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Nuclear Fission & Fusion

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History: 

Hahn & Strassman (1939) 

•Bombarded Uranium-235 samples with neutronsexpecting the Uranium-235 to capture neutrons 

•Instead, the products showed different chemicalproperties that they could not explain 

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•Explained Hahn & Strassman results.

•Instead of heavier Uranium, it had splitinto smaller elements =  Nuclear Fission

Meitner & Frisch 

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Nuclear Forces

1. Electric repulsion – ________ charge particlesrepel each other 

same

2. Strong Nuclear Force – causes protons andneutrons to ________ each other 

attract

•Stable Nuclei = strong nuclear force is ________ than repulsion force 

greater

•Unstable Nuclei = strong nuclear force is ________ than repulsion force 

oHave too many or too few neutrons in nucleus 

oHave more than 83 protons in nucleus 

oWill decay into a more stable nucleus 

less

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Nuclear Fission  – splitting of

heavier nuclei into lighternuclei.

U235

92n

1

0Ba

137

56Xe

84

36n

1

0energy +  +15 +  + 

How much energy? E=mc2 

_______= _______ x (_____ _ _____)2 c=3.0x108 Energy mass speed of light

E=mc2 explains _____ _____ (total mass of

nucleus is less than sum of individual particles) 

mass defect

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Nuclear Chain Reactions: 

•Nuclear fission releases more neutrons which trigger

more fission reactions 

•The number of ________ released determines thesuccess of a chain reaction 

neutrons

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Applications of ControllingChain Reactions

  Must have a minimum amount of radioactive isotope

to sustain a chain reaction =_________ _______  

1. Atomic Bomb (fission bomb) – Triggering a chain reaction in 

U-235 or Pu-239 

CRITICAL MASS

2. Nuclear Power Plants – Convert heat energy from fissionchain reaction into __________.electricity

Control chain reaction with ________ _____ thatabsorb ________ emitted after fission reaction. 

control rodsneutrons

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Nuclear Fusion - Energy released whentwo light nuclei combine or fuse 

•However, a large amount of energy isrequired to start a fusion reaction: 

o Need this energy to overcome ________ forcesof protons. o Extremely high temperatures can provide start-upenergy. 

repulsion

More energy in fusing hydrogen that fission of uranium

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Nuclear Fusion

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Stars energy is produced

through fusion reactions 

Fusion occurs until Fe is

produced because lessenergy is released thanrequired to fuse Fe nuclei =

 _____ ____ ____  Star burns out

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Cold Fusion:

Efforts are beingmade to start andsustain a fusion

reaction at lowertemperatures, in

other words with alower amount ofinput energy