Talk:Little Boy

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Japan To-do:

An event mentioned in this article is a August 6 selected anniversary'

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[edit] 600 or 550 metres?

In the article about the atomic bombings of Hiroshima and Nagasaki, Little Boy is said to have detonated 600 metres above the ground and not 550 metres, as stated in this article. Could someone please check the facts and update the incorrect one?

Richard Rhodes lists it as 1900 ft which would convert to 579.12 meters. I'm not sure whether they used feet or meters in the proximity fuzes but the differences might just be a rounding issue. --Fastfission 02:14, 6 August 2005 (UTC)
I know the altimeter had an accuracy of +- 5 feets. In the Nuclear FAQ : 0916:02 (8:16:02 Hiroshima time) Little Boy explodes at an altitude of 1900 +/- 50 feet (580 m), 550 feet from the aim point, the Aioi Bridge, with a yield of 12-18 kt (the yield is uncertain due partly from the absence of any instrumented test with this weapon design). A state-of-the-art, six year study ending in 1987, which used all available evidence, set the yield at 15 kt (+/- 20%). 83.77.253.54 19:51, 6 August 2005 (UTC)

[edit] German uranium

I'm just copying the following lines — which I originally included in the article source as a HTML comment, back when I contributed the German uranium assumptions — to this discussion page right here. I'm doing this because they probably won't remain in the article source indefinitely and also this is where they really belong.

From the article source:

<!-- I apologize for the bad quality ot the above contribution, I didn't have the time to do proper research or a proper writeup befitting the Wikipedia. I would ask and invite others to please help to straighten things out.

Sources are as follows:

Many thanks in advance folks! -->

Ropers 00:14, 12 Aug 2004 (UTC)

I seem to recall that General Groves said the Germans were nowhere near making a successful bomb when they surrendered. If the Germans had the materials to build a bomb as they were being overrun by the Allies, why would they give it to the Japanese instead of using it themselves? I seriously doubt the U-235 aboard U-234 was of the quality that we could have simply fueled Little Boy with it a few months later--as if the U.S. wasn't capable of producing the U-235 ourselves so we had to use the German's. This reeks of urban legend. Rsduhamel 08:49, 19 Dec 2004 (UTC)

If you read it over again you'll see that it says that it was uranium oxide (not u-235), and that it likely was of minimal use at most, and certainly doesn't say it fueled Little Boy. I'm not sure why it's on this page, to be honest, it has been qualified enough to be sort of nonsensical and maybe ought to just be moved to Manhattan Project if anywhere at all. German uranium oxide definitely helped with the assembly of the first Soviet reactor, but again, that's oxide, not 235 (the steps are ore -> oxide -> hexaflouride -> enrichment -> u-235).--Fastfission 18:32, 19 Dec 2004 (UTC)
I added on the french article (after searching a bit) that they got about 550 kg of oxide and that it could have been converted to about 4 kg of U-235. This could have been incorporated in Little Boy and Fat Man as a "security margin", is that completely wrong and should be removed ? Dake 19:09, 7 August 2005 (UTC)
Well, maybe it could have been, but without some evidence it seems somewhat silly to talk much about it in the context of Little Boy and Fat Man specifically, and should perhaps only be discussed in the context of the entire Manhattan Project or the Nazi project. At least, that's how I see it... --Fastfission 19:49, 7 August 2005 (UTC)

[edit] Changes to that last para

I have removed the invisible comment from the main article (it appears above) I have removed meaning the uranium had been intended for Japanese atomic bombs to get dropped on the US because this is conjecture. Japan was also persuing the use of nuclear reactors, so the former sentence is not a certainty. I have reworded and reworked the paragraph a bit. It is speculative, but interesting so I think it should stay in some form. 194.106.59.2 17:02, 16 Jun 2005 (UTC)

[edit] German Uranium?

Isn't that just a claim some guy wrote in his book? Not fact at all. I dont think it should be included in this article as fact. Also, from what I understand Germany would have needed a facility the size of Oak Ridge to enrich Uranium enough for weapons purposes, which they just didnt have.

