How hard would it be for China to muddy up the mix that is put into a nuke? So that the radiation signature would be unique and identifiable with no one! If the ChiComs are smart enough to go asymmetrical they are smart enough to do the above.
At this point Osama Bin Laden is the champion in asymmetrical warfare. For a total investment of 2 million tops he is causing us to spend half a trillion on fighting wars, enhanced security at home, destruction to lower Manhattan and Pentagon, bailing out airlines and others. Add in the damage to the economy, damage to stock prices, and I think half a billion worth of damage was done by the Bin Laden mafia.
How that for a leveraged investment. 2 million causes your enemy 500 million in damages. How much economic fallout would come from a few small nukes set off in a few downtowns...Downtown Seattle, New York City, Chicago?
Very hard. We can identify the source of the bomb material to not only which reactor it came out of, but which part of the reactor and which batch of fuel cycled through. Multiple reactors for material wouldn't help any--just implicate more sites.
Look up HAARP--some of the more exotic applications proposed would allow remote identification and tagging of radioisotope sources, even from underground tests that don't vent or nuclear reactors that are actually deep underground.
Stay well - stay safe - Stay armed - Yorktown