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.
Carl Schwamberger
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Re: The Japanese nuclear weapons program

Post by Carl Schwamberger » 21 Dec 2016 01:02

williamjpellas wrote:...

6) I stated that the Manhattan Project considered thermal diffusion for its own use in uranium separation -enrichment but rejected it as "too technically complex and, probably, too slow". Not quite. The Manhattan Project did, in fact, initially choose not to build a thermal diffusion plant. This was in part because its scientists and engineers thought, correctly, that thermal diffusion would probably be inefficient, messy, and slow---which it was---but the Project later returned to thermal diffusion when it ran into problems with its electromagnetic separators. The result, as we discussed upthread, was the S-50 plant, which was used in tandem with the gaseous and electromagnetic plants, with S-50 becoming the first step in the process. That is, it produced slightly enriched uranium that then became feedstock for the other two facilities. S-50 was built on the back of the Navy's own self-contained nuclear project led by Philip Abelson. Abelson's group had previously completed its own thermal diffusion pilot plant. So, on this point I used a poor choice of words. I should have said, Thermal diffusion was initially rejected because it was "cumbersome, relatively inefficient, and, probably, too slow" or something along those lines. However, thermal diffusion---obviously---does work, and as an existing, already proven, off the shelf technology, held some promise for the Japanese as they sought to build their own atomic bomb.

That's it as far as I have been able to determine thus far. More in a moment.
Mr Pellas
at this point I'm a lot more interested in this USN atomic research project.The only reliable source I have for this is a brief one page item from the US Naval Institute Proceedings. If you have any sources to recommend for this subject I'd greatly appreciate it. Thanks

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Re: The Japanese nuclear weapons program

Post by williamjpellas » 31 Dec 2016 21:29

An important factor in what you are posting is whether your translations are from the Kuroda Papers, or from the accompanying Tonizo Report(s), or both. Could you please provide clarification on that point?

Heisenberg's estimate of the nominal (naturally-occurring) critical mass of U-235 might or might not have been off. He appears at first to be badly mistaken about this, but then quickly "corrects" his thinking and related calculations. I am inclined to think that he probably knew full well what it was, based on 1) the 1940 paper circulated by Manfred von Ardenne's laboratory and probably written by Fritz Houtermanns that contained a very accurate estimate of the critical mass as well as an apparently perfectly viable nuclear reactor concept---as I mentioned previously in this discussion thread, and 2) reports of his lecture at the Kaiser Wilhelm Society in Germany, which took place in 1942, in which Heisenberg is said to have described the bomb core of a hypothetical U-235 bomb as being "about the size of a pineapple" which is obviously pretty close. Heisenberg's former Kaiser Wilhelm Institute colleague Dr. Kurt Diebner---the two men intensely disliked one another---is heard on the Farm Hall transcripts telling Heisenberg that he suspected (correctly) that the estate was thoroughly bugged. Heisenberg laughs him off and says "Oh, they wouldn't be so cute as all that", and then keeps on talking, but it seems to me that one must consider the possibility that Heisenberg was mouthing disinformation to the British microphones, whereas Diebner, along with his heereswaffenamt boss, Walter Gerlach, just kept his mouth almost entirely shut. And as I mentioned, the von Ardenne report was surely well known to Heisenberg, so I have a hard time believing he was really that ignorant of the likely configuration of a U-235 atomic fission bomb. (Nishina might have been groping more in the dark; it's hard to say for sure at this point.)

I am aware of the Japan Times article and in fact have posted it in this thread at least once if not more than that. The BBC News piece by Jane Warr gives a different impression. But even the Times states that "...The night the American B-29 warplanes came, Ryohei Nakane had been enriching uranium for Japan’s “super bomb.” ", and "...The 23 pages of Imperial army papers returned to Japan last April offer convincing evidence that Japanese scientists were years from completing their 20-kiloton A- bomb — which would have had more force than the 15- kiloton bomb dropped on Hiroshima but less than the 22-kiloton device that hit Nagasaki." The BBC article describes the Japanese design or design concept as "a weaker weapon", but the Times says its yield would have been more than 15 KT (larger than Little Boy) but less than 22 KT (Fat Man). So, what's going on here? You swear up and down that there was no actual bomb design as such, but both of the most well-known mainstream press articles about the Kuroda Papers obviously claim that actual design or no, there was enough information and calculations and what have you in the papers (and/or as described in the Tonizo Report(s)?) for contemporary scientists to give estimates of the explosive yield of a hypothetical Japanese atomic bomb.

