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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Japan Times WWII Japanese Nuke Article

Post by williamjpellas » 18 Dec 2003 10:02

Japan's own efforts to build a bomb are difficult for many here to accept because of the bombings of Hiroshima and Nagasaki, and the widespread feeling that Japan would never have even considered such a brutal attack. Japan Times 7 March 2003.

Slowly but surely, the truth about the Japanese atomic bomb projects in WWII is coming to the surface. But just as surely, the Japanese continue to try and spin doctor their way out of owning up to reality and responsibility. The latest disingenuous Japanese attempt at "setting the record straight", is from the Japan Times English language online newspaper, dated 7 March 2003.

There are three features of this article that stand out. First is the admission that, far from being innocent nuclear victims, the Japanese themselves were trying to build a uranium fission bomb with a yield of at least 20,000 tons of TNT. This would have made it about 25 % larger than America's "Little Boy" uranium bomb that hit Hiroshima. (Best estimate of that device's explosive yield was 12-15 KT.)

Having finally come clean about this fact, however, the Japanese immediately try to downplay the progress they made. This is the second point that stands out: In a very subtle move, the Japan Times article tries to suggest that the Japanese scientists were on the "slow neutron reaction" track, although they don't come right out and say it in so many words. While it is possible that they were in fact doing slow neutron reaction research, if they were, it was in parallel with their fast neutron reaction bomb research---the same thing the Americans were doing. (The US Navy had a small, almost forgotten WWII research program into the slow neutron reaction, which would later bear fruit, along with other work, in the production of reactors for powering ships and submarines.)

Remember that Yoshio Nishina, the lead scientist of the Imperial Japanese Army's Riken Institute atomic bomb project, did understand the fast neutron reaction very well. He had published scholarly papers on the subject prior to Japan's attack on Pearl Harbor, and he was also able to extrapolate a number of highly classified facts about Little Boy using nothing more than empirical observation and a slide rule. (For example, he was able to calculate to a high degree of accuracy both the actual number of neutrons that fissioned in Little Boy's core, and the force of the blast.) Given these truths, how likely is it that Japanese science in WWII was "nowhere close to a bomb"? The BBC article on which this thread is based quotes "experts" who have studied the Riken Institute / Nishina warhead design and pronounced it "not very powerful". I'd like to know what that means---"only" 2 kilotons? 5? 10?---but rest assured, if the Japanese warhead really was relatively weak, it was not because Japanese science didn't understand how to produce a supercritical chain reaction detonation. No way. It was because the engineering of the compression of the two sub-critical masses was lacking. (Couldn't ram the two pieces of the warhead core together fast enough.) A technical mechanical engineering problem like this is a totally different problem than a lack of understanding of bomb physics, which is what they're trying to say now.

It also strikes me as unlikely that Nishina would make the calculation error that the article says the blueprints show he did make. Supposedly, Nishina thought that the warhead would go off if the two subcritical warhead components were compressed in 1/20th to 1/30th of a second, and not the 1/200th to 1/300th of a second that was truly necessary. I wonder how likely it is that the world class physicist Nishina would forget to carry the ten. But even if he did make such an error in 1943 (when the Kuroda documents apparently were written), the Japanese warhead design would still have worked even at the slower compression speed had it had sufficient highly enriched uranium. And this is leaving aside any later research under Nishina at Riken and Bunsaku Arakatsu at Hungnam, Korea, for which there is currently little or no existing Japanese documentary evidence. (But we know it did happen. I would really like to see a bomb physicist do a calculation of the explosive force of a fission bomb with a slower compression speed, so we would know once and for all what kind of yield the Japanese weapon would actually have had---again, assuming they did not do any further refinement of their warhead design after 1943, an unlikely proposition, it seems to me. Unless the Nishina interview took place in 1943 and the warhead design was done later; the Japan Times article does not specify this.)