  • Well, I've seen the German claim recycled a number of different places by people with a flair for the dramatic and no sense about this stuff. I think the article does a pretty good job of implying that the idea that this was enriched uranium was pretty outlandish, that it was probably just ore and hence nothing special. --Fastfission 11:14, 20 July 2005 (UTC)

[edit] Blueprint of the bomb

I have drawn the diagram with the inner parts of Little Boy. I have based most of my work on the ascii diagram available in the nuclear faq and this one : [1] (which is probably based on the ascii). Unfortunately, I couldn't get a hand on a copy of the original blueprints. I know that some blueprints have been declassified and are sold for about $20 by some museum in US. Does anyone know a place where I could find a scanned version ? I have the blueprint of the outer case of Fat Man but I would like to draw the inner parts. Most schemas show the explosive sphere and plutonium core but nothing about altimeter, fuses, etc. fr:Utilisateur:Dake 19:45, 6 August 2005 (UTC)

There are no declassified blueprints of the interior of the Little Boy; just the outer casing (which is what the museum used to sell). Anything else is pure speculation, though some more supported than others. One of the most detailed (though ultimately fanciful) drawings of the interiors of the "Fat Man" and "Little Boy" bombs is in Chuck Hansen's U.S. Nuclear Weapons: The Secret History (1988). It can be a bit hard to find but most major libraries have it. If you use the "e-mail this user" function on my account I can send you a copy of the scans. Another source (albeit a more costly one) is John Coster-Mullen's "Atom Bombs" book, which is all about what the insides of the weapons probably look like. (You can read an article about him here if you are interested) --Fastfission 23:57, 6 August 2005 (UTC)
Just replied via e-mail. Thanks for these information, they will for sure be interesting for other people as well. When I will have some scans, I will try to draw the interior of Fat Man and improve the diagram of Little Boy. Danke vielmal :) Dake 00:16, 7 August 2005 (UTC)

[edit] Translation

I provided a paragraph-by-paragraph translation of the French article in the commented section. Some terms may be incorrect but it may be helpful. -- Ze miguel 10:25, 16 January 2006 (UTC)

[edit] Firing

The Little Boy bomb used a radio altimeter for detonation not a barometric altimeter. When Little Boy was dropped there was a predetermined delay set before the firing mechanism would fully arm. This was to prevent the bomb from predetonating in the vicinity of the aircraft. After this point the radio altimeter was armed and preset to go off at 1,980'. There was a barometric altimeter installed as a backup should the radio altimeter fail. This was set at a much lower altitude, but I can not recall the value. The bomb also did not have any contact fuses or other means of contact firing. However by design of the bomb contact with the ground would certainly produce some kind of effect. If the Uranium bullet smashed into the target with high enough velocity a detonation could have occured, however it was more likely to cause a "fizzle" explosion that was mentioned in the article.

All of this information comes from the book "Silverplate: Aircraft of the 509th Composite Group" by the 509th CG Historian Richard Campbell. I have the book but it is not with me at the time. It goes into great detail concerning the firing mechanisms of both bombs and would be an excellent source for these articles.

Also William Parsons is not a Lt. Col. as stated in the article. Parsons was a Navy man and held the rank of Captain at the time of the bombing and held the rank of Rear Admiral at the time of his death.

[edit] Firing, revisited

The Little Boy used a doubly-redundant RADAR (not radio) altimeter for final height determination (see my recent addition to the topic for a description). The description was partially taken from "The Making of the Atomic Bomb" by Richard Rhodes, but mostly from "American Prometheus"[1] The barometric section was in place to avoid accidental detonation at too high a height to cause damage. From "American Prometheus" comes this quote from Oppenheimer: "Don't let them detonate it too high. The figure fixed on is just right. Don't let it go up [higher] or the target won't get as much damage." The quote is attributed to Oppenheimer via Lieutenant Colonel Moynahan, a former newspaperman, who seemingly published it in a 1946 pamphlet. Must admit that I have been unable to track down the actual pamphlet to confirm the quotation.