And I don't see you giving any weight whatsoever to F-Go, F-NZ (the end of war crash program in Korea), or---perhaps most important of all---to Lt. Col. Tatsusaburo Suzuki, particularly his 1995 Tokyo press conference. In fact you've never said one word in this thread about any of that. Ever. Suzuki looks more and more like one of, if not the, top men in the entire Imperial Japanese Army nuclear effort. It turns out that one of the scientists on his team proposed building a colossal cyclotron in order to separate U-235; this machine would have weighed 50,000 tons, and is the reason for the curious and, in the AP article about Suzuki's press conference, previously unexplained statement that Japanese scientists had wanted to scrap several Navy warships to use the steel for something-or-other. We now know what that something-or-other was.

Japan ‘came close’ to wartime A-bomb
By Peter Hadfield


https://www.newscientist.com/article/mg ... me-a-bomb/

"A JAPANESE nuclear physicist says that he and many of his colleagues were convinced that they could make nuclear weapons during the Second World War. There was even a plan to drop an atom bomb on the American base of Saipan, an island in the Western Pacific. The only thing that held them back was a lack of resources.

“We believed in 1945 that we could build a bomb,” Tatsusaburo Suzuki revealed last week as the 50th anniversary of the bombing of Hiroshima approached. “But we had to work much harder.”

The critical problem at that stage was separating enough fissile uranium-235 from uranium-238. In the US, which was working with several separation methods, the 3000-tonne cyclotron at the University of California at Berkeley was producing 2.8 grams of uranium-235 a day.

In Japan one of the problems was finding the steel to build a cyclotron. “One of our officers suggested we should scrap five or six heavy cruisers to make a 50 000-tonne facility,” said Suzuki. But the idea was vetoed by the head of the research programme, Yoshio Nishina. He wanted Japan’s nuclear weapons programme to proceed on a more orderly, step-by-step basis.


Suzuki was a lieutenant-colonel in the Japanese army during the war. As a physicist, he became the link between the army and the nuclear weapons research team. Towards the end of the war, he helped to set up five large separators for enriching uranium. Now 83, Suzuki is one of the last surviving members of the team.

Little is known of the research programme, which lasted from 1940 to 1945. Japanese scientists destroyed all records at the end of the war, and gave only minimal cooperation to a postwar investigation by the US. Some of the Japanese scientists published memoirs in later years, but these have never cleared up several enduring mysteries.

The biggest question for American investigators was just how much progress Japan had made in developing nuclear weapons. Suzuki says research was in “a preliminary and primitive stage”. He and his colleagues succeeded in making uranium hexafluoride gas – the first step in the enrichment process – and were trying to separate uranium-235 from uranium-238 using thermal diffusion. “We were not successful in separating uranium-235 to a satisfactory degree,” said Suzuki. “But we were successful in preliminary experiments.”

On the other hand, Suzuki says Japanese scientists were “very advanced” in nuclear theory. Researchers at Kyoto University had calculated that each fission reaction produced 2.6 neutrons – an essential calculation when working out the amount of uranium-235 needed to create a critical mass. “This figure is very close to what is known today – 2.4 neutrons per fission,” says Suzuki. “We thought if we could obtain 1 kilogram of uranium-235, that would be equivalent to 18 000 tonnes of TNT … I was confident at the time we could have built a bomb if we had better equipment.” (Kyoto University was where the Navy's Project F-Go was headquartered and was one of a handful of epicenters of WWII Japanese nuclear weapons R&D, parenthesis mine.)

Many historians and scientists believe Japan got much further in its practical research than Suzuki suggests. The journalist Robert Wilcox in his 1985 book Japan’s Secret War, provides evidence that Japan may have shipped much of its research equipment to Hungnam in Korea, where there was a plentiful supply of uranium and energy. The region is in North Korea, and so is now inaccessible.

