Nuclear Fusion

Fusion nucléaire
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Reaction in which two atoms join to form one heavier atom, releasing energy. This is what creates light atoms, from helium to iron, in stars. Nuclear fusion in stars mainly concerns the fusion of hydrogen atoms (and its deuterium and tritium isotopes) into helium atoms at extremely high pressure and temperature. The reaction associated with hydrogen, the lightest element, is the most exothermic, meaning it releases huge amounts of heat and radiant energy.