Book

Nuclear Astrophysics (1967)

by William Alfred Fowler

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Summary

William Alfred Fowler's "Nuclear Astrophysics" (1967) establishes the central thesis that nuclear physics processes occurring within stars are directly responsible for the origin of chemical elements beyond hydrogen and helium. The book details the specific nuclear reactions that occur at stellar temperatures and densities, explaining how fusion builds heavier elements from lighter ones. Fowler systematically outlines nucleosynthesis pathways, from the proton-proton chain and the CNO cycle in stars like the Sun, to the alpha process and the s-process responsible for producing elements up to iron.

The reader gains a comprehensive understanding of how stellar evolution dictates the abundance of elements in the universe. Key takeaways include the understanding that different stellar masses and evolutionary stages produce distinct sets of elements, and that supernova explosions are crucial for the creation and dispersal of many heavy elements via processes like the r-process and explosive nucleosynthesis. The book's lasting impact is its rigorous quantitative treatment connecting stellar interiors to cosmic elemental composition.

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Key concepts

  • Nucleosynthesis — The process by which new atomic nuclei are created from pre-existing nucleons (protons and neutrons).
  • Proton-Proton Chain — The primary set of nuclear fusion reactions by which stars convert hydrogen to helium.
  • CNO Cycle — A set of nuclear fusion reactions that convert hydrogen to helium in stars more massive than the Sun, using carbon, nitrogen, and oxygen as catalysts.
  • Alpha Process — Nuclear fusion reactions where helium nuclei (alpha particles) are added to heavier nuclei, creating elements with atomic masses that are multiples of four.
  • s-process (slow neutron capture) — A process where atomic nuclei absorb neutrons one at a time at a rate slow enough that radioactive decay can occur between neutron absorptions, producing elements heavier than iron.
  • r-process (rapid neutron capture) — A process where atomic nuclei absorb neutrons at a rate faster than they can decay, leading to the rapid formation of very heavy elements.