Australians scour desert for dangerous radioactive capsule smaller than a penny
Radiation detection is my specialty. This source is Cs-137, few hundred mCi. It's easy to detect within a few seconds at distances of a few tens of meters or more with professional detection equipment if there is direct line of sight.If it was knocked off the road, though, the question will be if it fell into a crack or other such place because then the radiation is somewhat shielded and it would take much more measuring time to identify it.I suspect if a few passes with vehicle-mounted detectors don't find it then some drones with detectors traveling along the sides of the road would be a good next step. If a critter moved it or ate it then it's probably gone forever. At a distance of 1 meter the dose rate from that source is already not extremely hazardous unless a person were exposed for an extended period of time (like a full day or two). Getting closer, like putting it directly against your torso, would mean serious health effects in a matter of minutes.