North Carolina State University researcher physicist Dean Lee has taken a “snapshot” of the way particles combine to form carbon-12, the element that makes all life on Earth possible.  Carbon is far more crucial than carbon hysteria would allow.  Without it there would be no you or your humble writer let alone fuels, diamonds and pencils.

Lee and his colleagues Evgeny Epelbaum, Hermann Krebs and Ulf-G Meissner who are backed by the U.S. Department of Energy; the Deutsche Forschungsgemeinschaft, Helmholtz-Gemeinschaft Deutscher Forschungszentren, and Bundesministerium fuer Bildung und Forschung in Germany; European Union HadronPhysics3 Project and the European Research Council; and the National Natural Science Foundation of China set out to get a look at carbon 12.  It’s important to know both from a physics standpoint but a chemistry one as well. The group’s findings will appear this month in Physical Review Letters.

Carbon-12 can only exist when three alpha particles, or helium-4 nuclei, combine in a very specific way. This combination is known as the Hoyle state.  The Hoyle state is when carbon 12 is excited and is one of the most interesting, difficult and timely challenges in nuclear physics, as it plays a key role in the production of carbon via fusion of three alpha particles in red giant stars.

Hoyle State Carbon Graphic. Click image for the largest view.

To get carbon 12 atomic nuclei requires a nearly simultaneous triple collision of alpha particles (helium nuclei) within the core of a giant or supergiant star, which is known as the triple-alpha process.  The interiors of specific kinds of stars transform the three helium nuclei into carbon by means of this triple-alpha process.  In order to be available for formation of life as we know it, the carbon must then later be scattered into space as dust, in supernova explosions, as part of the material which later forms second, third-generation star systems that have planets accreted from such dust.

It’s a big deal, we and the earth have had a close call. Carbon is only the 15th most abundant element in the Earth’s crust, while it’s the 4th most abundant element in the universe by mass after hydrogen, helium, and oxygen.  Each of us is about 18.5 percent carbon by mass.  Earth and its inhabitants are creatures of carbon  – and there only seems to be plenty enough to cause trouble.

Lee’s group had previously confirmed the existence of the Hoyle state using a numerical lattice that allowed the researchers to simulate how the protons and neutrons interact. When the researchers ran their simulations on the lattice, the Hoyle state appeared together with other observed states of carbon-12, proving the theory correct.

The group also wanted to find out how the nucleons (the protons and neutrons inside the nucleus of an atom) were arranged inside the nucleus of carbon-12. That would enable them to “see” the structure of the Hoyle state. Using the same lattice, the researchers, along with collaborator Timo Laehde, found that carbon-12’s six protons and six neutrons formed three “alpha clusters” of four nucleons each. At low energy, the alpha clusters tended to clump together in a compact triangular formation.  But for the Hoyle state, which is an excited energy state, the three alpha clusters combined in a “bent arm” formation.

Lee said, “It’s interesting that a straight chain seems not to be the preferred configuration for the Hoyle state. A bend in the chain seems necessary. This work leads us to the question of what other nuclei have such alpha cluster shapes. These would be rather exotic structures in nuclear physics and open some really interesting questions regarding shape and stability.  For example, can we have longer chains of alpha clusters?  We are investigating these possibilities.”

What interests us here is that the excited carbon 12 attributes are of significance to chemists working on combustion.  The new view isn’t going direct to fuel, but it will be straight to some new breakthroughs in the coming years.

Chemical reaction releases of energy are for now the main sources of energy across the planet and will remain so for years to come.  Carbon with oxygen hydrogen and nitrogen are the big parts of life and our fuels both as food and heat, motion and light.

We’re one more step closer to full understanding how star stuff became us and what we can do to be more efficient and create more and better fuels as well as foodstuffs.


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