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"Nuclear Archaeology" Inspires Replica of Hiroshima's Little Boy 298

James Cho writes "Through a decade of painstaking reverse engineering, trucker John Coster-Mullen built the first accurate replica of the Hiroshima bomb. His work yielded a new history of the first nukes, 'Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man,' with historian Robert Norris saying, 'Nothing else in the Manhattan Project literature comes close.' Philip Morrison, one of the physicists who helped invent the bomb, deemed it 'a remarkable job.'"
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"Nuclear Archaeology" Inspires Replica of Hiroshima's Little Boy

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  • by Daniel Dvorkin ( 106857 ) * on Sunday January 25, 2009 @03:51PM (#26600349) Homepage Journal

    "Reverse engineering" is a pretty broad phrase. It can mean anything from taking an actual working example of a machine and figuring out how to build it, to the kind of thing you're talking about, observing what a machine does and figuring out how to build something that does the same thing (whether or not the internal mechanism is the same.) I'd say what Coster-Mullen did falls right in the middle of this range, so calling it "reverse engineering" is fair.

  • Re:How soon until... (Score:2, Informative)

    by Anonymous Coward on Sunday January 25, 2009 @04:09PM (#26600519)

    iirc, fat man was the "cannon" driven uranium bomb...

    Fat Man was the implosion type. Little Boy was the gun type.

  • Not so big a deal (Score:5, Informative)

    by Ancient_Hacker ( 751168 ) on Sunday January 25, 2009 @04:09PM (#26600521)

    The Hiroshima bomb was a very simple "gun" design. Plenty of published info on it. It used a navy gun barrel cut down to size, a U235 doughnut target, a polonium initiator, and a U235 projectile. Mighty simple. Any chopper shop could build one, with the exception of getting the Polonium and U235.

    This design was abandoned as it had many drawbacks-- it used about 8 times more U235 than absolutely necessary, there was a 7% chance of a fizzle, and there was no way to make it safe.
    But it had the advantage that it was dead-simple and guaranteed to work, well 93% of the time.

    Now if he made a replica of Fat Man, that would really be something.

  • Re:atomic weiner (Score:5, Informative)

    by Daniel Dvorkin ( 106857 ) * on Sunday January 25, 2009 @04:10PM (#26600527) Homepage Journal

    There are a lot of stories that appear on /. in which I have absolutely no interest. (The same could be said by practically anyone here.) So you know what I do when one of those stories comes up on the front page? I don't click on it. Easy, simple solution -- let the people who do care about that particular story talk about it, and go find something I care about to read and comment on instead. Everybody wins. It's not that hard a concept to grasp.

  • Re:How soon until... (Score:3, Informative)

    by NouberNou ( 1105915 ) on Sunday January 25, 2009 @04:12PM (#26600535)
    Fat Man was the implosion device. It was called Fat Man due to the size of the explosive lenses that were used to compress the Plutonium into a critical mass. Little Boy was the gun-type device.
  • by DrBuzzo ( 913503 ) on Sunday January 25, 2009 @04:15PM (#26600561) Homepage
    Assembling the bomb is not the difficult part. A gun-triggered uranium bomb mechanism, which is the simplest and least effecient, is relatively easy to built. The material, on the other hand, is a bit difficult. A critical mass sized assembly of u-235 requires gathering a lot of uranium ore, processing it to chemically pure uranium, converting the uranium into uranium-hexaflouride, a very corrosive gas that must be made using fluorine. Then the gas must be pumped through miles of special diffusion piping many times until it is isotropically enriched to 95%+ U-235. Alternatively, it can be pumped through a cascade of high speed drum gas centrifuges. Both methods require enormous industrial facilities.

    OR, you could go with creating plutonium using large reactors and chemical separation plants.

    Either way is going to be a big project. Even nation states take a good few years to get this going from nothing.
  • Re:Not so big a deal (Score:5, Informative)

    by Compholio ( 770966 ) on Sunday January 25, 2009 @04:15PM (#26600565)

    ...a U235 doughnut target, a polonium initiator, and a U235 projectile...

    If you'd actually read the article then you'd know that he discovered that the projectile was hollow and the target was solid. Personally, I just skimmed it - but it seems like he collected a lot of facts that lead him to believe that people were parroting incorrect information about how the bomb was constructed and he wanted to set the record straight.

  • Re:Not so big a deal (Score:5, Informative)

    by RDW ( 41497 ) on Sunday January 25, 2009 @04:23PM (#26600627)

    'The Hiroshima bomb was a very simple "gun" design. Plenty of published info on it. It used a navy gun barrel cut down to size, a U235 doughnut target, a polonium initiator, and a U235 projectile. Mighty simple.'

