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:Personally, I think the explanation is wrong, and the design has nothing to do with critical mass production. By the principle of Galilean relativity, how could nature tell the difference between a rod moving into a hole in a cylinder, vs a cylinder moving so that it passes over the rod at the same relative velocity? Which of these processes actually happens, only depends on your reference frame, which you can pick at will. The physics is guaranteed to be the same. <p> What I guess happened is this: the armory engineers looked at the problem and realized that it's a lot easier to accelerate a projectile with large cross sectional area-- one about the size of your bore-- than it is one with a smaller area, which is tricky. For a small diameter core they'd have needed some type of [[sabot]] very much like modern antitank uranium rounds use for their penetrators. But no such technology for uranium penetrators was in place in 1945, and it all would have had to have been invented fresh. So, the engineers simply turned the problem around and accelerated the set of rings with the larger area, which make a more "natural" projectile. This has only been recently revealed, but a little thought plus knowledge of uranium cannon sabot technology in 1945 should have allowed some smart person to figure out that the often-assumed and ignorantly proclaimed "core-into-cylinder" design was not used in the gun bomb, but probably cylinder-over-core instead. But nobody did. Once I read the alternate design, though, along with a lot of other people, I slapped my forehead and said "dohhhh!" Of course in 1945 they would have done it that way! <p> Thinking about this, now, you can see that with modern sabot technology they could get assembly velocities in the same type of gun bomb of 3 times what they did in 1945. That might be (should be) good enough to make a gun bomb with supergrade plutonium (since this is a function of assembly velocity and Pu-240 content, and reportedly modern plutonium grades are on the edge of being gun-assemble-able anyway). That gives yet another type of fundamental bomb design that has only recently become possible, basically due to antitank technology. Interesting! [[User:Sbharris|<font color="blue">S</font>]][[User:Sbharris|<font color="orange">B</font>]][[User:Sbharris|H]][[User:Sbharris|arris]] 19:03, 26 January 2012 (UTC)
:Personally, I think the explanation is wrong, and the design has nothing to do with critical mass production. By the principle of Galilean relativity, how could nature tell the difference between a rod moving into a hole in a cylinder, vs a cylinder moving so that it passes over the rod at the same relative velocity? Which of these processes actually happens, only depends on your reference frame, which you can pick at will. The physics is guaranteed to be the same. <p> What I guess happened is this: the armory engineers looked at the problem and realized that it's a lot easier to accelerate a projectile with large cross sectional area-- one about the size of your bore-- than it is one with a smaller area, which is tricky. For a small diameter core they'd have needed some type of [[sabot]] very much like modern antitank uranium rounds use for their penetrators. But no such technology for uranium penetrators was in place in 1945, and it all would have had to have been invented fresh. So, the engineers simply turned the problem around and accelerated the set of rings with the larger area, which make a more "natural" projectile. This has only been recently revealed, but a little thought plus knowledge of uranium cannon sabot technology in 1945 should have allowed some smart person to figure out that the often-assumed and ignorantly proclaimed "core-into-cylinder" design was not used in the gun bomb, but probably cylinder-over-core instead. But nobody did. Once I read the alternate design, though, along with a lot of other people, I slapped my forehead and said "dohhhh!" Of course in 1945 they would have done it that way! <p> Thinking about this, now, you can see that with modern sabot technology they could get assembly velocities in the same type of gun bomb of 3 times what they did in 1945. That might be (should be) good enough to make a gun bomb with supergrade plutonium (since this is a function of assembly velocity and Pu-240 content, and reportedly modern plutonium grades are on the edge of being gun-assemble-able anyway). That gives yet another type of fundamental bomb design that has only recently become possible, basically due to antitank technology. Interesting! [[User:Sbharris|<font color="blue">S</font>]][[User:Sbharris|<font color="orange">B</font>]][[User:Sbharris|H]][[User:Sbharris|arris]] 19:03, 26 January 2012 (UTC)
::The article currently correctly explains why there was a cylinder and a core rather than some other shapes (which were considered early on). I think you are absolutely right about it being better to accelerate a projectile with large cross sectional area than it is one with a smaller area. Sabot technology actually was available at the time; the design incorporated a 3" Boron safety sabot. I am certain that the key to the whole thing is the tungsten-carbide tamper. Whether it is the projectile or the target, the large cylinder cannot be in contact with the tamper. So it must be small cylinder plus tamper on one side, and large hollow cylinder with a Boron insert on the other. There was also the matter of deformation of the projectile in the barrel, which I know was a major concern. I have looked through the primary documents, and it is easy to see how the "cylinder into core" idea arose. I general, ''I would feel much better about this article if it were properly sourced''. [[User:Hawkeye7|Hawkeye7]] ([[User talk:Hawkeye7|talk]]) 20:26, 26 January 2012 (UTC)
::The article currently correctly explains why there was a cylinder and a core rather than some other shapes (which were considered early on). I think you are absolutely right about it being better to accelerate a projectile with large cross sectional area than it is one with a smaller area. Sabot technology actually was available at the time; the design incorporated a 3" Boron safety sabot. I am certain that the key to the whole thing is the tungsten-carbide tamper. Whether it is the projectile or the target, the large cylinder cannot be in contact with the tamper. So it must be small cylinder plus tamper on one side, and large hollow cylinder with a Boron insert on the other. There was also the matter of deformation of the projectile in the barrel, which I know was a major concern. I have looked through the primary documents, and it is easy to see how the "cylinder into core" idea arose. I general, ''I would feel much better about this article if it were properly sourced''. [[User:Hawkeye7|Hawkeye7]] ([[User talk:Hawkeye7|talk]]) 20:26, 26 January 2012 (UTC)

::: I have to disagree with a point made by the last post. The article does not in my opinion explain WHY the configuration was used although it does explain what was used. The most efficient shape for neutron containment is a sphere and to use a cylinder is reducing the efficency. [[Special:Contributions/2.217.150.216|2.217.150.216]] ([[User talk:2.217.150.216|talk]]) 18:03, 29 January 2012 (UTC)

Revision as of 18:03, 29 January 2012

600 or 550 metres?

