Talk:Little Boy/Archive 1

Archive 1

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)

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)

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

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)

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)

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)

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: http://www.ihffilm.com/840.html http://uboat.net/boats/u234.htm http://www.amazon.com/exec/obidos/ASIN/1557508119 http://www.ussvance.com/Vance/nazisub.htm http://www.google.ie/search?q=U-234&ie=UTF-8&hl=en&btnG=Google+Search&meta= http://www.spiegel.de/sptv/special/0,1518,230670,00.html http://www.antenna.nl/wise/447/4440.html http://news.bbc.co.uk/1/hi/uk/643913.stm [this one actually hasn't got anything to do w/ the German uranium story; I replicated it here purely because it somehow was in the original link list I added to the article source] http://www.antenna.nl/wise/435/4303.html 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)

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)

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)

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)

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)

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)

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)

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)

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)

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" 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)

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)

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)

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)

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)

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)

"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)

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: [3]. I fix the article - thanks for noticing that embarrasing snauu. -- Finlay McWalter | Talk 23:43, 3 December 2006 (UTC)

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)

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)

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)

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)

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)

References

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

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)

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)

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)

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)

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)

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)

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

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)

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)

The proposed changes have been made. HowardMorland 13:38, 27 September 2007 (UTC)

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)

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)

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)

I rephrased it.--Patrick 08:48, 29 September 2007 (UTC)

That works for me. HowardMorland 21:50, 29 September 2007 (UTC)

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)

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)

"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)

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)

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)

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)

"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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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

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)

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)

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)

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)

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)

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)

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)

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)

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)

"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 ${\sqrt {(}}1,900^{2}+d^{2})/1,125$ seconds. -- Boracay Bill (talk) 00:43, 6 April 2009 (UTC)

The shockwave is, at least initially, supersonic. Georgewilliamherbert (talk) 18:33, 6 April 2009 (UTC)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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. Why did they do it this way? 2.217.150.216 (talk) 18:03, 29 January 2012 (UTC)

No, it doesn't; references are required. But I can answer your question. A sphere is the shape that provides minimum surface area for the maximum volume. This is desirable if you wish to retain as many neutrons as possible. But you cannot keep a critical mass in a sphere shape, because it will go critical (by definition). If you want keep a critical mass without causing a chain reaction, then you want the exact opposite: the maximum surface area for a given volume, which will be a lamina. To save space, we bend it round to form a cylinder, and fill the centre with neutron-absorbing Boron 10. On detonation, the hollow outer cylinder and the inner cylinder inset are brought together in a supercritical mass, which it needs to be because a cylinder is less efficient than a sphere. A sphere would be better shape here but they could not get this to work in a gun-type design; implosion was required. Hawkeye7 (talk) 20:12, 29 January 2012 (UTC)

Missing mass

The article states “It contained 64 kg (140 lb) of uranium, of which less than a kilogram underwent nuclear fission, and of this mass only 0.6 g (0.021 oz) was transformed into energy.” So where did the remaining mass of up to 999.5 grams go? 2.217.150.216 (talk) 10:04, 30 January 2012 (UTC)

It went into fission products. Actually the mass "transformed" into energy (in this case kinetic energy) retains its mass-- it now has 0.6 g of kinetic energy! That's all relativistic mass-increase of the fast particles. Once these particles are slowed (cooled) the mass drops by 0.6 g, but that's only because 0.6 g of heat has escaped in the cooling, and the heat itself has mass, and carries away the "missing mass" with it (whatever absorbs the heat, gets the mass). Ultimately, mass is conserved, even in special relativity. See mass in special relativity. SBHarris 19:54, 30 January 2012 (UTC)

I think the wording used for the Fat Man page reads better: "The result was that in the Fat Man bomb, about 1 kilogram (2.2 lb) of the 6.2 kilograms (14 lb) of plutonium in the pit (about 17%) fissioned. In this process 1 gram (0.035 oz) of matter in the bomb was converted into the active energy of heat and radiation (see mass-energy equivalence for detail), releasing the energy equivalent of 21 kilotons of TNT or 88 terajoules." Could this be used as a template to reword the paragraph? 94.5.82.95 (talk) 08:48, 1 February 2012 (UTC)

Number of critcal masses comparison

The Article states:

"The core of Little Boy contained 64 kg of uranium, of which 50 kg was enriched to 88%, and the remaining 14 kg at 50%. With enrichment averaging 82.68%, it could reach about 2.5 critical masses. "Fat Man" and the Trinity "gadget", by way of comparison, had five critical masses."

but, given that Fat Man used implosive compression describing the amount of material in the critical mass depends upon the density of the fuel? Surely prior to compression there was less than a critical mass and after compression more than a critical mass, and this makes the comparison with little boy (which did not use compression) meaningless?

