(I am not a physicist). Can this be explained in laypersons terms? Can radioactive material such as a warhead or smuggled material be detected from a distance?

(I am not a physicist). Can this be explained in laypersons terms? Can radioactive material such as a warhead or smuggled material be detected from a distance? What distance? (the article says 10m which I assume means meters). Can it do so through material such as shell casing?