Schematic representation of the two methods with which to assemble an atomic bomb. An A-bomb produces its explosive energy through nuclear fission reactions alone. A mass of fissile material (enriched uranium or plutonium) is assembled into a supercritical mass—the amount of material needed to start an exponentially growing nuclear chain reaction—either by shooting one piece of sub-critical material into another (the "gun" method, shown on top here), or by compressing a sub-critical sphere of material using chemical explosives to many times its original density (the "implosion" method, at bottom).Image credit: Fastfission
 | This picture of the day has been featured on Portal:Technology. |