The Japanese nuclear weapons program

Discussions on all aspects of the Japanese Empire, from the capture of Taiwan until the end of the Second World War.
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williamjpellas
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Re: The Japanese nuclear weapons program

#346

Post by williamjpellas » 20 Sep 2013, 17:34

photografr7, unfortunately, you did not respond to my post. Your photograph is interesting but does not answer my question as to your "proof" for your assertion that Arakatsu's cyclotron "was not working" at the time it was destroyed and thrown into Lake Biwa. Nor did I say anything about how the document(s) that you claim to have would definitively answer the question of how far the Japanese Navy program progressed toward an actual, working atomic weapon. I said, quote, I am interested to know if Arakatsu's cyclotron was functioning in the later war years because that could have a bearing on how close the IJN program came to success, unquote. Now, either you have evidence for your assertion above, or you do not. If you do not, you should retract your assertion in the interest of scholarly and historical integrity. If you do have evidence, great. Why not share it so we can all get closer to answering the question of how close the Japanese came to a working atomic bomb during World War II? Thanks.

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Re: The Japanese nuclear weapons program

#347

Post by Machinga » 11 Apr 2014, 06:38

Just got a bit of down time and thought I would check the latest arguments.
Well, I guess that degree in Mathematics didn't take to well either....it is a simple math problem, 4 + 2 = 6. Of course you could do 4 + 2 = and then solve for Y.
Will Pellas and I might vehemently disagree about the extent of the German nuclear problem...but at least we can add 4 + 2.
By the end of the war Japan had a total of five cyclotrons in operation. Read some of those "secret" documents you have "discovered" in the archives and draw four straight lines, then a diagonal across those to equal five. Of course, if you were really a great researcher you could read the newspapers of the time...and count your fingers and thumbs up to the number "6." In addition to the operational system at Kyoto Imperial University under Arakatsu, there was a second, larger cyclotron at his lab under construction that was never dumped into either Tokyo Bay or Lake Biwa.
If you can get this wrong...you book should be an easy slam!!


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Re: The Japanese nuclear weapons program

#348

Post by Machinga » 11 Apr 2014, 06:39

One last thing, six, four, two? They only needed one

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Re: The Japanese nuclear weapons program

#349

Post by LWD » 11 Apr 2014, 14:45

Only needed one for what?

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Re: The Japanese nuclear weapons program

#350

Post by williamjpellas » 12 Apr 2014, 20:35

Actually, the extent of the disagreement between me and machinga re: the WWII German program(s) is overblown. I think the crucial difference between us is that I believe strongly that a thorough re-examination of the German work is merited and long overdue, and also that it might have direct relevance as to how far the Japanese project(s) actually got (how much relevance, I'm not yet sure). In other words, I believe I see enough to question some of the more or less standard narrative about the Axis atomic projects and to consider even some avant garde theories until they can be disproven or at least followed to the end of their respective roads (ie, as far as the legitimate documentation and evidence, as well as reason and common sense, can take them). Machinga disagrees and is certain there is nothing new to find about the German programs, and thus he is also certain---as I understand it---that therefore there is little to nothing new to learn about possible collaboration or "cross pollination" between the respective efforts of Germany and Japan. I am not so sure about that and believe that thorough investigation is needed.


Anyway, there are a number of threads on this and other sites that discuss the German projects in considerable detail, so I think it is probably best to boundary this particular thread to keep it focused most directly on the Japanese projects and on the R&D that they did themselves. If and when more documentation surfaces to show more comprehensive co-operation between them than is commonly understood to have occurred, I will speak to that. :milsmile:

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Re: The Japanese nuclear weapons program

#351

Post by Genro » 29 Jul 2014, 11:46

Looking back I note that this thread started with the Kuroda documents which were returned to Riken in 2002. Since then a number of article have been written and references were made to them by various historians and novelists.
I have recently had a chance to examine them carefully as a physicist and find what seems to be a considerable misunderstanding of what was written.
The documents were written up from notes taken at the time and presented some 3 days later. Ishida termed ‘gishi’ (technician/engineer) is the third person present at the meeting and probably the author.
Nishina estimates the critical mass of U235 as 10 Kg and using the data known at the time I calculate 10.5 Kg with a reflector. Using modern nuclear parameters this is 17 Kg. He is also aware that for a bomb to be effective is must be much larger than just one critical mass and that it also needs what is termed ‘inertial confinement‘. Further, that only a small portion of the uranium will undergo fission.
The documents also indicate a time scale for the explosion of 1/20 to 1/30 second but close examination of Nishina’s statements and some calculation shows that this is in ‘micro-seconds’.
There have been a number of misinterpretations of these documents especially Tokutaro Hagiwara’s so called H-bomb prediction.