94.5.82.95 (talk) 11:20, 20 February 2012 (UTC)

Agree. The number of "critical masses" in Fat Man is totally compression dependent (and all these things depend on neutron reflection anyway-- critical mass is a "no reflector" number, conditions never occuring in any bomb). Thus for BOTH bombs, the number given is specious. I think this whole cited section you quote above, should be removed. SBHarris 18:19, 20 February 2012 (UTC)

Removed the last sentence. I have assembled some sources, and will make a start on providing references for the entire article. Hawkeye7 (talk) 19:06, 20 February 2012 (UTC)

What is the photo?

A photo has the text attached which reads:

"Uranium for "Little Boy" was enriched in calutrons and by gaseous diffusion at Oak Ridge, Tennessee."

but this does not explain what the photograph shows. The caption would be no less helpful if it said "People prefer ice cream in the summer." 94.5.82.95 (talk) 11:26, 20 February 2012 (UTC)

A calutron under construction is what is shown in the photo (I have changed the caption). Those who want to know what a calutron is, can click on the link. SBHarris 18:13, 20 February 2012 (UTC)

victim's shadow

" One famous, anonymous Hiroshima victim left only a "shadow", permanently etched into stone steps near a bank building. Again, converse to popular knowledge, the "shadow" is not the remains or ash of the victim, but in fact it was the area around the shadow, not obscured by the person's silhouette that was lightened by X-rays from the burst, leaving a dark "negative" shadow"

isn't it the very definition of shadow? — Preceding unsigned comment added by 194.29.214.240 (talk) 16:45, 1 October 2012 (UTC)

Moreover this part is poorly written. What is the source for 'popular knowledge'. It is not WP policy to state which facts are popular, only which facts are correct.--Senor Freebie (talk) 05:23, 16 January 2013 (UTC)

Interesting criticism of a particular source

This book; http://books.google.com.au/books/about/Residual_Radiation_in_Hiroshima_and_Naga.html?id=w52nSgAACAAJ&redir_esc=y

Written by people under the employ of Oak Ridge National Laboratories appears to have used a suburb in Hiroshima which received considerable residual radiation as their control group, to measure the increase in Leukemia, which they subsequently found negligible. As it turns out, it was roundly condemned in another article in Science, also published during the 1960's ... and since it didn't survive peer review the claims made in this WP article can't be taken too seriously.--Senor Freebie (talk) 05:28, 16 January 2013 (UTC)

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)

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)

I am assuming that the sentence that started this bit was:

"Although occasionally used in later experimental devices, the gun design was only used once as a weapon because of the danger of accidental detonation."

The gun design was used only once to devastate a city and its population, as was the implosion design. Two devices used as weapons, one might argue, one of each type, and let's try and keep it that way. Lots of bombs manufactured, of course, overwhelming majority being implosion devices, almost all of them arguably weapons, none of them used intentionally to kill people or destroy their property. The quoted statement is incorrect, but just why it is incorrect depends on what you infer from "used as a weapon".Moletrouser (talk) 17:11, 11 August 2013 (UTC)

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) 21:52, 6 April 2008 (UTC)

Speaking of standard vs metric measurements, since Little Boy was an American invention, made in America, by American scientists who used the standard system, why is everything cited in metric first, and then converted to standard measurements? Or was this weapon made in France or Germany? Isn't this English Wikipedia, where most people are accustomed to standard measurements? Even the illustration-chart in the "Assembly details" section uses standard measurements. Press '1' for English? — Preceding unsigned comment added by 107.215.12.158 (talk) 22:16, 27 August 2013 (UTC)

The United States customary units article does say that the term Standard is one of the terms sometimes used in the U.S. to refer to system of units used in the U.S. However, most of the world would probably consider that a misuse of that term (see Metrication#Chronology and status of conversion by country). As to what system of units is appropriate for this article, that depends on whether the consensus is that this article is "science-related" or "non-science". See WP:UNITS for more specifics on that. As to "Isn't this English Wikipedia?", see WP:BIAS and WP:WikiProject Countering systemic bias. Wtmitchell (talk) (earlier Boracay Bill) 04:52, 28 August 2013 (UTC)

Why are you referring me to bias pages? I made reference to what English speaking people are mostly accustomed to. 'When in Rome ...' Here's a page you might want to review.

It was not built by Americans, but by an international team that included scientists from many countries. And yes, the Los Alamos Laboratory did use metric, as was customary in laboratories of the time. Hawkeye7 (talk) 08:03, 28 August 2013 (UTC)

Not by Americans? None? Seems to me if they wanted to keep the project a secret they would have made efforts to use as many American scientists as possible. Easier to check their backgrounds. This is not a scientific text, or a how to fix it manual. The illustrated chart on the page uses standard measurements so wouldn't it be best if the rest of the article was consistent? — Preceding unsigned comment added by 107.215.12.158 (talk • contribs)

I think this article is best described as a "science" article as it pertains to WP:UNITS. Right now, the article inconsistently flips between using imperial units first and using SI units first, with some non-SI metric units such as centimeters thrown in. I suggest making the article consistent in the format "1 meter (3.3 feet)". Sound ok? VQuakr (talk) 19:58, 28 August 2013 (UTC)

Not really. The article is best described as a military history article, which makes reference to some science on a superficial level. Since the illustrated chart uses standard measurements so should the rest of the article. — Preceding unsigned comment added by 107.215.12.158 (talk) 00:23, 29 August 2013 (UTC)

So, did "Little Boy" malfunction, or was it just an extremely inefficient design?