    A major point of the article is that many of the key (and repeatedly published) 'facts' about the bomb are quite wrong. e.g., according to Coster-Mullen, the projectile was actually a hollow cylinder and the target was a rod rather than a doughnut - 'little boy was female'. Wikipedia is now using his version of the bomb design in the Little Boy article: []

  • by Vellmont ( 569020 ) on Sunday January 25, 2009 @04:36PM (#26600739) Homepage

    Besides, a lot of the difficulty in making even an inefficient nuclear bomb at all obtaining the weapons grade fissile material.

    I'd say that the vast majority of the difficulty is obtaining the fissile material. Weapons grade uranium/plutonium doesn't exactly grow on trees. Creating it yourself (and preventing anyone from stopping you) takes the power of a government.

    This has essentially been the policy to control proliferation for 60 years now. Stopping the knowledge of the design details is merely security theater.

  • Re:How soon until... (Score:1, Informative)

    by Anonymous Coward on Sunday January 25, 2009 @05:36PM (#26601255)

    I realize this is serious reply to a funny post, but I thought I'd point out the difference between say, a gun, and an atomic weapon in respect to this argument.

    Owning a gun is a valid right - partially because it does not threaten another person's life until it gets pointed at another person.

    An atomic weapon, on the other hand, is pointed at everyone within the bombs kill radius every moment it remains active. Having a nuclear bomb around is like holding a gun to the head of everyone within several square kilometers, all the time - whether you are deliberately threatening them or not. A simple application of the United States constitution would be to recognize such as a "clear and present danger".

  • by Wes Janson ( 606363 ) on Sunday January 25, 2009 @08:02PM (#26602409) Journal
    It's only unsettling to those who are uneducated in the subject. Anyone with a passing knowledge of nuclear weapons can tell you why this is completely irrelevant from a security perspective. And anyone who pays real attention can tell you what you should really be worrying about.

    Unfortunately, the percentage of Americans who have even that passing familiarity with nuclear weapons is probably no greater than 2 or 3 percent. Which means 97-98% of the population is going to react out of fear, uncertainty, and doubt in anything related to the matter.
  •     Nope, if you had a working replica bomb in your basement, you'd never know when it went off. You'd simply be vaporized, as would your neighbors for a few miles. When they identified the center of the crater, then they'd know it was you, but there wouldn't be much to prosecute. I don't think they'd try to prosecute "the atoms previously known as Polygamous Ranch Kid".

        Skewing slightly off topic, how the heck do you manage to be polygamous? I can only handle being with one woman at a time. I couldn't handle a whole cluster of them. Even a Beowulf cluster of them. :)

  • by rubycodez ( 864176 ) on Sunday January 25, 2009 @10:24PM (#26603453)

    eh, most students don't know "critical mass" for a spherical shape of uranium of given enrichment, that's actually a pretty hairy calculation. Pure U-235's value is published but who outside of a hard care geek is going to remember it? And as for a "pile", of blocks of fissionable material and moderator and support structure, I've a big thick textbook on that subjects, ain't easy at all.

  • by demachina ( 71715 ) on Sunday January 25, 2009 @11:45PM (#26603975)

    Its a little sad to skim through the posts on this story and find pretty much all of them are lame.

    Its a long article but its really a fascinating read and I'm guessing almost no one did. It makes a couple really insightful points:

    A. All of the U.S. governments obsessive secrecy about nuclear bomb technology is pure security theater. The hard part is mastering the fuel cycle. If you can acquire the fuel or master the fuel cycle, making the bomb is pretty easy.

    B. Much of what we read and take for authoritative is in fact garbage. There have apparently been a number of works on Fat Man and Little Boy, often by well educated and authoritative authors that were apparently complete nonsense. It just took an obsessive photographer/truck driver with no college degree to debunk one authoritative work after another. In particular apparently everyone thought the Uranium bomb was a female target shot with a male shaped projectile because thats the way people expected it to be, when in fact it appears it was the other way around.

    One also wonders if the U.S. government intentionally propagated nonsense in these "authoritative" works thinking it would set back some aspiring bomb maker. For example, in one work it apparently said the barrel in the Uranium bomb was made of wood which was apparently pretty comical since it had to contain the explosion of several bags of cordite.

  • Re:Not so big a deal (Score:2, Informative)

    by NouberNou ( 1105915 ) on Monday January 26, 2009 @01:25AM (#26604505)
    No one said it was efficient. For example, according to wikipedia (and it seems very plausible) only one gram of the 13 POUNDS of Plutonium in Fat Man converted from mass into energy. I would assume that something similar happened with Little Boy, and probably was even less efficient. The force of the pusher plate against the uranium ring was probably just enough force to let it obtain a non-fizzle reaction.
  • by n6kuy ( 172098 ) on Monday January 26, 2009 @01:35AM (#26604551)

    ... of both Fat Man and Little Boy.

    See here [], for example.

  • by n6kuy ( 172098 ) on Monday January 26, 2009 @01:39AM (#26604563)

    Although that Little Boy replica at Los Alamos might not be as accurate as the previous one they used to have. See here [].

