Module 1

Question 1

What are the 3 lines of evidence for elemental abundances and
how do they agree/disagree?

Answer 1

Spectral analysis
-Elements absorb wavelengths which are reflected as black asborption lines on their spectra. These lines correspond with composition
-Lithium doesnt appear as it is lost in the sun (gets consumed)

Carbonaceous chondrite meteorites
-represent “primitive” material left over from solar system formation (preserved in space as extreme conditions would destroy the carbon)
-Volatiles don’t show up

Helioseismic data
-sound waves in the sun depend on material they pass through
-found more metals than other 2 methods
-heavier elements are in the centre and lighter elements are near the surface

Question 2

Compare nuclear and chemical reactions in terms of what products they make and their energy requirement/yield

 Broadly describe the major nucleosynthesis pathways. (No need to memorize all the reactions!)

Answer 2

Nuclear reactions:
-Change in # of protons in a nucleus.
-highly unstable nuclei release a lot of energy
-unstable elements have too many neutrons or protons and need to emit

Nuclear fusion is combining nuclei into bigger nuclei
Nuclear fission is when a nucleus sheds particles and gets smaller

Big bang nucleosyntheis
- origin of universe, rapid expansion
- H and He come from this

Stellar nucleosynthesis
fusion:
small stars:
- H burning proton-proton chain (H and He)
-He burning triple alpha - C, O
Large stars:
-H-burning (CNO cycle), N, He, and C
-He burning triple alpha - C, O
-C, Ne, O (produce up to Ca)
Si (produce Fe, final stage for most stars)
fission:
s-process: stellar nucleosynthesis, during stars life, slow, Cu to Pb

explosive nucleosynthesis
r-process: stars death, rapid neutron capture
p-process: photodisintegration during supernovae explosions

galactic nucleosynthesis
-Cosmic Ray spallation: Li, Be, B

Question 3

What is an isotope?

Answer 3

Isotopes have the same number of protons but a different mass (different number of neutrons)

Question 4

Why do we see other elements in the suns absorption spectra if its not producing them?

Answer 4

Stars can inherit elements from older stars that released their elements when they died

Question 5

Why does fusion stop at Fe-Ni?

Answer 5

For fusion to occur:
Energy produced > energy required
Elements leading up to iron release energy and nuclear fusion continues,

 Adding to nucleus of anything larger than iron requires energy

Question 6

What are magic numbers?

Answer 6

“Magic numbers” = full shells of either protons or neutrons
 2, 8, 20, 28, 50, 82, 126

• Double-magic number = both Z and N are magic
• 4He (2,2), 16O (8,8), 40Ca (20,20)

Question 7

Describe and explain the patterns observed in elemental abundances in the solar system

Answer 7

-H and He most common since they were made in big bang nucleosynthesis plus are made through stellar
-lighter elements more abundant since they are created through stellar nucleosynthesis
-after fe fusion stops, only fission, harder to make, thus less abundant
-even elements more abundant than odd - zigzag pattern (oddo harkins)
-Pm and Tc have very short half life, dont exist naturally
-Li, Be, B less abundant despite being light -> not made though stellar, made through cosmic ray spallation