Alpha capture (${}_Z^{A}X+\alpha ⟶{}_{Z+2}^{A+4}Y+\gamma$)

Capture of an alpha particle increases the mass number by four and atomic number by two. Radiative alpha capture releases a photon, while reactions such as $(\alpha ,n)$ can instead emit a neutron. Carbon-12 alpha capture competes with helium production of carbon during core helium burning.

Capture of an alpha particle by carbon-12 makes oxygen-16. Competition between this reaction and the Triple-alpha process helps determine the carbon-to-oxygen ratio after core helium burning.