Body

chem 100

November 19

Last of Chapter 8

Thermonuclear Power

Fission as Nuclear Power Source

In 1930-1940's physicists figured our sun's energy source
- reaction of small nuclei
- fuse together into larger nuclei
- decrease in mass
- mass converted to energy E=mc²
By 1950's we had harnessed nuclear fission
- neutral particle + nucleus--> fragments
- bombs
- reactors, power sources
Fusion was more elusive
- fuel is available
- D = ₁2H = heavy hydrogen
  - T = rare = ₁3H
- lots of water, traces of D
- easier to separate than²³⁵U and ²³⁸U
  - much larger relative mass difference
- lots of energy
  - 2 ₁2D ---> ₂3He + n + lots of energy
  - 2 ₁2D ----> ₂4He
Need to bring nuclei extremely close
- + charges repel
- need serious forces
- easiest with high temperature (>50,000 K)
  - collisions are hard, nuclei get close
- pressure is unlikely
  - except in dense stars
H Bomb is short term solution
- Fission bomb develops heat, pressure
- Fusion reaction occurs in few milliseconds

Much harder in a reactor
- Fission can run fairly cool, but fusion is intense heat
- Atoms can be ionized
  - Ions (charged) can be trapped in magnetic fields
  - With right design, can be heated and compressed
    - but energy release destabilizes the fields
- Newer methods try magnets to confine
  - laser pulses to heat
  - fuel in tiny capsules (microscopic)
  - fusion using lasers

Muon Induced fusion

muon based fusion (with animation)

physicists particle collection includes negative muon
- about 200 times mass of electron
- lives about 1 microsecond
- if stopped, will act briefly like fat electron
  - chemical bond length is inversely proportional to electron mass
  - muon bond holds nuclei very, very close
  - bond length < 1/200 normal bond
  - close enough that some nuclei will undergo fusion
- can actually see high energy (fusion) in liquid D₂ bubble chambers
- but, rarely make enough extra muons
- they last 1 microsecond, but fusion step is slower
  - can't sustain explosion

Cold Fusion

One of the great science stories of the 1980's-90's. An electrochemistry experiment with deuterium produced unexpected energy. After exhausting the usual explanations the authors tentatively assigned the energy to nuclear fusion by hydrogen within the electrodes. Since this could offer promise of low cost and very safe reactors, it got lots of press coverage. This was also very controversial. The work generally could not be duplicated under controlled conditions and all of the obvious tests for fusion came up negative (gamma ray signature of ³He and detection of He gas.) Although there still is fringe group pursuing the topic, it is generally accepted that this was either scientific fraud or self deception. (The major flaw is tied to accepting the hypothesis and fitting/selecting data to further support that one concept.)

A href="http://www.physlink.com/Education/AskExperts/ae330.cfm">cold fusion

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