Suzuki also confirmed what his colleague Yoichi Yamato wrote in 1976 – that the Japanese army planned to use its A-bomb on Saipan, a Japanese island captured by the Americans in 1944 and used as an air base. Suzuki says he and his colleagues had no qualms about using it if they could."
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Re: The Japanese nuclear weapons program

Post by williamjpellas » 01 Jan 2017 00:46

A quick postscript: estimates for the explosive yield of the American "Little Boy" gun-type U-235 atomic fission bomb range from a low of 12 to 15 KT to a high of 16.7. The figure of 16.7 is probably the most accurate one, as I am given to understand that it comes from a detailed study of the original bomb done by Los Alamos scientists some time in the 1980s or 90s. There may have been some kind of computer simulation or calculations done along with this study, I'm not sure.

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Re: The Japanese nuclear weapons program

Post by Genro » 01 Jan 2017 11:48

Seventy years or so ago there was only a pencil, a piece of paper and a slide rule available for calculating anything and that's all that is necessary.

Estimate of the yield of Little Boy the Hiroshima bomb.

U 235 enrichment 80 %, q = 0.8 Mf = 64 Kg.
Tungsten carbide tamper Mr = 311 Kg. Mt = 375 Kg.
Over the range of q = 0.8 to 1, the critical radius Rc to a first approximation is given by :-

Rc = ( pi Aw) / (2 p Av) { 1/[ 3 (n – 1) Gf* Gs* ]}^1/2.

Aw = atomic mass, Av = Avogadro constant, p = density, n = neutron yield, and Gf*, Gs* are the effective neutron cross-section for fission and scatter respectively.
Gf* = Gf235q + Gf238( 1– q ) and Gs* = Gs235q + Gs238( 1 –q ).
________ Gf_____ Gs.
U235____ 1.24____ 4.56 x10^-24 cm2.
U235____ 0.3_____ 4.8.

Gf* = 1.052×10^-24cm2, Gs* = 4.6 x 10^-24cm2, n = 3, p =18.95 gm/cm3.
Rc =6.63cm , Mc = 23 Kg.
M =64 Kg, R = 9.3 cm, n = 2.64, t = 1 x10-8 sec.

Et = Mt/2 { ( R – Rc )( 1 – (Rc/R)^2)( n – 1)/4t }^2 **.
Et = 5.39 x10^20 ergs and at 4.2 x10^16 ergs/ton TNT :- yield = 12.800 tons TNT.

Dr. Penney estimated from a ground survey a yield of 12+-1 Kilo ton TNT.
** Based on a lecture given by Werner Heisenberg 1945.

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Re: The Japanese nuclear weapons program

Post by Genro » 01 Jan 2017 15:20

Numerous people have written on the subject of Japanese’s atomic bomb from Snell, Wilcox, Dower, Yamazaki, Rhodes etc, to mention only a few. All based on newspaper reports, reminiscences, SCAP reports, hearsay, gossip and wish full thinking (documentary). All profess to be historians if not novelists but none are physicists.

The uniqueness of the Tonizo documents (Kuroda papers) is that they are in places, the minuted form of the actual words spoken. The Japanese language is contextual in nature, brilliant in negotiating intricate social relations, preserving nuances and saving face but is not known for its strength in clarifying thoughts or fostering open debate.

Because of his position in Japanese physics, Nishina is obligated to undertake this project. Within the social restraints outline, Nishina’s ambivalence toward this project is expressed in the technical impediments that he raises regarding the development of the atomic bomb. Such phrases as’ futokusaku’ not recommended and ‘tekito narazaru beshi’ not suitable and ought not to be done. ‘Narazaru’ is negative, a little old fashion and slightly authoritive. These are not the words of someone portrayed as in some books ’hell bent on destroying the world’.

Finally, both America and Japan have different alterior motives. One the one hand America has a sense of guilt and is looking for some major project to justify the atomic bombing and on the other hand Japan seeks victim hood and so belittles the project, if not sweep in under the carpet as did Yamazaki et.el.

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Re: The Japanese nuclear weapons program

Post by williamjpellas » 17 Jan 2017 04:18

Genro wrote:Numerous people have written on the subject of Japanese’s atomic bomb from Snell, Wilcox, Dower, Yamazaki, Rhodes etc, to mention only a few. All based on newspaper reports, reminiscences, SCAP reports, hearsay, gossip and wish full thinking (documentary). All profess to be historians if not novelists but none are physicists.

