Fusion Reactions in Stars
- In the centre of a stable star, hydrogen atoms undergo nuclear fusion to form helium
- The equation for this reaction is:
Deuterium and tritium are both isotopes of hydrogen. They can be formed through other fusion reactions in the star
- Fusion is defined as:
The joining of two small nuclei to produce a larger nucleus
- Low-mass nuclei (such as hydrogen and helium) can undergo fusion and release energy
- A huge amount of energy is released in the reaction
- This provides a pressure that prevents the star from collapsing under its gravity
The fusion of deuterium and tritium to form helium with the release of energy
- For two nuclei to fuse, both nuclei must have high kinetic energy
- This is because the protons inside the nuclei are positively charged, which means that they repel one another
- It takes a great deal of energy to overcome the electrostatic force between protons
- This is why fusion reactions can only be achieved in an extremely high-energy environment, such as a star’s core
- When two protons fuse, the element deuterium is produced
- In the centre of stars, the deuterium combines with a tritium nucleus to form a helium nucleus, plus the release of energy, which provides fuel for the star to continue burning
Exam Tip
In the fusion process, the mass of the new heavier nucleus is less than the mass of the constituent parts of the nuclei fused together, as some mass is converted into energy.
Not all of this energy is used as binding energy for the new larger nucleus, so energy will be released from this reaction. The binding energy per nucleon afterwards is higher than at the start.