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

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.'"

Comments

First homebrew nuke

[4D6963]

*BOOM*

Re:First homebrew nuke

[RichardJenkins]

Hopefully not that accurate.

Re:First homebrew nuke

[demachina]

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:First homebrew nuke

[Hal_Porter]

From TFA
"A circular steel plate was positioned inside the 17.0"-diameter tail cylinder at the front of the tail tube and another towards the rear of the tube," Coster-Mullen writes. "These allowed the tail to be slid over the 10.5"-diameter gun tube during assembly. The forward plate was positioned 26.5" in front of the aft plate and was welded to the front of the tail tube."

Though the bookâ(TM)s specificity about dimensions, shapes, and materials was mind-numbing, the accumulation of detail was strangely seductive.

Fucking liberal arts graduates.

Re:First homebrew nuke

[cyn1c77]

Get it straight.

The US government does not confirm or deny comments on classified technology. Nuclear weapons are classified. So if you write a book that is full of crap on nuclear bombs, all of the experts will general work for (or have worked for) the government and will not be able to comment on it.

Thus, people who are not in "the know" will read the book and say "Gee, this is really great stuff, very accurate." Meanwhile those who actually work on these weapons and who have security clearances will buy the book, read the book, laugh about the errors with each other... and not talk about it to the general public.

It's easy to be a self-proclaimed expert when all the real experts can't comment and you can't actually demonstrate that your technology works.

And finally, you really think making a bomb is easy if you have the fuel? Do you have personal experience here? Keep in mind you don't get a lot of testing opportunities with these things, and diagnosing what is going on during the explosion is also quite involved. There's a big difference between assembling your nuclear material to generate some nuclear yield and actually generating significant nuclear yield.

How soon until...

[www.sorehands.com]

How soon until homeland security shows up accusing him of terrorism?

Re:How soon until...

[philspear]

If he's built a WORKING replica, I would hope VERY soon!

Re:How soon until...

[Daniel Dvorkin]

According to Amazon, his book was published in 2002. If they were going to lock him up, they've had plenty of time to do so already.

Of course, it's a good thing for him his name is John Coster-Mullen instead of, oh, say, Ahmed al-Rashad. You can pretty much guarantee that in the latter case, even if all the other circumstances were exactly the same, he'd have been disappeared a long time ago.

Re:How soon until...

[sidb]

A working replica would be dangerous and surely illegal. It would not be terrorism unless he used it deliberately to terrorize a group of people. Just because something is bad doesn't make it terrorism.

Re:How soon until...

[telchine]

If he's built a WORKING replica, I would hope VERY soon!

Nuclear bombs don't kill people. People kill people. Why shouldn't this guy have a born right to bear nuclear arms? If he wants to defend his property from double-glazing salesman, he should have every right to make use of the second amendment and protect his property!

Re:How soon until...

[Anonymous Coward]

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

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

Re:How soon until...

[NouberNou]

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.

Re:How soon until...

[Anonymous Coward]

I think the law at least in CA says there's $200 fine for detonating one...

Re:How soon until...

[Cyberax]

But they can make you warm, fuzzy and positively glowing!

Re:How soon until...

[_Sprocket_]

You let private citizens have nuclear arms, the next thing you know is they'll sell them to pawn shops and then it's in the hands of gang-bangers nuking 7-Elevens. I've seen the Clerks documentary. I know how these things work.

Re:How soon until...

[philspear]

It worries me that there is one "insightful" mod on that post.

Re:How soon until...

[PacoCheezdom]

Well, it's a little steeper than a fine, but I still think it's pretty funny that there's a state law for this:

11418. (a) (1) Any person, without lawful authority, who possesses, develops, manufactures, produces, transfers, acquires, or retains any weapon of mass destruction, shall be punished by imprisonment in the state prison for 4, 8, or 12 years.

(California Penal Code)

Re:How soon until...

[PopeRatzo]

insert lame joke about all of us being really, really lucky that Germany didn't have any nukes during WW2.

I'm not sure that's a joke.

Re:How soon until...

