24-3: harnessing the nucleus. per gram, average energy produced by… chemical reaction nuclear...

24-3: Harnessing the 24-3: Harnessing the NucleusNucleus

Per gram, average energy Per gram, average energy produced by…produced by…

Chemical reactionChemical reaction Nuclear reactionNuclear reaction

50 kJ50 kJ 1,000,000 kJ1,000,000 kJ

Nuclear FissionNuclear Fission

Enrico Fermi: bombarded uranium with Enrico Fermi: bombarded uranium with neutronsneutrons

Hahn and Strassman: repeated Fermi’s Hahn and Strassman: repeated Fermi’s experiment, but produced bariumexperiment, but produced barium

Lise Meitner: found reason for barium Lise Meitner: found reason for barium impurity – first to identify a nuclear fission impurity – first to identify a nuclear fission rxnrxn

Nuclear fission rxnNuclear fission rxn: a large nucleus is split : a large nucleus is split into two smaller nucleiinto two smaller nuclei

Enrico Fermi

Lise Meitner

““Missing Mass”Missing Mass”

In a fission rxn, the mass of the In a fission rxn, the mass of the products is slightly less than the products is slightly less than the mass of the reactants. mass of the reactants. Missing mass is converted into energy:Missing mass is converted into energy: E = mcE = mc22

c = speed of light, 3 x 10c = speed of light, 3 x 1088 m/s m/s Nuclear chain rxnNuclear chain rxn: series of fission : series of fission

rxns started by extra neutrons in one rxns started by extra neutrons in one reactionreaction

Nuclear ReactorsNuclear Reactors

Nuclear power plants contain too little fuel Nuclear power plants contain too little fuel to explode like a nuclear bombto explode like a nuclear bomb

Three Mile Island (1979): scare of Three Mile Island (1979): scare of meltdown, due to operator errormeltdown, due to operator error

Chernobyl incident (1986): reactor Chernobyl incident (1986): reactor destroyed, due to graphite fire (operator destroyed, due to graphite fire (operator error); radiation leaded out, causing error); radiation leaded out, causing deaths and cancersdeaths and cancers

Nuclear waste disposal is a problemNuclear waste disposal is a problem

Three Mile Island Power Three Mile Island Power PlantPlant

Chernobyl Power PlantChernobyl Power Plant

A Chernobyl firefighterA Chernobyl firefighter

Nuclear FusionNuclear Fusion

Nuclear fusion:Nuclear fusion: two small nuclei join to two small nuclei join to form a larger nucleusform a larger nucleus

Ex: Ex: Problems: repulsion of atomic nuclei to Problems: repulsion of atomic nuclei to

come togethercome together Stripping off electrons creates plasmaStripping off electrons creates plasma Must reach high temp. in order for atoms Must reach high temp. in order for atoms

to move togetherto move together Thermonuclear rxnThermonuclear rxn: fusion with extreme : fusion with extreme

heat (stars)heat (stars)

Fusion ResearchFusion Research

Temp. cannot be withstoodTemp. cannot be withstood TokamakTokamak: magnetic device needed : magnetic device needed

to control temp.to control temp.

Cold FusionCold Fusion

Cold fusionCold fusion: fusion without the need : fusion without the need for extreme heatfor extreme heat

Pons and Fleishman: may have Pons and Fleishman: may have produced a cold fusion rxn with produced a cold fusion rxn with heavy waterheavy water