• Stars are huge balls of (mostly)?hydrogen?gas
• In the centre of star, hydrogen atoms undergo?nuclear fusion?to form helium
• The equation for the reaction is shown here:

Deuterium and Tritium are both isotopes of hydrogen. They can be formed through other fission reactions in the star

• 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

• In larger stars the helium that has been produced can then be fused to form heavier elements

• Within stars the atoms are ionised
• This means that the electron that is normally on a hydrogen atom would be lost
• A hydrogen ion, or a proton, is therefore?positively charged
• There exists a?repulsive force between protons?that has to be overcome for hydrogen fusion to happen

Hydrogen ions are protons, and their positive charge makes them repel one another

• In order to overcome this repulsion, the protons must have very?high kinetic energy?in order to be travelling towards each other at very?high speeds
• In order to make the molecules of a gas travel at such speeds, the gas has to be heated to millions of degrees Celsius – a temperature that is usually only reached at the centre of a star
• In regular conditions, ie. on Earth, the possibility of collisions between nuclei which result in fusion is very low
  • In order to increase the number of collisions (and hence fusions) that occur between nuclei, high?densities?(and hence?pressures) are also needed

   

• The difficulties in achieving and maintaining such high temperatures and pressures are the main reasons why fusion is not currently used as a source of power on Earth

• The conditions for fusion therefore are:
  • Very?high temperature?of fuel
  • Very?high kinetic energy?/ speed of nuclei to overcome repulsion
  • Very?high density?/?pressure?to increase the possibility of suitable collisions