The doomsday device on Stanley Kubrick's Dr Strangelove is also a fictional cobalt type bomb, or as quoted [0] in the movie:
"If you take, say, fifty H-bombs in the hundred megaton range and jacket them with Cobalt-Thorium G, when they are exploded they will produce a doomsday shroud. A lethal cloud of radioactivity which will encircle the earth for ninety-three years!"
It's a fantastic movie that I highly recommend to anybody that hasn't seen it yet.
"If you take, say, fifty H-bombs in the hundred megaton range and jacket them with Cobalt-Thorium G, when they are exploded they will produce a doomsday shroud. A lethal cloud of radioactivity which will encircle the earth for ninety-three years!"
It's a fantastic movie that I highly recommend to anybody that hasn't seen it yet.
[0] https://en.wikipedia.org/wiki/Cobalt_bomb#In_popular_culture