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!

Nuclear Fusion: A Light at the End of the Tunnel

Hello, friends!

I’m not an expert about, well… anything.  I love space.  I love science.  I love learning about space and science, and I love talking about the stuff I learn (whether the people around me want to hear about it or not).  Still, I’m not an expert.  With that in mind, let me tell you about nuclear fusion.

Nuclear fusion is super easy.  Here, let me show you.

The tricky thing is that you do need to squeeze really, really, really hard to make this work.  Atomic nuclei have matching magnetic charges—positive and positive—so whenever you want to fuse atoms together, you have to overcome the force of magnetic repulsion.  It takes enormous amounts of energy to do that.  Like, in the demonstration above, when I squeezed those two atoms together with my hands, I burned a ton of calories doing that.  Yes, the fusion reaction produced some energy at the end, but not as much energy as it took to make the reaction happen in the first place.  All things considered, this was a net energy loss for me.

But on December 5, 2022, researchers at the National Ignition Facility (NIF) in California—i.e., actual experts on this topic—caused a nuclear fusion reaction where the energy output exceeded the energy input.  How did they do it?  For one thing, they didn’t squeeze atoms together with their hands.  They did it with an elaborate system of lasers.  Specifically, they focused 192 lasers on one tiny capsule full of hydrogen isotopes.  It reportedly took 2.05 megajoules of energy to make the reaction happen, and 3.15 megajoules of energy came out of it.

This sort of nuclear fusion reaction, where hydrogen isotopes are fused together to make helium nuclei, does not produce radioactive waste.  There’s no carbon footprint.  If anything ever goes wrong, the reaction automatically stops itself; there’s no chain reaction that would lead to a Chernobyl-style or Three Mile Island-style nuclear meltdown.  NIF researches say that they should be able to improve the lasers, design better reaction capsules, and generally refine and perfect their nuclear fusion technique.  In a few decades, we should expect large scale nuclear fusion reactors to become commercially viable.

For anyone who (like me) worries about the climate and humanity’s growing energy needs, nuclear fusion sounds like a near perfect solution.  But I have learned, both in my personal life and by being a citizen of this planet, that whenever you solve one problem you inevitably create new problems.  You just have to hope your new problems are less problematic than the old ones.  When nuclear fusion becomes a commercially viable technology, it will be economically disruptive.  Companies will go out of business.  People will lose their jobs.  Also, one of the isotopes used in NIF’s experiment (a hydrogen isotope called tritium) is radioactive.  So in the future, nuclear fusion reactors may still require radioactive fuel, even if they don’t produce radioactive waste.

All that being said, commercially viable nuclear fusion is one of those Sci-Fi pipe-dreams that I never really expected to see happen in my lifetime.  Now, for the first time ever, I feel like there’s a light at the end of the tunnel when it comes to climate change and the energy crisis.  We’ll still have to survive the next few decades, and nuclear fusion will create new problems for us even as it solves some of our old ones.  But this is as near perfect a solution to our current problems as I can realistically imagine us finding.

However, as I said at the beginning of this post, I’m not an expert.  There’s still a lot I need to learn about nuclear fusion, climate change, and all the other stuff I mentioned in this post.  All I can say for certain right now is that I feel optimistic—more optimistic about humanity’s future than I have felt in a long, long time.

WANT TO LEARN MORE?

While researching this post, I saw a surprising amount of cynicism in the popular press.  I guess some people think if fusion can’t offer an immediate and 100% perfect solution to climate change, then it doesn’t offer a solution at all.  So if you want to learn more about this, I recommend watching this press conference from the U.S. Department of Energy and the following panel discussion with some of the researchers who were involved in NIF’s experiment.  Together, the press conference and panel discussion are about an hour and a half long, but you’ll be hearing straight from the people who did the work what they did and what it means.