In the article about the atomic bombings of Hiroshima and Nagasaki, Little Boy is said to have detonated 500 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)[reply]
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)[reply]

DS02 has identified the altitude. It is 600m. —Preceding unsigned comment added by 205.250.156.23 (talk) 21:02, 2 November 2008 (UTC)[reply]

I checked several of the references and I think 1900 feet is correct. As this is approximate, I think the 600 meter figure is due to rounding. I've changed the text in one place to use 1900 ft with a convert template. Rees11 (talk) 19:18, 30 April 2009 (UTC)[reply]

this source, cited in this article, says, "By mid-July, results of the successful TRINITY test of the FAT MAN caused the height of burst for the LITTLE BOY to be raised to 1,850 feet. Actual burst heights over Japan for the LITTLE BOY and FAT MAN were both around 1,850 feet.", citing "Memoranda dated 18 and 21 July 1945 to R. B. Brode from J. R. Oppenheimer; memorandum for Brigadier General T. F. Farrell and Captain W. S. Parsons, USN, dated 23 July 1945 from J. R. Oppenheimer." in support of the first sentence and citing no source in support of the second sentence. Wtmitchell (talk) (earlier Boracay Bill) 03:28, 26 September 2009 (UTC)[reply]

German uranium

On the subject of the German Uranium, the obituary of Capt. Tibbets in the respected Guardian Newspaper (UK) included the following reference:

"At the end of the month, Little Boy arrived. It symbolised global war. Some of its uranium was from the Congo, confiscated from the Belgians in 1940 by the Germans and snatched from Soviet-occupied Germany in 1945 by an Anglo-American special unit."

Is there any historical record to back this up?

The full obituary can be found at:

http://www.guardian.co.uk/military/story/0,,2204009,00.html


85.134.192.196 14:45, 3 November 2007 (UTC)[reply]

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)[reply]
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)[reply]

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)

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)[reply]

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)[reply]
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)[reply]
Can someone tell me if either bomb used a parachute retarder - my history references talked of the parachute, but recent film portrails of both drops do not show either bomb having this - any comments to kwp(at)thestingerreport(.)com
None of the references I have show any parachutes. Fat Man's tail assembly was pretty draggy - it had plates intended to simply block airflow for stability purposes - but no external parachute. Georgewilliamherbert 00:55, 19 May 2007 (UTC)[reply]
I believe that a weather plane was sent over about an hour earlier and this may have dropped a parachute radiosonde which was reported by eye-witnesses on the ground. Later reporting confused this with the bombing run itself. From descriptions of the flight path used (in Rhodes's book?) it is clear that a free-fall drop took place. They had about 40 seconds to get clear. Sorry, but I cannot provide references for any of this at the moment. 81.130.91.115 09:19, 26 June 2007 (UTC)[reply]
I've seen a reference somewhere that one of the accompanying planes dropped instrumentation by parachute either just before or after the detonations. This would seem to account for references to parachutes in accounts by observers on the ground. Guthrum 21:52, 8 July 2007 (UTC)[reply]

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)[reply]

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.

The barometric sensors were used to trigger the radar altimeter. Using the radar altimeters alone was too risky due to potential interference, not to mention reflections off the attack aircraft. But the barometric altimeter wasn't accurate enough to trigger the detonation at the desired altitude. They were not backups of each other, but rather the barometric altimeter was used to "gate in" the final measurement from the radar altimeter- all of course after the initial drop timer (15 or 45 seconds) had transpired.

There was a reference in a drawing or a museum display to a contact fuse, but that was pure imagination by someone who didn't have a clue. There was a nut in the front that held the rod which held the target plates in place, that probably created the original confusion. [Drevik] —Preceding unsigned comment added by 68.62.178.29 (talk) 05:08, 24 December 2008 (UTC)[reply]

Picture

The picture which illustrates "the canon type bomb" is not the right one. This picture is the right: [[2]]. Please edit it! —The preceding unsigned comment was added by 83.73.115.51 (talk • contribs).

Sorry, nope, the diagram in the article now is correct. The one you link above is known incorrect. The tamper and pit assembly was at the front, and the projectile fired from rear to front. In addition, though this was not widely known until a little while ago, the projectile was the hollow cylinder part, and the target was a solid rod that the projectile fit down around, inside the tamper/reflector target assembly. Georgewilliamherbert 18:18, 23 May 2007 (UTC)[reply]

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) [reply]

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)[reply]

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)[reply]

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...

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)[reply]

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.

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)[reply]

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)[reply]

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)[reply]

Perhaps the problem is that "test" is such a vague term. The gun-type mechanism *was* tested, multiple times, without the fissile U-235 core, by using dummy cores. Testing demonstrated that the critical mass was assembled sufficiently quickly, and that the massive steel casing which received the projectile would hold together under the impact. I don't know how many test firings there were, beyond a vague "at least three", but when the bomb developers found quality problems among some of the steel components delivered to them, they selected an item which had already survived multiple test firings for use in the actual combat weapon because it was of a higher quality than the alternatives on hand. 76.100.17.21 (talk) 08:55, 2 August 2011 (UTC)[reply]

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)[reply]

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)[reply]
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)[reply]
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)[reply]


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)[reply]

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)[reply]
It's covered in Rhodes. Why the skepticism? Georgewilliamherbert 21:21, 20 October 2006 (UTC)[reply]

"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)[reply]

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)[reply]

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)[reply]

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

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).[reply]

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)[reply]

Yep, I agree with GWH. Do these talk entries need to stay around forever if its clear that one person on the planet finds it relevant, and the remainder do not, as I believe might be the case here? JoGusto (talk) 11:52, 8 April 2010 (UTC)[reply]

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)[reply]

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


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)[reply]

Ought to at least be consistent within itself. Guinness 09:48, 19 February 2007 (UTC)[reply]
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)[reply]

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)[reply]

