Midterm Solutions

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Midterm Solutions
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NE 201 Midterm Exam
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CNO cycle
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Clayton
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Helium Burning in Red-Giant Stars
Burbidge, Burbidge, Fowler, Hoyle B2FH (1957)
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No stable nuclei with A5 or A8
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Clayton
t1/2(8Be) 10-16 sec
At T 1x108K and r 105 g/cc N(8Be)/N(4He)
1x10-9
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Triple Alpha Reaction
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Gpair
Clayton
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12C(a,a)12C Ncoin12C-a(7.65 MeV) /Na(7.65
MeV) Grad(7.65 MeV)/Gtot(7.65 MeV)
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Nuclear Physics A 233 (1974) 495
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Subthreshold resonance important in 12C(a,g)16O
reaction
E0 300 keV
Clayton
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Dyer and Barnes
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Fate of Stars

• For stars with masses lt 10 MSun
• No further nuclear reactions possible
• ? White Dwarf (maximum mass 1.4 MSun)
• For more massive stars,
• No such quiet fate possible
• ? Neutron Star or Black Hole

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Advanced stellar burning

• 12C 12C ? 24Mg g, 20Ne 4He
• 16O 16O ? 32S g, 28Si 4He

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Through successive photodisintegration and
captures of 4He, 28Si ? 56Ni At this
point the star is on its deathbed, No further
energy generation possible
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Late stage massive star
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Clayton
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Supernova Explosion

• Temperature goes up
• Density goes up
• p e- ? n ne
• e e- ? n n
• 99 of SN energy comes off in neutrinos

SN 1987a
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Neutrinos from SN1987aobserved by Kamiokande and
IMB underground telescopes
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Compton Gamma-Ray Observatory
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26Al gamma rays
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44Ti gamma rays observed from CasA
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56Co gamma rays observed from SN1987a
b/EC
56Co t1/2 77 days
847 keV
56Fe stable
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Pre-solar graphite grains from Murchison
meteorite containing TiC inclusions
E. Zinner et al. Washington Univ.
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