  • It's about the mass (Score:5, Informative)

    by DG ( 989 ) on Monday January 26, 2009 @07:34AM (#26605855) Homepage Journal

    Actually, it is a pair of nested cylinders, and the rationale behind it is brilliant.

    To get the biggest possible boom, you want to bring together the largest possible mass of fissile material. Problem: if you accumulate too large a mass, it starts a chain reaction on its own.

    But if you form that mass into a ring shape, and make the hole in the ring large enough, you create extra surface area for neutrons to escape, but the gap is too big for them to have sufficient energy to split an atom on the other side of the gap.

    For a given outer diameter (fixed by the inner diameter of the bomb casing) the maximum mass of fissile material is obtained with a cylinder whose height is determined by the mass on the "side" of the cylinder nox exceeding criticality. A mating cone shape results in a smaller usuable mass.

    So why make the projectile hollow instead of shooting a slug into a hollow target? Because the sides of the gun barrel constrain the movement of the projectile and ensure that the mating surfaces are aligned.

    It's actually, for such a "crude" design, brilliant engineering.


  • by vlm ( 69642 ) on Monday January 26, 2009 @08:37AM (#26606149)

    Even though it is difficult to obtain the fissile material needed, the engineering is not particularly easy. Keeping the engineering details classified makes the job of someone trying to recreate the bomb harder. This keeps the risks of proliferation down.

    Dude, you've got to be kidding. It's a cannon with a projectile and target made of nearly pure U-235. Making a target is pretty easy, I'm sure there is some old joke about civil engineers that can be inserted here. Civil engineers have been building targets for centuries, or something like that. Making a cannon has not been the pinnacle of technological development since the middle ages. Rather than make your own cannon, just cut down an artillery piece like the Manhattan project did. Then you've got the mind-bending engineering challenge of casting a projectile and turning it on a lathe, which stopped being challenging in the mid 1800s. Admittedly U is harder to cast than perhaps Al or Zn, but not much harder than Mg or Be or W.

    Now I admit there is complicated engineering involved in modern top of the line weapons. Since the bean counters know the special materials are quite expensive and hard to make, if you intend to make tens of thousands of them, there is extreme pressure to use extreme engineering to make it lighter cheaper more powerful, etc. An implosion device is extremely hard to design and needs alot of testing (and even the best designs occasionally failed during tests), but the bean counters approve that expensive design since special nuclear materials are so expensive in thousand device production runs. Also given the cost and bother of launching every gram on a missile, any extreme engineering is worth it to reduce weight, because one less pound of weapon might be one hundred less pounds of missile. Also, given the pain and suffering of working with special materials, extreme engineering to reduce maintenance is worth it if your device will sit around unused for decades, or at least you hope so. And if the extreme engineering occasionally fails, like maybe 25%, that is OK if you have thousands of warheads with multiple ones assigned to each target.

    But it you just want to make a big bang to make the political statement that you've joined the club, then its pretty easy, once you get the special stuff, and extreme engineering is not a good idea for the first bang. For example, the first terrorist detonation will almost certainly be from an uninspected 60000 lb ocean shipping container, so there is no point in extreme engineering to make it light enough to fit on a missile. Then again since the borders are basically wide open (re illegals, etc) the first might be on a semi truck, but still no engineering pressure for light weight. Why make a suitcase nuke when you don't need to, because you can just as easily haul in cubic yards and tons?

    Once a country or other group joins the nuclear club, I'm sure their bean counters will want the fancy designs that the US and USSR spent zillions optimizing. But then its waaaaaaay too late to prevent proliferation, by the definition of proliferation. Since the borders of the US are wide open for giant heavy weapons there is no point in making tiny light ones anyway. If in the 1950s the usa could have simply sent shipping containers of weapons to the USSR or driven semis across from alaska, we'd never have wasted the engineering time and money on the tiny light devices.

    Here's the mandatory slashdot car analogy. You're saying that if the 2009 indy-500 car racing team A wants to prevent team B from winning, they should classify the design of the original ford model T car. Or maybe, if in 2009 we want to stop china from competing with ford, we should classify the model T blueprints.

  • by goodmanj ( 234846 ) on Monday January 26, 2009 @10:19AM (#26606861)

    the gap is too big for them to have sufficient energy to split an atom on the other side of the gap.

    This can't be right. The area inside the ring is filled with air, right? Neutrons go through a few cm of air like it's not even there.

    Besides, to prevent a chain reaction, you need to reduce the odds that an average fission neutron will collide with and split another U nucleus. Reducing the energy of those neutrons doesn't help -- in fact, it generally *increases* the odds of causing fission, which is the point of moderators in nuclear power plants.

    Your point about conical geometry reducing the total possible fissile mass is a good one, but I wonder if there's some intermediate shape, like a hyperboloid, that might give a better trade-off between collision time and fissile mass.

"Atomic batteries to power, turbines to speed." -- Robin, The Boy Wonder