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Re: The Japanese nuclear weapons program

#352

Post by williamjpellas » 18 Sep 2014, 04:45

Genro, if you have a full English rendering of the Kuroda documents, I would love to have that in my possession. Please contact me through the private message function on this site if you have that and are willing to mail or email it to me. I am pretty certain that there is "considerable misunderstanding of what was written", but am not sure exactly where the misunderstandings come in without going over the original wording with a fine-toothed comb. If Nishina in fact meant "micro-seconds" and not 1/20th to 1/30th of one second, then he probably had an accurate calculation of the reaction that would actually detonate an atomic bomb. Which would, in turn, mean that the assessment of the BBC article that indicated the Riken bomb concept / design would not have been very powerful, would be wrong. In short, it would probably mean that the Japanese had solved the issues of how to set off an atomic explosion to a high degree of accuracy, and came short of a functioning weapon only in terms of completing the industrial process. Again, I really want to see the full (and accurate) English translation of the documents before I go on record with anything definitive, but if Genro's post is accurate it would be a significant step forward in the scholarship on this issue.

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Re: The Japanese nuclear weapons program

#353

Post by Genro » 18 Sep 2014, 19:35

Williamjpellas, On my visit to Riken they were kind enough to give me copies of the Kuroda papers. The translation has been a long and difficult task and still needs further refinement. Japanese being a contextual language present some unusual problems which is why I have looked closely at the mathematics of the atomic bomb to elucidate the meaning. There is no short hand in Japanese so it would appear that Ishida ( engineer/technician ) took notes and wrote them up afterwards. There are some obvious mistake which would indicate that Ishida was not fully conversant with the subject but by the third meeting he is certainly more knowable than General Nobu-uji.
Heisenberg emphasised the huge weight of such a bomb to the German military as also Nishina to the Japanese military. In a meeting on 6th July 1944 with General Nobu-uji, Nishina tells him “ the weight is so great that it is viewed as not suitable as a bomb.” ( tekito narazaru - not suitable )
Incidentally, there is no reference to ballistic assembly, the 1/20 to 1/30 second is not an assembly time but the expansion time in micro-seconds to 2nd criticality.

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Re: The Japanese nuclear weapons program

#354

Post by williamjpellas » 19 Sep 2014, 17:11

Okay, so if "there is no reference to ballistic assembly", then the Riken / Kuroda papers---in and of themselves---do not constitute a bomb design as such, but rather are a series of advanced atomic weapon conceptual studies. In other words, they are deeply into discussions about the nuclear physics of how a detonation would be achieved, but they are not (yet) involved in the nuts and bolts engineering of the device / bomb itself. Would you say that that is an accurate summary of what you are saying here?


Seems to me that someone is wrong, somewhere, about exactly what the Riken / Kuroda papers say. Which, again, is why I am eager to acquire a reliable English translation of them. Consider this passage from the obviously contrarian but still somewhat useful article "Japan's A-Bomb Goal Still A Long Way Off in '45", from The Japan Times on 7 March, 2003:

The papers show that Nishina believed he could fashion a bomb from 1 kg of weapons-grade U-235 with 1 to 2 tons of natural uranium ore.

While that would have been a sizable device, it would not have been so large as to have been impractical as a weapon, even allowing for the absence of a suitable heavy bomber in Japan's inventory of weapons. I am guessing that Nishina's rough suggestion here was probably from very early in the project, because he knew the neutron cross-section of U-235 to a high degree of accuracy from his work with Riken's cyclotron and thus certainly knew the necessary size of the mass of U-235 that would be needed, and because he was also able to reverse-engineer to a high degree of accuracy the scope and nature of the American U-235 bomb that destroyed Hiroshima just from his onsite observations and quick calculations (as Wilcox describes in Secret War). It strikes me as doubtful that Nishina believed he could really create an atomic explosion with just 1 KG (probably 2 or 3 pounds) of HEU given the state of the art in the 1940s, unless he was thinking about boosted fission or some other method of detonation that would have dramatically reduced the amount of bomb fuel that would be needed. I am not aware of any evidence that suggests that this was the case other than photografer's mention of Nishina's brief musings about what we would today call lasers, but this was never given any serious attention or consideration and to my knowledge there was never any attempt by the Japanese to pursue any kind of detonation mechanism that had anything to do with any form of directed energy such as a laser or what would have been the 1940s equivalent.


So, what was the meaning of the 1 kilogram figure? It could be that Nishina meant that this would be the amount of the critical mass that would actually be "burned" (disintegrated to release atomic energy in the form of an explosion) and that the natural uranium ore would add somewhat to the total yield of the weapon. Turns out that 1 kilogram is very close to what actually exploded in the Little Boy gun-type U-235 bomb. Isn't that interesting. Although there was about 180 pounds of 80 to 85% HEU in the core of that bomb, only a couple of pounds actually fissioned completely. The rest of the material was a fizzle and added little or nothing to the explosive yield.


