Atomic WeaponsSelected critical massesPol179.lec3.S09 1Atomic WeaponsPol179.lec3.S09 2Two basic processes: fissionPol179.lec3.S09 3And fusionPol179.lec3.S09 4Nuclear fission by a neutron releases fission fragments plus 2 or 3 neutronsPol179.lec3.S09 5The extra neutrons can then split other nuclear, leading to a chain reactionPol179.lec3.S09 6Boom! http://www.youtube.com/watch?v=SBcyuwUHIbUPol179.lec3.S09 7If too many neutrons escape, you get a “fizzle”Pol179.lec3.S09 8If excess neutrons are absorbed, the result is a controlled chain reaction, as in a nuclear reactorPol179.lec3.S09 9The critical massis the amount of fissionable material required to sustain the chain reactionPol179.lec3.S09 10The weight of a CM depends on composition and density of the fissionable materialPol179.lec3.S09 11Fissionable materialTamper (e.g., beryllium)A tamperwill reflect neutrons back into the mass and reduce the weight needed for a critical massPol179.lec3.S09 12Uranium, thorium, plutonium can be fissionedPol179.lec3.S09 13Selected critical massesMaterial Weight (kg)Bare & tampedUranium-235 47.9/15Uranium-238 InfinitePlutonium 238/239 ~10/5 Curium 247 7Pol179.lec3.S09 14Higher purity reduces critical mass required for both U-235 and Pu-239Pol179.lec3.S09 15Original criticality tests done with spheres of plutonium & a screwdriverPol179.lec3.S09 16Gun-type device propels a slug of U-235 into a cylinder of U-235 to achieve critical mass—this is the type dropped on HiroshimaNB: this diagram is incorrect: the “target” is actually shot at the “bullet”Pol179.lec3.S09 17Implosion bomb uses explosives to compress PU-239 to critical mass—this was tested at Trinity and dropped on NagasakiPol179.lec3.S09 18Animated schematic of implosion devicePol179.lec3.S09 19Trinity deviceFat Man & Little BoySuitcase bomb modelPol179.lec3.S09 20Fusion reaction requires special conditionsPol179.lec3.S09 21These can be achieved only if the fusion fuel can be compressed and containedPol179.lec3.S09 22Teller-Ulam design for H-bomb uses a fission bomb to compress the fusion fuelPol179.lec3.S09 23How a thermonuclear device worksPol179.lec3.S09 24Pol179.lec3.S09 25Pol179.lec3.S09 26Pol179.lec3.S09 27Pol179.lec3.S09 28Thermonuclear bombs have gotten smallerPol179.lec3.S09 29Pol179.lec3.S09 30Neutron BombPol179.lec3.S09 31Low yield earth penetratorPol179.lec3.S09 32Pol179.lec3.S09 33Nuclear effects computerPol179.lec3.S09 3415 kiloton detonationThermal (speed of light)Blast (speed of sound)Pol179.lec3.S09 35Pol179.lec3.S09 36Teapot Test Series, February -May 1955Pol179.lec3.S09 37Ten kilotons at the White HousePol179.lec3.S09