[PopeRatzo]

with war torn, terrorist lead countries on the verge of being able to design model and acquire materials for even small nuclear weapons I am not sure that is a good idea.

Yeah, I don't like Israel or Pakistan having the bomb, either.

Re:How soon until...

[WolfWithoutAClause]

Never mind that, what about the right to arm nuclear bears? You're just not thinking about the big picture!

Re:How soon until...

[Hognoxious]

an inanimate object cant be dangerous on its own.

If you're going to quote the mayor of Pompei, at least give proper attribution.

Re:How soon until...

[Opportunist]

Yeah, but realize that when you have da Bomb, you have to go to all those nuclear disarmament conferences. And, be honest, would you wanna spend all your spare time with Putin?

Re:How soon until...

[epine]

I've read a lot on this subject over the years, but not much recently, and what I recall best at this point is the portions I decided to believe at the time from the accounts I found most compelling.

I'm inclined toward accounts based on the premise that America and Russia had an agreement (what blend of official/unofficial I can't recall) that Russia would pressure the Japanese from the Kamchatka peninsula and that territorial control in the post-war world would be to some degree be established by how much territory in the region of Japan the Russians had managed to occupy at the point in time of formal Japanese surrender.

To fully appreciate the political situation, you need to realize that the Americans were reading Purple. Purple never got as much press as Enigma because it was considered somewhat unsporting to crack a diplomatic code. The Americans had a sense that Japanese surrender was already in the works, but then the Japanese began to haggle among themselves about exactly how this would be done and how the internal post-surrender pecking order would unfold.

Meanwhile the Russians are progressing far faster than the Americans wished. Japan had long understood that the American military economy was humming along at a fever pitch, and was pretty much impossible to mess with short of capturing Hawaii. The Japanese civil servants were long resigned to the outcome, while the royal crust was dithering.

Also, don't forget that conventional Tokyo fire bombing destroyed 50% of the world's most densely inhabited city. The McNamara movie "Fog of War" has some good stuff on this. (Complicated man, that guy.) It's not as if Japan was lacking reasons to cease hostilities. Memo for next war: less wooden housing.

I think one American perspective about the bomb was "hurry up and get on with the surrender, before we have to concede every square inch of east Asia to the rapidly advancing Russian borg".

The other perspective is that they had spent 1/7'the of their entire wartime economy on this project, and along the way denied a lot of conventional armaments to their generals and enlisted troops. A lot of powerful people who hadn't been in on the Manhattan project were pissed about this. Really, they're going to spend a billion 1940 dollars on this program and then cancel the big demonstration, when you have no end of detractors within the ranks of power?

Even with large contingents of Japanese officialdom resigned to surrender, there's always a risk that a survivalist faction rallies around some blood-thirsty cause about how much American blood will be spilled on the land invasion. Remember the Iwo Jima! The Americans will never be willing to pay this price in blood! No, actually, they'll turn entire cities, one by one, into glass ponds with a single bomb dropped from a single airplane. Sure takes the spit out of "dead to the last drop" jingoism.

Turn the tables and imagine it was America on the brink of surrender, with California and New York conceding the inevitable, while Texas and Utah are piling on the guns and sand bags. How many Americans have bothered to conceptualize what surrender feels like? To my knowledge, the only military superpower to have transgressed upon American soil is Canada, which hardly gives a nation much practice in fearing the worst.

Another factor I think is that the American physicists realized that making the bomb was not all difficult given the progression of technology, and decades instead of years for the program to unfold. Feynman has described that some of the computational challenges were dealt with by circulating punch card in fancy tabulating machines. There's more computational power available these days in a Palm Pilot. I'm sure guys as smart as Feynman concluded early on that this particular genie was not being coaxed back into the bottle, not even for a short decade-long snooze. It was going to be a post-nuclear world order, one way or another. Would the nuclear arms race have played out better without the deva

Re:How soon until...

[Shakrai]

I'm inclined toward accounts based on the premise that America and Russia had an agreement (what blend of official/unofficial I can't recall) that Russia would pressure the Japanese from the Kamchatka peninsula and that territorial control in the post-war world would be to some degree be established by how much territory in the region of Japan the Russians had managed to occupy at the point in time of formal Japanese surrender.

