Saturday, April 28, 2012

Making of the elements - nucleosynthesis

Sections of the introduction to nuclesynthesis in wikipedia (paragraphs and emphasis added)

In the beginning primordial nucleosynthesis
Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons (protons and neutrons).

It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees. 

A few minutes afterward, starting with only protons and neutrons, nuclei up to lithium and beryllium (both with mass number 7) were formed, but only in relatively small amounts.

Some boron may have been formed at this time, but the process stopped before significant carbon could be formed, because this element requires a far higher product of helium density and time than were present in the short nucleosynthesis period of the Big Bang.

The Big Bang fusion process essentially shut down due to drops in temperature and density as the universe continued to expand.

This first process of primordial nucleosynthesis was the first type of nucleogenesis to occur in the universe.

500 million human years later stellar nuclear reactions
The subsequent nucleosynthesis of the heavier elements required heavy stars and supernova explosions.

This theoretically happened as hydrogen and helium from the Big Bang condensed into the first stars 500 million years after the Big Bang.

The primordial elements still present on Earth that were once created in stellar nucleosynthesis range in atomic numbers from 6 (carbon) to 94 (plutonium).

Synthesis of these heavier elements occurs either by nuclear fusion (including both rapid and slow multiple neutron capture) or by nuclear fission, sometimes followed by beta decay.

Ongoing destruction of elements by cosmic rays
By contrast, many stellar processes actually tend to destroy deuterium and isotopes of beryllium, lithium, and boron which have collected in stars after their primordial formation in the Big Bang.

This effective destruction happens via the transmutation of these elements to higher atomic species.

Quantities of these lighter elements in the present universe are therefore thought to have been formed mainly through billions of years of cosmic ray (mostly high-energy proton) mediated breakup of heavier elements residing in interstellar gas and dust.

The making of additional elements found on Earth
In addition to the major processes of primordial nucleosynthesis in the Big Bang, stellar processes, and cosmic-ray nucleosynthesis in space, many minor natural processes continue to produce small amounts of new elements on Earth.

These nuclides are naturally produced on a continuing basis
via the decay of long-lived primordial radionuclides (via radiogenesis),
from natural nuclear reactions in cosmic ray bombardment of elements on Earth (cosmogenic nuclides)
from other natural nuclear reactions powered by particles from radioactive decay, (producing nucleogenic nuclides).

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