introduction to nuclear astrophysics

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

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

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

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