CHEM H90 Lecture Notes - Lecture 18: Lise Meitner, Nuclear Fission, Racquetball
Nuclear Power
• Lisa Meitner
o working with Hahn, first argued that a chain reaction was possible
o fled Germany in late 1930’s
o her work led to Einstein letter to Roosevelt
• Fission
o nuclear fission is the splitting of a large nucleus into smaller ones with the release
of energy
o energy is released because the sum of the masses of these fragments is less than
the original mass
o this “missing” mass (about 0.1% of the original mass) has been converted into
energy according to Einstein’s E=mc2 equation
• critical mass
o for given enrichment of U, the critical mass is the amount that can be put together
without a chain reaction
o Pure 235U in a sphere goes critical at diameter 17cm, weighing 52kg
o brining sub-critical masses together fast enough is vital to avoid fizzle of nuclear
bombs
o cannot have decaying impurities, as they will start reaction
• nuclear weapons
o the isotopes U-235 and U-238 behave essentially the same in all chemical
reactions, so the separation of these two isotopes is extremely difficult and relies
on advanced technology that is not readily available
• Quiz #15
o first law of thermodynamics is energy is always conserved
o burning fossil fuels releases CO2
• nuclear power
o reactors
o safety
o waste
o reactors now built for commercial use, submarine power, and spacecraft
• basic idea
o create a controlled sustainable chain reaction (about 1 neutron re-absorbed per
fission)
o first done by Fermi using a ‘pile’ of uranium bricks in disused racketball court at
U of Chicago
o used graphite blocks as moderator (absorbs neutrons)
o went critical 1942
• nuclear power worldwide
o about 15% of electricity is generated by 440 nuclear power plants
Organometallic Chemistry and Catalysis (Kristen Hewitt)
• why study catalysis
o speed up reactions
o lower the activation energy
o gain access to new and unusual structures
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