I feel the external details of the actual L11 bomb in this article are not complete--in particular the antennae. I have no documentary proof of this, but back in the 1950s, many TV programs, don't ask which :), showed videos and photos of nuclear weapons--Mk 4, Mk 6, Mk 17 casings--including Little Boys; from what I assume was the nuclear arsenal. This was before the 1960s clamp down on pics in the media; after McCarthy (sp?) etc. My point is, these TV "shots" were surprisingly accurate, based on what I've seen in later(Hansen, Sublette, et al) documentation. I recall is that all showed Little Boy mounting long, thin, antennae, originating from where that diagram shows the Yagi antenna and trailing back to the tail of the bomb. I remember seeing this on TV but not in any subsequent, recent documentation. Sorry about the lack of proof, but is anyone else here old enough to have seen this also? Mytg8 16:40, 16 April 2007 (UTC)[reply]
There are lots of good photos of Little Boy units with antenna mounted, etc; there are only the four Yagi antennas around the front. There are no long thin antennas trailing backwards. Howard Morland's book has plenty of good photos (other references have some of the same material, but Howard got a lot, huge number of very high quality photos, including hands-on up close photos of surviving LB type weapons which were held in stockpile, photos by the crew that assembled the Little Boy L11 bomb, etc). Georgewilliamherbert 19:24, 16 April 2007 (UTC)[reply]

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).[reply]

Article semi-protected

I have indefinitely semi-protected the page; edits by IP or newly registered users are now blocked. This is to reduce the otherwise nearly constant daily stream of minor and major vandalisms applied to the page by IP addresses. Georgewilliamherbert 01:21, 17 May 2007 (UTC)[reply]

Since the article is locked, could someone make this edit for me? In the section "Development of the bomb", third paragraph, the current text begins with the claim "With plutonium found unsuitable for the gun-type design ...". In fact, the problem was not with plutonium in general, but with the specific plutonium received in quantity from the Oak Ridge and Hanford reactors, whose isotope mix (Pu-239 + Pu-240) resulted in a much higher rate of spontaneous fission than that of the small samples of Pu-239 originally produced by cyclotrons, and around which the gun-barrel method had been originally designed. A "Thin Man" plutonium gun-barrel design could have been built using pure Pu-239, had enough been available -- but the need for isotopic separation of plutonium, as was being done with uranium at Oak Ridge, negated the advantage of chemical separation which made plutonium a worthwhile alternative to uranium in the first place. 76.100.17.21 (talk) 10:40, 2 August 2011 (UTC)[reply]

What Ended the War

The statement that dropping the bomb ended the war is POV or original research. Choose your poison. It is also extremely controversial. It needs to be modified or deleted. —Preceding unsigned comment added by Bsharvy (talk • contribs)

It's extremely well-referenceable, though. It's widely found as a conclusion in the historical coverage of the end of the war. The Emperor and cabinet used the three levers of the two A-bombs and the Russian entry into the war after spurning peace negotiations to overcome the military's residual desire to fight to the death and effect a surrender. The transcripts of the final cabinet meetings are rather illustrative of the events... Georgewilliamherbert 20:01, 24 July 2007 (UTC)[reply]

Then reference it, i.e. identify someone prominent who is on record as saying it, and also (since the opposite is also a "widely-found conclusion" some prominent individuals who disagree with it. In the meantime, I am deleting it.Bsharvy 10:01, 30 July 2007 (UTC)[reply]

Please stop editing controversial material without discussion. To say that something contributed to ending a war is original research and/or a point-of-view. To say that an invasion would "likely" have been bloody has the same problem. The proper way to discuss these topics is by referencing the positions of reliable experts, not to claim them directly and then back up your conclusions with references to experts who have the same opinion. This is a controversial subject.

I agree with Bsharvy on this one. Both sides of the controversy are well covered in the linked article Atomic bombings of Hiroshima and Nagasaki. To summarize that complex controversy by citing an emotional argument often made by one side is gratuitously preemptive. Let the reader decide.

In particular, to assert that a "drawn-out and likely bloody invasion of the Japanese home islands would have taken place" is, in my opinion, simply wrong. It is always hard to say whether something "would" have happened, but I think an invasion was unlikely, with or without the bomb. An invasion could certainly have been drawn-out and bloody, and it could actually have delayed, rather than hastened, the end of the war by inflaming Japanese patriotism. However, World War II was clearly over. Japan's allies had surrendered. Its navy and air force were destroyed, unable to protect the island nation against blockade and continued bombardment. Russia was declaring war on Japan. If an invasion was inevitable without the bomb, its cause would have been insanely bad judgment on the American side, not Japanese intransigence.

I could throw in a sentence summarizing my point of view on this, but I prefer Bsharvy's solution of simply referring the reader to the full argument.

While I am at it, I think the entire section on Possible Nazi Origins of Uranium is silly. Even if true, it is of no consequence. I think it should be deleted. HowardMorland 11:20, 31 July 2007 (UTC)[reply]

The Little Boy Picture

I cleaned up the picture at the top of the article, removing the 3-ring binder holes in the picture. Does anyone object to putting it in a box to make this article match the look of the Fat Man article? If there is no objection, I will make the change tomorrow. HowardMorland 22:22, 30 July 2007 (UTC)[reply]

Done. HowardMorland 11:43, 1 August 2007 (UTC)[reply]

Physical Effects of Little Boy, and Other Changes

I have posted a proposed addition to this article at http://en.wikipedia.org/wiki/User:HowardMorland/Sandbox and will insert it tomorrow if there is no objection here. I also will remove the entire last section on possible Nazi origins of uranium and replace it with a single sentence in an earlier section. As I noted above, I think this story detracts from the article. Even if true, the amount of uranium involved is too little, too late to make any difference. In any case, uranium supply was never a constraint. HowardMorland 14:26, 26 September 2007 (UTC)[reply]

I have a comment regarding the gun design tradeoffs stuff; I put it on the talk page for your sandbox. I agree that the Nazi origin stuff is so marginal that we're significantly over-portraying it right now, and should either remove it or minimize it to a sentence or some such. Georgewilliamherbert 00:31, 27 September 2007 (UTC)[reply]
The proposed changes have been made. HowardMorland 13:38, 27 September 2007 (UTC)[reply]

The ratio of mass to surface area determines criticality?

