English: This animation shows how directional information, related to the location of a radioactive source, can be inferred with use of a collimator. The radioactive source is dead centre on the plane of the collimator face. A single photon with a direction normal to this plane passes along a single collimator channel and alludes to the radioactive source location. Unfortunately, another photon partakes in septum penetration and is transmitted directly into the Nal crystal. This erroneous event demonstrates the penetrative ability of radiation – albeit this event is less likely than the first – thereby degrading the image. To suppress the effect of such erroneous events it would be necessary to play the stats game and build up an image on many millions of events; increasing the fraction of collimated events in the final image.