1. Energy and Breakout from the (Hot) CNO Cycle
University of York
(Replace with institution name)
Proton number (Z)
Neutron number (N)
Chart from:
Nuclear physics in stars
The CNO cycle – catalysts for stars
HotCNO
Where do heavy elements come from?
Breakout to make heavy nuclei

2. Nuclei and decay modes
Nuclei: bound collections of neutrons and protons
Mass of nuclei
Binding energy
Proton number (Z)
Decay modes:
Beta decay (beta+ or beta )
Alpha decay
Fission
Proton emission
Neutron emission
Neutron number (N)

3. 4⨉H → 4He + 2⨉νe + 2⨉β+ + E Why does the sun shine?
Where does its energy
come from?
Image above from: release-x3.1-class-solar-flare-on-oct
4⨉H → 4He + 2⨉νe + 2⨉β+ + E
Heard of the proton-proton chain?
The CNO cycle?

4. (p,α) Carbon as a catalyst for hydrogen fusion
CNO cycle
Carbon as a catalyst for
hydrogen fusion
Neutron number (N)
Proton number (Z)
(p,α)
The CNO cycle – most stars
do this…

5. …happens in hot astrophysical sites e.g. X-ray bursters Novae
Hot CNO Activity….
…happens in hot astrophysical sites
e.g.
X-ray bursters
Novae

6. Hot CNO Activity….

7. Hot CNO Activity….

8. Hot CNO Activity….

9. Questions Where did you get stuck?
Did anyone end up back at the same place?
In groups…
Can you find all three H-CNO loops? Draw the loops – different colour for each
process
What are the nuclear processes involved?
What were the catalyst nuclei in each loop?
For the loop, what has been lost (from the star), what has been gained?
Where did you get stuck? Why don’t 14O and 15O absorb 1H?

10. How are Heavier Elements Formed?
Image top left left from:
Image right from:
X-ray bursts
Breakout from catalytic hydrogen fusion
Igniting the rapid proton capture process
Supernovae or neutron-star mergers:
the site for rapid neutron-capture?
Creation of iron-group elements in massive stars
Helium fusion (triple-alpha)

11. Breakout from HCNO – creating heavier elements
Image top left left from:
X-ray bursts
Breakout from catalytic hydrogen fusion
Igniting the rapid proton capture process
Add an alpha particle to 15O
BREAK-OUT!

12. Breakout from HCNO – creating heavier elements
Image top left left from:
X-ray bursts
Breakout from catalytic hydrogen fusion
Igniting the rapid proton capture process
An 18Ne nucleus absorbs an alpha particle and
emits a proton.
BREAK-OUT!