The uniqueness of the Tonizo documents (Kuroda papers) is that they are in places, the minuted form of the actual words spoken. The Japanese language is contextual in nature, brilliant in negotiating intricate social relations, preserving nuances and saving face but is not known for its strength in clarifying thoughts or fostering open debate.

Because of his position in Japanese physics, Nishina is obligated to undertake this project. Within the social restraints outline, Nishina’s ambivalence toward this project is expressed in the technical impediments that he raises regarding the development of the atomic bomb. Such phrases as’ futokusaku’ not recommended and ‘tekito narazaru beshi’ not suitable and ought not to be done. ‘Narazaru’ is negative, a little old fashion and slightly authoritive. These are not the words of someone portrayed as in some books ’hell bent on destroying the world’.

Finally, both America and Japan have different alterior motives. One the one hand America has a sense of guilt and is looking for some major project to justify the atomic bombing and on the other hand Japan seeks victim hood and so belittles the project, if not sweep in under the carpet as did Yamazaki et.el.

This is among the more sensible comments you have posted in this thread, genro, and you raise a valid point. None of the writers who have explored the WWII Japanese atomic bomb projects are physicists, including me. That is so. And I even sort-of, halfway agree with your summary. It is true, as far as I am concerned, that some in America are "....looking for some major (Japanese) project to justify the atomic bombing" and "...on the other hand Japan seeks victimhood and so belittles the project, if not sweep (it) under the carpet as did Yamazaki et al".


However: I have already addressed your thesis upthread and several pages back, on page 26. This is in my post which begins, "No 'redemption over the bombing' is necessary or needed." I also posted a number of straightforward questions for you to answer regarding the WWII Japanese atomic bomb projects---all of which you have ignored completely. And I have posted numerous quotes, testimonials, and articles from numerous sources, including some of the major military officers involved, particularly Army Lt. Col. Tatsusaburo Suzuki. You have ignored these, as well. By the way, Suzuki himself was a physicist and probably also the top man in the Ni project after Nishina was pushed aside in late 1944 and the Army took direct control. Why doesn't Suzuki's testimony count with you?


So: while it is true that none of the historians are physicists, neither are you---apparently an actual physicist---any kind of historian. If you were, you would know that while the Kuroda Papers are unquestionably one of the most important primary source documents that has emerged from the Japanese nuclear effort, they are in no way the complete record of Project Ni, let alone the complete record of everything the Japanese attempted and accomplished during the war. Not even close.


Therefore, with due respect for your time and diligence in seeking out an apparently correct translation of the Kuroda Papers and in posting them here on AHF---which was no mean feat when they are written in Kanji, an archaic form of Japanese that is nearly extinct today---until and unless you are willing to consult and address the totality of scholarship and documentation about the WWII Japanese nuclear effort, it would seem that this discussion is at an end.
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Re: The Japanese nuclear weapons program

Post by williamjpellas » 17 Jan 2017 04:36

Mr Pellas
at this point I'm a lot more interested in this USN atomic research project.The only reliable source I have for this is a brief one page item from the US Naval Institute Proceedings. If you have any sources to recommend for this subject I'd greatly appreciate it. Thanks


Hi, Carl. There are some good articles around the web about Philip Abelson and the US Navy's own atomic project in WWII.

http://www.atomicheritage.org/profile/philip-abelson

https://www.britannica.com/biography/Ph ... ge-Abelson

https://www.britannica.com/science/tran ... #ref622146 According to this piece, Abelson was a more prominent figure in US and world physics than most realize. He is said to have been the first person, along with Edwin Mattison McMillan, to positively produce and identify a transuranic element, in this case neptunium (element 93 on the periodic table). This work was done at Cal - Berkeley using a cyclotron. Just guessing, but I think this was most likely the one designed by E. O. Lawrence, which also became the basis for Nishina's first cyclotron at the Riken Institute. Nishina's machine was the one he used to measure the neutron fission cross section of uranium. To this day, the Japanese love their cyclotrons. The Riken currently houses one of the the largest ones in the world, the Superconducting Ring Cyclotron (SRC).

http://www.nishina.riken.jp/facility/SRC_e.html

Abelson apparently continued his explorations into the application of nuclear power for submarines even as his thermal diffusion pilot plant was scaled up for use in the Manhattan Project. He is said in the Britannica article that bears his name to have written a report at the end of the war "...that gave birth to the US program in that field". Abelson's R & D during WWII was carried out at the Naval Research Laboratory in Washington, DC, so it would seem logical that his work would have come to the attention of Admiral Hyman Rickover, the "father of the nuclear navy".

