for anyone who is interested here's some info about different dirty bomb materials [hello, NSA]
...dirty bombs do not use fissile material. ... These materials...are not radioactive enough
. Their radioactive emissions don't travel far and are blocked by simple barriers, including skin and clothing
. A dirty bomb would use small amounts of highly radioactive materials such as cesium or cobalt, not uranium. Even specks of these elements send out deadly gamma rays that penetrate walls and bodies causing immediate injury. The Federation of American Scientists has calculated
that a mere 41 grams (1.4 ounces) of cesium-137
in a dirty bomb could contaminate most of Manhattan. By contrast, it would take 1,460 tons of low-enriched uranium
to get the same levels of radiation.
Home > Programs > Strategic Security > Nuclear Information Project > Non-Proliferation and Arms Control
Uranium and Dirty Bombs
Even tiny amounts of a material with a half life of days will be intensely radioactive because the material is disintegrating so fast. It will not, however, be a good dirty bomb material because too much will decay while the bomb is being built. Even if the bomb disperses the material, just waiting several days for the material to decay naturally will allow people to return to the contaminated areas. At the opposite extreme, radioactive materials with extremely long half lives just do not decay quickly enough to cause much radiation. Looked at another way, to get dangerous levels of radiation requires huge quantities of material if the material decays very slowly. Uranium is more than 99% U-238, which has a half life of almost five billion years
IsotopePrimary RadiationWeight of 1 CurieWeight of 3500 Curies
Americum-241 alpha 0.30 grams 1.05 kilograms
Cobalt-60 gamma 0.91 milligrams 3.20 grams
Californium-252 alpha 1.88 milligrams 6.59 grams
Cesium-137 beta/gamma 11.8 milligrams 41.40 grams
Iridium-192 beta/gamma 0.11 milligrams 0.39 grams
Plutonium-239 alpha 16.8 grams 58.70 kilograms
Plutonium-240 alpha 4.54 grams 15.90 kilograms
Radium-226 alpha 1.04 grams 3.64 kilograms
Strontium-90 beta 7.17 milligrams 25.1 grams
Uranium-238 alpha 3.06 tons 10.7 thousand tons
Depleted Uranium (0.2%) alpha 2.10 tons 7.35 thousand tons
Natural Uranium (0.70%) alpha 1.50 tons 5.24 thousand tons
Commercial Uranium (5%) alpha 0.42 tons 1.46 thousand tons
We're talking about 900 lbs of yellow cake per a single curie.
And if it's enriched to U 238 we're talking 6700 lbs of enriched uranium per single curie.
It doesn't seem that turning this yellow cake into a dirty bomb is going to be reasonably feasible. Certainly more could be done with the same resources.