164. Uncle Tungsten - XVI. Fusion & the End

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Uncle Tungsten

What has confused me about "protonation" -- the donation of protons to another atom or molecule -- is that the term suggests to me that protons leave a nucleus much like a wife breaking free of the strong force of a polygamous marriage. But the reality is quite different. A hydrogen proton (really the nucleus so, technically speaking a protium or at least a positive hydrogen ion or, let's say, a hydrogen cation) departs one (acid) family and moves on to another (base) family leaving its electron behind. I'm sorry, having introduced the polygamous marriage idea it's now hard not to see the proton as a heartless mother abandoning her small (probability distributed) child. (So it can't even be said where it is with any degree of certainty. And it's probably left behind in a negative hydroxide ion or anion.)


So now I have all this but I still have no idea why the proton leaves it's old family behind and is drawn to the base -- thus turning it's old family into an anion and its new family into a cation. With ionic and covalent bonds I get how valency is the motivation, if you will, that brings atoms together. There's something essential about acids and bases here that I'm missing.

This includes a very helpful animation showing a particular kind of protonation in action. From reading the text, it would seem that I'm not the only one having a hard time visualizing how this works. 

The cationic forms of hydrogen are called hydrons and there are three types: proton, deuteron (with a neutron), and triton (with two neutrons). If you de-ionize them by giving them an electron, they become hydrogen, deuterium, and tritium. Unless you have a plasma (like in the sun, as we shall see) naked hydrons are very rare but what you will find in acidic water is hydronium ions H3O+. Or if the water is alkali you will find more hydroxide anions OH-.

And I'm going to leave it at that and not even get into salts.

Chapter 24 - Brilliant Light - Continued

...
p305 It was not until 1929 that another idea was put forth: [about what powered the sun] the notion that, given the prodigious temperatures and pressures of a star’s interior, atoms of light elements might fuse together to form heavier atoms -- that atoms of hydrogen, as a start, could fuse to form helium; that the source of cosmic energy, in a word, was thermonuclear. Huge amounts of energy had to be pumped into light nuclei to make them fuse together, but once fusion was achieved, even more energy would be given out. This would in turn heat up and fuse other light nuclei, producing yet more.  

The use of “light” in “light nuclei” is a little confusing since we are talking about “light” in the other sense as well. Also, Nothing here supports or explains his contention that “more energy would be given out.” This is obviously the case, but the details of it remain a mystery to me. 

At temperatures and pressures like this [20 million degrees inside the sun]. atomic nuclei -- naked, stripped of their electrons -- would be rushing around at tremendous speed (the average energy of their thermal motion would be similar to that of alpha particles) and continually crashing, uncushioned, into one another, fusing to form the nuclei of heavier elements. 

In the sun, they would actually be forming alpha particles, since that’s what a helium nucleus is. 

...
Converting hydrogen to helium produced a vast amount of heat and light, for the mass of the helium atom was slightly less than that of four hydrogen atoms -- and this small difference in mass was totally transformed into energy, in accordance with Einstein’s famous e=mc2... 

I have to pause here. We will return to this chain of thought below.

This finally sent me to Wiki for more information. Wiki repeats what he says about the four hydrogen atoms but this makes absolutely no sense to me. Here’s the way I would describe it: 

Two free protons collide, with enough energy that they overcome the natural tendency of positively charged bodies to repulse each other, and stick together. Only the impact also shakes loose a positron and a neutrino. And this is where we have to get into the (seemingly intentionally) confusing world of Quantum Chromodynamics (QCD). 

A proton is not a fundamental particle but is currently understood to be composed of two up quarks and one down quark bound together by gluon fields. (The mass of the proton comes almost entirely from the gluon fields and the kinetic energy of the quarks.) 

A neutron is described the exact same way except that it has two down quarks and only one up quark. According to Wiki, “A free neutron is unstable, decaying to a proton, electron and antineutrino with a mean lifetime of just under 15 minutes... This radioactive decay, known as beta decay, is possible since the mass of the neutron is slightly greater than the proton. The free proton is stable.”