"The ratio of mass to surface area determines criticality" does not seem correct. For example, criticality of a combination of two pieces depends on their distance. --Patrick 21:51, 27 September 2007 (UTC)[reply]

The Nuclear Weapons FAQ uses density of the effective mass, which accounts for spaced parts or hollow components. The surface area issue is part of it, but not what I consider the determining one. You really have to look at neutron MFPs to see what criticality is getting at... Georgewilliamherbert 22:06, 27 September 2007 (UTC)[reply]
I wasn't sure how technical to get here. Mean free path takes a while to explain and it might intimidate the reader. To me the density idea, while technically correct, might suggest compression, as in the implosion design, rather than the fitting together of two uncompressed pieces. In Glasstone's Sourcebook on Atomic Energy, the surface area explanation is used at the first mention of criticality, followed by several pages of clarification. What really matters, of course, is how many neutrons escape the system without causing more fission. HowardMorland 04:14, 29 September 2007 (UTC)[reply]
I rephrased it.--Patrick 08:48, 29 September 2007 (UTC)[reply]
That works for me. HowardMorland 21:50, 29 September 2007 (UTC)[reply]
I have to apologize for not having responded effectively; I have had some real life problems interfering with my Wikipedia time for several days now. I will follow up and review when time allows. Georgewilliamherbert 23:18, 2 October 2007 (UTC)[reply]

Development of the bomb

I removed this explanation from the second sentence 'Because enriched uranium was known to be fissionable, it was the first approach to bomb development pursued' because according to wikipedia Pu was discovered February 1941 while the Manhattan Project is defined to have started December 1941:

(plutonium was, when the project began, still undiscovered)

-Wikianon 12:16, 30 September 2007 (UTC)[reply]

"Cordite" as propellant.

The article makes several mentions of the insertion of cordite into the gun mechanism and its use as a propellant in launching the uranium projectile towards its target. Do we have any confirmation that cordite was used? Cordite is a very specific family of propellants used in British and Commonwealth-produced small arms and artillery ammunition. To my knowledge, it was never produced in the US, which mostly used cut extruded or ball propellants, as opposed to the distinct spaghetti-like cordite. I am also unaware of any properties that cordite has that would be preferred over US made equivalents. —Preceding unsigned comment added by 75.184.84.42 (talk) 19:10, 25 November 2007 (UTC)[reply]

Every reference I can find (on the internet and in several text books in my possession) refers to the Little Boy propellent being "a bag of cordite" and there is no mention of any other kind of explosive being utilised. In no document can I trace a raison d'etre for using cordite above any other explosive but the weight of evidence seems to be in favour of cordite being the chosen material. See for instance http://www.robinsonlibrary.com/military/engineering/air/equipment/littleboy.htm 21stCenturyGreenstuff (talk) 09:06, 17 March 2008 (UTC)[reply]
It was probably used because James L. Tuck was more familiar with Cordite. —Preceding unsigned comment added by 213.40.253.31 (talk) 12:34, 3 November 2009 (UTC)[reply]
Both Cordite and the Baratol used in the Fat Man weapon were British explosives, and used because of the key British involvement in the Manhattan Project, something that is only now coming to public awareness.

Deaths from the Bombing of Hiroshima

There is a problem with the sentences "Approximately 70,000 people were killed as a direct result of the blast, and a similar number were injured. A great number more later died as a result of nuclear fallout and cancer.[13] Unborn babies died or were born with deformities.[14]".

This is not born out by the quoted reference 13. The 70,000 and "a similar number injured" do not accurately match the table figures at the reference, but more significantly "A great number more later died as a result of nuclear fallout and cancer" has to be erroneous as there was no nuclear fallout from the Hiroshima Bomb, it was an airburst and created no fallout...and a little later down the page it refers to 700 subsequent deaths from cancer not the previously reported 100,000. Comments anybody? 21stCenturyGreenstuff (talk) 08:47, 17 March 2008 (UTC)[reply]
"The Japanese and the Americans launched a giant epidemiological study after the war. The study included ALL residents of Hiroshima and Nagasaki who had survived the atomic explosion within a 10-kilometer (6.2-mile) radius. Investigators questioned the residents to obtain their precise locations when the bomb exploded, and used this information to calculate a personal radiation dose for each resident. Data was collected for 86,572 people.
Today, 60 years later, the study's results are clear. More than 700 people (actually 777) eventually died as a result of radiation received from the atomic attack:
87 died of leukemia;
440 died of tumors;
and 250 died of radiation-induced heart attacks. In addition, 30 fetuses developed mental disabilities after they were born.
Such statistics have attracted little notice so far."
In none of the references can I find confirmation for the statement a greater number more died later or unborn babies died or were born with deformities. It seems to be just urban myth and needs to be updated. I propose doing so unless there are any objections21stCenturyGreenstuff (talk) 08:57, 8 June 2008 (UTC)[reply]


The source quoted (Der Spiegel) does not cite primary source. It is therefore unreliable at best and editorially biased at worst. Unless we can reference the japanese and american studies directly, we may not call the idea of subsequent injuries an "urban myth". I have corrected that and more accurately explained that the large numbers are unsupported by primary sources. —Preceding unsigned comment added by 78.148.53.110 (talk) 15:04, 12 July 2008 (UTC)[reply]
The study was the ABC, listed in wikipedia as Atomic Bomb Casualty Commission. OK, so an addition C was added. I grew up with a kid of a survivor (we used to kid him a lot) and know POW survivors and ABC members (one attempted to convince me to get an MD to be a radiologist). 198.123.51.96 (talk) 21:52, 29 September 2010 (UTC)[reply]

600 ft. = 300 meters?

