1Reminders:• Research Paper #1 due in class today, October 31.• Homework #8 due next Wednesday• Finish Reading Chapter 6 on Nuclear Energy• Extra Credit #5 due next FridayChemical reactions also release energy from massÆenergyconversion.However, chemical reactions involve the orbital electrons and typical mass differences are very small.Recall the 109difference in energy!Chemical versus NuclearNeutron Induced FissionFermi first did it, Lise Meitner and “helpers” figured out what was happening.Chain reaction: neutrons making fission that makes more neutrons, that makes more fission that makes more neutrons,that makes more fission that makes more neutrons, that makes more fission that makes more neutrons, that makes more fission that makes moreIf don’t get swallowedthe 3 free neutrons can goinduce more fission.Ur 2351stgeneration2nd generation3rdgeneration100 generationsper microsecond!2 x 2 x 2 .…x2 fissionseach with LOTS of energy.BOOM!BOOM!Fission Nuclear Explosion“atomic bomb”Uranium 235or plutoniumEach fission releases multiple neutrons. Each of them can induce further fission reactions.This means it is possible to have a chain reaction.However, one cannot allow too many neutrons to “escape” or be “absorbed” by other materials or there is not “runaway”reaction.That is why one needs a “critical mass” which depends on the shape to keep the volume to surface area ratio large.Reactors are designed to give steady, self-sustained fission. They use the released neutrons to induce more fissions.Bombs are designed to get exponential buildup 2Æ4Æ8Æ16Æ2Manhattan ProjectWorld War II project to design and build atomic weapons.Starting in New York City in the basement of the Columbia University Pupin Physics Building.My old office 6 floors above some of the original labs.First reactor built in 1943 in Chicago by Enrico Fermi under the football stadium.First Chain ReactionSpecial control rods are inserted by hand to add material to absorb neutrons, and thus prevent a full “runaway” reaction. Fermi was calculating when to insert them as they did the experiment!Only certain heavy nuclei can be induced to fission easily.Uranium(235) and Plutonium(239) are the most common.Natural Uranium (mined from the earth) is 99.3% U(238) and only 0.7% U(235).U(238) is a different isotope. Same number of protons, but three extra neutrons. How big a difference can this make? Big!Why Ur 235 not 238? U 238 has 3 extra neutrons help hold it together.urp!Eats extra neutrons!Atomic weapons development involves two major aspects.One is designing the warhead and explosives.The other is separating U(235) from the mostly U(238) in Uranium ore.Two Plutonium(239) bombs developed. One tested in July 1945. One dropped on Nagasaki in August 1945.One Uranium(235) bomb developed. No testing. One dropped on Hiroshima in August 1945.Weight 4 tons. Energy released ~ 12.5 kilotons of TNT equivalent.Estimated 140,000 killed. Almost everyone within 1 kilometer radius killed instantly.Hiroshima3Uranium Bomb: “Little Boy”Neutron initiatorUranium targetUraniumprojectileExtract nearly pure Uranium 235 (90%+)GunBarrelTrinity and “Fat Man”Bomb based on plutonium 239Prepare “critical mass”Neutron initiatorConventionalexplosivesAtomic weapons are viewed very differently around the world.• They abruptly ended World War II.• Americans who developed these weapons were often viewed as heroes.• They represent the most destructive weapon every made.What do you think?A) Dropping the bombs was justified to end the war and save the lives of Allied forces.B) They should have done a test to show the new weapon and forced a surrender, taking a risk that it would not work.C) Dropping the bomb was a warning to the Russians and was unjustified.D) Any mass killing of civilians is unjustified even in wartime.Where do countries obtain their Uranium Fuel?Uranium mine in NamibiaUranium pit mine in Saskatchewan4Years ago, ceramic plate manufacturers thought it was a good idea to add Uranium Oxide to the ceramic glaze that covered their dinner plates. It did make a bright orange attractive color, but it also made them radioactive.Uranium Dinnerware?Demonstration with Geiger Counter and plate.Uranium mining and milling became a large industry (1950’s) on the Colorado Plateau. The Grand JunctionOperations Office of the United States Atomic Energy Commission was headquarters for the enterprise, and bought all the uranium produced. Grand Junction also was home base for as many as 35 mining companies, including area offices of major mining corporations.Colorado UraniumWhere does the United States currently get Uranium?“Given the structure of the consortiums that operated the mines, it would be exceedingly difficult for Niger to transfer uranium to Iraq. Niger's uranium business consists of two mines, Somair and Cominak, which are run by French, Spanish, Japanese, German and Nigerian interests. If the government wanted to remove uranium from a mine, it would have to notify the consortium, which in turn is strictly monitored by the International Atomic Energy Agency. Moreover, because the two mines are closely regulated, quasi-governmental entities, selling uranium would require the approval of the minister of mines, the prime minister and probably the president. In short, there's simply too much oversight over too small an industry for a sale to have transpired.”Published on Sunday, July 6, 2003 by the New York TimesWhat I Didn't Find in Africa by Joseph C. Wilson 4thRemember though this is just the Uranium ore. The job of isotope separation is a big challenge.5In the “Gulf War I” in the early 1990’s the Iraqi government was developing a full facility for uranium enrichment.They were attempting to use electrostatic separation, which is a very large scale operation.Claims were made that they were restarting this program prior to the “Gulf War II”. It turned out not to be true.Enriching UraniumGaseous diffusion– Uranium gas pumped through porous membranes– Isotopes have different speeds at the same kinetic energy• Requires thousands of stages of separationRequires very large electric power inputRecall that natural Uranium is mostly U(238) which does not easily fission. Thus, to use in power plants it must be enriched in U(235) up to 3% and higher for weapons.Efficiency ~ (rpm)2Zippe design90,000 rpmElectrostatic Separation - utilizes very small difference in mass
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