Mr. Holowicz builds a bomb

As for Mr. Holowicz, his students used to whisper that he was in a kaiju unit in the war and that was why he didn't give a damn. It was true he was in a kaiju unit, but Jake Holowicz was an airplane mechanic. He never set foot outside of Illinois in the entire conflict except for a few weeks of basic training, and he never saw a slant-eyed Jap, or a lizard more than six inches long, outside of the movies. At the end of the war he went to teacher's college on the G.I. Bill and that was how he ended up teaching high school chemistry. He didn't give a damn just because of his personality.

In those days you could order uranium nitrate standard solution from Union Carbide. They wouldn't sell it to just anybody. The order had to come in on official letterhead from a person with a legitimate purpose, like let's say a high school chemistry teacher. The largest amount they'd sell in one order was half a gallon, which would be enough to supply the needs of a major mining company's assay lab for a couple years if they didn't manufacture their own. Union Carbide knew the score. If a small-town high school ordered one of those half-gallon bottles every day for a week and nothing else, the company would reasonably conclude that the students must be doing a whole lot of quantitative analysis labs, and make no comment.

When the bottles arrived Jake used to put one in each corner of the supply room and one on a card table in the middle to keep them as far apart as possible, five little jugs of Hellfire waiting for the last day of class. He did this every year until Shouwa 41 when the government started requiring Union Carbide to put cadmium in the solution for safety. Cadmium is horribly poisonous, but it wasn't for that kind of safety. Cadmium nuclei suck up neutrons like nothing familiar to the average person, and it shut down people like Jake Holowicz. If there were anything legitimate you could do with uranium nitrate in a high school, then you can also do it with a neutron absorber in the mix, so it was hard to complain. In the last few years of the Shouwa Era the mail-order people had to stop selling uranium entirely, and by then it was Aldrich, not Union Carbide anymore, but Jake was well retired by then.

But in Shouwa 40, it was the much-anticipated highlight of the year for students in Mr. Holowicz's twelfth grade chemistry. He spent the Saturday before the last week of school working in the lab, removing most of the water from the solution and putting in methanol and a little bit of beryllium and some other stuff. Less irresponsible chemistry teachers would have used ethanol, but Jake Holowicz really didn't give a damn.

That was the hard part. The easy part came on Friday, 11-day 6-month Shouwa 40. He kissed his wife goodbye in the morning, not his usual practice but there was always the chance it would really be goodbye this time. In all the years Jake did this he never actually told her about it; it was a sort of open secret shared by him and the kids. He never had kids of his own and that was probably just as well.

Friday afternoon, right after the buzzer sounded, they gathered on the ball field - thirty-five students and their teacher and a couple of curious parents but no other staff members because everybody knew the score and didn't want to be forced to officially acknowledge that this was happening. Just over the fence was a patch of waste ground that sloped down to the crick. Jake had a big glass carboy and a funnel. He honoured three marginally responsible boys with half-gallon jugs of the Saturday brew and strict instructions, mostly for showmanship rather than necessity, that they were under no circumstances to stand too close to one another while holding those. With the carboy and funnel set up on the slope he invited his first two assistants to approach one at a time and pour in their contributions. The third one was only allowed to take a few steps and set the bottle down on the ground. Mr. Holowicz himself brought it up to the carboy, poured it in, and ran back to the fence without looking back to lead his class, quick-march, back to the school.

From the school building nobody could directly see the carboy hidden below the slope; there were at least a hundred yards of earth in between. If anyone had been watching directly they'd have seen that the pool of liquid in the bottom of the carboy was already bubbling a little, and a cloud of condensed methanol droplets had formed in the empty space above it. That pool of liquid contained five times the maximum amount of uranium Union Carbide would sell you at one time, and in a more concentrated solution with a lot of methanol. Methanol evaporates very easily.

The exact details of all the reactions and the equations governing them go far beyond high school level, but the basic idea is simple and Mr. Holowicz covered it in his class. The carboy contained a total of about 68 milligrams of uranium-235 and about 9.4 grams of uranium-238; that is about 175 billion billion of the lighter nuclei alone. Each one had a thermal neutron fission cross section of about 500 broadsides. A broadside is a tenth of a billionth of a trillionth of a square centimetre. They call it a broadside because of the joke that it's huge - "as big as the broad side of a barn."