Here I would emphasize that the papers that Kuroda's widow gave to the Riken in 2002 date from 1943, nearly two full years before the war ended. It is not credible to think that they were (or are) the final word on Japanese progress toward a working atomic bomb. I don't believe that that is even close to the truth. Unfortunately, it appears that there is little to no available documentation---or rather, little to none that has survived or that has surfaced to this point---regarding the Navy's "F-Go" end of the war crash project in Korea, but even that is not the end of the road. I am given to understand through another poster / researcher on this site that there was at least one more major epicenter of wartime Japanese atomic R&D in addition to the Riken and F-Go's Kyoto Imperial University - Hungnam, Korea nexus. (Robert Wilcox mentions in his second edition of Secret War that there was a rail line connecting Hungnam to the area in the interior of China where this third epicenter was apparently located, but he did not find the documentation regarding a possible third Japanese a-bomb program that the other researcher did. In this one instance, in other words, Wilcox did not connect the dots, and I mean no disrespect to him in saying that, I'm just summarizing where the scholarship is at the moment.) Rumors of a second, wartime test detonation by this third group have come to my attention through his kind correspondence, but he is far more informed about that end of the spectrum and so I cannot say any more until and unless I can devote proper and sufficient time to do the necessary archival digging.

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Re: The Japanese nuclear weapons program

#355

Post by williamjpellas » 19 Sep 2014, 17:27

Since you mention Heisenberg, it may perhaps be true that he believed that a U-235 bomb would be very large and that it would be impractical for Germany to attempt to build one during the likely duration of the war. I am skeptical about this story because it has been propagated by Heisenberg's friends and apologists and to some degree by Heisenberg himself, and there is what I believe to be significant evidence to the contrary. Specifically, Rainer Karlsch---in his much (and to my mind, wrongly) vilified book Hitler's Bombe---posts information that he dug out of KGB archives that describes Heisenberg, in a lecture at the "Harnack Haus Conference" in 1942 or 43 (I don't recall which year), discussing in some detail an alternate route to an atomic bomb that involved uranium-233. The KGB was the only Allied intelligence agency, as far as we know, that managed to penetrate the Harnack Haus meeting. U-233, like plutonium-239, can be produced in either a breeder reactor or by cyclotron, and while there are some difficulties in producing and working with it that are not as pronounced as those in U-235 and P-239, nevertheless it IS a viable atomic explosive. A U-233 bomb also has certain advantages that would have solved a number of difficulties for the Germans, among them that a U-233 manufacturing base would probably not have needed to be as large as what would have been required to produce sufficient U-235, and a U-233 bomb would also have required a smaller amount of bomb fuel because U-233's explosive properties are closer to plutonium that they are to U-235. Etc and so forth.

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Re: The Japanese nuclear weapons program

#356

Post by williamjpellas » 19 Sep 2014, 18:00

Heisenberg emphasised the huge weight of such a bomb to the German military as also Nishina to the Japanese military. In a meeting on 6th July 1944 with General Nobu-uji, Nishina tells him “ the weight is so great that it is viewed as not suitable as a bomb.” ( tekito narazaru - not suitable )


I have never before heard of General Nobu-uji, nor was I aware of the conversation which you describe that apparently took place on 6 July 1944 between the General and Dr. Nishina. Can you tell me your source for this conversation? Thanks again.

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Re: The Japanese nuclear weapons program

#357

Post by Genro » 19 Sep 2014, 18:27

Based on the Tonizo reports, your first statement I would agree with.

The first report on the Kuroda papers appeared in the Asahi Shinbun and was picked up by the BBC in August 2002 who of course had it translated. The Japan Times later published it in English of course in March 2003. I suspect that in the translation between the papers, Nishina’s critical mass of 10 Kg was ‘mistakenly’ changed to 1 Kg.
Much of the Times article was based on an analysis by Yamazaki, Prof. of history and while I would agree with him that Japan was a long way from producing a bomb, I do not think he understood the technical aspects outlined in the Tonizo documents.

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Re: The Japanese nuclear weapons program

#358

Post by Genro » 20 Sep 2014, 10:43

2/2/1944 Attendants: Dr. Nishina, Major General Nobu-uji, Technician Ishida.

Nishina ;
According to (my) calculation, it is better to operate gradually in order to produce energy. That is to say that the density of the U is lowered due to the expansion caused by the heat at the reaction. The lower density makes the reaction come to a halt. When this happens, the temperature comes down and the density increases again to re-enabling the reaction. This assumes an ideal situation and (we) don’t know for sure yet.

