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Nuclear Astrophysics. by Richard Cyburt. Creation of new elements is energy source of stars (and the sun). “We are made of star stuff….” Carl Sagan. The sun shines. 3.85e33 erg/s = 3.85e26 Watts. for at least ~4.5 bio years. The entire sun made of coal would last ~ 4000 years.

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Nuclear Astrophysics

by Richard Cyburt


Creation of new elements is energy source of stars (and the sun)

“We are made of star stuff….” Carl Sagan


The sun shines sun)

3.85e33 erg/s = 3.85e26 Watts

for at least ~4.5 bio years

The entire sun made of coal would last ~ 4000 years


Nucleus sun)Factories


Question 3 sun)How were the elements from iron to uranium made ?

(main question: r-process)

Committee for the Physics of the Universe (NRC/NAS)

“Connecting Quarks with the Cosmos” – 11 science questions for the new century



Elements in nature sun)

Made in the Big Bang


Elements in nature sun)

Made by fusion in stars…


Elements in nature sun)

How are the elements heavier than iron made?


Burning stages of a 25 solar mass star sun)

initially present: mostly hydrogen (~70% - from big bang)

Hydrogen burning

Hydrogen (1p,0n)

Helium (2p, 2n)

7Mio yrs

Helium burning

Helium (2p,2n)

Carbon (6p, 6n), Oxygen (8p,8n)

700,000 yrs

Carbon(+Ne) burning

Carbon (6p,6n)

Oxygen (8p,8n)

400 yrs

Oxygen burning

Oxygen (8p,8n)

Silicon (14p,14n)

8 months

Silicon burning

Silicon (14p,14n)

Nickel (28p,28n)

1 day


Average binding energy per nucleon (MeV) sun)

For stable nuclei !!!



Precollapse structure of massive star sun)

Iron core collapses and triggers supernova explosion


How to make Gold sun)

... and the other heavy elements


Atomic Nucleus sun)

Proton

Neutron


What is the universe made of? sun)

Hydrogen:

Helium:

Mass number = 1

Mass number = 4

Observed Nuclei in the Universe:

91.0%

Iron ?

8.9%



Iron: sun)

Gold:

26 protons + 30 neutrons

79 protons + 118 neutrons

Mass number = 56

Mass number = 197


Gold ( sun)197Au)

197Au: Au has 79 protons197Au has 197 – 79 = 118 neutrons

number of protons

Helium

number of neutrons

Hydrogen


Gold ( sun)197Au)

197Au: Au has 79 protons197Au has 197 – 79 = 118 neutrons

number of protons

Helium

number of neutrons

Hydrogen


So how is gold made ? sun)

Some earlier failed attempts (1590)

… by Alchemy:

For example:

with the “Philosopher’s Stone”

Making gold/silver from base metals

NSCL (present day)

Alchemists lab + NSCL

… by a nuclear reactionfor example: 208Pb + 9Be -> 197Au + p + ….

Makes gold from lead…

at a very slow rate

(20,000 nuclide/sec)


Iron from a previous generation of stars is exposed to a flux of neutrons

  • How does this create heavy elements ?

  • Neutron Capture Processes

    There are 2:

    - s-process (slow neutron capture)

    - r-process (rapid neutron capture)

Do neutron capture process exercise


Where does the s-process happen ? flux of neutrons

there !

in red giants – and it takes several million years !

(or, low mass TP-AGB stars)

AGB = Asymptotic Giant Branch

TP=Thermally Pulsing


How can we tell ? flux of neutrons

Analyze light from a red giant:

Star contains Technetium (Tc) !!!(heavy element Z=43, T1/2 4 Mio years, Merrill 1952)


197 flux of neutronsAu: Au has 79 protons197Au has 197 – 79 = 118 neutrons

Gold (197Au)

number of protons

?

Helium

number of neutrons

Hydrogen


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