Sciency Words: P-P Chain

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we discuss the definitions and etymologies of scientific terminology.  In today’s post, we’ll be discussing the scientific term:

P-P CHAIN

I have, in the past, been accused of covering scientific terms on the basis of how silly they sound, rather than on the basis of pure scientific merit.  But I would never do such a thing.  I have far too much respect for both science and linguistics.  Now with that unambiguously established, let’s talk about the p-p chain.

Definition of the p-p chain: In the field of nuclear physics, the p-p chain refers to a series of nuclear fusion reactions, starting with the fusion of two protons and leading, ultimately, to the creation of a helium-4 nucleus.  The p-p chain is by far the most common fusion process occurring in the core of the Sun, as well as other stars of similar or smaller sizes.

Etymology of the p-p chain: The p’s in p-p chain refer to the two individual protons that fuse together in the very first step of the process.  English astronomer Sir Arthur Eddington first proposed that proton-proton fusion might be occurring inside stars, writing about it in a 1926 article titled “The Internal Constitution of the Stars.”  German-American theoretical physicist Hans Bethe worked out the step by step details of the process in a 1939 paper called “Energy Production in Stars.”  Sadly, I cannot give credit to either Eddington or Bethe for coining this term.  They came up with the idea and worked out the details, but I have not been able to determine who, exactly, first introduced the term “p-p chain” into the scientific literature.

There are at least three versions of the p-p chain, each with different intermediate steps between the individual protons at the start and the helium-4 nuclei at the end (a fourth version is possible in theory, but has yet to be verified in reality).

Recently, scientists at the National Ignition Facility (NIF) in California made significant progress in nuclear fusion research.  That recent experiment has been described as recreating the power of the Sun here on Earth, which is true enough.  But NIF did not recreate the entire p-p chain from start to finish; they did something loosely equivalent to the very last step only.  It seems that reproducing the whole chain is still beyond our current scientific abilities.

So the next time you notice the Sun, shining yellow-gold in the sky, just remember that she can still do p-p chains in ways we humans cannot.

WANT TO LEARN MORE?

If you’re looking for a more detailed and technical explanation of the p-p chain (and the three or four variations thereof), check out this article from encyclopedia.pub.  That article was my main source of information while writing this post.

You can also find Arthur Eddington’s “The Internal Constitution of the Stars” by clicking here and Hans Bethe’s “Energy Production in Stars” by clicking here.

And if you’re looking for a fun way to try nuclear fusion for yourself, check out the game Fe[26].  You slide around tiles marked with the names of different atomic nuclei, trying to combine them to make bigger and bigger elements.  Which nuclear combinations work and which ones don’t?  Play and find out for yourself!