Uranium-235: Part 1
My dad died in 1992.
He’d been ill for a while, but his death and its aftermath have remained as the most emotionally vivid, significant, and shattering experience of my life.
This is after more than two decades, after living through 9/11 in New York City, after surviving Hurricane Fran, after saying goodbye to more family members and friends than I want to think about.
I defined myself through him. I know that’s true for most young men. But from an early age (surprisingly early) I defined myself as the opposite of how I saw him. He was straightlaced, sober (never smoked or drank), law and order (literally a federal agent), and truly, deeply religious.
Of course I because the rebel, bending and breaking the law, living on the edge (the “edge”), and authentically not believing. Or not experiencing belief as he did.
This lasted through college of course, and began to change once I began working as a journalist — specifically, an investigative reporter for a well-regarded regional newspaper.
Dad read my work, and had to consider there was more to me than the pain-in-the-ass underachiever (in his eyes — after all, who needs an English/journalism degree when there are real jobs out there?) who always wanted the last word.
I kept up my habit of calling home every week. We’d talk about the issues I was writing about; the politics, the crime, the sad human stories. These were things he also dealt with in his job, before he was forced into too-early retirement (federal agents who carry firearms usually have to retire at 55).
We found common ground. We began to see each other as men, on our own, and with similar beliefs and causes. We began to really talk to each other.
Then he was gone.
He’d been diagnosed with Chronic Lymphocytic Leukemia (CLL) a decade before that. But here’s the thing about CLL — unless you test positive for a specific marker (known as ZAP-70), it’s supposed to be chronic, treatable, survivable.
Dad didn’t indicate for ZAP-70. His CLL was treatable at the beginning. At the end, though, his leukemia mutated (a few times) and his doctors were left essentially powerless, treating symptoms and offering palliative care. When the end came, it was incredibly fast; really, a matter of hours — a stark contrast to the years he’d spend living a chronic life.
So what happened?
War. Service. History. Radiation. Time.
Setting the Stage: The Atomic Age
The first atomic bomb used in warfare — Little Boy, detonated over Hiroshima, Japan on August 6th, 1945 — was an enriched-uranium bomb developed through the Manhattan Project.
The very first man-made nuclear detonation in history, the Trinity test conducted just three weeks earlier in New Mexico, used an implosion-design plutonium device (named “The Gadget”), which was also used in the Fat Man bomb detonated over Nagasaki on August 6th.
It’s stunning to realize we as a species went from no nuclear detonations in our history to three in less than a month. (I’m not going to debate it: Little Boy and Fat Man helped conclude a war with Japan that could have gone on far longer with an even more staggering death toll.)
Back to enriched uranium. Natural uranium (fully organic!) is radioactive but isn’t usable as fissable nuclear fuel. Natural uranium primarily consists of Uranium-238 (about 99.28% by weight) and just a tiny bit of Uranium-235 (about 0.71%).
U-235 is also known as enriched uranium, and it was the material used in Little Boy.
Enriched uranium is rare in nature. (Plutonium is even rarer, practically but not quit non-existent, but that’s a different article.) Highly enriched uranium (also known as weapons-grade) is a concentration of 20% or higher U-235, and is DEFINITELY not found in nature.
Enriching U-238 to weapons-grade U-235 at industrial scale — what’s needed to produce atomic weapons — was nasty work that began in the middle of World War II.
Most of that work was done in a place called Oak Ridge National Laboratory, in Tennessee.
Oak Ridge the town was known as the Secret City, because it was built as a production site for the Manhattan Project, and by presidential proclamation was declared a military district not subject to state control.
The population grew from 3,000 in 1942 to about 75,000 in 1945.
A uranium-diffusion facility named “K-25” was built during this time, and it covered 44 acres. That’s right: 44 acres. It was the largest building in the world at the time, and was constructed in near-total secrecy, at a cost equal to about $10 billion in today’s dollars.
My father arrived in Oak Ridge in 1944.