From this book that was recently released, it concurs with the statement of the article that just 7/10 of a gram of material underwent fission in the bomb, essentially "the bomb just blew apart in the air." Nodekeeper (talk) 12:29, 12 August 2014 (UTC)

1 "Approximately 600 to 860 milligrams (9.3 to 13.3 grains) of matter in the bomb were converted into the energy of heat and radiation."

2 "It contained 64 kg (141 lb) of enriched uranium, of which less than a kilogram underwent nuclear fission."

I assume that nuclear fission is the same than 'matter converting into the energy of heat and radiation'. Why does sentence 2 use a limit of a kilogram, istead of gram? — Preceding unsigned comment added by 130.60.69.144 (talk) 16:08, 25 March 2015 (UTC)

When a nucleus fissions, only a small proportion of its matter is converted into energy. Most of the matter in the fissioned nucleus ends up in the nuclei of the nuclear fission products and as neutron radiation. In Little Boy, a bit less than a kilogram of uranium fissioned. Of that kilogram, 600-860 mg of matter were converted into energy. The rest of the kilogram stayed as matter and became fission products and radiated neutrons. A2soup (talk) 19:32, 25 March 2015 (UTC)

Photos

Would a photo of the Little Boy replica at the Air Force Museum be helpful to the article? 21:02, 18 May 2015 (UTC)

Aircraft carrier aircraft?

"The Navy Bureau of Ordnance built another 25 Little Boy assemblies in 1947 for use by the nuclear-capable Lockheed P2V Neptune aircraft carrier aircraft."

I do not believe that the Neptune was an airplane capable of operating from an aircraft carrier. Is this a typo for "antisubmarine aircraft" or "ASW aircraft"? NelC (talk) 21:04, 28 June 2015 (UTC)

It would have been carrier-launched if used in the nuclear strike role. Here is a photo of it taking off from a carrier, though its principal usage was land-based maritime patrol. VQuakr (talk) 21:08, 28 June 2015 (UTC)

At the time only the Midway class aircraft carriers were large enough to handle them. Chick Hayward was able to land one on a carrier, but it was considered so difficult that the plan was for them to to take off from the carriers but return to land bases. Hawkeye7 (talk) 00:13, 29 June 2015 (UTC)

Grammar Check

Didn't read the whole article, but "Parsons's"? Drop the s after the apostrophe. — Preceding unsigned comment added by 192.158.48.13 (talk) 11:50, 17 July 2015 (UTC)

There are three acceptable ways to do possessive apostrophes after singular nouns ending in s, and MOS:POSS holds all of them to be acceptable if used consistently throughout an article. Usually, the convention in an article is not changed once it is established by the original author. Deciding on this sort of thing is kind of a reward for writing the article, if you will. A2soup (talk) 13:08, 17 July 2015 (UTC)

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mass equivalence

There is some disagreement over the mass equivalent of 15 kilotons TNT equivalent. 15 kT is 6.3e13 Joules; using MKS units

m = E / c^2, where c is 3e8 m/sec^2

6.3e13 [kg m^2 / sec^2] / 3e8 [m / sec] ^2 = 6.3e13 / 9e16 [kg] = 0.7e-3 kg = 0.7 gm

This is the mass equivalent of the energy released by Little Boy. It is not the amount of uranium contained (64 kg of 80% enriched U-235) or uranium fissioned, which was around 900 gm. SkoreKeep (talk) 21:10, 8 March 2018 (UTC)

Agreed. I already checked the calculations and reverted this change once before. [4] Hawkeye7 (discuss) 21:40, 8 March 2018 (UTC)

Who is Groves?

"Groves ordered that a number of Little Boys be prepared as an interim measure until a cure could be found"

That seems like a decision that would be made by someone very senior, but Groves is not introduced in the article and never mentioned again.

190.236.205.253 (talk) 20:27, 6 May 2018 (UTC)

Resolved

The reference is to the Director of the Manhattan Project, Major General Leslie Groves. Added a link to the article. Hawkeye7 (discuss) 21:02, 6 May 2018 (UTC)

What altitude was the bomb dropped from?

