EXPLOSIVE SCIENCE
Dear HIW,
How do nuclear bomb makers find out the critical mass of the uranium used before it explodes? If they were to get it wrong, surely they would be killed in a premature explosion. Stephen
The first controlled fission experiment to determine the critical mass of uranium for a nuclear chain reaction was carried out by physicists Enrico Fermi and Leo Szilard in 1942. Critical mass is how much material is needed in order to start a nuclear reaction. They used 40,000 graphite blocks coupled with 19,000 pieces of uranium to conduct their experiment. They found that the critical mass of uranium-235 was around 50 kilograms. They also found that the shape and type of fuel changed its critical mass. During construction, the fuel is kept separate within the bomb in masses below the critical mass. Only when they are detonated do these masses combine to trigger a reaction.