When a star has exhausted its hydrogen fuel, it may fuse...

When a star has exhausted its hydrogen fuel, it may fuse other nuclear fuels. At temperatures above $1.00 \times 10^{8} \mathrm{K}$ , helium fusion can occur. Consider the following processes. (a) Two alpha particles fuse to produce a nucleus $A$ and a gamma ray. What is nucleus $A$ ? (b) Nucleus $A$ from part (a) absorbs an alpha particle to produce nucleus $B$ and a gamma ray. What is nucleus $B$ ? (c) Find the total energy released in the sequence of reactions given in parts (a) and (b).

Key Concepts

Gamma Ray Emission

Gamma rays are high-energy photons emitted during nuclear reactions, particularly when the nucleus transitions from an excited state to a lower energy state. In the context of stellar fusion, the emission of gamma rays is a clear indicator of energy release, reflecting the conversion of nuclear binding energy into electromagnetic radiation.

Nuclear Binding Energy and Energy Release

Nuclear binding energy is the energy that holds the nucleus together, and differences in binding energy between reactants and products in nuclear fusion reactions are responsible for the energy released. When the products have a higher binding energy per nucleon, the reaction results in a net release of energy according to the principles of mass-energy equivalence.

Alpha Particles

Alpha particles are helium nuclei, consisting of two protons and two neutrons. They serve as the building blocks in various nuclear fusion processes in stars, and their interactions help synthesize heavier elements as they merge under conditions of extreme temperature and pressure.

Triple-Alpha Process

The triple-alpha process is a critical sequence in stellar nucleosynthesis in which three helium nuclei (alpha particles) combine to form carbon. The process typically occurs in two steps: first, two helium nuclei fuse to form an unstable intermediate nucleus, and then a third helium nucleus is captured, resulting in a stable carbon nucleus along with the emission of gamma ray energy.

Helium Fusion in Stars

This refers to the process whereby, after a star has exhausted its hydrogen fuel, it begins to fuse helium nuclei under extremely high temperatures and pressures. Helium fusion reactions are fundamental to stellar evolution and lead to the creation of heavier elements, thereby altering the chemical composition and life cycle of the star.

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