Nuclear technology the element plutonium possesses an isotope that is sufficiently unstable for this process to be usable. Terrestrial plutonium does not currently occur naturally in sufficient quantities for such use, so it must be manufactured in a nuclear reactor. Ultimately, the Manhattan Project manufactured nuclear weapons based on each of these elements. They detonated the first nuclear weapon in a test code-named "Trinity", near Alamogordo, New Mexico, on July 16, 1945. The test was conducted to ensure that the implosion method of detonation would work, which it did. A uranium bomb, Little Boy, was dropped on the Japanese city Hiroshima on
Mark 18 nuclear bomb from the Mark 13 nuclear bomb and its ancestors the Mark 6 nuclear bomb, Mark 4 nuclear bomb, and Fat Man Mark 3 nuclear bomb of World War II. Its normal mixed uranium/plutonium fissile core ("pit") was replaced with over 60 kg of pure highly enriched uranium or HEU. With a natural uranium tamper layer, the bomb had over four critical masses of fissile material in the core, and was unsafe: the accidental detonation of even one of the detonator triggers would likely cause a significant (many kilotons of energy yield) explosion. An aluminum/boron chain designed to absorb neutrons was