A short description of scintillating fibers

A scintillator can be built also as an optical fiber. In this case the internal nucleus is typically a polistirene base doped with organic moleculae. The internal nucleus is called core while the external protection (typically plexiglass) is called cladding. The cladding has a lower refractive index respect to the core (tipically 1.5 vs. 1.6)
The difference between the two refraction indecies gives origin to a special quality in the propagation of light in the fiber since it is limited by total internal reflection in a cone within an angle of 21 degrees (trapping angle) respect to the fiber axis.
The quantity of the light reaching the fiber end is small (not exceeding 3%) but the forward propagation decrease the number of reflections on the cladding guaranteeing a long attenuation length and small time dispersion along the fiber length.
The light trapped in the cladding that is more strongly attenuated is essentially captured by the external glue that has a refractive index comparable to the one of the fiber core.