This is a more casual venue than the encyclopedia proper, correct? In my addition to the "Little Boy" section, I wrote: "...and designed to kill as many people as possible." This quickly got diluted to: "…and designed to detonate at the most destructive altitude." This is the Smithsonian Exibit thingie revisited in spades. But a spade is a spade is a spade, and the revision, while somewhat accurate, eliminates, mealy-mouths the purpose of the well-thought-out design. —The preceding OutRIAAge 01:53, 3 March 2007 (UTC)

[edit] Little Boy VS Little Bøg

The first paragraph:

"Little Bøg was the codename of the atomic bomb which was dropped on Hiroshima, on August 6, 1945 by the 12-man crew of the B-29 Superfortress Enola Gay, piloted by Lieutenant Colonel Paul Tibbets of the United States Army Air Force."

Little Bøg? Is this a case of vandalism or was the codename really Little Bøg?? --TonyM ｷﾀ━( °∀° )━ｯ!! 11:49, 11 March 2006 (UTC)

  • Uh, yeah, that was vandalism. --Fastfission 22:18, 13 March 2006 (UTC)

[edit] Internal Diagram

We have to get rid of the current internal diagram, it's grossly inaccurate. The only thing it gets right is that it's got the projectile fired forwards into the target in the nose of the bomb... 8-(

I won't nuke it until I replace it, but it's got to go. Georgewilliamherbert 06:54, 21 April 2006 (UTC)

[edit] Atom Bomb Codenames

Just noticed it says ----> ("Fat Man or Little Boy" was the codename of the atomic bomb which was dropped on Hiroshima, on August 6, 1945 by the 12-man crew of the...) Was the uranium-gun bomb dropped on hiroshima also know as "fat man"? This seems very weird...I thought little boy = uranium gun/hiroshima and fat man = plutonium compression/nagasaki. Im going to change it unless someone says otherwise...

  • Yes, that was vandalism or something along those lines. Little Boy was the uranium bomb dropped on Hiroshima. Fat Man was the plutonium bomb dropped on Nagasaki. --Fastfission 23:07, 25 April 2006 (UTC)

In an episode of the X-Files, the atomb bomb is referred to by the code name "Thor's Hammer". Is this an X-Files creation, or was this name actually used at some point? --gavin6942 11:44, 29 June 2006 (CST)

That's an X-files creation. --Fastfission 18:04, 5 August 2006 (UTC)

[edit] Basic weapon design

According to The Nuclear Weapon Archive this is not true. South Africa produced about 6 bombs of this type. See also South Africa and weapons of mass destruction.

  • What statement are you saying is not true? --Fastfission 01:45, 29 May 2006 (UTC)
I think they're referring to the statement that no more of the Little Boy design bombs were used.
To the unknown questioner (in the future, sign your comments with ~~~~ to get the name/date stuff you see on other comments)...
There were numerous gun-type nuclear weapons produced after WW II. The US Mark 8 nuclear bomb and Mark 11 nuclear bombs, W9, W19, W33 artillery shells (and a few others, though those were the most popular) were all gun-type, as was the south african design.
No more units of the Little Boy specific detailed design were fully assembled for use. Gun type bombs in general is a wider category, which was used. Hope this clears it up some. Georgewilliamherbert 01:50, 30 May 2006 (UTC)

Second paragraph reads: "Additionally, the weapon design was conceptually simple enough that it was only deemed necessary to test the gun-type assembly (known during the war as "tickling the dragon's tail"). " Should it read "test the implosion type".

I think what it meant was laboratory test (not test detonate), so I've tried to correct it. --Fastfission 14:19, 17 July 2006 (UTC)

No. It reads correctly. They would have no doubt tested the gun-type uranium bomb if there had been enough uranium-235 around to test, but given the shortage of U-235, they were sufficiently convinced by the "dragon's tail" experiments to drop the damn thing untested. I'm not saying their decision was wrong. On the other hand, they really needed to test the plutonium implosion weapon, not because they were unconvinced of its fissionability, but because they were unsure that the complex implosion, compressing the plutonium to critical mass, would work. Oppenheimer was aware that a full implosion test (with a dummy plutonium core) had recently misfired, but shortly before the Trinity test, he got a call from Hans Bethe who assured him that the failure was only due to a wiring problem. OutRIAAge 02:21, 3 March 2007 (UTC)

[edit] Mere contact

"The mere contact of the two uranium masses could have caused an explosion with dire consequences (from a simple fizzle explosion to a large explosion on the scale of the destruction of Tinian Island)"

This seems wrong, or at least somewhat misleading. Mere contact doesn't result in an explosion - it would just make the consequenses of spontaneous fission much larger. Put another way, it still takes a free neutron to trigger fission; it just forms a supercritical mass needed to sustain a chain reaction.