The third point is that the article implies---not so subtly---that anyone who thinks there might be more to the story of Japanese bomb making efforts at Hungnam is basically a right wing whacko and/or believes in little green men. Robert Wilcox's book Japan's Secret War does a great job of documenting the many suspicions of late WWII and Occupation US intelligence that something big was going on. Wilcox cites a number of original OSS and G-2 documents that he had to pry out of the Suitland, MD archives using the Freedom of Information Act. It is also a fact, contrary to the Japan Times article, that American intelligence was never able to penetrate Hungnam in any effective or comprehensive way. A B-29 that may or may not have been snooping around in the fall of 1945 was shot down by Russian Yak fighters when it came too close. We also know that the Russians got a lot of heavy water from the gargantuan Hungnam military industrial complex after the War, and that they captured a number of high ranking Japanese atomic scientists working there who were later ruthlessly tortured for information. It is a fact that Soviet intelligence was the best in the world during WWII. It even managed to penetrate the Manhattan Project, and there were at least two moles working for the Soviets in the American atomic programs. Atomic espionage was one of Moscow's highest wartime priorities, and obviously the Russians thought there was a lot to be gained from the Japanese scientists whom they captured in Korea, but we are to believe nothing was going on there? Uncle Josef Stalin may have been many things, but he was nothing if not a ruthless pragmatist. I have long suspected that the biggest reason the Russians jumped into the Pacific War at the very end was to get their hands on Japanese atomic research at Hungnam.

The bottom line is that initially, the official Japanese and American mantra was, "Well, yeah, the Japanese had a few bright guys, but their overall science was poor and they were nowhere close to atomic weapons."

Then, after Deborah Shapley's 1978 Science magazine article started to expose them, it was "Well, yeah, they did a little preliminary work in the field, but they were nowhere close to a bomb."

Now, after Wilcox, the FAS assessment, and the BBC article, it's, "Yeah, they did some work and even produced a warhead design, but they were nowhere close to a bomb and certainly would never have done the unthinkable and actually used it, as those evil Americans did."

Baloney. :x

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Post by Pansaar Jaeger » 19 Dec 2003 04:14

gabriel pagliarani wrote:NO URANIUM LIGHT ISOTOPES ( U235, U233) NO BOMB!

...Niels Bohr, Nobel prize and nazi party member, argued that the secret of the bomb was not in design (easy to do) but in reaching as soon as possible the critical mass of 9 Kg. of U235, U233 fixile isotopes each bomb...

Niels Bohr, Nazi Party member?
Is this all wrong, then?

When Denmark was overrun and occupied by the Germans in 1940, Bohr did what he could to maintain the work of his institute and to preserve the integrity of Danish culture against Nazi influences. In 1943, under threat of immediate arrest because of his Jewish ancestry and the anti-Nazi views he made no effort to conceal, Bohr, together with his wife and some other family members, was transported to Sweden by fishing boat in the dead of night by the Danish resistance movement.

Bohr was one of the thousands of Jews who escaped Nazi occupation in 1943, travelling via Sweden to the US. While in exile there he worked together with Einstein, among others, on the construction of the first atom bomb, though he later campaigned against its use, publishing an open letter to the United Nations in 1950 asking for international co-operation on nuclear weapon development.

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Post by gabriel pagliarani » 29 Dec 2003 22:48

The effective rule played by Niels Bohr is one of the most hidden secrets of all WW2 and the official version about his own escape in England is not true, but only "socially" acceptable. He was not a sure of this! Heisemberg was not alone and a "deep throat" among Allieds cooperated with him till the escape of Fermi in USA. The secret meeting between Bohr and Heisemberg in an hotel of 3rd Reich really occurred. About Clusius's Z-potential diffusion high-vacuum tube mentioned by WilliamJPellas in other parts of the forum, that technology based on electronic driven Gaussian magnetic field used to split heavy U238 ionized flux from U233-235 ones by mean of a Magnetron valve was developed in late 1954 in UK as evolution of a cathodic grid array. No contest and out of thread "A-bomb". A lot of words without a theme having a closed sense from him. Where is Jap Uranium? 8) I have never seen a paper-project exploding. Go to for such an hoax.

