Geek Trivia: Pulp fission

What famous detective novels inspired the codenames of the world's first atomic weapons?

Sixty-one years ago this week, the United States employed the world's first nuclear weapons when it dropped a pair of atomic bombs on Japan, thereby forcing an end to World War II. On Aug. 6, 1945, B-29 bomber Enola Gay released the device code-named Little Boy on Hiroshima. Three days later, B-29 Bocks Car dropped the Fat Man device on Nagasaki.

The events of these days have been present in every comprehensive 20th-century history book written ever since. But what you won't find in most of those history books is a mention of the third bomb from the Fat Man/Little Boy development series—one that never saw completion due to the technical limitations of the era and the inherent flaws of the bomb's design.

That "first-generation" U.S. atomic weapon design was actually the second bomb planned, and it was basically a failed refinement of the first bomb design. The so-called Thin Man bomb (formally known as the Mark 2 nuclear device) was a variation of the "gun" design successfully employed in Little Boy (i.e., Mark 1).

The difference between Thin Man and Little Boy, however, was in its designated materials. By design, Little Boy worked with uranium isotopes, and Thin Man used plutonium.

What was the problem with the plutonium isotopes available in 1945? To use a painfully simplified analogy, they were finicky.

Technical complications arose that eventually forced the Manhattan Project to abandon work on Thin Man and throw more resources behind the highly experimental and vastly more complicated implosion design that was the basis for Fat Man (i.e., Mark 3). The code-named Gadget device detonated during the first Trinity test in 1945 was a field-proof of this implosion principle.

While this mere Trivia Geek is butchering the technical and theoretical complexities of the Manhattan Project's hard design choices, you can get a fascinating lowdown on this seminal scientific undertaking by reading The Los Alamos Primer, a series of lectures given to all scientists who signed onto the Manhattan Project. The primer brought all the nuclear newbies up to speed, so they could begin working ASAP.

Its author was Robert Serber, a protégé of Manhattan Project director Robert Oppenheimer. It was Serber who code-named Fat Man, Thin Man, and Little Boy, choosing the names based on the relative size and shape of the devices themselves.

Of course, that's not the whole story, as Serber admitted that Fat Man and Thin Man were names he cribbed from some popular detective fiction and that he chose the name Little Boy merely to distinguish from these two.


From what famous detective novels did Manhattan Project scientist Robert Serber draw codenames for two of the first three U.S.-developed atomic weapons?

Serber named Thin Man after the title character from the 1933 Dashiell Hammett detective novel, The Thin Man. The work later spawned a series of movie adaptations.

The Fat Man bomb drew its namesake from Kasper Gutman(AKA The Fat Man) from another Hammett novel, The Maltese Falcon. Sidney Greenstreet's legendary portrayal of The Fat Man in the film adaptation of The Maltese Falcon reputedly influenced Serber's choice of namesake.

Serber chose Little Boy merely to distinguish it from the Thin Man, which employed the same elongated gun design. For the full story, we must take a look back at the distinctions between the designs for Fat Man and Little Boy—and the technical realities that made those differences necessary.

In some respects, the design of all nuclear weapons centers around one basic physical principle: Critical mass. If sufficient quantities of certain radioactive isotopes come together quickly enough, the collective radioactive decay of the isotopes will start a chain reaction—leading to nuclear fission, which in turn leads to a monstrous release of energy.

The trick to critical mass explosions is timing. You need to combine the two sub-critical portions of the radioactive fuel fast enough that they don't pre-fission—or "fizzle."

The original Manhattan Project solution to the fizzle problem was the gun design. It divided a critical mass of radioactive fuel into a large target core and small slug. It then fired the slug—much like a bullet from a gun—into the rest of core.

If the slug fired fast enough, the two sub-critical masses would meet with sufficient speed to cause a nuclear explosion. This was the principle behind the Little Boy bomb, which fired together two sub-critical masses of uranium-235.

The problem with the gun model was that it wouldn't work with the isotopes of plutonium available in the early 1940s. The design required separating the Pu-239 sub-critical masses by such a distance and firing them together so quickly that it wasn't feasible to assemble a large enough bomb with a long enough gun barrel. The Thin Man would have to be too tall and too thin to work.

Thus was born the Fat Man, which used shaped explosives to crush a hollow sphere of plutonium into a solid critical mass. The result was a large round design that looked for all the world like a fat counterpart to the Thin Man, which made a mysteriously inspired set of codenames obvious—and an obvious choice for Geek Trivia.

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The Quibble of the Week

If you uncover a questionable fact or debatable aspect of this week's Geek Trivia, just post it in the discussion area of the article. Every week, yours truly will choose the best post from the assembled masses and discuss it in the next edition of Geek Trivia.

This week's quibble comes from the July 19 edition of Geek Trivia, "First in (space)flight." TechRepublic member wLamia busted me for claiming that Bell Labs built the Lunar Lander Research Vehicle.

"[The] LLRV was made by Bell Aerospace, not Bell Labs. . . Bell Labs, subsidiary of AT&T and developer of the transistor and UNIX, had nothing to do with Bell Aerospace, developer of the P-39, Bell X-1, [and] the Bell 47 helicopter."

I am once again guilty of conflating two namesake titans of industry. Thanks for setting me straight, and keep those quibbles coming!

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The Trivia Geek, also known as Jay Garmon, is a former advertising copywriter and Web developer who's duped TechRepublic into underwriting his affinity for movies, sci-fi, comic books, technology, and all things geekish or subcultural.