Fusion of Hydrogen in Stars

The radiation we receive from the Sun is caused by the energy released during nuclear reactions in the star. The Sun’s main nuclear fuel is hydrogen nuclei (a proton), which are fused together to produce helium nuclei (two protons and two neutrons). In this activity, students will create a diagram that shows how hydrogen nuclei fuse together to produce helium nuclei and energy.

During the first stage in the process, two protons fuse together to form a proton and neutron pair, known as Hydrogen-2, or deuterium. This releases a neutrino and a positron. Another proton fuses to the deuterium nucleus, creating a double proton, neutron triplet, known as Helium-3, which also releases a positron. When one Helium-3 nucleus fuses with another Helium-3 nucleus, a Helium (He-4) nucleus is formed, releasing two protons. At each stage of this reaction, energy is released.

All the elements up to iron (Fe) are created during fusion reactions in stars. Elements heavier than iron are created in supernova explosions in a reaction called neutron capture reactions.

To challenge more advanced students, have them think about why neutrinos and positrons are released at each stage. For students who need support, cut up the completed example storyboard and have them put the pieces together in the correct order. Another idea is to have your students make different descriptive visualizations of different fusion reactions, such as the fusion of helium nuclei to make carbon nuclei.