You comment is fantastic because it demonstrates we are beyond finding it with a rolling road block and sensors on trucks. This is a recovery operation where you're going to want surveillance for when someone shows up somewhere (medical care provider) with radiation sickness and to start contact tracing. If a human has it in their possession, exposure is ongoing. If it's sitting in a ditch somewhere, maybe it's years before it's found, maybe it's never found (and perhaps buried if and when a torrential rain passes through the area, typically in the upcoming winter months).