It's a minor point, but reading The bomb was dropped at approximately 08:15 (JST) 6 August 1945. After falling for 44.4 seconds, the ... detonation happened at an altitude of 1,968 ± 50 feet (600 ± 15 m). under Little Boy#Bombing of Hiroshima makes me wonder what altitude the bomb was dropped from. Note 137 from Atomic bombings of Hiroshima and Nagasaki discusses this, but with regards to Little Boy, only the altitude at which it detonated. Is the altitude of release known? --Usernameunique (talk) 18:26, 7 January 2019 (UTC)

"no local radioactive fallout"

Article says this, citing a quote about air bursts (not specifically about this bomb). The article then talks about direct radiation effects.

The quote does not say how significant the induced radioactivity is. Mitsuo Fuchida article says, "The day after the bombing, he returned to Hiroshima with a party sent to assess the damage. All members of Fuchida's party later died of radiation poisoning, but Fuchida exhibited no symptoms."

So either there was fallout, or there was induced radiation, or the source is incorrect and the other members of the investigative party did not die from radiation. 23.121.191.18 (talk) 04:28, 29 April 2019 (UTC)

I would wonder how Fuchida, an Army officer, would have knowledge about Acute Radiation Syndrome sufficient to diagnose his party at that point in time; it would be days at least before news accounts about the nature of the weapon could make it to Japan from the US. SkoreKeep (talk) 06:52, 29 April 2019 (UTC)

Fuchida was a Navy officer who liked to tell stories that made himself out as special. Several of his stories have been challenged by historians. As the Fuchida article says, the veracity of Fuchida's statements on a variety of topics has been subsequently called into question. Hawkeye7 (discuss) 20:29, 29 April 2019 (UTC)

A Commons file used on this page has been nominated for deletion

The following Wikimedia Commons file used on this page has been nominated for deletion:

• Shinkolobwe mine.jpg

Participate in the deletion discussion at the nomination page. —Community Tech bot (talk) 22:22, 14 June 2019 (UTC)

Cordite?!

Did it really use cordite? Why? What was so special about it? — Preceding unsigned comment added by 220.101.38.242 (talk) 04:40, 18 January 2020 (UTC)

I've added a bit to the article for you:

Cordite was a widely-used smokeless propellant consisting of a mixture of 65 percent nitrocellulose, 30 percent nitroglycerine, 3 percent petroleum jelly, and 3 percent carbamite that was extruded into tubular granules. This gave it a high surface area and a rapid burning area, and could attain pressures of up to 40,000 pounds per square inch (280,000 kPa). Cordite for the wartime Little Boy was sourced from Canada; propellant for post-war Little Boys was obtained from the Picatinny Arsenal.

Hope this answers your question. Hawkeye7 (discuss) 05:15, 18 January 2020 (UTC)

Who were the professor and two students who thought up this nuclear bomb design?

In this lecture the professor says that a college professor and two of his students are the people who thought up this bomb design. Who were they? https://www.youtube.com/watch?v=zVhQOhxb1Mc — Preceding unsigned comment added by 50.40.222.90 (talk) 18:07, 11 April 2020 (UTC)

Nicely Done

This is a very very good article by the way

This section needs a timestamp or it won't be archived. Adding one with this comment. {{u|Sdkb}} ^talk 20:35, 6 August 2020 (UTC)

"4 feet"?

The data box contains both a "Length" and a "length", the latter said to be 4', which is way too short for the bomb. So I'm going to remove it. Andyvphil (talk) 14:46, 29 May 2021 (UTC) Turns out that the line in the data box was "| part_length = About 4 feet", but that "part_" wasn't printing. It's also unclear what "part_length" might refer to. So I just removed it anyway. Andyvphil (talk) 14:55, 29 May 2021 (UTC)

Did I calculate it correct?