Let M = 20 Kg, and the reflector adjusted for M/Mc = 1.015
then R/Rc = 1.005 and the expansion r = Rc 2.51x10^-3.
Coefficient of expansion of uranium = 14x10^-6 / degree C.
Temperature rise = 180 C.
The specific heat capacity of uranium = 116 Joule /Kg C.
For 20 Kg the total energy released = 4.2x10^12 ergs.
At 3x10^-4 ergs/fission the number of fissions Nf = 1.4x10^16 .
Neutron yield (2.6 - 1) 1.4x10^16 = 2.2x10^16. neutrons.
T = 2t/ (n-1)( 1 - ( Rc/R)^2 ) at n =2.6 T = 1.26 micro-seconds
Total fission time T* = T + t ( ln Nf - 1 ) approx. 25 micro-seconds.

Just such an idea was implemented in the Los Alamos ‘Godiva ’etc. facility with a very similar performance. Godiva also had a steady state power level of about a kilowatt.
Godiva II ORNL.-FBR

Burst yield: neutron pulse 1.0 x 10^16 1.0 x 10^17
Pulse width: micro-seconds 80 38
Maximum temperature degrees F 180 ( 82C ) 740 ( 393C )

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Re: The Japanese nuclear weapons program

#359

Post by Genro » 23 Sep 2014, 17:25

To put this matter of just 1 Kg to rest :-

Nishina:
The result of the measurement may reveal whether 10kg is enough or 20kg, or
even 50kg is necessary.
Whether uranium becomes a bomb or not, we don’t know without determining the speed of the reaction. The speed is so high that it is not practical to measure it, so we can only do it by calculation.

Calculation.
The exponential increase in the neutrons e^u(time) is such that 99% of the energy is released in the last few periods of ’ t ‘. For simplicity, ‘ u ’ will taken to be constant until the expansion starts at which point it diminishes to zero when the chain reaction ceases. Setting the mean value of u to u/2, then T= 2/u

T = 2 t/ ( n - 1 ) [ 1 - ( Rc/R) ^2 ]

Substituting M for R and Mc for Rc :- T = 2t/(n-1)(1 - [Mc/M]^2/3

Setting Kc = Rc p the radial expansion ‘r*’ is :-

r* = ( M / Kc 4/3 pi )^½ - ( M / p 4/3 pi )^1/3

Assuming ballistic assembly, then the energy released :- E = M*/2 ( r*/T )^2

Where M* = mass of ‘bombe’ + mass uranium 235 = 200Kgm , n = 2.6 ,
t = 10^-8 sec. and 4.2x10^10 ergs/gm of TNT.
‘Bombe’ is in katakana, a pressurised container as in ’chiso bombe, a cylinder of compressed nitrogen. This is the reflector / tamper or inertial confinement.

M/Mc = 2 3 4
T = 34 22 20 ns
r* = 0.8 1.5 2,2 cm
E = 1.5 12 26 K tons TNT.

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Re: The Japanese nuclear weapons program

#360

Post by williamjpellas » 23 Sep 2014, 17:56

I am no physicist, but this sounds like really advanced calculations that are apparently very accurate in terms of their prediction and description of how the hoped-for Japanese atomic explosion would work and behave. I had heard of the "Godiva" facility before but only in passing and would never have drawn the apparently direct parallel with Nishina's work that you do here. Okay, so the figure of "1 KG" was a mistranslation, and what Nishina really said was that he didn't know if the size of the critical mass would be 10 KG or 20 or 50 until they did more work. Is that correct?

Also, by "ballistic assembly", I assume he meant, some kind of gun-type uranium bomb, probably fueled by U-235 according to a TV documentary I saw once that showed a couple of pages of the Kuroda papers that had the term "U-235" prominently written on them. The reflector in this case is meant to turn at least some of the fissioning neutrons back into the fissioning critical mass to cause more fissions and to increase the yield. Apparently Nishina expected "26 kilotons". Nice. A significantly bigger kaboom than Little Boy's 16.7 KT (according to my recent reading, assuming it is accurate) and even a bit larger than Fat Man, actually. Obviously this would NOT have been "a weaker weapon", as the BBC article put it. I presume that that article and the Japan Times piece said that the Japanese bomb would have been weaker because of Nishina's alleged calculation error, which you are saying was a "misunderstanding". I wonder if it wasn't outright disinformation, but we can dig deeper as we go.

I am guessing that if Nishina told the General that a Japanese bomb would not be practical because it was too large, this would be because the degree of enrichment of Japanese HEU would have been much lower than the 80 to 85% used by the US Little Boy bomb, and thus the size of the critical mass would have been much greater. Higher enrichment = less bomb fuel needed to cause an explosion, though the shape of the bomb core and the efficiency of the detonation mechanism also factor in.

Lastly, what are "the Tonizo reports"?

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