Fred Niell, AB’99 (left), and Justin Kasper, AB’99, in front of the nuclear reactor they built for Scav. The radiation bunny suits were “just theater,” Niell says. (Photography by Buffy Wajvoda, SB’01)

The homemade breeder reactor

An excerpt from We Made Uranium! And Other True Stories from the University of Chicago’s Extraordinary Scavenger Hunt

Item 240. A breeder reactor built in a shed, and the boy scout badge to prove credit was given where boy scout credit was due. [500 points]

It was spring quarter 1999. Justin Kasper [AB’99] and I were roommates and physics majors, and we had just sent our acceptances to graduate school. We were looking forward to coasting for the last three months of college and we weren’t really concentrating on our studies. We were too busy ... “accessing” the physics department after hours for our assorted nefarious purposes. Once I assembled a 1.2GW (that’s right, gigawatt) pulse power system for—well, let’s be honest. It was for blowing stuff up. Justin (J for short) and I had stolen some parts and bought others, used the machine shop at all hours, and basically hewn this thing from the primordial forces of nature herself. It was amazing, and in the following weeks we blew up whatever we could get our hands on. We vaporized apples and made water explode like dynamite. We were gods in the lab from eleven at night until six in the morning. We cleared out before any of the staff arrived to open up.

We were misbehaving, but not in a malevolent way. We were applying what we had learned in our advanced lab classes in a practical setting. In essence, we were being good experimentalists. The faculty may even have known this, but plausible deniability, in the words of one of my favorite physicists, goes a long way.

This paradise, this Eden of partying and blowing stuff up for class credit while breaking as many university rules as possible, lasted for a few months. Then the 1999 Scav Hunt came along.

Initially, I wasn’t interested in putting much time or effort into Scav that year. I was by then working full time at the Fermilab, a Department of Energy national lab near Chicago specializing in high-energy particle physics, while also taking a full load of those core classes I was supposed to have already finished. Every night I brought home cheap beer, and J and I blasted techno from our embarrassingly large and complex stereo system and threw parties in our dorm room. Cocktail parties and Tuesday parties and “day-of-the-week-ending-in-Y” parties. Why would I plug into the frenetic energy required by the Hunt when I was already burning the candle at both ends and dousing it with gasoline? On the night of List Release, I skipped the midnight reading. I went downtown instead and had some fun with my friends.

The next morning, in the dining hall, I was minding my own business (working the newspaper Jumble) when Connor Coyne [AB’01] ran up to me and threw down his tray. He nearly spilled his breakfast on me, grinning like an idiot and saying something about “the reactor.”

“What?” I said.

“There’s a nuclear reactor on the List!” he said. “There’s an article about him—the Nuclear Boy Scout. You have to go look it up! You know how to make a nuclear reactor, right?”

I figured that Connor had slept maybe thirty minutes in the last seventy-two hours, and it was only Thursday morning. His tone bounced somewhere between desperate and manic. I explained that a nuclear reactor is a complex device, and that the physics involved is too complicated for a Scav Hunt item. He answered that the item was worth, like, infinity points and that if we (Justin and I) built something, Mathews would totally win. Back then, Mathews House was its own team, and all forty-five or so of us faced the barbarian hordes alone. I told Connor that I would look into it, but I still didn’t believe that there could be something as insane as a nuclear reactor on the List. I mean, really, how irresponsible were the Judges, and how lame were the “reactors” that other teams put together going to be?

After work I stopped at the library and found an article in Harper’s about David Hahn, “the Nuclear Boy Scout,” who had built a modest but plausibly functioning nuclear reactor in a shed in his backyard. Much has been written about David (RIP) in the intervening twenty-plus years, but in the end he did accomplish something in his garden shed. He had assembled a neutron source of some impressive strength for a total amateur, and when unleashed, it met the loosest definition of a nuclear reactor one can imagine. Then the Environmental Protection Agency got involved—but that’s another story. An idea was seeded in my brain. On the way home, I ran into Geoff Fischer [AB’00], a friend and a Judge. No hello or anything. “Are you guys really going to build a nuclear reactor?” he asked. The rumor mill was already in full swing.