WP:FORUM

I tried to calculate the mass in grams of Uranium-235 that was fissioned in the bomb. I asked Google to do that for me: (((4e9 J) / (200 MeV)) / 6e23) * (235 g) = 0.0488918211 grams Oh sorry, I see my misstake now. I calculated the mass to create 1 kilo ton TNT. I need to multiply the value by 15 to find the total mass of Uranium-235 that was fissioned in the bomb. But it's still not very much. — Preceding unsigned comment added by Franz Scheerer aus Wiesbaden (talk • contribs) 18:12, 26 April 2023 (UTC) So the mass is about 0.75 grams. Franz Scheerer aus Wiesbaden (talk) 18:00, 26 April 2023 (UTC) Whether correct or not, it's going to be viewed as original research, and won't be suitable to include in the article. You need to find a reliable source that has reported on that. signed, Willondon (talk) 18:09, 26 April 2023 (UTC) I think Google has calculated it correct. Is that a reliable source? Franz Scheerer aus Wiesbaden (talk) 18:17, 26 April 2023 (UTC) In Wikipedia I found: " The ton of TNT is a unit of energy defined by that convention to be 4.184 gigajoules (1 gigacalorie), " Franz Scheerer aus Wiesbaden (talk) 18:22, 26 April 2023 (UTC) and the Avogadro Constant It is an SI defining constant with an exact value of 6.02214076×1023 reciprocal moles. Franz Scheerer aus Wiesbaden (talk) 18:26, 26 April 2023 (UTC) You really should give WP:OR a thorough read to understand how policies on original research are applied at Wikipedia. signed, Willondon (talk) 18:48, 26 April 2023 (UTC) WP:OR: Routine calculations do not count as original research, provided there is consensus among editors that the results of the calculations are correct Hawkeye7 (discuss) 19:18, 26 April 2023 (UTC) So I explain it once more again in detail. The mass of one mole of uranium-235 is 235 grams. The number of atoms is calculated as the energy divided by the energy per fission (200 MeV). The amount of substance in moles is obtained by dividing the number of atoms by Avogadro's constant. The energy is 15 kilo tons of TNT. One kilo ton of TNT is 4.18 GJ. Franz Scheerer aus Wiesbaden (talk) 05:13, 27 April 2023 (UTC) When a uranium nucleus fissions into two daughter nuclei fragments, about 0.1 percent of the mass of the uranium nucleus appears as the fission energy of ~200 MeV. For uranium-235 (total mean fission energy 202.79 MeV), typically ~169 MeV appears as the kinetic energy of the daughter nuclei, which fly apart at about 3% of the speed of light, due to Coulomb repulsion. Also, an average of 2.5 neutrons are emitted, with a mean kinetic energy per neutron of ~2 MeV (total of 4.8 MeV). The fission reaction also releases ~7 MeV in prompt gamma ray photons. Franz Scheerer aus Wiesbaden (talk) 05:18, 27 April 2023 (UTC) That sounds about right. But there is an average of ~8.13 photons per fission, so they are in the X-ray range, not the gamma ray range. Hawkeye7 (discuss) 05:40, 27 April 2023 (UTC) In this talk already a source is given for a value of 0.7 grams, which is approximately true. " Less than a kilogram of uranium underwent nuclear fission, and of this mass only 0.7 g (0.025 oz) was transformed into several forms of energy, mostly kinetic energy, but also heat and radiation. According to: Glasstone, Samuel; Dolan, Philip J. (1977). The Effects of Nuclear Weapons, Third Edition. United States: United States Department of Defense and United States Department of Energy. ISBN 978-1603220163. " Franz Scheerer aus Wiesbaden (talk) 05:54, 27 April 2023 (UTC) You are mixing two different concepts, the mass of uranium that underwent fission and the mass equivalent energy that was released in the explosion. They are different by 3 orders of magnitude. VQuakr (talk) 06:03, 27 April 2023 (UTC) One mole of Uranium-235 is 235 grams, no doubt. The number of fissioned atoms is about 15 kilo tons TNT divided by 200 MeV. It is not 100 percent correct, since the 15 kilo tons do not include neutrinos and decay energy of the fission products. It does not matter for our estimate. Franz Scheerer aus Wiesbaden (talk) 06:17, 27 April 2023 (UTC) @Hawkeye7: I do not agree that this unit conversion is "routine calculation". It would be OR to use in the article in my opinion. @Franz Scheerer aus Wiesbaden: can I direct you to WP:RD/S, where this sort of question would be more suitable? Meanwhile: 200 MeV is equal to about 3.2 E-11 J. 15 kilotons of TNT is equal to about 6.3 E13 J. That's 2.0 E24 uranium fissions, or 3.3 moles with an initial mass of around 750 grams; roughly 1% of the uranium in the bomb. The Little Boy design was extremely inefficient. VQuakr (talk) 05:38, 27 April 2023 (UTC) 200 MeV = 200 * 1e6 * 1.6e-19 J = 3.2 e-11 J is ok 15 * 4e9 = 6e 10 not 6.3E13 this is the error in your calculation. Franz Scheerer aus Wiesbaden (talk) 06:03, 27 April 2023 (UTC) Yes, the rest is correct. Franz Scheerer aus Wiesbaden (talk) 06:06, 27 April 2023 (UTC) No, a ton of TNT is around 4 E9 J. A kiloton of TNT is around 4 E12 J. The explosive yield of Little Boy was roughly 15 kilotons of TNT. VQuakr (talk) 06:07, 27 April 2023 (UTC) I cite it again: The ton of TNT is a unit of energy defined by that convention to be 4.184 gigajoules (1 gigacalorie), which is the approximate energy released in the detonation of a metric ton (1,000 kilograms) of TNT. Franz Scheerer aus Wiesbaden (talk) 06:20, 27 April 2023 (UTC) Yup. The Little Boy explosion was equivalent to 15,000 tons of TNT. 15,000 * 4.2 E9 is 6.3 E13. This information is also in the infobox of the article (63 TJ). VQuakr (talk) 06:24, 27 April 2023 (UTC) Yes, the kilo is missing here. The right answer is about 0.7 kg of Uranium-235, that is still about a factor 100 less than the amount of Uranium-235 in the bomb. 99 % was not fissioned. Franz Scheerer aus Wiesbaden (talk) 06:40, 27 April 2023 (UTC) Now, it is really correct. I'm sure, it is in the order of magnitude as I remenber it from school. ;-) Franz Scheerer aus Wiesbaden (talk) 06:45, 27 April 2023 (UTC) Yes, if we start with the 63 TJ it is much more easy. I asked Google again: (((63 TJ) / (200 MeV)) / 6e23) * (235 gram) = 770.046182 grams Franz Scheerer aus Wiesbaden (talk) 07:08, 27 April 2023 (UTC) And how much percent is this from 64 kilograms? Google found: ((((63 TJ) / (200 MeV)) / 6e23) * (235 gram)) / (64 kg) = 1.20319716 percent Franz Scheerer aus Wiesbaden (talk) 07:13, 27 April 2023 (UTC) In other words 98.8 percent of the Uranium-235 was not fissioned. Franz Scheerer aus Wiesbaden (talk) 07:24, 27 April 2023 (UTC) There is still a lot of room for improvement. Nuclear fission can be made much more efficient and, of course, the amount of fissile nuclei can be increased. — Preceding unsigned comment added by Franz Scheerer aus Wiesbaden (talk • contribs) 08:22, 27 April 2023 (UTC) Is there even a need to build a fusion bomb and does a fusion bomb really work? — Preceding unsigned comment added by Franz Scheerer aus Wiesbaden (talk • contribs) 08:27, 27 April 2023 (UTC)

