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Nucleosynthesis and formation of the elements
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Cosmic abundance of the elements
Mass number
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Nucleosynthesis Big Bang – ca 12 000 Ma Supernova – ca 5 000 Ma
Condensation of matter and formation of the known elements . . .
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In the seconds following the Big Bang
Condensation of matter into p and n Formation of the fuel of the stars H et He T 3 x 109 K p + e– n + v 1H + n 2H + g 2H + p 3He + g 3He + n 4He + g
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Diagramme Hertzprung-Russel
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1st Generation Stars - H fusion and production of 4He
1H + 1H 2H + b+ + v MeV 2H + 1H 3He + g MeV 3He + 3He 4He + 1H + 1H MeV
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2nd Generation Stars (Our sun today) Fusion by CNO reaction
12C + 1H 13N + g 13N 13C + b+ + v 13C + 1H 14N + g 14N + 1H 15O + g 15O 15N + b+ + v 15N + 1H 12C + 4He
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He Fusion in Red Giants (~ 106 to 107 years)
4He + 4He 8Be 8Be + 4He 12C + g 12C burning (<1000 years) 12C + 4He 16O 12C + 12C 20Ne + 4He + g 16O burning (<1 year) 16O + 16O 28Si + 4He + g 12C + 16O 24Mg + 4He + g
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End of a Red Giant's life: Si combustion: lasts about 1day
28Si + 4He 32S + g 32S + 4He 36Ar + g 36Ar + 4He 40Ca + g 40Ca + 4He 44Ti + g 44Ca + 2b+ 44Ti + 4He 48Cr + g 48Ti + 2b+ 48Cr + 4He 52Fe 52Cr + 2b+ 52Fe + 4He 56Ni + g 56Fe + 2b+ 56Ni / 56Fe + 4He impossible . . .
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Nuclear binding energy maximum
maximum at 56Fe after, fusion becomes endothermic nucleosynthesis beyond 56Fe is by neutron capture and by fission of nuclides with Z > 90 (uranium and transuranics)
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Supernova and 2nd generation stars
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Supernova remnants Cygnus Loop (HST): green=H, red=S+, blue=O++
Cas A in x-rays (Chandra) Vela Remnant of SN386, with central pulsar (Chandra) SN1998bu
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Nucleosynthesis by n and p capture
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Elements > Fe: neuton activation
CNO Fe: produced in the final stage of fusion Equilibrium burning Elements > Fe: neuton activation in supernova Mg Ar Na Al Cr P Ti Mn Cl Fissionable Elements K Co F V Instable
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