The Japanese, by the way, also explored nuclear propulsion as part of the Imperial Navy's nuclear project in WWII. Hidehiko Tamaki, who was a member of the Riken team that went to Hiroshima to collect evidence and conduct field research in the immediate aftermath of the American attack, asserted repeatedly when personally interviewed by Robert Wilcox that the entire purpose of the Japanese nuclear projects was propulsion. Wilcox spoke with Tamaki in the 1980s as part of the research he did for his book, Japan's Secret War. According to Wilcox, Tamaki met him for dinner, then made Wilcox wait for a considerable period of time before he finally looked up from his plate, signaling that it was now alright for Wilcox to speak. All Tamaki would say was that the Japanese atomic project was solely about nuclear propulsion and that there was no attempt to produce a weapon. This was obviously a lie, or rather, a half truth. Japan was interested in nuclear propulsion for submarines and probably also for surface ships, but they were also unquestionably trying to build atomic bombs. Wilcox says that Tamaki didn't like him. It is Tamaki, by the way, who was the source for Genro's oft-repeated "novelist" smear (see Secret War, pgs 34-35). In later years, the Riken sponsored a "Tamaki Award" for promising physics students. He died in 2013 at the age of 103.

http://ribf.riken.go.jp/~dang/tamaki.html

Hope this helps! :milsmile:
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Re: The Japanese nuclear weapons program

Post by Genro » 17 Jan 2017 14:32

From Wiclox's book page 35; I was told by Miss Yokoyama that Tamaki had decided he didn't like me " He's just a novelist".
I concur.

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Re: The Japanese nuclear weapons program

Post by Genro » 27 Jan 2017 15:31

Japanese cyclotrons during WW2.

Riken; 26” 66cm, and 60” 152 cm 9 Mev protons at a beam current of 350 micro-amps
Osaka; 24” 60cm. 5 Mev Deuterons at 20 micro-amps.
Kyoto; 39” 100cm magnet only, completed in 1952.

Assuming Nishina’s 60”cyclotron could develop a magnetic field of 0.7 Tesla then a beam of uranium tetra-chlorine UCl4 accelerated by 35 Kilo volts would subscribe a semi-circular path of about 1.5 meter. The molecular masses of 235UCl4 and 238UCl4 are 375 and 378 respectively and the separation at the collector would be about 6 mm. Neglecting the fact that chlorine has two natural isotopes Cl 35 75.5% and Cl 37 24.5% (UFl6 is too unstable to use) the beam diameter will reduce the efficiency of separation.
If the proton beam of 350 micro-amps is replaced by one of UCl4, this would yield about 2 x 10^15 ions per second or 75 mg/day. Nishina estimated the critical mass of U235 with a reflector as about 10 Kg but pointed out that it does not make a bomb but needs extra say 10 Kg. To produce 20 Kg of U235 at 75 mg/day would take about 370 years.

The alternative separation techniques i.e. Clusius-Dickel column or centrifuge would have required a few thousand of either plus as many circulating pumps etc. Nishina had just two columns and the Osaka centrifuge was only on the drawing board.

Just exactly why American Intelligence came to the conclusion that the cyclotrons could make an atomic bomb and hence destroyed them, beggars belief.

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Re: The Japanese nuclear weapons program

Post by williamjpellas » 20 Feb 2017 03:02

Still at it with your anti-US axe to grind, eh, genro? You just can't help yourself, I guess.

Where and in what document, exactly, did you see evidence that leads you to your statement that "...American intelligence came to the conclusion that the cyclotrons could make an atomic bomb and hence destroyed them"? Considering the fact---which I have mentioned previously in this thread---that Americans invented the cyclotron in the first place, I would imagine they probably had a pretty good idea of what its capabilities were, and were not. And yes, if you want to get pedantic (again), I am well aware that Lawrence's cyclotron was probably more of a refinement of an earlier German concept than it was an original invention.