Amount of fissionable material turned into energy

Less than a kilogram of uranium underwent nuclear fission, and of this mass only 0.7 g (0.025 oz) was transformed into several forms of energy, mostly kinetic energy, but also heat and radiation.

According to: Glasstone, Samuel; Dolan, Philip J. (1977). The Effects of Nuclear Weapons, Third Edition. United States: United States Department of Defense and United States Department of Energy. ISBN 978-1603220163.

https://www.fourmilab.ch/etexts/www/effects/eonw_1.pdf#zoom=100

page 12, Table 1.45 EQUIVALENTS OF I KILOTON OF TNT

Complete fission of 0.057 kg (57 grams or 2 ounces) fissionable material

Thus 15 kilotons of TNT correspond to 855 grams of fissionable material.

Where 0.7 grams come from? Emerg.reanimator (talk) 15:56, 11 September 2022 (UTC)

The amount transformed into energy. Which differs from the amount fissioned. Hawkeye7 (discuss) 18:36, 11 September 2022 (UTC)

It is simply wrong. We easyly can check it using the Google calculator:

((((63 TJ) / (200 MeV)) / 6e23) * (235 grams)) / (64 kg) =

0.0120319716

About one percent of the Uranium-235 was fissioned. 178.202.60.40 (talk) 18:26, 27 April 2023 (UTC)

The mass unit is 931.49 MeV/c^2, so a little more accurate calculation gives

(((63 TJ) / 200) * (235 * 931.49)) / (c^2) =

767.211682 grams

Because of the energy of the neutrinos and delayed decay of the fission products is the energy per fission a little less than 200 MeV and the mass of fissioned Uranium-235 a little higher. Franz Scheerer aus Wiesbaden (talk) 12:24, 30 April 2023 (UTC)

The value of 855 grams of fissionable material is probably the best estimate. Franz Scheerer aus Wiesbaden (talk) 12:27, 30 April 2023 (UTC)

This is neither here nor there, really, but all of this depends on whatever ultimate yield one sets to the Little Boy bomb, which is not at all known well-enough to make these calculations as precise as this (it is +/- 20% or so, or a difference of 3 kilotons in either direction). So these equations contain a false precision to them. It doesn't really matter; the general point that about a kilogram of material fissioned, with the exact number depending on the yield of the bomb, which we don't know precisely (and never will!). So "less than a kilogram" seems fine, though if the yield was on the high point of that range (18 kt) then it would be slightly over 1 kilogram of material that fissioned (the complete fissioning of 1 kilogram of U-235 releases about 17 kt). When I talk about this I usually say "about a kilogram" of material fissioned because that gives the relevant information without committing me to one interpretation or another of the yield. --NuclearSecrets (talk) 19:18, 30 April 2023 (UTC)

You are right, the Mass excess is smaller. 178.202.60.40 (talk) 18:39, 27 April 2023 (UTC)

The mass of the fission products is smaller, by 0.7 grams, because of E = mc². 178.202.60.40 (talk) 18:58, 27 April 2023 (UTC)

"Number built"

