11th Week: The s,r and p-Process

Production of elements heavier than iron

As the nuclear charge increases, the transmission probability decreases drastically. This in turn makes the charged cross sections to be very small and therefore at moderate stellar temperatures it is very difficult to form heavy elements. However, the elements heavier than $A=60$ are observed which requires explanation. Below we explain the main possible processes that might have occured in stellar nucleosynthesis.

Neutron capture

Neutron capture plays an important role in the cosmic nucleosynthesis of heavy elements. In stars, it can proceed in two ways - as a rapid process (an r-process) or a slow process (an s-process). By neutron capture, nuclei of masses greater than 56 can be formed that could not be formed by thermonuclear reactions, i.e., by nuclear fusion.