Stellar Nucleosynthesis — PP Chain

Stellar Parameters

Core Temperature (MK): 15

Core Density (g/cm³): 150

Hydrogen Mass Fraction X: 0.70

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Gamow Peak (keV)

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ε (erg/g/s)

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PP-I fraction

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H lifetime (Gyr)

¹H+¹H→²D+e⁺+ν

²D+¹H→³He+γ

▶ PP-I: ³He+³He→⁴He+2¹H

▶ PP-II: ³He+⁴He→⁷Be→⁷Li→⁴He

▶ PP-III: ⁷Be+¹H→⁸B→⁸Be→2⁴He

Gamow window: balance between Maxwell-Boltzmann tail and tunneling probability. Peak at E₀ = (πe²μc²/2)^(2/3)·(kT)^(2/3).
Energy gen: ε ∝ ρX²T^n where n≈4 for pp-chain. Branch ratios depend strongly on T.