David Hahn (born October 30, 1976) is a man known for his attempt to build a fast breeder nuclear reactor in 1994 in his backyard shed in Commerce Township, Michigan, a suburb of Detroit, at age 17.

Hahn, nicknamed the "Radioactive Boy Scout", is an Eagle Scout who got a merit badge in Atomic Energy and spent years tinkering with basement chemistry which sometimes resulted in small explosions and other mishaps. He was inspired in part by reading The Golden Book of Chemistry Experiments, and tried to collect samples of every element in the periodic table, including the radioactive ones. Hahn diligently amassed this radioactive material by collecting small amounts from household products, such as americium from smoke detectors, thorium from camping lantern mantles, radium from clocks and tritium (as neutron moderator) from gunsights. His "reactor" was a large, bored-out block of lead, and he used lithium from $1,000 worth of stolen batteries to purify the thorium ash using a Bunsen burner.

Hahn posed as an adult scientist or professor to gain the trust of many professionals in letters, despite the presence of misspellings and obvious errors in his letters to them. Hahn ultimately hoped to create a breeder reactor, using low-level isotopes to transform samples of thorium and uranium into fissionable isotopes.