Well I don't know how much of the agreement covered territory but there was an "official" agreement at Yalta for the Soviet Union to enter the war against Japan 90 days after the end of hostilities in Europe.

To fully appreciate the political situation, you need to realize that the Americans were reading Purple. Purple never got as much press as Enigma because it was considered somewhat unsporting to crack a diplomatic code.

The Pacific War in general has never gotten as much press as the European War. Purple was actually broken before the war. There's a mostly historically accurate representation of this in the movie 'Tora Tora Tora'

You can figure out an awful lot about who collaborated on a nuclear bomb by the residue signature it leaves behind. If everyone out there is working from exactly the same blue print, some of that capability falls apart.

IANANP (I am not a nuclear physicist) but my understanding is that the signature doesn't really have much to do with the design of the bomb itself. Rather it has to do with the reactor(s) that produced the fissile material used in the bomb. If you built fat man using American plutonium and built it again using Russian plutonium the signature would still be different.

Japan had long understood that the American military economy was humming along at a fever pitch, and was pretty much impossible to mess with short of capturing Hawaii.

Capturing Hawaii wouldn't have been enough either. It would have extended the war by another year or so but it wouldn't have altered the outcome. It's a moot point in any case as the Japanese didn't have the resources to capture Hawaii or the logistical resources to hold onto it if they did. What's more impressive is the fact that we devoted the overwhelming majority of our resources (upwards of 85% according to some estimates) to the European theater. We literally beat the Japanese with one hand and two feet tied behind our back. Makes you wonder what the hell they were thinking going to war with the United States. The disparity in economic resources was that large.

Re:How soon until...

[Pollardito]

I believe it's ok in California as long as the bomb mechanism is a female target shot with a male projectile, rather than a male target by a male projectile

NOT "Reverse Engineering"

[93 Escort Wagon]

FR1ST PEDANTIC POST

The guy went through declassified government documents to gather all the information he could find (including design information), and went from there. I don't think this is anything like reverse engineering.

If he "reverse engineered" the bomb, wouldn't it mean he put the design together based on blast data from known explosions of this particular device?

Re:NOT "Reverse Engineering"

[Daniel Dvorkin]

"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.

FUD, censorship, and freedom.

[B5_geek]

While many people may exclaim that this information is 'dangerous' to be released in the public domain let me remind you of a few small details.

1) ANY high-school/college student should be able to tell you what the critical mass of U235/238 is.
2) Most handymen should be able to make atleast ONE method of creating a critical mass pile.
3) It takes a GOVERNMENT to build multiple copies and revisions and tests to make it bigger/better.

This information does not mean "the terrorists can now make a bomb!" This changes NOTHING that hasn't been known for 50+ years. I would rather live in a society that does not suffer a knee-jerk reaction everytime something unusual is expressed. If anybody knows if this place exists, let me know; I'll start packing.

Re:FUD, censorship, and freedom.

[Tacvek]

The simple facts are that he (a truck driver!) is collecting detailed information about some of the worlds least efficient nuclear bomb designs. Bombs with the same amount of equal quality fissile material can be made far more powerful. No terrorist orginaization would want to create such wasteful bombs, so the information he is publishing is not very dangerous at all. Besides, a lot of the difficulty in making even an inefficient nuclear bomb at all obtaining the weapons grade fissile material.

Now his material is extremely accurate, coming from both logical analysis which has found inaccuracies in some published records. (Some records include masses of components that imply absurd material densities, so those measurements get discarded), measurements of the actual shell casings, and leaked information from those who actually built those bombs. Most of those people are customers of his book, and have publicly stated that very very few of his details remain inaccurate.

Re:FUD, censorship, and freedom.

[NouberNou]

No terrorist orginaization would want to create such wasteful bombs, so the information he is publishing is not very dangerous at all.

You seriously think that a terrorist organization would NOT take any sort of nuclear weapon?