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Re: Reply to Caldric

Post by DrG » 02 Jan 2004 03:35

gabriel pagliarani wrote:Some days after the discovery Quirino Majorana, the finest mathematical brain of Fermi group, was throwed down in Thyrrenian Sea out of the ferry from Naples to Palermo. Not a single phormula or document was found in his luggage: the killers raped all his writings. In my opinion Majorana found the critical mass of the bomb: but some secret service oughted to quit him definitely. Someone says he was fascist killed by Soviets, someone from westerns.

I've to make a correction: the scientist who disappeared was Ettore Majorana, nephew of Quirino (who was a professor too, and who opposed Einstenian relativity, disliked also by Ettore). His fate is still unknown, and I think it's difficult to say he had been killed, it's quite possible he committed suicide or even that he fled somewhere hiding his true identity.
About his fascist faith, it has been a taboo for years, but it's certainly demonstrated by his letters; moreover he was openly a Germanophile and a close friend of Heisenberg. Nevertheless he had a Jew friend (Emilio Segrè, who hid the pro-Nazi letters of Majorana for years after WW2); but he disliked Fermi (who had a Jew wife) and hand't good relations with the other members of via Panisperna laboratories (except with Giovanni Gentile jr., son of the omonimous Fascist philosopher, and Edoardo Amaldi). By the way, the other scientists (Fermi, Segrè, Pontecorvo, Racah, Pincherle, Fubini-Ghiron, Fano, Wick, etc.) were all Jews or with Jew relatives (except Gentile, Majorana, Amaldi and Rasetti). Moreover Amaldi and Rasetti left Italy in 1939 because they were anti-Fascists (or, more probably, they were against the alliance with Nazi Germany); Amaldi returned because his famly wasn't allowed to leave Italy. In other words, except Gentile (a good physic, but nothing exceptional) and Majorana (who was a genious,but "disappeared"), all the other were anti-Nazi, or because of their ideals or because of the Jewish origin of them or of their relatives.

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Post by gabriel pagliarani » 02 Jan 2004 20:50

You are right. Ettore non Quirino. You pointed the real fact that the only not-jew or not jew-linked-to fine italian scientist was simply cut off. Why I must believe the official version of a fascist elimination of the only friend PNF had in Panisperna Group?

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OT, sorry

Post by DrG » 03 Jan 2004 02:50

gabriel pagliarani wrote:Why I must believe the official version of a fascist elimination of the only friend PNF had in Panisperna Group?

In fact we must not. ;) If you are interested there is an excellent book about the fate of Majorana: La Scomparsa di Ettore Majorana: un Affare di Stato? by prof. Umberto Bartocci (you may read also this article:

Edit: updated the second link.
Last edited by DrG on 04 Jan 2004 13:05, edited 1 time in total.

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Post by gabriel pagliarani » 04 Jan 2004 10:46

Thank you! Your post confirms that an international "nuke-team" plotted against Mussolini and Hitler at the very beginning, probably till 1935-6. WW2 secretely began 4-5 years before the official incomings. Never forget that Emilio Segre was considered an Hero of the Soviet Union. 8)

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On The Subject of Uranium Separation