That positron I said was shaken loose is an anti-electron so when a proton becomes a neutron it gives off a positively charged particle and when a neutron decays into a proton it gives off a negatively charged particle. 

Now, finally, that neutrino I mentioned is a type of lepton (like the electron) but without charge.

So to summarize, two protons (each a little less massive than a neutron) collide, knock off a positron and a neutrino, and one of the protons turns into a more massive neutron. And the only difference between the new neutron and the old proton is the lack of charge (that positron, I guess) and a quark has shifted from up to down.

If anything is clear in all this it is that when nuclear physicists talk about “particles” they have a very special meaning in mind. As with electron energy states, it would probably be more understandable if they just dropped the particle language and used a more musical metaphor since this is all really about energy states and fields. Neutrinos even travel at c so they clearly have no mass.

That’s the first step. And may I say that I blame (without any justification) Murray Gell-Mann for all this jargon.

Next, the two nucleons (the technical term for protons and neutrons as a class of particles), now form a deuteron, held together by the strong nuclear force (in what can also be thought of as a deuterium nucleus (2H), except that there are no electrons to round out the atom) and collide with another free proton. This time the proton is trapped by the strong force creating a helium nucleus wanna-be with an atomic weight of 3 (3HE), and at the same time a gamma ray is released. (“Gamma ray” seems to be a catch-all term for high energy emissions.)

Now for the final step, two of these 3HE things crash together. Two of the protons fly off, but the remaining two protons and two neutrons stick together in the form of a beta particle or 4HE nucleus. 

From beginning to end, six -- not four -- protons entered the process, two continued on as free protons while two turned into neutrons and ended up stuck together by the strong force to the remaining two protons. Also, two positrons, two neutrinos, and two gamma rays were released. 

And, while he never mentions it, this fusion process in a star is known as Nucleosynthesis.

Sorry about this long digression. I will now resume the story about how the sun actually works,  


...To produce the energy generated in the sun, hundreds of millions of tons of hydrogen had to be converted to helium each second, but the sun is composed predominantly of hydrogen, and so vast is its mass that only a small fraction of it has been consumed in the earth’s lifetime. If the rate of fusion were to decline, then the sun would contract and heat up, restoring the rate of fusion; if the rate of fusion were to become too great, the sun would expand and cool down, slowing it. Thus, as [George] Gamow put it, the sun represented “the most ingenious, and perhaps only possible, type of ‘nuclear machine,’ “ a self-regulating furnace in which the explosive force of nuclear fusion was perfectly balanced by the force of gravitation. The fusion of hydrogen to helium not only provided a vast amount of energy, but also a new element in the world. And helium atoms, given enough heat, could be fused to make heavier elements, [carbon] and these elements, in turn, to make heavier elements still.

And I can’t help mentioning that the sun is the perfect place to put a fusion reactor. Trying to make one on earth is just silly. 


p306 Thus, by a thrilling convergence, two ancient problems were solved at the same time: the shining of stars, and the creation of the elements... Hydrogen, element 1, was not only the fuel of the universe, it was the ultimate building block of the universe, the primordial atom, as Prout had thought back in 1815. This seemed very elegant, very satisfying, that all one needed to start with was the first, the simplest of atoms. (Footnote: The universe started, Gamow conceived, as almost infinitely dense -- perhaps no larger than a fist. Gamow and his student Ralph Alpher went on to suggest (in a famous 1948 article that came to be known, after Hans Bethe was invited to add his name, as the alpha-beta-gamma paper), that this primal fist sized universe exploded, inaugurating space and time, and that in this explosion (which Hoyle, derisively, was to call the Big Bang) all of the elements were created.

But here he was wrong; it was only the lightest elements -- hydrogen and helium and perhaps a little lithium... 

I’m going to stop there because even that is not strictly speaking true. The result of the Big Bang was a plasma that took quite some time to cool down enough for even atomic hydrogen to form.