Little Boy and Fat Man were in the 13-20 kiloton range. More than enough to kill a few hundred thousand people in a dense urban target like New York or LA or any other major American city!

Re:FUD, censorship, and freedom.

[Vellmont]

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:FUD, censorship, and freedom.

[khallow]

No terrorist orginaization would want to create such wasteful bombs

Article said it required about eight times critical mass. That's not bad for something you don't need to test first. Besides the design was good enough for the US to make first. Keep in mind that if you are committed to the terrorist act of blowing up an innocent city with a fission bomb, then you've divorced yourself from usual considerations of efficiency.

Re:FUD, censorship, and freedom.

[lysergic.acid]

that's just the way our society has come to think. in most people's minds (including many regular citizens) the masses are simply too stupid, selfish, immoral, and irrational to be treated as mature & rational adults and allowed to govern themselves. therefore they must be ruled over by others who are more trustworthy and level-headed, which coincidentally are the rich & powerful. and following this kind of thinking, information that can potentially be used for evil must necessarily be suppressed and hidden from the public at all costs.

but the knowledge that allows one to make nuclear weapons is the same knowledge that allows one to develop nuclear power plants. the only way you can suppress "dangerous" knowledge in this case is by suppressing nuclear research and forbidding anyone from teaching/studying nuclear physics. so unless we want to become a totalitarian state that promotes ignorance, a different approach must be found.

rather than throwing people in jail (or threatening to) for possessing "dangerous information," and trying to keep the public in the dark, it would be easier and more desirable just to create an enlightened society where people have no reason to blow each other or themselves up. this isn't something that can be achieved through force or coercion. granted, it's not something that will produce results over night, but it makes much more sense than our current approach.

similarly, changes in our foreign policy and ending the exploitation of other nations (for our own commercial interests) would do far more to increase our nation's security than any amount of military intervention and killing more innocent civilians. rather than abusing our position as the world's only superpower to ignore diplomacy and take whatever we want by force, we could simply be a better global citizen. then we wouldn't have to have a conniption fit every time a developing country builds a nuclear power plant.

Re:FUD, censorship, and freedom.

[vlm]

No terrorist orginaization would want to create such wasteful bombs, so the information he is publishing is not very dangerous at all.

You seriously think that a terrorist organization would NOT take any sort of nuclear weapon?

You don't understand terrorism. All you need to create terror and cause chaos and evacuations is a bomb that is just dirty enough to make a geiger counter click somewhat above background rate in front of a TV camera. Heck a granite countertop would probably do (they are quite radioactive). Although potassium based salt substitute (also quite radioactive) is scarier looking. One "real bomb" might destroy a city. But ten thousand hand grenades detonated in the ten thousand largest cities all going clicky clicky on camera is way more effective at generating terror.

The proof that there is no real terrorist threat, and the whole terrorist threat thing is the equivalent of government conspiracy theory daydreams, is that something this simple and easy has never happened despite ex-communist countries being awash in rad-waste free for the pickings, small IEDs are not apparently too hard to find either, add a roll of duct tape, and instant celebrity.

It doesn't matter if you actually destroy the city or not, all you need to do is make the residents act like it's another Katrina (except its even scarier because its "nuclear") and you've won. Prodding the sheep won't be too hard, with the media's help.

That is why a terrorist organization (assuming such a thing even exists) would never be so "wasteful" as to make a traditional a-bomb, when they could make ten thousand dirty hand grenades using the same stuff.

Re:FUD, censorship, and freedom.

[S-100]

Sure there is. All you need is an RC car and a plastic bottle filled with green shampoo.

Re:FUD, censorship, and freedom.

[rubycodez]

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.

Re:FUD, censorship, and freedom.

[vlm]

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.

Funny, then not so much...

[pjt48108]

This is yet another example of things which, eight years ago, might have seemed merely odd, rather than somewhat unsettling.

How quaint the 20th Century already seems.

Re:Funny, then not so much...

[Wes Janson]

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.

"Most of the time, I'm somebody else's problem"

[PolygamousRanchKid]

A working replica would be dangerous and surely illegal.