I told him I’d need a little clarification on what they meant by “nuclear reactor,” and Geoff put me on the phone with Tom Howe [AB’00, SM’07], the Head Judge. “A net-power-positive nuclear reactor that could power a city or even a hair dryer is incredibly dangerous and insane,” I told Tom. “It’s certainly not in the spirit of the item.” Item 240 said that the Judges would give credit where Boy Scout credit was due. It clearly referenced Hahn’s experiment and not the type of multimegawatt fuel-recycling reactor that Connor and Geoff seemed to be envisioning.

The breeder cycle, for those of you who don’t know, creates a larger amount of fissionable fuel material than it uses. By recycling this product, it is able to efficiently generate a large amount of nuclear power, which is why these reactors were popular in the first place. “We can demonstrate the breeder cycle,” I told Tom. “We can turn thorium into uranium and uranium into plutonium.”

“That’s all we want,” said Tom, “but we’ll have experts there to make sure you’re not jerking us around. So be prepared.” And he hung up.

By now it was Thursday night. J came home from work and we talked about the idea over a few beers. We agreed that we could use a simple, highly active alpha source to create a weak neutron howitzer that could, in turn, create thermal neutrons. Just like what we used in our physics lab experiments. From there we could make small quantities of whatever isotopes we wanted.

With thorium*, it’s only a double capture up to uranium with a big cross section.

From there it’s another capture up to plutonium, but whatever. We had all weekend, man.

Fred Niell, AB'99, and Leila Sales, AB'06
Niell and Lelia Sales, AB’06, editor of We Made Uranium!, after a book launch event at the Seminary Co-op, held during Scav weekend 2019. (Photography by Nathan Keay)

All we needed was a proportional tube and a pulse height analyzer, a NIM crate with preamps and high-voltage power supply, and a few check sources to do a rock-solid calibration. I already had a good alpha source (a few microcuries of radium from World War II–surplus aircraft gauges) and thorium dioxide (from the inside of junk vacuum tubes from old TVs that we had salvaged). All we really needed was analytical equipment to verify that it all worked.

The next day, Justin and I visited our favorite lab coordinator, Van Bistro, and asked him ever so nicely if we could borrow a pulse height analyzer, proportional tube, and all the other stuff we needed “for an experiment.” Plausible deniability in full effect, Van even loaned us some check sources so we could do an appropriate calibration. All told, we probably signed out on the order of $20,000 worth of highly sensitive equipment. Van basically told us that if anyone so much as sniffed in his direction, he’d claim it was all stolen. And that he had photos of the thieves. We thanked him and carted the junk off to our dorm room.

That night, Justin and I went out to Fermilab to pick up some radiation bunny suits before disappearing into the machine shop. We soldered together some pieces of scrap metal to make an appropriate holder for the radium and thermalizing carbon sheets. It was mostly built of aluminum scrap pieces, but you know—even a boring piece of aluminum I-beam looks impressive with a bit of ingenuity and some face milling. We assembled the main reactor around eight or nine on Saturday night.

By midnight we had finished the energy calibration of the detector. Since our neutron source (the thing driving the nuclear reactions) was laughably weak, we needed to be able to detect down to a single atom whether or not we had indeed created the reactions associated with a breeder reaction. This is where the $20,000 worth of sensitive equipment and our calibrations came into play. By two or three in the morning we had detected the characteristic radiation from neutron capture of thorium, and from there we knew that it was just a waiting game.

At six in the morning we had a solid 3-sigma signal (> 99.7 percent likelihood) demonstrating the production of 235U. You may have heard of 235U as “weapons-grade uranium.” That’s right. We had created the highly fissile isotope of uranium from garbage found under our dorm room workbench. It was an amazing, Promethean moment. We ran down the hallway screaming “We did it! We made uranium!” at the top of our lungs—but this was the Sunday morning of Scav Hunt. Nobody was asleep. As the sun came up on Judgment Day, J and I acquired the same statistical evidence for the production of 239Pu. Weapons-grade plutonium.