I would also like to point out that this is a reminder of -- if not exactly support for -- my argument against the existence of God as Creator. Things almost always start small and simple and grow in complexity. That everything would start with God is like suggesting that some super-transuranic element was the origin of chemistry. 


p307 Bohr’s atom seemed to me ineffable, transcendently beautiful -- electrons spinning, trillions of times a second, spinning forever in predestined orbits, a true perpetual-motion machine made possible by the irreducibility of the quantum, and the fact that the spinning electron expended no energy, did no work. And more complex atoms were more beautiful still, for they had dozens of electrons weaving separate paths, but organized, like tiny onions, in shells and subshells... [I’m not sure where he’s going with this, but I would rather imagine the electron shells as musical notes with more complex atoms generating chords. This reaches back to his original musical interpretation of the periodic table and forward to String theory.] Bohr’s atoms were surely close to Leibniz’s optimum world.

“God thinks in numbers,” Auntie Len used to say. “Numbers are the way the world is put together.” This thought had never left me, and now it seemed to embrace the whole physical world. I had started to read a little philosophy at this point, [uh-oh] and Leibniz, so far as I could understand him, appealed to me especially. He spoke of a “Divine mathematics,” with which one could create the richest possible reality by the most economical means, and this, it now seemed to me, was everywhere apparent: in the beautiful economy by which millions of compounds could be made from a few dozen elements, and the hundred-odd elements from hydrogen itself; the economy by which the whole range of atoms was composed from two or three particles; [prior to QCD] and in the way that their stability and identity was guaranteed by the quantal numbers of the atom itself -- all this was beautiful enough to be the work of God.

Chapter 25 - The End of the Affair

Like thousands of boys before him -- well, maybe a couple -- young Oliver finds he is growing out of his passion for chemistry and drifting towards other, and more social, interests. Here’s one of his reasons for this,  

...
p311 With the “new” quantum mechanics, developed in the mid-1920s, one could no longer see electrons as little particles in orbit, [sorry for jumping ahead last chapter] one had to see them now as waves; one could no longer speak of an electron’s position, only of its “wave function,” the probability of finding it in a particular place. [Nice alive and dead kitty.] One could not measure its position and velocity simultaneously. An electron, it seemed, could be (in some sense) everywhere and nowhere at once. All this set my mind reeling. I had looked to chemistry, to science, to provide order and certainty, and now suddenly this was gone. [This is an amazing recapitulation of Zen Physics!]  I found myself in a state of shock, and I was past my uncles now, and in deep water, alone. 

I can’t get over how perfect this is. What he doesn’t mention -- that was Darling’s focus -- is how quantum mechanics brought consciousness, the subjective, into the previously objective reality of science (the Socratic/Alexandrian perspective on reality). 

But Sacks wanted science to give him the truth about the world, certainty independent of what people wanted to believe. Instead it dumped him back in a place where cats were both alive and dead (and neither alive nor dead) until you peeked. What’s left then but philosophy and psychology? 


p312 This new quantum mechanics promised to explain all of chemistry. And though I felt an exuberance at this, I felt a certain threat, too. “Chemistry,” wrote Crookes, “will be established upon an entirely new basis. . . . We shall be set free from the need for experiment, knowing a priori what the result of each and every experiment must be.” I was not sure I like the sound of this. Did this mean that chemists of the future (if they existed) would never actually need to handle a chemical; might never see the colors of vanadium salts, never smell a hydrogen selenide, never admire the form of a crystal; might live in a colorless, scentless mathematical world? 


As with Richard Dawkins, he saved the good stuff for the end. I see the sense of this, of course, it's the only way you can appreciate the position the scientists were in as chemistry progressed step by step. But, like those people, you can't really understand the underlying reality of the chemistry until who get those last degrees of electronic and quantal understanding. Fortunately, I have to re-read it for blogging so I get the best of both worlds. 


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