Fixed fluorescent images of an 80 MeV proton pencil beam

We have used an organic radio-fluorogenic gel to make fixed fluorescent images of the track of an 80 MeV proton pencil beam NB this is not a scintillation effect; rather a small fraction of the molecules of the medium are converted permanently from a non-emissive to an emissive form. The spatial resolution of the images is better than 0.1 mm and the cuboid form of the gels allows the track to be viewed along the direction of the beam or transverse to it. The fluorescence diverges and increases in intensity with increasing depth up to the Bragg peak with 80a20% post-peak fall-off in 1.4+/-0.1 mm. From the effect of interposed polystyrene sheets on the proton range in the gel, its water equivalent thickness is determined to be 0.91.