Post by williamjpellas » 27 Mar 2004 06:13

With respect to Mr. Pagliarani for his fascinating information about the possible "war in the shadows" over atomic secrets prior to the "official" start of WWII, he is mistaken when he states that the Clusius tube I was referring to was a British invention from the 1950s. In 1945, Henry De Wolf Smyth produced "Atomic Energy for Military Purposes:The Official Report on the Development of the Atomic Bomb Under the Auspices of the United States Government". In Chapter IX, General Discussion Of The Separation Of Isotopes, he has this to say: " The possibility of producing an atomic bomb of U-235 was recognized before plutonium was discovered. Because it was appreciated at an early date that the separation of the uranium isotopes would be a direct and major step toward making such a bomb, methods of separating uranium isotopes have been under scrutiny for at least six years. Nor was attention confined to uranium since it was realized that the separation of deuterium was also of great importance....The kinetic theory of gases predicts the extent of the differences in the rates of diffusion of gases of different molecular weights.... Such thermal diffusion effects were first used to separate isotopes by H. Clusius and G. Dickel in Germany in 1938. They built a vertical tube containing a heated wire stretched along the axis of the tube and producing a temperature difference of about 600 deg C. between the axis and the periphery. The effect was twofold. In the first place, the heavy isotopes (in the substances they studied) became concentrated near the cool outer wall, and in the second place, the cool gas on the outside tended to sink while the hot gas at the axis tended to rise. Thus thermal convection set up a countercurrent flow, and thermal diffusion caused the preferential flow of the heavy molecules outward across the interface between the two currents.... The theory of thermal diffusion in gases is intricate enough; that of thermal diffusion in liquids is practically impossible. A separation effect does exist, however, and has been used successfully to separate the light and heavy uranium hexafluorides."

Thomas Powers' excellent book Heisenberg's War---despite its mistaken conclusions about Heisenberg himself---is another good source for learning about how England first considered the problem of uranium separation in order to produce a bomb. The British MAUD committee in fact completed preliminary calculations on the industrial process necessary to produce a fission bomb in the late 1930s, including studies based on the construction of thousands of thermal diffusion Clusius tubes.

As to the issue of the Japanese uranium, again, as I myself have stated, it is unlikely---though not impossible---that Japan alone possessed enough of an atomic industrial infrastructure to complete the separation of enough U-235 for at least one warhead, ie, the rumored-to-have-been-test-fired genzai bakudan. Basically, the situation was this: Japan had the more advanced atomic science, Germany had more industry and more uranium, so the logical solution was to mate Germany's raw materials and tools with Japan's science. It nearly worked. It has also been rumored for years that the uranium captured by the US from the German submarine U-234 ended up in the American "Little Boy" bomb that destroyed Hiroshima.

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Japan's Secret War Author Comments

Post by williamjpellas » 10 May 2004 15:34

A few weeks ago I forwarded this thread to Robert Wilcox (, the author of the book "Japan's Secret War", which started me on my own research into this topic. Here is the text of Wilcox's email to me after he read all the posts:


Sorry, couldn't get very deep into this. Only read your pieces. Very good. I tried to register so I could commend you on line but could not get by the red tape. First it said I hadn't filled out everything and then it said I'd
already registered. I gave up.

In a general vein, everybody was working on the a-bomb prior to the war in Europe, especially after Germans published about fission. Since Fermi came from Italy, I don't doubt the Italians had something going. They are traditionally very good scientists.

One thing I saw that caught my eye. Somebody - could have been the Italian - made a statement that indicated if the Japanese didn't have tons of uranium they never could have done it. Wrong. They could have done it with a variety of fissionable elements. Thorium, for one. I know they were gathering that. I just never paid much attention. But that is a whole new avenue to explore.

I'll come back to this when I get some time and read what he said. Thanks for fowarding.



Note especially the whole thorium angle. There is at least one Joint Chiefs of Staff report unearthed by Wilcox that catalogs the large amounts of that element Japan was mining during the War. (The same report is cited in both "Secret War" and its most notable opposition book, John Dower's "Japan In War and Peace".) A fission bomb could in fact be produced using thorium, which is probably the most desireable naturally-occurring atomic element after uranium in terms of suitability for weapons. Could it be that Japan was forced to consider alternatives due to scarcity of uranium? Might this be the explanation for the purported-to-be-test-fired Japanese bomb? It's not likely, as the whole clandestine German-Japanese submarine network tried repeatedly to send uranium and not thorium (as far as is known) to Japan, and most available records indicate little or no effort by Japan to prepare thorium for detonation. However, it should be added that the vast majority of available documentation regarding Japan's WWII atomic projects has to do with the mainland "Ni" program at the Riken Institute north of Tokyo. There is not very much documentation, unfortunately, for the "F-Go" program which was based in what is today Hungnam (Konan), North Korea. It was "F-Go", not "Ni", so the story goes, that actually completed a single prototype warhead and set it off right after Nagasaki was bombed by the Americans. So, the thorium possibility is still worthy of further inquiry.

