How are elements produced in stars after iron?

[ajayguhan]

we know that elements are formed in the core of stars where fusion occurs.

The stars collapse on the formation of iron, if it so how come element after iron like cobalt, gold, silver were produced...?

 

[Drakkith]

As the core collapses, the outer layers of the star fall as well. Once the core reaches sufficient density for neutron-neutron repulsion to hold it up, it stops collapsing and the outer layers of the star rebound off of the surface. During this rebound, the temperature, pressure, and density reach a level high enough to cause fusion to occur, building up elements higher than iron/nickel. Note that this fusion process does NOT release energy. Instead it takes energy, as the heavier elements have less binding energy per nucleon than either iron or nickel.

There is also a large burst of neutrons released, some of which are then captured by the nuclei. Beta decay can then turn some of the neutrons into protons and result in an element with more protons than it had before.

http://en.wikipedia.org/wiki/Supernova_nucleosynthesis

 

[Chronos]

Technically, the process of synthesizing elements heavier than iron/nickel is endothermic, as opposed to exothermic, meaning less energy is released than absorbed. You are, however, correct in noting this extra energy is mainly supplied by the shock wave in a core detonation event. Neutrinos contribute to this process in ways not yet fully understood.

 

[snorkack]

During this rebound, the temperature, pressure, and density reach a level high enough to cause fusion to occur, building up elements higher than iron/nickel.

A number of stars have spectral lines of technetium. Technetium is heavier than iron, and is short lived (up to 4 million years) so it could not have been in the stars before, nor have these stars exploded yet.

 

[Drakkith]

A number of stars have spectral lines of technetium. Technetium is heavier than iron, and is short lived (up to 4 million years) so it could not have been in the stars before, nor have these stars exploded yet.

There is also the s-process, known as slow neutron capture, that takes place in stars. Neutrons produced in the star are captured, building up heavier isotopes of elements until they reach the point that beta decay turns them into the next element by converting a neutron into a proton. Also, see the following link for a paper about the production of technetium.

http://www.nature.com/nature/journal/v337/n6209/pdf/337718a0.pdf