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The Manhattan Project Bomb You Haven't Heard Of

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Wikimedia Commons

You probably know Little Boy and Fat Man as the atomic bombs detonated over Hiroshima and Nagasaki, effectively ending WWII. The U.S. rushed headlong into the development of the bombs, trying to actualize the atomic bomb ahead of the Nazis. And we did it.

But during the Manhattan Project scientists developed at least four bombs—Thin Man, The Gadget, Little Boy and Fat Man—three of which made it to fruition (The Gadget, Little Boy, and Fat Man) with two actually being used in war (Little Boy and Fat Man). Why haven’t you heard of Thin Man? Well, it never saw the light of day.

How to Build An Atomic Bomb

There are two different ways to build an atomic bomb. One is gun-type assembly, in which a hollow, sub-critical (less mass than needed to sustain a chain reaction) fissile “bullet” is shot at a solid supercritical (able to sustain a chain reaction) core. The bullet strikes and compresses the core, fission happens, and the bomb explodes. This type of assembly is relatively simple in design, involving one thing being shot at another, and we’d been building non-nuclear things of this sort for years before the Manhattan Project.

The second type of assembly is a bit more complex. Implosion-type assembly involves a hollow sphere containing a complex arrangement of high explosives and detonators, surrounding a solid fissile, but not yet supercritical core. The high explosives are detonated in such a way that the blast wave compresses the core to a supercritical density. This causes fission, which makes the bomb explode.

Thin Man was a gun-type weapon designed to use plutonium as fuel. But scientists found that the reactor-produced plutonium available at the time contained too many impurities, causing a greatly increased spontaneous fission rate, which basically means that the fuel would pre-detonate and blow itself apart while trying to attain criticality, rather than after, which was kind of putting the nuclear cart before the horse. So the bomb was scrapped, and focus turned to Little Boy.

Cue Uranium

Little Boy was the same type of weapon as Thin Man—except for the fact that it used uranium rather than plutonium. Since uranium isn’t as prone to pre-detonation, a much simpler weapon was designed, without many of the safeguards of the Thin Man design.

Even though plutonium wasn’t a good choice for gun-type weapons, it worked well in the implosion design, which included more safety features that prevented pre-detonation of the plutonium. While Thin Man and Little Boy were being developed, the scientists were also working on The Gadget and Fat Man, which were both implosion-type devices, using plutonium (and uranium) as fuel.

Since the implosion design was more complex, it was tested before being put into action. The Gadget was detonated in the New Mexico desert during the Trinity Test on July 16, 1945. The test was successful, and became the first man-made nuclear explosion in history, and we were now relatively certain that Fat Man would work as expected since it used the same design.

No Tests Necessary

We were so confident of our scientific prowess that we sent the pieces for Little Boy to the Mariana Islands for final assembly two hours before the Trinity Test. Now remember, this weapon design was completely different, and we had never done any of this before. So why didn’t we test the design for Little Boy?

Well, the gun-type assembly was thought to be simple enough that it would detonate without problem. And enriched uranium was much harder to come by than plutonium, so we didn’t want to waste the rare stuff on a test. Time was also a factor: It had taken years to enrich enough uranium to use in this one bomb, and the war was raging on. We simply didn’t want to wait the months or years necessary to accumulate enough uranium for another bomb.

Less than three weeks after the Trinity Test, Little Boy was successfully detonated over Hiroshima on August 6, 1945. Three days later, Fat Man was detonated over Nagasaki, adding atomic weapons to mankind’s arsenal for the first time.

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iStock // Ekaterina Minaeva
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Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
May 21, 2017
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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Name the Author Based on the Character
May 23, 2017
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