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Nuclear FissionNuclear Fission
The basis for The basis for
old bombs and old bombs and
new energynew energy
History of Nuclear FissionHistory of Nuclear Fission
In 1939, German scientists Lise Meitner and In 1939, German scientists Lise Meitner and Otto Hahn discovered that the uranium Otto Hahn discovered that the uranium nucleus could be split nucleus could be split (review atomic structure on board)(review atomic structure on board)
FissionFission is the fancy word for splitting is the fancy word for splitting The fission reaction produced The fission reaction produced a lot a lot of energyof energy
• MUCH more energy than burning fossil fuelsMUCH more energy than burning fossil fuels
Fission could result in a Fission could result in a chain reactionchain reaction that that could grow faster and more energetic quicklycould grow faster and more energetic quickly
The energy comes from E = mcThe energy comes from E = mc22
History of Nuclear FissionHistory of Nuclear Fission
Meitner sent the information to her nephew, Otto Meitner sent the information to her nephew, Otto Frisch, in the U.S.Frisch, in the U.S. Germans had the infoGermans had the info the info could be used to make a bombthe info could be used to make a bomb
Meitner’s colleague, Leo Szilard, wrote the famous Meitner’s colleague, Leo Szilard, wrote the famous letter to FDR letter to FDR the letter argued for an intense effort to create a nuclear the letter argued for an intense effort to create a nuclear
weapon before the Germansweapon before the Germans the letter was signed by Einsteinthe letter was signed by Einstein FDR initiated the FDR initiated the Manhattan ProjectManhattan Project as a result as a result
History of Nuclear FissionHistory of Nuclear Fission
Hahn received a Nobel prize, Meitner didn’t. Hahn received a Nobel prize, Meitner didn’t.
Meitner emigrated to the USMeitner emigrated to the US but she refused to work on the Manhattan Projectbut she refused to work on the Manhattan Project
The Fission ReactionThe Fission Reaction
U-235 + neutron U-235 + neutron U-236* U-236* U-236* is very unstable and undergoes U-236* is very unstable and undergoes
spontaneous fissionspontaneous fission
U-236* U-236* 2 fission products + 3 neutrons + 2 fission products + 3 neutrons + ENERGYENERGY
The 3 neutrons can go on to cause 3 more fissions, The 3 neutrons can go on to cause 3 more fissions, creating 9 neutronscreating 9 neutrons
The 9 neutrons can go on to cause 27 more fissionsThe 9 neutrons can go on to cause 27 more fissions etc…etc…
The Nuclear Fission ReactionThe Nuclear Fission Reaction
Notice that no GREENHOUSE GASES are produced
Fission WeaponsFission Weapons
Making the Making the Atom BombAtom Bomb is easy in theory is easy in theory the fission reaction does NOT need to be the fission reaction does NOT need to be
controlledcontrolled
The key is to rapidly create a The key is to rapidly create a supercritical supercritical massmass of fissionable material of fissionable material A A critical masscritical mass is the smallest amount of fissile is the smallest amount of fissile
material needed for a sustained nuclear chain material needed for a sustained nuclear chain reaction. reaction.
must bring together two must bring together two subcritical massessubcritical masses
The Hiroshima BombThe Hiroshima Bomb Gun barrel design called Gun barrel design called Little BoyLittle Boy
Uses enriched Uranium fuelUses enriched Uranium fuel Uranium is naturally occurringUranium is naturally occurring Uranium is a less efficient fuelUranium is a less efficient fuel Bomb was approx. 33 lbs fuel = 16 kilotons TNTBomb was approx. 33 lbs fuel = 16 kilotons TNT
= 32,000,000 lbs TNT = 32,000,000 lbs TNT = 800 semi-trucks = 800 semi-trucks
fully loadedfully loaded One subcritical mass is fired down a tube at the other subcritical One subcritical mass is fired down a tube at the other subcritical
massmass
Bomb resulted in approx 140,000 deathsBomb resulted in approx 140,000 deaths
The Little Boy designThe Little Boy design
The Trinity and Nagasaki BombsThe Trinity and Nagasaki Bombs Spherical implosion design called Spherical implosion design called Fat Man (or “The Gadget”)Fat Man (or “The Gadget”)
Very complicated, which is why they tested itVery complicated, which is why they tested it
Uses Plutonium fuelUses Plutonium fuel Plutonium is not naturally occurringPlutonium is not naturally occurring
• Must be Must be bredbred from from fertilefertile fuel, usually U-238 fuel, usually U-238 Plutonium is a more efficient fuelPlutonium is a more efficient fuel Bomb was approx. 11 lbs fuel = 20 kilotons TNT Bomb was approx. 11 lbs fuel = 20 kilotons TNT
= 40,000,000 lbs TNT = 40,000,000 lbs TNT = 1000 semi trucks fully loaded= 1000 semi trucks fully loaded
Two hemispheres of fuel are imploded inward toward each otherTwo hemispheres of fuel are imploded inward toward each other
The Nagasaki bomb resulted in approx. 80,000 deathsThe Nagasaki bomb resulted in approx. 80,000 deaths
The Fat Man designThe Fat Man design
Obtaining Weapons Grade FuelObtaining Weapons Grade Fuel The fuel in a nuclear bomb must be 80-100% pureThe fuel in a nuclear bomb must be 80-100% pure
Natural uranium is only 0.7% U-235 (99.3% U-238)Natural uranium is only 0.7% U-235 (99.3% U-238) Power plant fuel only about 3%Power plant fuel only about 3%
Uranium is naturally occurring Uranium is naturally occurring but it must be concentrated, or but it must be concentrated, or enrichedenriched Enrichment is VERY difficult, requires huge centrifugesEnrichment is VERY difficult, requires huge centrifuges
Plutonium does not occur naturallyPlutonium does not occur naturally but it can be made from waste nuclear fuelbut it can be made from waste nuclear fuel process is EASY, but requires a breeder reactorprocess is EASY, but requires a breeder reactor
Good news, Bad newsGood news, Bad news The bad news is that nuclear weapons are easy to The bad news is that nuclear weapons are easy to
make if you have make if you have weapons grade fuelweapons grade fuel
The good news is that The good news is that weapons grade fuelweapons grade fuel is VERY is VERY difficult to come bydifficult to come by
We are reluctant to let rogue nations build any kind of We are reluctant to let rogue nations build any kind of nuclear facility nuclear facility we’re afraid the plant might be a centrifuge for we’re afraid the plant might be a centrifuge for enrichingenriching
UraniumUranium or a reactor for or a reactor for breedingbreeding Plutonium Plutonium