| This is mostly a data analysis job. If the capsule is on or very near the road, a single trip from start to finish with a NaI(Tl) or CsI scintillation counter will find it. Every CBRN team in the world has these, so they have obviously completed the first run at this without finding it. The capsule is not on or near the road. Australia is famous for road trains on the Great Northen Highway. They travel fast and heavy on the paved road that runs through the outback. If the tires of one of those hit the capsule, they could fling it a fair distance into the desert. There's nothing between the road and the sandy desert to stop it. If the capsule is a fair distance off the road, the inverse square law is going to reduce gamma detections closer to background. There won't be a clear peak in the data. If the vehicle with the detector moves slowly, there will be a wide peak in the time dimension that may just look like a natural variation in the background. If the vehicle moves fast, it may miss the source completely. It will be a matter of looking at the data to try to find a pattern that indicates where the capsule may be. This will be made more difficult becuase they don't likely have a pre-capsule-loss run that would allow them to subtract normal variations of the background. Adding to the problem is the stochastic nature of radiation. It is entirely possible to have a significant peak in the count rates that is not a strong point source; just a random variation in the background. Lower peaks from random confluence of background sources are likely; higher peaks are less likely, but not impossible. It may require a large number of runs to eliminate random events. Real vehicles on real roads experience a lot of variations in speed, plus random starts and stops because the driver had to pee, or eat, or because there was a dead kangaroo on the road or something. A fair bit of work will need to be done to standardize multiple runs. This can be partly solved by using multiple detectors on the same vehicle, with the idea being that peaks that are the result of natural variations in the background should only affect one detector at a time--so they can be subtracted out. But, again, CBRN teams have enough resources that they have already done this and they haven't found it. So it is reasonable to conclude that the capsule is either quite far off the road, or has been picked up by a passing vehicle. Another possibility is that the idea that it "fell off a truck" is wrong and that some human grabbed it by dissasembling the apparatus. This could be out of curiosity, or ignorance, or a misguided attempt to steal the source or use it for nefarious purposes. If that is the case, the capsule is going to be nearly impossible to find unless it happens to pass a fixed gamma detector somewhere, such as a port. The incident is a good argument for building scintillation crystals into all cellphones. This would be cheap and easy. Small scintillators are not very sensitive, and they are not great for spectroscopy, but they are extremely cool, very small, don't interfere with the workings of the phone, and use extremely little power. A network of scintillators in every phone would be amazing for finding stuff like this. |