The info box says, without citation, that 33 LB units were built. What is the source for this number? Carey Sublette says 5. John Coster-Mullen seems to say 13 partial assemblies ("Since units L1, L2, L5, and L6 were dropped in tests at Tinian and L-l1 was used at Hiroshima, this would seem to indicate that there were at least eight (partial or complete) Little Boy weapons available in the inventory at the end of the war. Combined with the five produced at Sandia between 1945 and 1950, it would appear that a total of 13 LB units may have been in existence at that time, although some of these might also have been scrapped."), but that might just be a different way to talk about Carey's 5. RDD-8 says (page 107) there were no more than 2 LB non-nuclear assemblies by 1948 and 0 nuclear assemblies. Anyway 33 seems pretty large to me, and somewhat unlikely! NuclearSecrets (talk) 04:57, 6 September 2023 (UTC)

The article says:

The Navy Bureau of Ordnance built 25 Little Boy assemblies in 1947 for use by the nuclear-capable Lockheed P2V Neptune aircraft carrier aircraft (which could be launched from, but not land, on the Midway-class aircraft carriers). Components were produced by the Naval Ordnance Plants in Pocatello, Idaho, and Louisville, Kentucky. Enough fissionable material was available by 1948 to build ten projectiles and targets, although there were only enough initiators for six. All the Little Boy units were withdrawn from service by the end of January 1951.

Hawkeye7 (discuss) 05:25, 6 September 2023 (UTC)

If you look at the Hansen (Swords, v.2, V-115 and V-117), you'll see that there is some trickiness in terminology here. BOA produced 25 "revised" MK I "mechanical assemblies" (?), but by the end of 1948 there were "no stockpiled fissionable components" and "only two outer casings." He then confusingly blends the "enough fissionable material" for ten (but only 6 initiators) by the end of 1947 (in version 2 of Swords), but then confuses things a bit by saying that there were no gun-type targets and projectiles in the stockpile until 1949 (which implies there may have been a few between 1949 and their retirement by fall 1950). Earlier he says "Only five complete LITTLE BOY weapon assemblies were built between August 1945 and February 1950; all were retired by November 1, 1950." (V-115) It is all very typical Hansen; a lot of miscellaneous quotes that don't quite add up to a coherent whole. He was a fantastic acquirer of documents, but his abilities as a writer and at historical synthesis...

None of this quite gets to 33 by my count, but in any event, 33 seems like the most exaggerated and overly-generous read of the word "built" (it seems to be including partial non-nuclear assemblies, which I think nobody would count a steel gun-tube by itself, or even just a casing, as an actual "atomic bomb" that has been "built"). I would find "5" to be a much more sensible figure to put with "number produced" for an info box, and it would jibe with the other sources (including Hansen), with more details in the article itself. The source of the "5" is apparently Furman, Sandia National Laboratories: The Postwar Decade, University of New Mexico Press, 1990, which I do not have immediate access to, but have made a request through my Interlibrary Loan as I am curious about it in general... -

Anyway I propose (and have made the change) to say that the "number built" for the infobox is 1 wartime + 5 postwar. That seems like a reasonable read of the above, and is more clear than just saying "6" (which is the other alternative way to do the count, I think -- it is interesting that the wartime one is rarely counted!). -NuclearSecrets (talk) 12:07, 6 September 2023 (UTC)

There were eight Little Boy wartime assemblies deployed to Tinian: L-1, L-2, L-3, L-4, L-5, L-6, L-7, and L-11. Hence the total of 33 = 8 + 25. What if we change the number to 13 = 8 + 5? Hawkeye7 (discuss) 19:35, 6 September 2023 (UTC)

I think it comes down to what definition of "built" or "produced" is used. I don't consider any but L-11 to be truly a "built Little Boy." Any more than I consider John Coster-Mullen's reproduced casing to be a "built Little Boy." I think if you told people that "8 Little Boy bombs were produced during World War II" they would be very surprised — because they would (I think correctly) assume you meant that those were complete bombs, and not just partial assemblies of non-nuclear components in all but one case. In my mind, having 8 non-nuclear assemblies + 1 nuclear core means you only have produced one atomic bomb, not eight. I think the goal here needs to be clear. 1 wartime + 5 postwar implies that the US never had more than 6 actual Little Boy bombs that could be detonated, which sounds right to me. Further details in the text can (and should) explain that other non-nuclear assemblies were created in whole or in part, but I don't think most people would consider those anything but incomplete without the (all important) nuclear fuel that converts these from "things that would kill you only if they happened to hit you in the head and break your neck" to "atomic bombs." --NuclearSecrets (talk) 21:12, 8 September 2023 (UTC)

Furman: "Only five complete Little Boy weapon assemblies were built". So we are talking about assemblies here, not "complete" bombs. My understanding is that all the wartime assemblies were used or scrapped. This is the same as with Fat Man; what they had was components to build bombs, but they had to be assembled. The Fat Man cores were stored separately. We don't know how many Little Boy cores were produced post-war; there was only the one during the war. If there was any, they would have been stored separately too. Hawkeye7 (discuss) 22:17, 8 September 2023 (UTC)

I know they had their cores kept separately, of course. "Weapon assemblies" can mean a lot of different things in different Sandia docs, from what I can tell.

