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 radiation pressure that prevents the star from collapsing under its gravity
The fusion of deuterium and tritium to form helium with the release of energy
- When two protons fuse, a deuterium nucleus is produced
- In the centre of stars, the deuterium combines with a tritium nucleus to form a helium nucleus
- The total mass of the helium nucleus is less than the total mass of the individual nucleons
- Hence, the reaction releases energy, which provides fuel for the star to continue burning
Fusion & The Strong Nuclear Force
- For two nuclei to fuse, both nuclei must have high kinetic energy
- This is because
- Nuclei must overcome the repulsive coulomb forces between protons
- The strong nuclear force, which binds nucleons together, has a very short range
- Therefore, nuclei must get very close together for the strong nuclear force to take effect
- This means an extremely hot and dense environment is required to achieve fusion
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.