The pp-I Chain

Plate 69 speaks for itself: “Four in, one out.”

The Physics

In the Sun's core, four protons become one helium-4 nucleus through the proton–proton chain. The mass difference is released as energy, a little of it carried off by neutrinos.

4p + 2e⁻ → ⁴He + 2ν_e

• p: proton
• e⁻: electron
• ⁴He: helium-4 nucleus
• ν_e: electron neutrino
• Q: energy released, J (quoted in MeV)

Q = 26.73 MeV in total. Solar core ≈ 1.57×10⁷ K.

Sources

• H. A. Bethe, Phys. Rev. 55, 434 (1939).
• J. N. Bahcall, Neutrino Astrophysics (1989).

On the poster

Plate 069, “The pp-I Chain”: the pixel-art plate with its slogan “Four in, one out.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.