Right?

Warthog32 23:00, 31 August 2006 (UTC)

Spontaneous fission is happening all the time ... it's an unavoidable background process, statistically extremely predictable within known-isotope-ratio fissile materials.
No additional human intervention is required once you bring a critical or supercritical mass of HEU together - spontaneous fission happens at the rate of 0.16 fission/kg for pure U-235 and around 5.6 per kg for U-238. The Little Boy weapon had 64 kg at 80% enrichment - 51 kg of U-235 (around 8.2 SF/sec) and 13 kg U-238 (around 73 SF/kg). Total is around 81 spontaneous fissions per second for the assembled mass, so you're looking at typically something like 12 ms between SF events, statistically very rare for it to be much more than twice that long.
It will just happen... and pretty darn fast. Georgewilliamherbert 06:39, 1 September 2006 (UTC)
Would it be efficient enough not to fizzle? I imagine that higher efficiency is what a neutron initiator gets you, though I don't know whether not having one would guarantee a fizzle or not. --Fastfission 18:19, 6 September 2006 (UTC)
That's what predetonation is all about. If you slowly assemble a nearly critical or just barely critical mass, then the natural spontaneous fission rate means that you will constantly have some neutron activity; with k just under 1.0, the chain reactions take a while to die out from each parent spontaneous fission event, taking longer to die out the closer you get to k = 1.0.
With 12 ms between spontaneous fission events, as you just 'bring together' a supercritical mass slowly, it reaches criticality before it's fully densely assembled, and then starts to run away rapidly into an exponential supercritical reaction as you push the assembly up past merely critical. If you're pushing the pieces together slowly, shortly after you reach criticality it goes supercritical and you have a criticality excursion, but it heats up rapidly and the neutron cross sections drop and it usually goes subcritical from that, plus 1E15 or 1E16 fissions, neutrons, big blue flash, lethal radioactivity in the immediate environment, etc.
With 12 ms between "initiating events" the bomb has to assembly relatively rapidly to reach fully supercritical configuration before the reaction reaches high rates and quenches itself. Criticality is easy; what makes bombs hard (with high yield) is reaching supercriticality fast enough that the neutron chains that start when you reach criticality don't cause dissassembly first.
The problem with Little Boy is that if you squashed the bomb hard enough, such as running it into a solid rock volcano or something, it could have collapsed fast enough to assemble a moderately supercritical mass (or under worst circumstances, had the "bullet" travel down the barrel into the target assembly into more or less full supercritical configuration). That could have a high yield explosion, not just a little criticality excursion.
If you squash it a little or flood it with water, there's a minor criticality excursion (no explosive yield, but brief lethal at close range radiation pulse). If it collapses pretty quickly and completely but not ideally, it could have reached sufficiently supercritical configuration to give a moderate explosive yield (tens or hundreds of tons, maybe at the extreme around a kiloton of yield). If the geometry was perfectly wrong, and statistical distribution of the spontaneous fission timing was optimal in the worst way, the bullet could reach the target assembly fast enough to reach nearly full yield after that next spontaneous fission kicked off.
The gun bomb assembly action is designed to assemble to full supercriticality so fast that the odds of predetonation are extremely low, because if it predetonates then it's useless militarily, and high reliability is a design goal. Georgewilliamherbert 19:53, 6 September 2006 (UTC)


[edit] Arming Altitude

Little Boy was armed in flight about 10 minutes after takeoff, just after Col. Tibbets leveled off at 4,700', not at 31000' over Hiroshima as described in the article.

The cordite was inserted after takeoff, as is described in the article. The arming plugs were inserted near Hiroshima. Inserting the cordite didn't activate the detonation system; the arming plugs did. That's the usual definition for arming. Georgewilliamherbert 18:17, 8 October 2006 (UTC)

I agree, the previous statement was concerning the insertion of the cordite, but the red and green plugs were exchanged at around 9,300' almost 1 hr 45 min from Hiroshima.

