Help me out here. By Zimmerman’s own estimation, the dose that killed Litvinenko was “perhaps the size of a couple of grains of salt.” What he doesn’t mention is that the street value of those grains was a cool $10 mil. Doctors believe that he would have been killed with even 1/10th the dosage, which means we’re talking about $1 million per lethal dose. Do the world’s jihadis have nothing better to do with the Saudis’ money than drop half a billion dollars on a “smoky bomb” that would kill 500 people?
A grain of salt seems too large to me, something more like a 10 micron sized particle would do. Lets run through some numbers. If a 10 µm sized particle is LD50/30 -- 50% mortality in 30 days -- then a volume of Po-210 equivalent to a human hair 1 inch long would suffice to kill or sicken about 200,000 people. How large a dose would individuals receive while breathing in a cloud dispersed throughout a large volume? Let us suppose that same hairsized volume of Po-210 dispersed in a stadium, say a football field that holds ~100,000 and a cloud 100 m high. Such a cloud would have dimensions of about 250m x 250m x 100m and a volume of about 6e9 liters. If we further assume a spectator inhales 20 L/min for 15 minutes, or about 300 L, then the fraction of the LD50/30 inhaled by each spectator would be about 1%. Looks like most folks would survive such an attack, although those close to the bomb probably would not.
How does that dose compare to a grain of salt, say a little cube 1 mm on a side? Such a cube has a volume of about five times that of the hair, so about 20 such cubes would poison the whole stadium. Assume $10 million a cube, then for a price of about $200 million in materials one could cause some real damage. Hmmm, decisions, decisions. Still, it looks to me like the money would be better spent on widely available plastic explosives or dynamite.
These numbers are very rough, but I think they do highlight one of the prime problems of chemical warfare: delivery. If that same amount of material could be individually targeted then one could kill millions. Biological warfare at least has the advantage of contagion if the right pathogen is chosen.
Caveat: I haven't rechecked all the numbers. Later.