Place in order the following steps in the fusion of hydrogen into helium. If two or more steps happen simultaneously, use an equals sign ( =). a. A positron is emitted. b. One gamma ray is emitted. c. Two hydrogen nuclei are emitted. d. Two \(^{3}\) He collide and become \(^{4}\) He. e. Two hydrogen nuclei collide and become \(^{2} \mathrm{H}\). f. Two gamma rays are emitted. g. A neutrino is emitted. h. One deuterium nucleus and one hydrogen nucleus collide and become \(^{3}\) He.

Nuclear fusion is a natural process where two lighter atomic nuclei combine to form a heavier nucleus. It powers stars, including the Sun. The energy generated during fusion is due to the conversion of mass into energy as described by Einstein's equation, E=mc². This release of energy is what fuels the brightness and heat of stars. In fusion, strong nuclear forces overcome the electrostatic repulsion between positively charged nuclei, allowing them to combine. This process requires extremely high temperatures and pressures to initiate and sustain. As a result, fusion is not only fundamental in stellar processes but also being explored as a potential source of energy for human use, offering a clean and virtually limitless energy source.

Key Points:

• Combines light atomic nuclei into a heavier nucleus.
• Releases energy based on Einstein's equation, E=mc².
• Powers stars and potentially future human energy sources.

The proton-proton chain is the series of reactions started in stars like the Sun to convert hydrogen into helium. It's a type of nuclear fusion and one of the primary processes in stellar nucleosynthesis. The sequence starts with two protons (hydrogen nuclei) colliding to form a deuterium nucleus, emitting a positron and a neutrino. This deuterium nucleus then merges with another proton to form a helium-3 (³He) nucleus, emitting gamma rays. Finally, two helium-3 nuclei collide to produce a helium-4 (⁴He) nucleus and release two protons, which can start the chain again. This set of reactions efficiently sustains the star's energy production for billions of years.

Key Points:

• Starts with the collision of two protons.
• Forms intermediate nuclei of deuterium and helium-3.
• Ends with the formation of helium-4 and release of energy.

Stellar nucleosynthesis refers to the process by which elements are produced in stars through nuclear reactions. This includes both lighter elements like hydrogen and helium and heavier elements up to iron. Fusion processes in the cores of stars generate the vast amounts of energy that make them shine. Different fusion reactions occur at different stages of a star's life, leading to the creation of new elements. For example, during the main sequence phase, stars primarily fuse hydrogen into helium through the proton-proton chain or CNO cycle. As stars evolve, they can produce carbon, oxygen, and other heavier elements in their cores or during supernova explosions.

Key Points:

• Creates elements in stars through nuclear fusion.
• Powers the energy output of stars.
• Leads to the formation of heavier elements as stars evolve.

Helium production in stars is mainly due to the fusion of hydrogen nuclei. This process not only generates helium-4 but also releases a tremendous amount of energy. In the context of the proton-proton chain, helium production occurs in several stages. First, two protons combine to form deuterium. The deuterium nucleus then fuses with another proton to create helium-3. In the final step, two helium-3 nuclei collide to form helium-4, releasing energy and protons. This regular production of helium is crucial for the balance of the star's life cycle, influencing its expansion, heat, and light.

Key Points:

• Combines hydrogen nuclei to produce helium-4.
• Releases significant amounts of energy in stars.
• Influences star's life cycle and energy output.