introduction to nuclear astrophysics
TRANSCRIPT
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Zach Meisel, JINA-CEE PAN 2020 slide 1
Introduction to Nuclear Astrophysics
Zach MeiselPAN 2020
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Nuclear Astrophysics is the study of:
Extremely dense matter
Energy generation in stars and stellar
explosions
The origin of the elements
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Why is this barn red?
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Wm. F. Sheehan Ref. Chem. 1976
Lots of iron!
A lot less gold!
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Nuclear reactions provide the power for starsThis was known as of ~1920 due to the sun’s age:
- Chemical bond energy: ~eV- Nuclear bond energy: ~MeV = 106 eV- Solar Energy release: ~2x1045 eV/s- Nuclei in the sun: ~6x1056
If the sun were powered by chemical energy:Age=(#nuclei)(energy/nucleus)/(solar energy release)
=(6x1056 atoms)(1eV/atom)/(2x1045 eV/s)=3x1011 s~9,500 years …much too short!
For nuclear energy, 1MeV/nucleus: ~9.5 Gyr…about right!
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What drives fusion in stars? Binding Energy
FePb
H
C
FePb
H
C
Fusion winds up making a lot of iron! ⟶ Barns are red
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What drives fusion in stars? Binding Energy
E=mc2
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“I am the badge of Phanes”
Numismatik Lanz
Where did this come from?
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Numismatik Lanz
Where did this come from?
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Where is gold made?
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Where is gold made?
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LIGO/VIRGO NS Merger: https://www.youtube.com/watch?v=_SQbaILipjY
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LIGO BH Merger: https://www.youtube.com/watch?v=QyDcTbR-kEA
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Zach Meisel, JINA-CEE PAN 2020 slide 15NASA, ESA, ESO, Tanvir et al.
Kilanova: a signature of gold production
(many other elements too!)
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How is stuff heavier than iron made?
Fe
Pb
H
C
fusion
?neutron capture
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Detour: The valley of beta stability
FePb
H
C
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Detour: The valley of beta stability
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Zach Meisel, JINA-CEE PAN 2020 slide 19https://www.youtube.com/watch?v=UTOp_2ZVZmM
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Unstable nuclei decay back to the valley of stability
Z
N
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Nucleosynthesis can proceed through exotic nuclei
s -processr -process
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How fast are ‘slow’ and ‘rapid’ neutron captures?‘Slow’ or ‘rapid’ neutron capture is with respect to a nucleus’s β-decay half-life.
Z
N
Z
N
Case a: 𝜏𝜏𝑛𝑛−𝑐𝑐𝑐𝑐𝑐𝑐 ~500𝑦𝑦𝑦𝑦𝑦𝑦Example paths for neutron-capture, starting with 150Sm:
Case b: 𝜏𝜏𝑛𝑛−𝑐𝑐𝑐𝑐𝑐𝑐 ~1𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤
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Neutron-capture time-scale: ‘s’-process
Time-scale for ‘slow’ neutron capture1. ~108 neutrons in a box of 1cm3, each moving from thermal velocity2. ~1/6 leave a single box side with a velocity given by:
• E~kT ~mv2 v= 𝑘𝑘𝑘𝑘𝑚𝑚≈ 25𝑘𝑘𝑘𝑘𝑘𝑘
10−27𝑘𝑘𝑘𝑘≈ 109cm/sec
3. 1/6 of the neutrons leave from a cube face, with 1cm2 area every10-9 seconds• neutron flux ~1017 neutrons/cm2/sec
4. neutron-capture cross-section (at ~25keV): ~100mb = 10-25cm2
5. neutron-capture rate = (flux)x(cross-section)≈ 1017 neutrons/cm2/sec x 10-25 cm2 = 10-8/sec
6. neutron-capture time = 1/Rate ≈108seconds ~ 1 decade
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Neutron-capture time-scale: ‘r’-process
Time-scale for ‘slow’ neutron capture1. ~1020 neutrons in a box of 1cm3, each moving from thermal velocity2. ~1/6 leave a single box side with a velocity given by:
• E~kT ~mv2 v= 𝑘𝑘𝑘𝑘𝑚𝑚≈ 1000𝑘𝑘𝑘𝑘𝑘𝑘
10−27𝑘𝑘𝑘𝑘≈ 109cm/sec
3. 1/6 of the neutrons leave from a cube face, with 1cm2 area every10-9 seconds• neutron flux ~1029 neutrons/cm2/sec
4. neutron-capture cross-section (at ~1000keV): ~10mb = 10-26cm2
5. neutron-capture rate = (flux)x(cross-section)≈ 1029 neutrons/cm2/sec x 10-26 cm2 = 103/sec
6. neutron-capture time = 1/Rate ≈10-3seconds ~ 1 millisecond
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Zach Meisel, JINA-CEE PAN 2020 slide 26https://youtu.be/LHK6yy-NMKo
The r-process in action
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Where does strontium come from?
Sr is a Ca substitute
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Where does strontium come from? Sakurai’s Object
P. Woodward, U Minn.Yukio Sakurai
F. Herwig, U. Victoria
Model Results
Knobs were tuned here!
Sakurai’s Object Modeler:
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Big BangFusion
Fe-peak
Neutron-capture
s-process
r-processN=50N=82
N=126
“Magic” numbers
Everything around you was processed in a star
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Everything around you was processed in a star
Jennifer Johnson, OSU
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Regular stars made ~1/2 of the stuff around you Stellar explosions made most of the rest
The gas released formed everything around you
Most stars eventually become ‘planetary nebulae’ Some stars explode, like ‘supernovae’
Everything around you was processed in a star
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Astronomicalobservations
Nuclear physicsexperiments Nuclear physics
theory
Astrophysicstheory Nuclear
Astrophysics
What do nuclear astrophysicists actually do?
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Nuclear Physics ExperimentsMeasure properties of nuclei, e.g.
masseshalf-livesreaction cross sectionsnuclear structurefission products
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Nuclear Physics TheoryCalculate properties of nuclei, e.g.
masseshalf-livesreaction cross sectionsnuclear structurefission products
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Simulate astrophysical environments, e.g.stellar burningsupernovaenovaex-ray burstsneutron star mergers
Astrophysics Theory
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Observe astrophysical environments, e.g.old starssupernovaenovaex-ray burstscooling neutron stars
Astronomical Observations
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Summary
Nuclear astrophysics is the study of the origin of the elements,extremely dense matter,and cosmic nuclear energy generation.
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You are star stuff