That's not why it is in short supply. Plutonium based RTGs use Plutonium 238, a non-fissile isotope. Being an alpha emitter, it is a terrible choice for a dirty

That's not why it is in short supply. Plutonium based RTGs use Plutonium 238, a non-fissile isotope. Being an alpha emitter, it is a terrible choice for a dirty bomb - certainly no better than any other potential RTG fuel candidate. Obviously it is a radioactive isotope, and a hazardous one at that, but it is not meticulously tracked for security purposes. Indeed up until lithium batteries rendered them obsolete, Plutonium-238 was used in nuclear powered pacemakers. Plutonium-328 is a trace impurity in general plutonium production, but production of RTG-grade Plutonium-328 needs to be done in special reactors, where Neptunium-237 is bombarded with neutrons. The US shut down its only Pu-238 producing reactor in 1988, along with the rest of the Savannah River Site. Since then, Russia has been the sole source of Pu-238. Since 2013 the US has been trying to set up a new Pu-238 production plant at Oak Ridge National Labs, but even at full scale production it can still only produce 1.5 kg per year.