrons and positrons at the CERN North Area: in particular, a comparison between the outcomes obtained with electrons and positrons is made. Moreover, output radiation measurements on a thinner oriented PWO sample have been recently performed in the sub-GeV regime at the MAMI-B facility: an overview on the resulting characterisation is given.