3 mg of U-235 is 0.003/235 or 1.3e-5 moles of U-235, which contains 6e23 x 1.3e-5, or 7.8e18 atoms. Each one, when fissioned, turns out about 200 MeV of energy, so that’s 1.6e21 MeV = 6.1e5 kT = 61 kg TNT equivalent. That’s enough to demolish a small-sized office building,  95% pure U-235 is sold … Continue reading Cabover Drive Building Could Fly Through the Air