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Re: Japan's Secret War Author Comments

Post by DrG » 10 May 2004 16:37

The Thorium theory is really very interesting. While I'm pretty sure that Japan (or Germany or anybody except the USA) hadn't the technical knowledge and the resources to enrich enough Uranium for a bomb, with Thorium it's a fully different thing.

Thorium can be used in a bomb only if transmuted into Uranium-233, and to do so you need a reactor (needless to say that Japan hadn't it) or an accelerator, like a cyclotron. By the end of the war, Japan had 5 cyclotrons (they were dumped in the ocean by the men of Alsos in 1945). The only problem is that the output of U-233 from 1 (or even 5) ciclotron would be at least tiny (but here I'd like the help of an expert). Once Thorium has been "bombed" by neutrons, it must be separated from U-233 (but also a few U-232) using chemical processes (as happened for the separation of Plutonium from Uranium in the bars used in reactors), that are not too difficult and certainly far less expensive than the physical (mechanical) process used to enrich Uranium (in other words, to separate U-238 from its fissile isotopes, that are less heavy).

I think that a good technical reading just to start before talking about A-bomb developement is:
From that site:

The nuclear-explosive nuclide uranium-233 is, like plutonium, essentially non-existent in nature. Also like plutonium, however, it can be produced by exposing a common, naturally occurring nuclide to a flow of neutrons in a nuclear reactor or an accelerator. The "fertile" nuclide in this case – which, upon absorbing a neutron, undergoes two subsequent nuclear transformations to become U-233 – is thorium-232. As noted above, U-238 is the analogous fertile nuclide for the production of Pu-239. The thorium-232 isotope constitutes 100 percent of naturally occurring thorium, which is about three times as abundant in the Earth's crust as uranium is.

The properties of U-233 as a nuclear explosive would seem to make it quite attractive to bomb-makers. Its bare-sphere critical mass is very similar to that of delta-phase plutonium-239, which is to say it's only 50 percent greater than that of alpha-phase plutonium-239 and about one third that of uranium-235. (Its greater reactivity compared to that of U-235 is reflected in the fact that a mixture of only 12 percent U-233 in U-238 is considered weapon usable, as opposed to the corresponding figure of 20 percent for U-235.) The rate of neutron generation from spontaneous fission in U-233 is low enough, moreover, to permit its use in the simpler gun-type weapon designs as well as in implosion designs; and its decay heat is one sixth that of Pu-239. Its gamma-ray dose rate is in the same range as that from weapon-grade plutonium.

Notwithstanding these apparent attractions, no country has yet produced U-233 for nuclear weapons as far as is publicly known. Neither has U-233 been produced in significant quantities in civilian nuclear-energy operations (although its use as the fissile component in a "thorium fuel cycle" has been much analyzed and discussed). There are two main reasons that the U-233 option has not been exercised so far:

First, it's much easier to produce plutonium-239 than U-233 in reactors fueled by natural uranium, which are the kinds of reactors with which countries seeking weapons tend to start. If a country seeking weapons has the capacity to make enriched uranium (which is needed to fuel the type of reactor best suited for making U-233), that country's easiest route to bombs is to use that capacity instead to enrich natural uranium to weapon-grade in U-235.

Second, U-233 is invariably accompanied by at least a small admixture of U-232, whose radioactive-decay chain contains a powerful emitter of a very penetrating gamma ray (thallium-208). Even at an initial U-232 concentration as low as 1 part per million, the gamma dose-rate after two years of build-up of its decay chain is twice as great as the gamma dose-rate from correspondingly aged reactor-grade plutonium. This would pose significant problems in the form of radiation exposure to workers in a weapon program (or a nuclear-power program) using U-233, and it would also make weapons containing U-233 quite difficult to conceal.
These reasons continue to make U-233 production an unlikely path for new proliferators to try to take to a bomb, and the fact that no significant stocks of this material appear to exist anywhere in the world mean it is also not a theft risk.
Last edited by DrG on 10 May 2004 18:00, edited 1 time in total.

