# Nucleosynthesis: other than big bang and supernova

According to many texts, hydrogen and helium and traces of lithium-7 were created in a brief period after the big bang; helium is created through fusion (pp, CNO) in main sequence stars; elements like carbon, nitrogen and oxygen and neon are net created in main sequence stars heavier than the sun.

I've also learnt that sun-like stars enrich the interstellar medium with hydrogen and helium through mass loss after leaving the main sequence; that stars with a greater mass but too light to end as a supernova (roughly up to 8 Msun) also enrich the ISM with C, N, O, Ne after dregde-up phases. A lot of the stellar ashes is buried in white dwarfs, so much of the heavier elements remain in the star for the most part, if I'm correct.

I've learnt that essentially all elements heavier than these are created in supernova events.

But according to the Astronomy Picture of the Day for 2015-01-25 a significant fraction of many elements (also) has another origin.

1. Are Li, Be, B on earth produced in significant amounts through spallation by cosmic rays of C, N, O high in the atmosphere of the earth? (Not in stars: no stable nuclei with A=5 or A=8 and lithium undergoes fusion.)

2. Are the "green" elements in the diagram (e.g. F, K, Zn, La) produced in the red (super)giant phase of moderately heavy stars and liberated through dregde-up and mass loss (stellar wind)? Or by novae of white dwarfs?

3. How is gold produced by collisions of neutron stars (text below the diagram)?

4. Elements up to Pu are produced through r-process neutron capture in supernovae, but why not Am, CM etc.? Or are they produced but too unstable ($\alpha$, $\beta$ decay) to survive long enough?

• I think that each of these questions probably could be dealt with individually, rather than all together. That is to say, this is probably too broad of a question for our format. – Kyle Kanos Jan 25 '16 at 20:31
• Small correction, elements beyond He are not produced in main sequence stars. – Rob Jeffries Dec 13 '16 at 14:27

The answer to the first question is no, not in significant quantities. Li, Be and B are produced in spallation reactions in the cosmos, but here on Earth they were part of the gas cloud that formed the Sun (almost entirely).

The second answer is yes, during the Asymptotic Giant Branch (AGB) phase, along with many other heavy elements and Carbon. The mechanism by which intermediate stars create heavy elements beyond iron is (slow) neutron capture onto pre-existing iron-peak nuclei via the "s-process". These elements, along with others (e.g. C, F) produced in nucleosynthesis are brought to the surface by convection and expelled in slow winds, driven by radiation pressure. About half the elements beyond iron are produced mainly by this s-process and not in supernovae.

The third answer is "possibly" and by the r-process; rapid neutron capture by heavy elements in dense, neutron-rich environments. Gold, platinum, osmium and iridium - the elements around the "third r-process peak" - may especially be produced in this way. Some evidence for this has now emerged by analysing infrared spectra from a merging neutron star event identified through a gravitational wave detection.

The fourth answer is that all kinds of unstable isotopes are produced in supernovae and then decay.

More details and references can be found in my answer to Origin of elements heavier than Iron (Fe)

• Neutron star collisions might have also created extremely heavier elements like heavier isotopes of gold and silver. – Roghan Arun May 30 at 17:33
• @RoghanArun That is exactly what the third paragraph says. – Rob Jeffries May 30 at 19:07
• It looked like you did not include the neutron star merger when I checked. – Roghan Arun Jun 1 at 0:43