I went down a deep rabbit hole to see if I could find any info on postwar core manufacturing. I did find some evidence that they clearly cast some LB core pieces in the postwar, e.g. this document from January 1947 which describes them casting, machining, and electroplating a number of target rings, projectile rings, bolts, and LB initiators at Los Alamos. (JCM says in one place that LB had rings each in the target and projectile, and in another place he says there were six target discs, and it is separately interesting that the DOE says that no complete nuclear components for LB were available in the stockpile in 1947, and I can't explain those contradictions, but I thought this all was interesting.) Los Alamos was clearly in charge of doing all of the U-235 machining at that point, and had a pretty substantial inventory of HEU on hand by 1948 (see page 6, at bottom).

My sense in going over Sandia records is that they did make some number of postwar nuclear components as part of the "Road" program for MK I and MK III bombs (which was a kind of postwar standardization program of the part kits for these early bombs in the late 1940s). For example, this document from February 1949 describes a component catalog (on page 11) for the "nuclear material" of the LB bombs, and item 2.3.3 (on page 12) describes parts "LB-12, LB-13, and LB-14," which I suspect correspond to the projectile, target, and initiator pieces. However it also may indicate that at that time, they hadn't actually made those pieces as such (there is a tentativeness to the description, "in the event that the need... occurs"). The same document also makes reference to the idea that there were at least three different models of postwar LB (Type AAA, B, and C, on page 13). The grammar is a little hard to parse; it may be that B and C were the "mockup" and "ballistic assembly," or they may be different things entirely. There is an interesting discussion of "inventory" on page 14, which makes it clear that in 1949, they had lots of parts available or close to being available, but it sounds like nothing had really been put together. This document says that during FY 1949, they finished the "Road catalogues" of components and turned the components over to the AFSWP, but that can't include nuclear components, since those were not given to the military at this stage of things. It also says manufacturing of "major components" was completed in November 1948, but doesn't specify what those are, of course. This May 1948 progress report says that "two gadgets" of the LB type had been prepared for "possible military emergencies", and those must be the cited 2 non-nuclear LB's ready in 1948 (it's nice to be able to at least find something that verifies that number!).

The whole history of the Navy's involvement with the Manhattan District and then Sandia on this is pretty interesting (a USAF historian in the late 1950s considered it "somewhat devious," and apparently the USAF strongly, strongly opposed this program, because they felt that this was a misuse of scarce fissile material), and it seems to overlap with the history of the Mk 8 in interesting ways. The inter-service rivalry aspect is pretty fascinating to me. I am very interested in the early Truman admin nuclear stockpile at the moment, which is why I am diving into this (beyond the inherent interest of scratching around at an issue that is not super well-documented).

ANYWAY. All of this is very sketchy, obviously, and not likely usable in the article (too WP:OR), but I thought it was interesting and worth just writing down. My sense is that we might just want to not condense all of this into a "number produced" at all, because it's just not a meaningful number at present, and instead just indicate the various numbers and their possible meaning in the text. I consider it very likely that the number of five produced in the postwar means that they considered these "full" (including nuclear) assemblies that could have been put together on short notice (e.g., without casting projectile or target pieces), because otherwise that distinction of "five" makes no sense and it seems to be one that Russ makes (versus the 20ish mechanical assemblies number). I sort of feel like if the Furman book says five (and everyone else says "five") then that's the sensible postwar number, assuming it doesn't include LB-11 in it. --NuclearSecrets (talk) 21:00, 10 September 2023 (UTC)

Sounds good to me. Thanks for going down the rabbit hole. Much appreciated. (I've always enjoyed scratching around at an issue that is not super well-documented myself.) LB-12, LB-13, and LB-14 sound like assemblies to me, continuing the series from the wartime one that ended with LB-11. I first came across the Navy's post-war nuclear ambitions plans in I wrote the article on the Armed Forces Special Weapons Project mainly because having read about the Manhattan Project, the question of "what happened next?" came up, and I thought that other people would be interested too. (Page counts say otherwise though.) Hawkeye7 (discuss) 21:30, 10 September 2023 (UTC)

References

Critical mass and amount of uranium

The assembled fissile core had more than two critical masses of uranium-235

Where does this come from? Critical mass of U235 is 52kg, and the article says the bomb contained 64kg of uranium. Thus, it can not be "more than 2 critical masses", and the statement saying one of the parts had to have "over one critical mass" is wrong too. — Preceding unsigned comment added by 181.74.144.146 (talk) 07:18, 31 January 2024 (UTC)