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Re: Japan's Secret War Author Comments

Post by DrG » 10 May 2004 16:44

williamjpellas wrote:Since Fermi came from Italy, I don't doubt the Italians had something going. They are traditionally very good scientists.

Just a footnote to this thread, Dr. Enrico Cernuschi had told on the forum that in 1934 Fermi had started researching for the construction of a nuclear reactor for a submarine. But in 1937 Marshal Badoglio, chief of Supreme Staff and of the CNR (Consiglio Nazionale delle Ricerche = National Research Council; it is the central direction of the Italian scientific research), stopped the program because it was too expensive.

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Post by DrG » 10 May 2004 16:51

I've found some interesting articles about the Japanese nuclear program in WW2, but just for comparison I suggest to read something about the Manhattan Project, at least to see the huge difficulities (also of theoretical physics) and resources needed (see for example this photo of the K-25 plant of Oak Ridge) for the developement of the A-Bomb. There are many books and sites about Manhattan, a simple description of it (expecially for the technical matters) can be found here:

Now let's return to Japan.



Nuclear Weapons History: Japan's Wartime Bomb Projects Revealed
By Deborah Shapley

[This is an abridged and slightly edited version of the article
appearing in Science, 13 Jan 1978, pp. 152-157]

A little-publicized chapter in the history of atomic weapons
is the Japanese effort to develop an atomic bomb during World War
II. The effort centered around Japan's university physics
laboratories, and its chief figure was Yoshio Nishina, who was
Japan's leading scientist and a physicist of international
Much has been written about how the United States and Britain
during the war were concerned that the Germans, who had
discovered atomic fission in the 1930's, would develop the
world's first superbomb based on this principle. Indeed, the
German wartime atomic research effort was a major rationale for
the Manhattan Project in the United States.
But in the case of Japan it seems that no one in the U.S.
government took the possibility of a Japanese atomic bomb project
Still more curious is the curtain of silence which the
Japanese themselves seem to have pulled over the subject, and
which they have kept tightly drawn since the war. Even the
Americans who interrogated Nishina concluded that Japan had had
no atomic bomb project.
Even today in Japan, when historians tell Japanese that there
was such a project, many Japanese react with disbelief. Japan's
postwar official policy, that she does not and never will seek to
be a nuclear-armed country, seems to have inhibited discussion of
the project. Japan's wartime atomic research, in Japan, has
become a social secret.
The effort is documented in two authoritative Japanese
histories. One is a history of science and technology in Japan
of which volume 13, published in 1970, deals with science and
technology during World War II. The second is a social history
of science, by Tetu Hirosige, published in 1973, that has an
entire chapter devoted to the wartime science mobilization,
including among other things, atomic research. Nishina died in
1951 and there is no known account by him of his wartime
activities. But there are other firsthand accounts, notably the
diary of Masa Takeuchi, a worker at Nishina's laboratory who was
assigned to the thermal diffusion project, and a memoir of
Bunsabe Arakatsu, a physicist from Kyoto.
These materials have been collected independently by Herbert
F. York, Jr., director of the Program in Science, Technology and
Public Affairs at the University of California at San Diego, and
Charles Weiner, professor of history of science at the
Massachusetts Institute of Technology (M.I.T.). Weiner is now
completing a full-scale historical study of the subject.
It is no surprise that physicists in Japan were tempted,
around 1940, to study the military applications of fission.
Throughout the 1930's, Japan had kept pace with the exciting
developments in physics -- with theory in Europe and experimental
techniques in the United States. Nishina spent several years in
Copenhagen in the laboratory of Niels Bohr.
The Japanese also became schooled in the techniques of the
cyclotron, through a small machine built at the Riken, Nishina's
laboratory in Tokyo, and by sending a much younger physicist,
Ryokichi Sagane, to Berkely to work under E.O. Lawrence.
Lawrence arranged for the contribution of a 200-ton magnet for a
second cyclotron at the Riken. The cyclotron was not finished
until 8 years later, shortly before the war's end.
While Japanese physics at the outset of the war was strong
enough to carry researchers naturally into the problem of the
fission weapon, it was "too brittle," to bring the project to a
successful conclusion. Nishina, Sagane, and some others were
clearly world class physicists; but Japanese physics included a
"comparatively large number of nonadvanced fields."