The reasons why the US destroyed the Japanese cyclotrons were quite obvious. The US paid the lion's share of the blood and treasure necessary to defeat a determined, capable, and fanatical opponent and wanted to secure their hard-won victory. The US also had a monopoly (as far as we can reliably know at present) on atomic weaponry at war's end and was determined to keep that monopoly for as long as possible. Cyclotrons were used by the US, Japan, and probably by Germany to conduct experiments to accurately determine the neutron fission cross section of U-235. Nishina himself, at the Riken Institute, performed such experiments. Meanwhile, Bunsaku Arakatsu, from the Japanese Navy's F-Go nuclear weapons project, was telling anyone who would listen that the US would not long enjoy its preeminent position in nuclear weapons.

Obviously, then, the destruction of the cyclotrons was done to cement the US' position as the preeminent military power in the world and to make 110% certain that Japan was thoroughly beaten and not a threat to rise like a phoenix from the ashes on the wings of her own atomic bombs. Best to be absolutely sure. I suppose Britain would never have done anything so ignorant, gauche, unsubtle and unsophisticated in their own postwar occupation sphere, right? Oops, they did. German wartime nuclear weapons scientist Kurt Diebner (the man behind the 1945 heereswaffenamt hybrid fission-fusion bomb tests at Ohrdurf) wanted to publish a history of the German atomic bomb effort in WWII and was forbidden to do so by the British. What harm could possibly have come from Diebner's book? Wasn't Britain in the driver's seat in the postwar order in the 1950s, along with the other victorious Allied powers? Surely this was overkill along the same lines as what the US did in Japan. Rather draconian of you chaps, wouldn't you say? Except that it wasn't.

All of which is leaving aside the fact that cyclotrons (or cyclotron-derived machines like the Calutron) can be, and were, used in the Manhattan Project specifically to produce fissile material. Yes, it took dozens of these, but nevertheless. Japan was keenly interested in cyclotrons during the war and one of the members of Lt. Col. Suzuki's team proposed the construction of a gargantuan, 50,000 ton machine to make bomb fuel for Japan's atomic bomb----as I have already mentioned and documented in this thread.

It would really be nice if you would cease and desist with your passive aggression and just stick with the facts, but I know you won't. I'm just responding for the sake of anyone reading who is not as familiar with the facts.

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Re: The Japanese nuclear weapons program

Post by Genro » 20 Feb 2017 17:23

As far as I am aware Lawrence and may in the scientific community protested at the destruction of the Japanese cyclotrons even American newspapers treated it as a scandal which led to a government enquiry. The outcome of which was a statements by the Secretary of War that it was a ’mistake’ and due to a breakdown in communications.

‘The destruction of the cyclotrons was done to cement the US position as the preeminent power in the world and to make 110% certain that Japan was thoroughly beaten and not a threat to rise like a phoenix from the ashes on the wings of her own atomic bombs’.
‘The US paid the lion’s share of the blood and treasure necessary to defeat a determined, capable and fanatical opponent and wanted to secure their hard-won victory.’

Of cause Britain was never in the war, it never stood alone for over a year against Nazi Germany. Neither did Britain foster the idea of an atomic weapon or have to cajole the US into taking an interest, and London, Liverpool, Coventry and others where never bombed day and night. (civilian deaths 40,0000.) Fourteen 1000 lb bombs were dropped on my town’s railway works, 51 dead 157 injured not to mention a V2 flying bomb. What where the civilian casualties in America?
The US report on German’s atomic bomb project was a gross distortion until the British Government was persuaded, if not cajoled, by the British Institute of Physics to release the Farm Hall Transcripts for publication. The Japanese atomic bomb project received similar distortions but this time by novelists and so called historians. The Japanese script no doubt perceived as impenetrable compared with German seems to have perpetuated the idea of some dark secret.
In 1945, America having won the war immediately cut off all atomic bomb research with Britain which had then to develop it on its own. It is an example of those ‘special relations’ that are so talked about now!
For some fact it might be worth looking at the Root-Takahira agreement or the Taft-Katsura agreement. Then there is the Paris Peace Treaty of 1919 and the Racial Equality Proposal and then ask what part in the precipitation of the war was America responsible for.