Mind you, this might all sound scary, but we detected something like 8,000 individual atoms of uranium, and 2,000 atoms of plutonium, or something like 1×10-18 grams, or way, way less than can be detected by typical chemical tests. This is below the threshold of what might be considered detectable, even in good lab conditions. Our experiment detected the radiation emitted when these elements are created instead of detecting them directly. To detect them directly, given the mind-bogglingly small quantities, would have required a considerable investment of time and effort—two things scarce on Scav Hunt budgets.

Realizing that we would need to show the results to the Judges at some point, we decided to jot down some numbers and essentially write up the experiment like we would in any undergrad physics lab. At 8:45 a.m. Tom called to say that he was at the front desk of the dorm and that he had brought some guests. Next thing we knew, our hallway was filled with four Judges and a jovial but somewhat skeptical guy in his forties. He identified himself as a nuclear engineer from the Kansas City nuclear reactor facility, and he would be passing judgment on our apparatus.

We all piled into Justin’s room, some of us tripping over the empty cans. Clothes lay strewn everywhere, over and under crumpled beer cans, and piles of cigarette butts and physics textbooks littered the floor. The nuclear engineer, doubtless accustomed to hyper-clean safety gear and class-10-plus cleanrooms, was less than impressed.

But then Justin and I went into full-on thesis defense mode. J presented some numbers on the capture cross sections and explained the entire capture-decay-capture chain, and I showed him our equipment and explained the design of the reactor and the energy calibration that proved the system’s functionality. Five minutes into our argument, the engineer’s look turned from mild amusement into complete shell shock. After ten minutes, he had a grin on his face. He wanted to hear all the details of the capture cross sections and the energy calibration. Needless to say, he vouched for us with Tom and the other Judges.

Tom told us to show up at Judgment with our apparatus and a shed to get the points. We piled the reactor in my car and headed over. We threw up a six-cubic-foot drywall shed and spent the rest of the day in radiation suits, dancing to techno music. We kept a cooler in the shed for VIPs. Included among them was a writer covering the Hunt for the AP Wire and another for the New York Times. The AP guy seemed afraid of us and, frankly, more interested in the keg toss. The New York Times guy, on the other hand, was happy to share our bottle of Veuve Clicquot, as was the winner of College Jeopardy! from that year.

Mathews House placed second in the Hunt that year, which was quite an accomplishment for a team of that size. The reactor and all of its baby isotopes were disposed of in accordance with all applicable regulations the following week. A few days later, the editor-in-chief of Scientific American contacted us but eventually decided that it wasn’t a good idea to publish detailed plans for the production of isotopes in an internationally known magazine, no matter how safe the experiment.

The fallout on campus was pretty mild, all told, although the Resident Heads of the neighboring house evidently asked college housing for our expulsion. Fortunately, the head of housing was familiar with our escapades. As far as I know, any university-level complaints ended at her desk. J and I defended ourselves on several online bulletin boards and communities for the first several months, and then the whole thing more or less faded from the zeitgeist. But the nuclear reactor lives on as a Scav Hunt legend, the prime example of just how far Scavvies will go.

* Thorium (atomic number 90) has 90 protons in the nucleus. Transmuting an atom of thorium into uranium (atomic number 92) requires adding two protons. This is accomplished by bombarding a sample of thorium with slow neutrons from a device called a neutron gun. These neutrons can interact with the thorium nucleus and become “captured” there. After a single successful “capture,” the atom of thorium becomes a “heavy” isotope, 233Th. This isotope quickly decays into an isotope of protactinium (atomic number 91). A similar capture and decay process brings the atomic number to 92: uranium.

Fred Niell graduated from U of C in 1999 with a degree in physics. He lived all four years in Mathews House and Scavved for that team in 1996 and 1997. After Mathews House’s dismal outing in 1997, Niell took a year off from Scav in 1998 (save for a spud gun and small item support). Niell went on to graduate school at the University of Michigan and then a string of start-up companies in Boston. He now runs an electrical engineering design consulting company in Tampa, Florida, specializing in high-power and pulsed applications. Read a Q&A with Niell. 

Essay by Fred Niell. Reprinted with permission from We Made Uranium! edited by Leila Sales and published by the University of Chicago Press. © 2019 Leila Sales All rights reserved.

Read more in the web exclusive “Physicist with a Wrench.”