Sources / references ? 62.203.78.228 20:00, 20 October 2006 (UTC)
It's covered in Rhodes. Why the skepticism? Georgewilliamherbert 21:21, 20 October 2006 (UTC)

[edit] "Received, one gun type bomb"

Can someone with a copy of Rhodes' book check something for me - I seem to remember him mentioning that when the army handed the bomb assemblies over to the Navy at Hunters Point that they made some lowly sailor sign a receipt (which I think Rhodes reproduces) saying something like "Received - one gun type bomb". If my memory of that is correct, that'd make a nice addition to the "delivery" section. -- Finlay McWalter | Talk 15:37, 2 December 2006 (UTC)

I can't find that in The Making of the Atomic Bomb; perhaps it's in Dark Sun, but my copy of that is in a box at the moment. Georgewilliamherbert 17:53, 2 December 2006 (UTC)

[edit] Construction and Delivery

500 B-52s on Tinian? I don't think so. Perhaps B-29s. I've flown over it, it was a gigantic airfield, but I question the number 500. LorenzoB 23:39, 3 December 2006 (UTC)

Yeah, you're quite right, it's obviously B29s. Ref: [2]. I fix the article - thanks for noticing that embarrasing snauu. -- Finlay McWalter | Talk 23:43, 3 December 2006 (UTC)

[edit] uranium or plutonium?

in this little boy article it says "'Trinity' test), and it was the first uranium-based detonation ever" but then when you click the trinity test it says "It was a test of an implosion-design plutonium bomb" so i honestly dont know which is right but they contradict themselves.... someone fix that please. —The preceding unsigned comment was added by 69.239.114.11 (talk) 05:12, 22 January 2007 (UTC).

It's clear to me, and correct. Can you be more specific regarding what section is confusing you? Georgewilliamherbert 08:05, 22 January 2007 (UTC)

[edit] Diagrammatic contradiction

The two images showing how the bomb worked appear to contradict each other. The first shows that the uranium 'bullet' is fired from the nose, into the tail, and the second shows the opposite is true. Can we do anything to resolve this? Guinness 23:52, 13 February 2007 (UTC)

I got a simple solution... Take one off. Prep111 17:04, 16 February 2007 (UTC)


Either one could be true as the design is classified, so both are just educated guesses. 69.246.66.92 11:06, 18 February 2007 (UTC)

Ought to at least be consistent within itself. Guinness 09:48, 19 February 2007 (UTC)
We do know which one is wrong. Please don't overstate the degree of uncetainty - we know a lot more about the Little Boy than you're assuming, anon user...
The problem is that the "wrong" one is the top one, which uses a Little Boy outer case to generically illustrate a gun-type bomb, and it's been a Featured Image twice so modifying it seems blasphemous ;-)
Fastfission's comment for that image does indicate that he knew it's wrong (in the sense of firing backwards rather than forwards). He also did the more detailed one below, after I did a different more detailed one which was not nearly as pretty. These are both based on detailed descriptions from sources such as Rhodes and Sublette.
The design isn't really very secret. The details have all leaked - we don't have the blueprints per se, but enough is out there that we know how big the parts were and what they were made out of. It's really sort of silly to keep it classified, more modern gun-type bombs are 30 times smaller (250 lb for a W33 vs 7,500-ish lb for Little Boy), and no existing bomber owned by a non-nuclear nation, or missile, could carry a Little Boy. Any nation wanting to build one would do their own, much smaller design (South Africa's were only around 1,000 kg / 2,200 lb, which even so was extremely conservative...).
Georgewilliamherbert 20:30, 20 February 2007 (UTC)

Both drawings have now been updated to reflect the latest information, and they are now consistent with each other. HowardMorland 21:22, 29 March 2007 (UTC)

[edit] References

  1. ^ Kai Bird and Martin J. Sherman: "American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer", Knopf, 2005. ISBN 0-375-41202-6

—The preceding unsigned comment was added by OutRIAAge (talk • contribs) 01:58, 2 March 2007 (UTC).

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