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Re: The Japanese nuclear weapons program

Post by williamjpellas » 21 Feb 2017 20:24

Yes, I am well aware of the standard "explanation" for why the US Occupation forces destroyed Japan's cyclotrons. Yes, some US scientists did protest that event. Very few if any were aware of the Japanese nuclear weapons projects during the war, though they absolutely should have had some inkling that atomic bombs were possible for Japan. That's because so many western scientists visited Japan and in particular, the Riken Institute, in the years between the world wars.
main-qimg-949e17d0a8a99cca2cede946362e6a69.gif
That's Albert Einstein Posing With Japanese Scientists at the Riken
main-qimg-38a437702888dd659e9c46e243d50e0b.gif
In This Photo, Also Taken at the Riken, Nishina is at Far Left, and Werner Heisenberg is Fourth From Left.

Quite obviously, the US high command ordered the cyclotrons destroyed because they knew that Japan had done very advanced nuclear weapons physics research and development, in many cases by utilizing the very machines we are discussing here.
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Re: The Japanese nuclear weapons program

Post by williamjpellas » 23 Feb 2017 06:01

I recently took another look at the two most prominent public domain articles about the Kuroda Papers being returned to the Riken Institute in 2002, and I noticed some details that had escaped me in previous readings.

First, and most important, it appears from the BBC News Article "Atomic Plans Returned to Japan" by Jane Warr that the idea that the Papers contained an actual bomb design, as such, actually came from the Asahi Shimbun Japanese newspaper, and not from the Kuroda Papers themselves. (However, the Papers, as I have stated previously in this thread, definitely do contain a detailed and apparently viable atomic bomb concept, and they also contain considerable and very advanced nuclear weapons physics calculations, as genro's translations certainly illustrate. More on that in a moment.)

The last paragraph of the article, dated 3 August 2002, has the heading "Weaker Weapon" and reads as follows:

"Kuroda, who was a professor emeritus at the University of Arkansas before his death in 2001, kept the documents secret for more than half a century.

His widow has sent the documents to the Riken scientific research institute just north of Tokyo where Kuroda worked as a young man, the Asahi newspaper reported.

A photograph published in the newspaper shows diagrams and drawings of a bomb, together with text written by a military officer who interviewed the scientist at the head of the atomic bomb development team.

But the newspaper says experts who have examined the documents do not believe the bomb would have been very powerful."

http://news.bbc.co.uk/2/hi/asia-pacific/2170881.stm

At the time that I wrote my article, "The Japanese Bomb and Why It Matters"---subsequently published in the June 2004 edition of the Cold War Times---I took the BBC's word for it, and assumed that the Papers contained some kind of bomb design that would have worked had it been translated into a real world device. Since I have now, finally and after a great deal of effort, obtained my own copy of the Papers, I can confirm that they do not include or contain any kind of "diagrams and drawings of a bomb". Therefore: either the Asahi Shimbun had access to some other authentic WWII Japanese papers that did include such a drawing, OR perhaps they had an artist or some expert sketch out their best guess at what a Nishina-Riken-Japanese Army-WWII atomic bomb would have looked like, OR they included some kind of generic photo of a bomb, OR Ms. Warr saw the U-235 machinery concept sketches that are included in the Kuroda Papers and mistook them for a bomb design or schematic of some kind. I won't know for sure until and unless I can find the relevant article(s) from the Shimbun, presumably from around the time that the BBC piece appeared, that is, 3 August 2002.

The letters sent from Kuroda's widow, Louise, to the Riken---included along with my copy of the Kuroda Papers---shed light on a couple of details. First, she confirmed that the Papers were ordered destroyed by the Japanese Army immediately after Emperor Hirohito and the Big Six decided to surrender. Instead, "a friend" gave them to Kazuo "Paul" Kuroda, who kept them safe and, for many years, hidden from the world. In his later years, he would show them to some of his graduate students at the University of Arkansas, and he discussed them openly at a number of professional conferences that he attended, including one in 1989 at which Glenn Seaborg was also present. Second, according to Mrs. Kuroda, she never asked Paul who gave the Papers to him and he never volunteered that information to her. Nor did anyone ever approach him to ask for them to be returned to the Riken during her husband's lifetime. Kazuo himself wondered if the documents in his possession "were the only authentic ones in the world, or could there be others somewhere".