This sentence is in the Construction and Delivery section of this article:"This launched the uranium projectile towards the other end of the gun barrel at an eventual muzzle velocity of 600 feet per second (300 meters per second)." Is 600 feet really 300 meters? I thought it would come out to something more like 200 meters because a meter is about three feet. Am I wrong? Bobhultin (talk)

Time of Fall

The article says the bomb fell for 57 seconds (undocumented) but other sources such as Global Security say 43. http://www.globalsecurity.org/wmd/ops/hiroshima2.htm So does "Enola Gay" by Gordon Thomas and Max Morgan Witts (p.309) Furthermore, it's unclear whether detonation occurred 1900 feet AGL or MSL (mean sea level.) That would make a difference, depending upon Hiroshima's elevation. Presumably somebody with more detail can clarify these matters.

B Tillman May 1 '08 —Preceding unsigned comment added by BTillman (talk • contribs) 16:12, 1 May 2008 (UTC)[reply]

Well, the four radars in the fuse mechanism would have been taking their actual readings from the ground below them as the bomb fell, not the distant sea. Does that answer the question? 21stCenturyGreenstuff (talk) 17:36, 1 May 2008 (UTC)[reply]

AGL or MSL are probably not very different in this case -- Hiroshima is a port city on the coast, and "the distant sea" isn't so distant. The elevation of Hiroshima-Nishi Airport, for example, is nine feet above MSL. 76.100.17.21 (talk) 09:56, 2 August 2011 (UTC)[reply]

Number of critical masses in bombs

From paragraph "Development of the bomb":

"Fat Man" and the Trinity "gadget", by way of comparison, had five critical masses.

From Nuclear weapon design:

Fat Man, the Nagasaki bomb, used 13.6 lb (6.2 kg) of Pu-239, which is only 39% of bare-metal critical mass.

I am guessing the second is correct - who knows for sure?Moletrouser (talk) 10:04, 14 June 2008 (UTC)[reply]

No fallout?

The article claims that there was no fallout at Hiroshima, but doesn't back this up with any citations. (There is a footnote, but that leads to a generic claim that "an air burst is defined as a blast that doesn't create any fallout" -- the source does not appear to be asserting that the Hiroshima blast was an instance of this, so it is not really a valid citation.)

Meanwhile, sources such as the city of Hiroshima itself appear to claim that the explosion did take up mud and dust, which were then deposited on the city in the form of "black rain". In other words, radioactive material did "fall out" of the sky after the blast. Is this somehow different from "fallout" in a technical sense, and if so, could an authoritative explanation perhaps be added to the article, along with a proper citation for the "no fallout" claim that is actually talking about Hiroshima, not just about air bursts in general?

78.105.167.145 (talk) 22:15, 21 July 2008 (UTC)[reply]

I added to following quote to footnote #10: "From p. 36, 'at Hiroshima . . . injuries due to fallout were completely absent.'" This is the official U.S. government position, as stated in Glasstone and Dolan, The Effects of Nuclear Weapons, 1977. The salient fact in this discussion is the absence of a bomb crater at Hiroshima. The mildly radioactive "black rain" from the mushroom cloud is insignificant compared to the intensity of fallout from bomb crater debris, had there been any. The radiation injuries at Hiroshima were from direct fireball radiation and from neutron-induced radioactivity in the environment. HowardMorland (talk) 15:06, 24 July 2008 (UTC)[reply]

Really fast prompt neutrons?

Article: "Approximately 10 milliseconds later the chain reaction occurred, lasting less than 1 μs."

This seems physically impossible.


Numerous prompt neutron generations in a highly supercritical U235 mass geometry must occur before there is enough energy generated to explode a fission bomb.

If a prompt neutron production occurs about 1 picosecond after a fission event, and the prompt neutron generation time (lp or "ell-sub-p") between a prompt neutron being released due to fission and it subsequently being thermalized and absorbed by another U235 nucleus) is about 50 microseconds/generation on average with the fastest lp taking about 1 microsecond/generation, then how is it possible for the entire Little Boy fission event to have occurred within 1 microsecond as the article states?

Once the device was fired, the first generation of prompt neutrons would be simply due to the spontaneous decay of U235. The fission explosion could not have occurred until those prompt neutrons were absorbed and the next prompt neutron generation released (with a corresponding energy release).

Even if only one prompt neutron generation would generate enough energy to complete the fission explosion (it isn't), the fission explosion still took a minimum of about 50 microseconds.

Since the first generation of prompt-supercritical neutron and fission fragment production produces exactly the same energy as the same fuel components in a non-critical mass geometry, and (assuming that all prompt neutrons cause the next generation of fission) then the second generation of prompt fission creates, on average, 2.47 times the energy of the first fission generation†, which is still miniscule. In reality, many ~50μs generation multiples must have occured before there was enough energy created for a 12KT blast to have occurred. That is at a minimum several magnitudes longer than the 1 μs cited in the article.

† Since each U235 fission event produces on average 2.47 prompt neutrons, if all of the prompt neutrons are absorbed and cause fission event, then there are 2.47 times as many fission events in each subsequent generation. Delayed neutrons can be ignored because numerous prompt-supercritical lifetimes will occur before the first delayed neutrons begin to affect the neutron economy, and even then have such a small fraction in the neutron population compared to fast neutrons in a prompt-supercritical geometry that the explosive event is likely over before the delayed neutrons appreciatively affect the event (the total event taking less than perhaps a couple of seconds).

http://www.tpub.com/content/doe/h1019v1/css/h1019v1_136.htm

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

Since the bang doubles at each generation, you can ignore everything but the last five or six generations and you won't be too far wrong. The generation before that only adds about 1% to the bang, so it's not too inaccurate to say the real bang happened during the last microsecond. All else was prologue.