Once in a while a uranium-235 nucleus will, all by itself, break in half. The pieces go their separate ways carrying what is for things their size a fair bit of heat, and a couple of fast neutrons get shot out as well. Something else that both kinds of uranium tend to do is to spit out alpha particles, and when those hit beryllium nuclei they can spawn neutrons too. In Mr. Holowicz's carboy, the neutrons bounced around among the heavy uranium-238 nuclei and the light elements in the mixture, and eventually most of them escaped through the glass walls of the carboy. But a few would slow down and get sucked into uranium-238 nuclei, which would transmute into plutonium-239, and fewer still hit those 500-broadside cross sections, and that was where the fun really started.

Right at the start it wasn't a big deal because of the neutrons escaping through the glass. But as the methanol evaporated the solution got more concentrated. Just as many of those fidgety U-235s that don't play well with others were now crammed into a smaller space to be hit by slow neutrons. Pretty often a uranium-235 nucleus hit by a slow neutron would take the opportunity to split and create an average of two and a half more neutrons. As long as most of those escaped or got absorbed it was still no big deal; but as the solution got more concentrated, the rate of neutron loss slowly dropped. There were still only traces of newly-created plutonium in the solution, but those traces would matter later. Plutonium-239 is even more fissile than uranium-235. It has a thermal neutron fission cross section of about 700 broadsides, and when it fissions it produces an average of almost three neutrons. And every time anything fissioned it carried a tiny bit of heat into the solvent mixture.

Methanol boils at 148 degrees Farenheit, which was how Jake Holowicz would have measured it if he'd been foolishly standing there. As bubbles formed they created spaces in the liquid, reducing its overall density and therefore the reaction rate. So after a few bumps and burps the solution settled down to a steady boil. At that point exactly the right number of neutrons were hitting fissile nuclei for the newly-produced neutrons to balance out those lost through the sides of the carboy. It would have been dangerous to stand near the carboy because of the neutron and gamma radiation, but back at the school the class still hadn't seen or heard anything and they were quickly becoming impatient.

The power output of the makeshift reactor was only a few hundred watts, and as long as the methanol kept boiling, that stayed more or less constant. If the mixture got a little hotter, the bubbles would grow bigger, decreasing the density and the reaction rate, and it would cool down. If it got a little colder, the bubbles would shrink and raise the density. But it wasn't a closed system: a steady stream of vapour poured from the mouth of the carboy, forming a plume overhead. As the alcohol escaped, the bubbles took up a larger and larger fraction of the volume to replace the lost liquid.

When the methanol ran out, it happened all at once. All the bubbles popped and the mixture collapsed into a much thinner pool at the bottom of the carboy and started heating up to 212 degrees, the boiling point of water. This is where ethanol would have been a more responsible choice - it boils 25 degrees hotter, so there would have been less heat left for the water to absorb, less time until the water boiled, less time for Pu-239 to build up, and a lot less total energy released.

In a few milliseconds the water went from hot to boiling, switched into the gas phase, and attempted to occupy about a thousand times its original space. In that time a fair percentage of the uranium-238 nuclei swallowed neutrons, became plutonium, and some of those fissioned and continued the cycle. At its peak, when the expansion rate of the cloud of gas broke past the speed of sound, the power output in the steam ball hit a few billion watts.

As soon as the steam ball expanded a little, its density dropped enough that the chain reaction could no longer sustain itself; too many neutrons were escaping in all directions. Most of the uranium and plutonium would remain unreacted, lifted on the vapour to eventually end up in the crick below and carried away downstream. But the mechanical force of that expanding steam ball blasted the carboy, and the discarded empty jugs nearby, to powder; the buoyancy of the surrounding atmosphere carried the steam up into the cloud of methanol; and the heat ignited that as ordinary non-nuclear fire. The ball of fire rose further in the air and spread out into a mushroom shape, ten or fifteen metres high. The alcohol burned away almost immediately, and the fission chain reaction had long since extinguished itself, but the hot air glowed long enough to make an impressive display for the class. As they opened their mouths to cheer, the shock wave hit and silenced them for a few seconds. Then, they cheered for real. The total amount of nuclear energy released had been equivalent to the detonation of about a kilogram of trinitrotoluene; maybe add on a little more for the methanol fire.

"That," said Mr. Holowicz to his assembled students, "is why we have duck and cover drills. Now go have a good Summer."

And they all went home, and the chemistry teacher's wife, who knew more than she let on, kissed him hello and gave silent thanks to St. Barbara that the glorious fool hadn't managed to kill anyone for another year.