Scientists Suggest Project

The scientists themselves initiated atomic bomb research in
September 1940. Army sponsorship was arranged, and "fairly
large-scale research" began at the Riken "from December, 1940."
The years 1940 and 1941 were a period of intense military
interest in the possibilities of atomic weapons. In 1941, Prime
Minister and War Minister Hideki Tojo's order for investigation
of the possibilities for a fission weapon were passed on to the
But in the first of what was to be a series of uncoordinated
orders to the scientists, the Navy also engaged the Riken's
services, and launched an inquiry into the feasibility of the
weapon in late 1942. This led to the "Physics Colloquium," a
galaxy of Japan's leading scientists who met for ten sessions
between December 1942 and March 1943, to investigate the
feasibility of Japan's achieving a weapon.
The Colloquium's conclusion, relayed to the Navy in March
1943, was that an atomic bomb would be impossible "even" for the
United States for the current war. Another account says that it
estimated Japan would need "ten years" to develop such a weapon.
So it seems that the scientists viewed the project as extremely
long term at best, or, as one of them would later write: "if not
for this war then in time for the next one."
On the other hand, the military viewed the bombs as something
to be pursued immediately, although it often did not back up this
commitment with resources. The planners of Pearl Harbor, it is
known, assumed that the war in the Pacific would be short,
brutal, and brilliant. They believed that America, then being
irrevocably drawn into hostilities in Europe, would retreat
quickly from fighting on a second front in the Pacific.
It is well established that another faction in the Japanese
government was restrained and realistic, and probably this
element took a wait-and-see attitude, and relegated the problem
to the scientists. But the zealots were still there. A new
book, Enola Gay*, quotes the physicist Tsunesabo Asada's
recollection that discussions of the subject right after Pearl
Harbor were characterized by a "mood of blind patriotism" and
"promises of generous funding."
Arakatsu, writing after the war, said he did atomic bomb
research to prevent young scientists from being sent to fight and
die. Takeuchi, in his diary, which was also compiled after Japan
had surrendered, says that he did the research only when ordered,
and that other Riken scientists were equally unenthusiastic.
However well these rationales suited the postwar climate of
opinion, there is evidence that the actual situation was
different. At several junctures when the scientists might well
have closed down the work altogether -- for they knew better than
anyone how great were the odds against success -- they kept the
work going.
September 1940 had been one such juncture; March 1943 was
another. Following the physics colloquium's negative report, the
Navy branch that had sponsored it lost interest in the atomic
bomb. But Nishina managed to keep the Riken atomic research
going. The Army, which had been funding the work since December
1940, became the sole sponsor of Riken atomic research.
But this was by no means the beginning of coordination among
the military. Just as the Naval Institute of Technology bowed
out of support of atomic research in March 1943, another Navy
branch, the Fleet Administration Center, was sponsoring another
group of researchers at Kyoto University, under Arakatsu, to work
toward an atomic bomb.
The Kyoto project began in 1942 and was enlarged with a grant
of 600,000 yen in 1943. Among other things, the money went to
construct a cyclotron at Kyoto university. But the military's
commitment to the work -- however strong in spirit -- was not
backed up with material aid.
Takeuchi's diary also indicates that atomic research at the
Riken was anything but coordinated. Takeuchi complains that
although he was told to consider the possibility of separating
uranium by electromagentic means, Miyamoto, who had developed
such a method, had gone to another university. So Takeuchi gave
up on electromagnetic separation because he couldn't have
Miyamoto around to help. Similarly, although Takeuchi found
gaseous thermal diffusion "the most promising" method, Eiichi
Takeda, who had done small-scale thermal diffusion work using a
glass column, was not assigned to the project. So, Takeuchi had
