Hiroshima Day – The Mathematics of Nuclear Chain Reaction

The atomic bomb dropped on Hiroshima (Aug 6, 1945) used a critical mass of uranium‑235. The mathematics of neutron diffusion and multiplication is described by the neutron transport equation. A ‘critical’ assembly has a multiplication factor k = 1 (each fission causes one subsequent fission). For k > 1, the reaction grows exponentially. The bomb’s design involved solving partial differential equations for neutron flux, often using the Fermi age model. The same mathematics now powers nuclear reactors, with control rods to keep k = 1. Mathematics gives both destruction and clean energy.