There now seems to be a great deal of question and confusion about Nishina's bomb concept, which was described in considerable detail in the Kuroda Papers. I have read some pieces that claim that he was so far off track that any bomb constructed using his methodology would have been more like a runaway reactor than anything else. On the other hand, he is unquestionably talking about detonating various amounts of U-235, and he includes another source of neutrons---beryllium---as an initiator for the prompt supercritical reaction (atomic explosion). Both of the first Manhattan Project atomic bomb designs featured something nearly identical. The "ABNER" device in the Little Boy bomb and the "URCHIN" utilized in the Fat Man design were both beryllium-polonium structures known as "modulated neutron initiators" that fed additional neutrons into the critical mass in order to kick-start the chain reaction. All sources that I have read are in agreement that the somewhat simpler ABNER was not really necessary in order for Little Boy to go off. Whether it added to the yield and efficiency of that bomb, I don't know, though I would guess that it helped at least a bit. In the Fat Man bomb, the more complex URCHIN was crucial, and that device may not have functioned at all without it.

https://en.wikipedia.org/wiki/Modulated ... _initiator

More to follow....
Last edited by williamjpellas on 23 Feb 2017 19:33, edited 7 times in total.

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williamjpellas
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Re: The Japanese nuclear weapons program

Post by williamjpellas » 23 Feb 2017 07:00

The other most prominent mainstream media article from about the same time that the Kuroda Papers were returned by Kuroda's widow to the Riken Institute is the Japan Times piece, "Japan's A-bomb Goal Still a Long Way off in '45", dated 7 March 2003.

http://www.japantimes.co.jp/news/2003/0 ... K5ofdQrLs0

This one is all over the map.

First, we get this from author Kenji Hall:

"All official records were believed to have been burned in the closing days of the war, forcing historians to piece together an answer from less reliable clues.

Now, long-lost wartime documents are setting the record straight.

The 23 pages of Imperial army papers returned to Japan last April offer convincing evidence that Japanese scientists were years from completing their 20-kiloton A- bomb — which would have had more force than the 15- kiloton bomb dropped on Hiroshima but less than the 22-kiloton device that hit Nagasaki."

But immediately after that statement, we have this:

"Historians say that not only had Japan’s scientists underestimated how much of the rare isotope uranium-235 they would need for the bomb, they misunderstood the mechanics of an atomic explosion.

“The documents are one of a kind. We can finally prove that even if Japan had built a bomb, it would not have been powerful at all,” said Masakatsu Yamazaki, a professor of science history at the Tokyo Institute of Technology who analyzed the papers. “And it might have taken them another decade to complete one.”"

Okay. So the same article tells us:

1) Japan was trying to complete a 20 kiloton atomic bomb---a device that would actually have been considerably stronger than the US Little Boy bomb that destroyed Hiroshima---but somewhat less powerful than the subsequent Fat Man that fell on Nagasaki with an explosion equivalent to 22 to 24 kilotons of TNT.

2) Japan's scientists underestimated how much U-235 they would need.

3) They also "misunderstood the mechanics of an atomic explosion", so much so that---

4) ...."even if Japan had built a bomb, it would not have been powerful at all...and it might have taken them another decade to complete one".

Umm, exactly what is going on here? Are the Kuroda Papers describing a Japanese atomic bomb concept that would have yielded / might have yielded 20 KT? (Or 26KT---genro's translation gives this figure but he says it is somehow not a projected bomb yield.) Or are they describing something that even had it been built, "....would not have have been powerful at all"?

How can the same article be making such obviously contradictory statements? Clearly somebody is screwing up, somewhere.

From genro's posts, it is clear that Nishina was making quite advanced calculations, and also that he had in mind a bomb powered by U-235 and detonated at least in part by a beryllium neutron initiator. The Americans called their own initiator a "spark plug" in the Manhattan Project. Obviously these or very similar ideas worked perfectly well for the US and Allied scientists. So it would seem that at least in this part of his concept, Nishina was clearly on the right track.

By the way, another researcher brought something to my attention about Nishina's mention of beryllium. This could be an indicator that he was thinking not of a gun-type bomb---which I have always assumed, given that it is the simplest to engineer and build---but rather of an implosion bomb. From what genro has posted, unless I'm missing something it doesn't look like Nishina specifies what sort of detonation method his bomb would utilize beyond the inclusion of a beryllium "spark plug".

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Re: The Japanese nuclear weapons program

Post by steverodgers801 » 24 Feb 2017 03:18

considering the US spent a billion dollars and vast resources to build a bomb, I don't know where Japan would have been able to even consider starting to try building a bomb

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