66.41.31.163 (talk) 20:48, 25 January 2009 (UTC)[reply]


Davidl9999 (talk) 18:25, 6 August 2008 (UTC)[reply]

I think these are fast neutrons of roughly 10,000 km/s travelling 10 cm, so it takes 10 ns per generation.--Patrick (talk) 23:05, 6 August 2008 (UTC)[reply]
Yeah. Nuclear bombs don't use moderated neutrons - they use fast neutrons. They are, precisely, supercritical prompt fast fission systems. There were two experimental moderated neutron weapons fired in the 1950s ("hydride" tests, with UH3 and UD3 fuel). They fizzled (hundreds of tons yield, but not tens of kilotons that was hoped). But all other nuclear weapons are fast fission, which is operating on timescales of the order that Patrick mentions. Georgewilliamherbert (talk) 23:40, 6 August 2008 (UTC)[reply]
A little embarassing, but I did not include the initiators in the lifecycle. Of course there is a lot of neutron leakage from the tungsten with carbon (as a carbide) providing some thermalization, but the thermalization process is relatively slow time-wise compared to the fast n flux. "The math" works if enough neutrons are included due to the initiators when the device is fired. (It's pretty straightforward, really). D'oh. Thanks for posting your responses to my comment.Davidl9999 (talk) 21:32, 7 August 2008 (UTC)[reply]


Po/Be Initiators

The diagram shows Polonium/Beryllium initiators. They are not discussed in the article. It would be helpful to add a sentence on what their purpose is. —Preceding unsigned comment added by Substar (talk • contribs) 18:14, 28 November 2008 (UTC)[reply]

Weight of Little Boy??

The article's infobox gives Little Boy's weight as "8,818.49 lb / 4,000 kg". The given weight in pounds is clearly an excessively precise conversion from exactly 4,000 kg into pounds. Unless there really is a source giving an exact weight of the bomb to an accuracy of less than an ounce (!), I would propose changing the weight info to "8,800 lb / 4,000 kg" — or possibly even "9,000 lb / 4,000 kg" — so that the precisions of the two measurements are roughly comparable.

Also, it seems to me that the article should contain at least some passing mention of why Little Boy was so heavy. The total weight of the bomb far exceeded the amount of fissile material which it contained, and the designers presumably wouldn't have made such a massive device if a much lighter bomb would have done the job. I would assume that the main reason for the weight was probably because the gun mechanism needed to be strong enough to withstand the forces of the conventional explosion that drove the two pieces of U-235 together, but it would obviously constitute original research for me to just say that (or any similar assumption) without a source. Does anyone know a source that can be cited on this point? Richwales (talk) 17:09, 14 February 2009 (UTC)[reply]


Physical effects of the bomb: Fire

The page says "any humans were either vaporized or turned to carbon in an instant. One famous, anonymous Hiroshima victim left only a shadow, permanently etched into stone steps near a bank building."

This is becoming an almost romantic urban myth of atomic bomb destruction mechanics. —Preceding unsigned comment added by 206.165.101.124 (talk) 15:07, 13 March 2009 (UTC)[reply]

The text and exhibits in both the Hiroshima Peace Museum (HPM) and the Nagasaki Atomic Bomb Museum (NABM) don't confirm this. NABM have a display case with roof tiles from a range of distances from hypocenter to several hundred metres out. The museums report an initial surface temperature of 4,000C and 6,000C respectively. The NABM tiles at the hypocenter are only rippled on the surface at the top few millimeters. They are not completely burned or deformed. Also the human body is mostly water which takes a lot of energy to heat and is hundreds of millimeters thick. —Preceding unsigned comment added by 206.165.101.124 (talk) 15:05, 13 March 2009 (UTC)[reply]


The idea that people were vaporized or turned to carbon by the initial explosion is preposterous. (A simple computation using only high-school physics shows that the energy delivered to any victims on the ground was too small by a factor of more than 10 and probably about 100 to do this). Also, the statement "near ground zero, everything inflammable burst into flame" is contradicted by paragraph 7.64 in the Glasstone and Dolan reference, and the statement about melting sand and glass is somewhat dubious and has no reference to back it up. This section also includes the silly statement about a victim leaving only a shadow etched into stone steps. (Obviously, someone removed the victim's body.)

I propose deleting the statements about vaporizing and carbonizing (including the statement about the shadow), and changing "everything inflammable" to "easily ignited materials." Some of the other material should be checked by someone and either backed up by reliable references or deleted. Dongennery (talk) 21:38, 2 May 2009 (UTC)[reply]

Fair enough. Although the body may have been removed by cremation and wind during the ensuing urban firestorm. HowardMorland (talk) 04:08, 13 May 2009 (UTC)[reply]

"a fraction of a second later"

In this edit, my edit summary (1) was done too quickly and (2) didn't consider that this was an airburst detonation. The Fuze system section of the article seems to say that the detonation was set for 1,900 feet. Using 1,125 ft/s for the speed of sound, and presuming relatively flat topography (a presumption which I have not checked), the shock wave would have reached the ground at a point directly below the detonation point about 1.7 seconds after detonation. If I remember my very rusty math properly, the delay between the flash and shock wave at distance d from that point, neglecting topography and earth curvature, would be something like seconds. -- Boracay Bill (talk) 00:43, 6 April 2009 (UTC)[reply]

The shockwave is, at least initially, supersonic. Georgewilliamherbert (talk) 18:33, 6 April 2009 (UTC)[reply]
May be—my physics classes are too many decades in the past for me to dispute this offhand. One wonders by how much (multiples? orders of magnitude?) and for how long (a large fraction of a second? several seconds?). -- Boracay Bill (talk) 17:02, 7 April 2009 (UTC)[reply]
If you look at 5.3.1.2 Blast Wave Development and Thermal Radiation Emission - for a 20 KT bomb (larger than Little Boy, but only by 25-35%) the shockwave separates from the fireball at around 15 milliseconds after detonation, at a radius of around 220 meters, and shock velocity of 4 km/s.
There's no easy model for the spreading shockwave to the point it becomes subsonic, but it doesn't drop subsonic until overpressure is below about 30 PSI. 20 PSI, with a wind velocity of 500 mph, is transonic/near sonic - and the 20 PSI damage radius for a 16 KT bomb is 705 meters. To grossly oversimplify, one can model the overpressure with a 1/R^2 so the 30 PSI radius will be 575 meters or so. So at burst altitude of 1900 feet (579 m) the shockwave would have been roughly right at the point of slowing below the speed of sound as it reached ground level.
If average velocity of the shockwave to that point, between 220 meters at 4 km/s and 575 meters at 330 m/s is 2 km/s, then it would have taken about another 178 milliseconds to reach ground level. That's a grossly simplistic assumption - but should be within a factor of 2-3 of the most correct value.
The fireball / shockwave details aren't my strong point, I wish I could give you more detail here but it's not what I focus my research on. Hope this is helpful enough. Georgewilliamherbert (talk) 21:04, 7 April 2009 (UTC)[reply]
Thanks a lot; I appreciate the info. This is way outside of my expertise, but within my sphere of interest. All that is probably too much technical detail for the article, but it sounds like those at "ground zero" would have felt the blast perhaps 0.175 of a second after the flash, and those further out somewhat later according to sonic speed and their slant-range distance from the airburst point. Cheers. -- Boracay Bill (talk) 03:27, 8 April 2009 (UTC)[reply]
I found some more shockwave propogation information in Cooper's textbook "Explosives Engineering" last night, I'll try to type it in tonight if I have time. Georgewilliamherbert (talk) 22:18, 9 April 2009 (UTC)[reply]

