How are elements heavier than Iron produced in stars?
1 Answer
Elements heavier than Iron can only be created in stars by neutron capture.
Explanation:
Fusion reactions can only create elements with an atomic number less than or equal to that of Iron. The reason for this is that fusing heavier elements requires more energy rather than releasing energy.
Element Iron and heavier can capture neutrons. If the result of capturing a neutron is an unstable nucleus then a neutron undergoes beta decay to convert a neutron into a proton, an electron and an electron antineutrino. This beta decay produces an element with a higher atomic number.
There are two neutron capture processes which can occur in stars. The s-process (s for slow) happens in red giant stars which were created with heavier elements. As the beta decay weak interaction is slow it is a very gradual process. The neutrons are a by product of the normal fusion reactions in these stars.
The r-process (r for rapid) happens during a supernova explosion where there is a high concentration of neutrons due to core collapse. Elements capture neutrons at a rapid rate and get transformed into heavier elements.
