Introduction to Geochemistry

Fusion of Heavier Elements
! Alpha capture reactions
• Mainly important in stars more massive than our Sun
• Concentric shells inside the star are dominated by different fusion
reactions, yielding products that are fused in the adjacent inward shell of
gas
• Produces elements up to the Fe-group (first row transition elements)
• Examples:
12 C + 4 He
16 O + 4 He
52 Fe + 4 He
He
16 O
He
20 Ne
He
56 Ni
• Some products undergo fission due to nucleon bombardment, neutron
capture… leads to a state of “nuclear statistical equilibrium”
• Does not lead to elements heavier than Ni…. . electrostatic repulsion
between positively-charged nuclei and alpha particles dampens fusion