If I had a working replica of a nuclear bomb in my basement, I don't think I would give a rat's ass about whether it was dangerous or illegal.

If I did have a nuclear bomb, I would not have a problem.

Some other folks would have a problem.

Re:"Most of the time, I'm somebody else's problem"

[Superdarion]

Right, because it's a well known scientific fact that those who actually make a bomb are totally immune to the bomb's effects.

Besides, having explosives is not illegal just because you could use them for therrorism, but because accidents happen; accidents which might not only harm yourself (being stupid enough to have a bomb with you, whatever happens, you had it coming), but those around you as well. More so with something as powerful as a nuke.

Re:"Most of the time, I'm somebody else's problem"

[PopeRatzo]

If I did have a nuclear bomb, I would not have a problem.

Some other folks would have a problem.

This was precisely America's attitude about nuclear weapons for more than thirty years after Trinity.

Turns out they were wrong. There was no way to say England yes, France no, India yes, Pakistan no, Israel yes, Iran no.

The Atomic Bomb created the sense in American leaders that our overwhelming advantage in power created an American hegemony.

Like the Jurassic Park geneticist believing his "sterile" dinos would not spread, Truman and subsequent presidents believed in the myth of "control" that would keep the genie in the bottle. Worse, they thought they could be the "decider" of who gets to rub the lamp and who doesn't.

Me, I just hope Fallout 3 doesn't turn out to be predictive. I've run out of Rad-Away.

Re:"Most of the time, I'm somebody else's problem"

[Luscious868]

If I did have a nuclear bomb, I would not have a problem. Some other folks would have a problem.

Signed,

Ayatollah Ali Khamenei

Re:"Most of the time, I'm somebody else's problem"

[JWSmythe]

    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. :)

Re:"Most of the time, I'm somebody else's problem"

[shmlco]

"That's pretty much why I didn't care too much whether Saddam (or anyone in that area) had the bomb."

Yeah. So he could only take out a LOCAL city containing a few million people, start a major war, and potentially devastate a region. Big deal.

"How's he gonna send it over? FedEx?"

Noticed the increased security around the ports recently? That comment's closer than you think...

Not so big a deal

[Ancient_Hacker]

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:Not so big a deal

[Compholio]

...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

[RDW]

'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:

http://en.wikipedia.org/wiki/Little_Boy
 

Re:Not so big a deal

[Ancient_Hacker]

Well a cylinder and rod sound like a really poor design. You want a quick transition to super-criticality, not a slow linear slide. Much more likely they were a conical target and a mating projectile.

  Maybe this guy is trying to disinform certain rogue scientists?

Re:Not so big a deal

[NouberNou]

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.

Re:atomic weiner

[Daniel Dvorkin]

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.

Comment removed

[account_deleted]

Comment removed based on user account deletion

Intentional misdirection

[sphealey]

One thing to keep in mind when you read statement such as "Destroy R. Worlds, former Director of Bomb Design at Los Alamos, said of Joe Amateur's work 'That's very well-done'" is this: reading between the lines of many interviews, articles, and books about and by former weaponeers they give out a lot of misleading, and/or misdirecting, information about how _exactly_ devices are built. They talk openly about the general principles and their scientific and political implications, but when the discussion/interview/chapter turns to the actual details of design, well, the replies turn a bit fuzzy or clever. I suspect that either by explicit training or shared values they give away very little and much of what they say would deliberately lead anyone following down the wrong path.

sPh

Pictures? Plans?

[nurb432]

Its got some abstract image and a story.. But where is the actual scientific meat?

Oh, thats right, knowledge is forbidden in this country.

Best Line in the Article

[dd1968]

From the article: "Actually, he said, nothing about the bomb is secret. He smiled and added, 'The secret of the atomic bomb is how easy they are to make.'"

must.... not....

[Iamthecheese]

Somebody set up us the bomb!

There are numerous replicas

[n6kuy]

... of both Fat Man and Little Boy.

See here, for example.

Re:There are numerous replicas

[n6kuy]

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

[DG]

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.

DG

Re:It's about the mass

[goodmanj]

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.