s-process

The s-process or slow-neutron-capture-process is a nucleosynthesis process that occurs at relatively low neutron density and intermediate temperature conditions in stars. Under these conditions heavier nuclei are created by neutron capture, increasing the atomic mass of the nucleus by one. A neutron in the new nucleus decays by beta-minus decay to a proton, creating a nucleus of higher atomic number. The rate of neutron capture by atomic nuclei is slow relative to the rate of radioactive beta-minus decay, hence the name. Thus if beta decay can occur at all, it almost always occurs before another neutron can be captured. This process produces stable isotopes by moving along the valley of beta-decay stable isobars in the chart of isotopes. The s-process produces approximately half of the isotopes of the elements heavier than iron, and therefore plays an important role in the galactic chemical evolution. The more rapid r-process differs from the s-process by its faster rate of neutron capture of more than one neutron before beta-decay takes place.