Thanks
So, what do you do? First, restrict access so you don't spread it around more than necessary. Second, restrict traffic in products or artifacts from the area, again to limit spread. You might prohibit sales of foodstuffs produced in the area (milk, veggies, etc.).
Cleanup means collecting the particles as best you can. If surfaces are contaminated, you wash them off, and control the runoff in some way. Chelating agents are often helpful here. If water supplies are contaminated, you filter the water. If the material has worked its way into the soil, you may have to remove the very top layer of dirt from an area. Depending on the nature of the release, that may or may not be practical. For limited contamination, it is eminently practical. In fact, many of the DOE sites formerly used in weapons production are undergoing restoration and this techniques is used quite frequently.
At some point in the decontamination process, you have to call it quits. You're not going to scavenge every single radioactive atom. You have to say "this is good enough". What is good enough? Generally, when sites are decommissioned the criteria is that the doses a person might receive in those areas decontaminated must be about equal to that they would get from the natural environment. The theory is that if a person lives in the natural radioactive environment and experiences no ill effects, they should likewise experience no deleterious effects from the decontaminated environment if the dose is comparable. If you can't get down to those levels, you can't use that area until either radiological half-life has worked its magic, or dilution into the surrounding environs has reduced exposure rates. This has been the fate of some of the areas surrounding the Chornobil site. But a radiological dispersion weapon will not produce the kinds of contamination that Chornobil did (for reasons related to the physics of the process).
The article is correct in that 137Cs is one of the more mobile radioactive forms. Cesium tends to get around in the biosphere. It has a relatively long half-life (about 30 years) and a reasonably-penetrating gamma emission (about 662 KeV). So if you disperse a lot of 137Cs over a large area you would complicate the cleanup. But for the same reasons that make 137Cs a problem, it is also difficult to work into a radiological dispersion weapon. You need to get a lot of it (hundreds or thousands of curies of activity) and package it into the weapon. That is a tricky handling problem. You just aren't going to go out and slap some ingots of cesium around a few sticks of dynamite using your hands. You'd not survive that attempt.
And that's why a radiological dispersion weapon capable of producing the kinds of wild-a$$ scenarios being bandied about in the media and on discussion boards (billions of fatalities and trillions of square miles of territory rendered unhabitable for the next few billion years) is somewhat speculative. To really produce a lot of contamination you need a lot of dispersive agent. If its radioactive material, you're talking about one hot tamale. It may kill you and your whole gang before you have a chance to set it off. OTOH, that may be a good way to get rid of some of these scum...