U-235
“Experimentalists assembled perfect shining cubes of uranium into near-critical masses by hand. One man, Harry Daghlian, working alone at night, let slip one cube too many, frantically grabbed at the mound to halt the chain reaction, saw the shimmering blue aura of ionization in the air, and died two weeks later of radiation poisoning. Later Louis Slotin used a screwdriver to prop up a radioactive block and lost his life when the screwdriver slipped. Like so many of these worldly scientists he had performed a faulty kind of risk assessment, unconsciously mis-multiplying a low-probability of accident (one in a hundred? one in twenty?) by a high cost (nearly infinite).”
-J. Gleick, “Genius: The life and science of Richard Feynman”
The work done in Los Alamos was stranger and more dangerous than anything from a science fiction novel. There we chemical-based humans were messing around with atomic-based interactions; we were completely out of our league because our bodies simply can’t tell the difference between no radioactive danger and immediate radioactive danger until it’s too late. And keep in mind the general level of technology being used in the research: this was still 1944.