Headline

Ins't the headline a bit provocative? Without drawing a comparison between Allied casualties and Nipponese casualties, it seems POV. Just saying. —Preceding unsigned comment added by Foamking (talk • contribs) 06:01, 6 August 2009 (UTC)[reply]

Graffiti

Any references to graffiti on Little Boy? I bring this up because on a 1993 Discovery channel special about submarines there was mention of graffiti. —Preceding unsigned comment added by 76.182.224.116 (talk) 00:12, 3 October 2010 (UTC)[reply]

John Coster-Mullen's book has a bunch of good photos; I'll check that when I have a chance. Georgewilliamherbert (talk) 22:33, 3 October 2010 (UTC)[reply]

Latest corrections

Since I am considerd by many to be the leading civilian expert on both the Little Boy and Fat Man weapons, I thought it appropriate to step in at this point and make some minor corrections to this article.

Basic weapon design-The Little Boy was 120” in length, 28” in diameter, and 9,700 pounds.

Assembly Details-“It consisted of a stack of 9 uranium rings, each 6.25 inches (159 mm) in diameter with a 4-inch-diameter (100 mm) hole in the center, pressed together into a thin-walled canister 7 inches (180 mm) long.” The total length of the uranium itself was 7 inches, but that consisted only of the front end of the projectile which was a total of 16.25” long

Development of the Bomb-“The core of Little Boy contained 64 kg of uranium, of which 50 kg was enriched to 89%, and the remaining 14 kg at 50%. With enrichment averaging 80%, it could reach about 2.5 critical masses.” According to the actual Oak Ridge Calutrons output tables, the highest enrichment level achieved was 88.38% with the overall enrichment rate average at 82.68%.

The Bombing of Hiroshima-“The bomb was armed in flight 31,000 feet (9,400 m) above the city, then dropped at approximately 08:15 (JST). After falling for 43 seconds, the time and barometric triggers started the firing mechanism. The detonation happened at an altitude of 1,900 feet (580 m). With a power of 13 to 16 kilotons, it was less powerful than "Fat Man", which was dropped on Nagasaki (21–23 kt). The official yield estimate of "Little Boy" was about 15 kilotons of TNT equivalent in explosive force, i.e. 6.3 × 1013 joules = 63 TJ (terajoules).[25” According to Los Alamos and Japanese/American reports, Little Boy fell for 44.4 seconds and exploded at 1,968  50 ft (600 m) with a new official yield of 16 kt (DS02 published in 2002 by the joint Japanese/American Radiation Effects Research Foundation or RERF located in Hiroshima). This new height-of-burst (HOB) and yield supersedes the previous 580 M and 15 kt established in 1988 by John Malik and published as LA-8819. —Preceding unsigned comment added by 69.217.165.167 (talk) 19:45, 19 March 2011 (UTC) Atomicjohn (talk) 17:14, 25 March 2011 (UTC)[reply]

That unfortunate mass-energy conversion thing

One of the problems with E=mc2 is that its simplicity is partly superficial. The equation means that mass and energy are the same thing. The mass being defined as invariant mass in COM frame or relativistic mass in any inertial frame. The equation means that mass and energy can be viewed in either terms, merely using the conversion factor. It does NOT mean, however, that mass can be "converted to energy" or vice versa. It means that all energy HAS mass, and that all mass IS a form of energy. However, system mass (by any definition you like) and energy (by any definiton you like) are separately conserved over time, and both remain the same during any reaction, either chemical or nuclear (including blowing up a nuclear weapon). See mass-energy equivalence for a detailed discussion.

Unfortunately, another process in physics is that matter (a poorly defined word, but generally taken as "the stuff that makes up ordinary objects") CAN be converted to "energy" in the form of electromagnetic radiation, kinetic energy, and the various kinds of thermal energy. An example is antimatter and matter combining to form pure gamma radiation. However, in such a process, the mass of the system does not change. Likewise, in the inverse process, two gamma rays can combine to form matter and antimatter particles, but the mass of these doesn't just appear and start generating gravity!

When an atom fissions in a nuclear weapon (or indeed when atoms fuse in thermonuclear weapons) no real particles (things like protons, neutrons, or electrons) are destroyed. Instead, what is transformed is a part of the "matter" of the weapon (the weighable atoms), This part is the various types of potential energy locked up in the electromagnetic and nuclear forces in the atoms, and which show up on a scale as binding energy. These fields are turned into other kinds of energies (86% kinetic energy at first, and 4% gamma radiation-- see nuclear fission), but the total mass remains the same, because kinetic energy has mass in special relativity and so do photons (in a system). The system of a bomb does not weigh less until the parts have cooled down (so notes Richard Feynman), and for that to happen, the light and heat which escape the system, have carried away the "missing mass". It isn't missing at all. The mass doesn't disappear, it simply moves to something else which absorbs it and gets heavier (for a 21 kiloton bomb, the light and heat have a mass of about a gram). So it isn't that a 21 kt bomb converts a gram of mass into light and heat, but rather that gram of rest mass is turned into a gram of light and heat, which escape and deposit that mass into whatever absorbs them. Mass, like energy, cannot be destroyed in any reaction, but it can be transformed, and moved. The same considerations apply to chemical reactions also-- their heat retains its mass.

