4.4-5

Question 1

Hydrogen Burning Zone Composition

Answer 1

Typical elements:

• ¹H, ²H
• ³He, ⁴He
• ¹²C
• ¹⁴N
• ¹⁶O

Question 2

Hydrogen Burning in Low Mass Stars

what is low mass and which reaction is involved?

Answer 2

• Occurs in stars < 3 M_⊙
• Involves proton-proton (pp) chain reactions

Question 3

First two reactions in PP chain

Answer 3

• 2 · ¹H → ²H + e⁺ + 𝛎
• ²H + ¹H → ³He + γ
• ³He proceeds through three alternative branches: pp1, pp2, pp3 chain with pp1 the most dominant branch

Question 4

PP1 Reaction

Answer 4

2 · ³He → ⁴He + 2 · ¹H

Question 5

Reaction preceding pp2 and pp3 chain

Answer 5

³He + ⁴He → ⁷Be + γ

Question 6

PP2 Reaction

Answer 6

• ⁷Be + e^- → ⁷Li + 𝛎
• ⁷Li + ¹H → 2 · ⁴He

Question 7

PP3 Reaction

Answer 7

• ⁷Be + ¹H → ⁸B + γ
• ⁸B → ⁸Be + e⁺ + 𝛎
• ⁸Be → 2 · ⁴He

Question 8

CNO Cycle in High Mass Stars

when does it occur and what processes are involved?

Answer 8

• Occurs in stars > 3 M_⊙
• Carbon-Nitrogen-Oxygen (CNO) cycle with:
  – proton capture (4x)
  – β⁺-decay (2x)
  – 𝛂-decay (1x)
• Carbon, nitrogen and oxygen present and act as catalysts then hydrogen synthesized into helium in CNO cycle

Question 9

Slowest Process in CNO Cycle

Answer 9

Proton capture by ¹⁴N

Question 10

Products of CNO Burning

Answer 10

• He
• ¹⁴N

Question 11

He-Burning and Triple-Alpha Reaction

Answer 11

Involves ⁴He particles. Occurs after hydrogen is exhausted.

⁴He + ⁴He + ⁴He -> ¹²C + γ.

Question 12

Alternative He-Burning Reaction

Answer 12

¹²C + ⁴He → ¹⁶O + γ

Question 13

Fate of Low Mass Stars

Answer 13

Stars < 8 M_⊙:

• End with a carbon-oxygen rich core
• They form planetary nebulae
• Then cool down to white dwarfs

Question 14

Nuclear Processes in High Mass Stars

Answer 14

Stars > 8 M_⊙:

• undergo additional nuclear processes:
  – Carbon burning
  – Oxygen burning
  – Silicon burning
• leading to an onion structure with various layers of elements (lightest to heaviest except N & C):
  – H
  – He & N
  – C & O
  – Ne & Mg
  – Si
  – Fe

where the last three lines are products of the respective burning above.

Heather and Henry Noted Clouds Over New Mexico, Savoring Iron Flavored Enchiladas.

Question 15

Solar Neutrino Experiments

Answer 15

Focus on detecting neutrinos from the sun, with experiments like:

• 1) Davis
  – reaction 37Cl + v_sun -> 37Ar + e-
  – n + v -> p + e
  – neutrino energy of E(v) > 0.81 MeV can be detected
  – detected only 1/3 of expected neutrino flux
• 2) Kamiokande
  – Cerenkov radiation from neutrino collision with water
  – works only for E(v) > 7 MeV
  – proven that they come from sun
  – detection rate was ≈ 0.5 SNU (solar nutrino unit)
• 3) Gallium
  – 71Ga + v_sun -> 71Ga + e-
  – E(v) > 0.2 MeV from pp-chain detected
  – no doubt on the solar model (Luminosity of sun)
  – but still only 1/2 SUN detected

Question 16

Final Outcome of Neutrino Experiments

Answer 16

• Confirmed the model for nuclear burning in the sun
• Indicated neutrino oscillation and mass
  Discrepancy
• three types of neutrinos: electron, muon, tau
• solar reactions produce only electron neutrinos and experiments can only detect electron neutrinos
• possible for one type of neutrino to spontaneously convert into other type
• discrepancy of measured SNU to theoretical SNU: some of electron neutrinos converted and then not detected

Question 17

What is SNU?

Answer 17

• Solar Neutrino Units
• 10^-36 interactions per target atom per second