Posted on 05/01/2019 5:26:02 PM PDT by BenLurkin
Back in 2013, Timothy Koeth, an associate research professor at the University of Maryland, received a rather extraordinary birthday gift: a little cloth lunch pouch containing a small object wrapped in brown paper towels. As Koeth peeled back the layers, his eyes grew wide with astonishment. He immediately asked, "Where did you get that?"
Inside he found a heavy metal cube and a crumpled message, a provocative note wrapped around a stone that came crashing through the window of history. It read, "Taken from Germany, from the nuclear reactor Hitler tried to build. Gift of Ninninger."
Koeth's friend grinned, picked up the 5-pound block of uranium metal and handed it to him. Though modest in size, the cube was heavy, dense and steeped in lost history. Koeth accepted the cube and its note as an invitation to the adventure of a lifetime.
In the May 2019 issue of Physics Today, Koeth and Miriam Hiebert, a doctoral candidate working with him on this project at UMD's A. James Clark School of Engineering, describe what they've discovered while exploring the German quest and failure to build a working nuclear reactor during World War II.
Uranium is weakly radioactive, and this particular cube measures about 2 inches on each side. "It's surprisingly heavy, given its size, and it's always a lot of fun to watch people's reaction when they pick it up for the first time," said Hiebert.
(Excerpt) Read more at phys.org ...
Regardless, the Germans could never have refined enough uranium to build one by 1945.
The atomic pile that was built under the bleachers at Stagg Field in Chicago was as big as a house. It was designed to be a sphere, but when it became clear that it would become critical long before they reached the top, they truncated the upper courses of carbon blocks and uranium slugs, so that in the end it was shaped more like a doorknob as big as a house.
It needed to be so big in order for the graphite moderator to slow the U-235 emitted neutrons from the tiny fraction of that isotope in the natural uranium used to fuel the pile enough to have a decent probability of being captured by other U-235 nuclei, and thereby create a chain reaction.
I seem to recall reading somewhere that a German A-bomb would have required a cargo ship for delivery.
I’m given to understand that German graphite contains a wee bit, just a whisper, of boron.
Boron sops up neutrons, and those missing neutrons skewed the data just enough to convince the German scientists that a deliverable bomb was impossible.
Search your attics, folks. And remember, Rick from Pawn Stars is always buying. He’ll have his expert look at it to make sure it’s an authentic uranium cube and go from there.
Almost any graphite does and it doesn’t take much to screw it up for this purpose. It took an entirely new process to make graphite for the pile.
File under "things that make one say 'hmm...'"
My understanding was they were not serious and didn’t think they could make it work in a timeframe that would be useful in the German war effort. They also feared for their own lives if they committed too enthusiastically to the project and failed to meet over-optimistic timelines.
As far as I know; the Germans had no way to enrich natural uranium; which is over 99% non-fissionable U-238 and only about .7% U-235. Perhaps in fractional-gram quantities. Without the enrichment, there is only the possibility of creating a low power chain reaction, as did Fermi in Chicago at CP-1. using over 5 tons of natural U.
An additional requirement is a moderator to sustain a chain reaction in unenriched U by slowing down neutrons and increasing the odds that said neutrons could be captured by another U nucleus. Szilard theorized that carbon; in the form of graphite, would make a suitable moderator...but critically, the Germans were not aware that a common impurity in graphite, Boron, was a voracious neutron absorber. Graphite was commonly used for arc-lights at the time and the boron impurity did not present a problem for that application. But not knowing this nuance, the Germans rejected carbon and believed they would have to produce thousands of gallons of heavy water. Which they did at Norsk Hydro; a plant that was bombed by the Allies. The US reactor effort was 100% dependent upon the development of low-Boron content graphite which was produced after Szilard went to National Carbon and persuaded them to produce what was and is called “nuclear grade” graphite.
The Germans in reality were nowhere near being able to produce a weapon. That’s not to say that the fears of them doing so were unfounded. They certainly led the world in chemistry in the first half of the 20th century.
But remember, poor rick would have to clean it up, put a frame around it and then it would sit on the display shelf for years- maybe even decades and by then he would only make a minimal profit on it.
So he will off you $0.39 cash for it and that’s the best he can do ya know because he’s here to make money.
Cool artifact. I think you need a license to hold more than 1kg. I have a little sliver around here somewhere.
“Chum, what did you do with that uranium cube I bought?”
“You mean that square thing that was sitting there? I sold it to Johnny for $1. He said it would make a good Borg cube for his Star Trek diorama!”
When the thing was getting ready to explode, Heisenberg had no idea what to do as the thing went out of control. That was pretty much the end of any serious German work towards a nuclear weapon.
Let me add my vote to that excellent and very entertaining book.
I have a background of dealing with radioactive materials and a military background, so for me, it was doubly interesting to read the accounts in that book!
Expedition Wild (Josh Gates) had one show where they were exploring buried Nazi caves. They had to back out when their Geiger counter had a really high reading.
I could see where that would happen...the Nazis probably just dumped some nuclear wastes from their limited program in caves they presumed would be out of the way.
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