Nuclear reactions aren't special in somehow converting mass to energy. Rather, they convert so much matter into energy (such a large fraction of what is weighed) that the lost energy is weighable after the reaction (not possible yet in chemistry). But that is all. And matter is not the same as mass.

To avoid all this, I'm simply going to note that in these early bombs, a certain amount of matter (a bit less than a gram) is converted to heat and radiation. It's not mass that disappears in the conversion, it's matter-- for the light and radiation have the "missing" mass. Then I will refer to mass-energy equivalence. Then I'll add a note to future authors who want to insert the high school view of Einstein's equiation into this article on a nuclear weapon. SBHarris 00:04, 28 March 2011 (UTC)[reply]

I noticed that the article introduction stated that matter is converted to energy. I disagreed with that and decided to look at this discussion. I found the above comments and I am a bit confused. The above comments seem to clearly explain that matter (things) are not converted to energy, but the conclusion seems to go in the opposite direction. I must agree with the analysis that indicates that things are not converted to energy. In my opinion, energy that is stored in the atoms is simply converted to other energy. While that energy is contained in the static atoms, they posses extra mass, not matter. 141.0.8.156 (talk) 01:47, 30 August 2011 (UTC)[reply]
It is always presented as something magical, while the energy source is for the most part just the work one by the electromagnetic force accelerating the positive charges in the nucleus.Viridiflavus (talk) 05:36, 31 August 2011 (UTC)[reply]
While no "matter particles" (massive particles) are annihilated in an atomic explosion, there is some confusion as to whether or not the mass that is removed as the energy of heat and light, should be counted as part of the bomb's "matter". Yes, it's the mass of various static fields that is converted to kinetic energy and light. The electromagnetic (EM) force field pushing fission fragments away from each other gets "blamed" for the bomb's energy, but remember that this energy must make up for half as much energy input from nuclear force that you do work against first, in order to get the EM process "going". So a 21 kT bomb destroys 2 grams of EM field, but creates 1 gram of nuclear force field (in fission processes it's the other way around and you destroy more nuclear field while creating less EM field). "Aha" you say, but you may create and destroy static fields but no particles, and thus no MATTER. Well, yes and no. You destroy no complete matter particles, but you do destroy some of the fields that give matter some of its mass (in fact, 99% of its mass, see quantum chromodynamics binding energy.) So in a way you destroy some matter, and in a way you don't. That's because we're not really sure about whether to define ordinary matter by its property of rest mass, or some other properties. SBHarris 18:43, 26 January 2012 (UTC)[reply]

Improper photo

The photo in this article with the caption 'The "Little Boy" mushroom cloud as seen from Enola Gay' should be removed since it is actually the Nagasaki mushroom cloud.Atomicjohn (talk) 20:30, 29 March 2011 (UTC)[reply]

Counter Intuiative Design

The Articile states "However, critical mass considerations[citation needed] dictated that in Little Boy the larger, hollow piece would be the projectile." What are the critical mass considerations? The ones given about there being more than two critial masses does not lead to the conclusion that the outer sheath was the projectile. This needs more explanation please? 2.217.150.216 (talk) 12:53, 26 January 2012 (UTC)[reply]

Personally, I think the explanation is wrong, and the design has nothing to do with critical mass production. By the principle of Galilean relativity, how could nature tell the difference between a rod moving into a hole in a cylinder, vs a cylinder moving so that it passes over the rod at the same relative velocity? Which of these processes actually happens, only depends on your reference frame, which you can pick at will. The physics is guaranteed to be the same.

What I guess happened is this: the armory engineers looked at the problem and realized that it's a lot easier to accelerate a projectile with large cross sectional area-- one about the size of your bore-- than it is one with a smaller area, which is tricky. For a small diameter core they'd have needed some type of sabot very much like modern antitank uranium rounds use for their penetrators. But no such technology for uranium penetrators was in place in 1945, and it all would have had to have been invented fresh. So, the engineers simply turned the problem around and accelerated the set of rings with the larger area, which make a more "natural" projectile. This has only been recently revealed, but a little thought plus knowledge of uranium cannon sabot technology in 1945 should have allowed some smart person to figure out that the often-assumed and ignorantly proclaimed "core-into-cylinder" design was not used in the gun bomb, but probably cylinder-over-core instead. But nobody did. Once I read the alternate design, though, along with a lot of other people, I slapped my forehead and said "dohhhh!" Of course in 1945 they would have done it that way!

Thinking about this, now, you can see that with modern sabot technology they could get assembly velocities in the same type of gun bomb of 3 times what they did in 1945. That might be (should be) good enough to make a gun bomb with supergrade plutonium (since this is a function of assembly velocity and Pu-240 content, and reportedly modern plutonium grades are on the edge of being gun-assemble-able anyway). That gives yet another type of fundamental bomb design that has only recently become possible, basically due to antitank technology. Interesting! SBHarris 19:03, 26 January 2012 (UTC)[reply]

The article currently correctly explains why there was a cylinder and a core rather than some other shapes (which were considered early on). I think you are absolutely right about it being better to accelerate a projectile with large cross sectional area than it is one with a smaller area. Sabot technology actually was available at the time; the design incorporated a 3" Boron safety sabot. I am certain that the key to the whole thing is the tungsten-carbide tamper. Whether it is the projectile or the target, the large cylinder cannot be in contact with the tamper. So it must be small cylinder plus tamper on one side, and large hollow cylinder with a Boron insert on the other. There was also the matter of deformation of the projectile in the barrel, which I know was a major concern. I have looked through the primary documents, and it is easy to see how the "cylinder into core" idea arose. I general, I would feel much better about this article if it were properly sourced. Hawkeye7 (talk) 20:26, 26 January 2012 (UTC)[reply]
I have to disagree with a point made by the last post. The article does not in my opinion explain WHY the configuration was used although it does explain what was used. The most efficient shape for neutron containment is a sphere and to use a cylinder is reducing the efficency. 2.217.150.216 (talk) 18:03, 29 January 2012 (UTC)[reply]
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