This is really cool.I worked on PET scanners for a while, and the typical detectors consist of Bismuth Germinate crystals glued onto photomultiplier tubes. The Bismuth Germinate crystals are transparent, and convert the impinging gamma rays (511KeV) to blue light (Cerenkov), which is detected by the photomultiplier tube and amplified to give an electrical pulse.
These devices use Positronic Flourine as indictaced, but also Positronic Oxygen (half life 30 seconds) and other Positronic elements typically generated on-site using a low cost cyclotron.
It's very difficult to detect gamma rays. One of its signature is that gamma rays tend to knock off electrons from atoms of the material, and these electrons are often so energetic, that it has a relativistic speed higher than the speed of light in that material. When this happens, you get Cerenkov radiation.This is really cool.
What does it have to with Cerenkov radiation? How can Cerenkov radiation be created with gamma rays?