to start from scratch.
After much delay and red tape the apparatus was ready in a
separate building in early 1945. It took Takeuchi 18 months to
do this work, whereas physicists in the United States were able
to set up comparable or larger experiments in a matter of weeks.
In April 1945, as the gaseous thermal diffusion apparatus and
the cyclotron were finally working together in an experimental
mode, the building housing the apparatus -- but not the cyclotron
-- was ruined in the American bomber raids over Toko. The
wrecking of their experiment caused the scientists to give up on
their atomic research -- that is, until after Hiroshima.
After Hiroshima, the government seems to have become
interested yet again in having an atomic bomb. According to one
account, the morning after the bomb was dropped, Nishina was
summoned and asked first whether the bomb could have been atomic
and "whether Japan could have one in six months."
Nishina was flown over Hiroshima on 8 August. The pattern of
destruction and the presence of radiation convinced him the bomb
had been an atomic one. Arakatsu reached a similar conclusion
when he was flown over the city on 10 August.
After Hiroshima, the scientists at the Riken resumed their
atomic studies, but with a different goal, namely to learn about
the effects of the weapons at Hiroshima and Nagasaki. Philip
Morrison, now of M.I.T., who served on the Manhattan Project, and
arrived in Japan on the first day of the American occupation,
recalled what he found when he visited the Japanese scientists.
Nishina was "guarded and self contained ... impassive and
almost antagonistic," toward the arriving Americans. On the
other hand, many other Japanese physicists seemed to welcome the
Americans with "rueful pleasure." Morrison recalls that the
feelings of internationalism, of a bond among physicists, seemed
to reestablish itself between the Americans and Japanese -- with
the exception of Nishina. And as for whether Japan had been
developing an atomic weapon, he recalls, "they didn't talk about
it and we didn't ask about it much."
The Riken buildings and laboratories "looked frayed,
unrenovated, starved of attention." In places, work had just
stopped and people had gone away. "As we looked around we
concluded this could not have been the site of a Japanese
Manhattan Project."
It is not surprising that U.S. scientists visiting Japan who
knew firsthand the "panoply" of installations and people that was
the American Manhattan Project, concluded that the Japanese could
not have had a comparable project.
So it went in the fall of 1945. Visiting American scientists
were sympathetic to Japanese "colleagues" and tended to find no
evidence of a bomb project. The Japanese were silent to their
American military interrogators; thus the military, by and large,
also found no evidence of such a project.
The Joint Chiefs of Staff ordered on 30 October that all
research facilities and equipment "on atomic energy and related
subjects be seized." "No research ... on atomic energy shall be
permitted in Japan."
On 24 to 26 November 1945, on orders from General Groves'
office, which oversaw the Manhatttan Project, American military
teams proceeded to hack Japan's five cyclotrons, including the
two at Riken, to pieces. The remains were dumped into the sea.
In the furor which arose in the United States, scientists' and
citizens' groups protested to the Secretary of War. For the most
part they were told that the destruction order had been a
mistake. But this confession of error only whetted the appetites
of many of the scientists, who had now become embroiled in a
fight for future civilian control of atomic energy. The
destruction of the cyclotrons was used to show how insensitive
the military would be to the special needs of science and

Admiral Nakamura "Talks"

But was the destruction completely mindless?
There is a U.S. Army document, dated before the order to
destroy the cyclotrons, in which a Rear Admiral Nakamura reports
in detail on atomic bomb research conducted during the war at
Kyoto University. Among other things, it says that the project
included the construction of a cyclotron.
So far there is no evidence that the report reached Groves'
office. But its existence suggests that some Americans learned
of the wartime atomic research and concluded that the cyclotrons
should be destroyed.
On 31 December when Lee DuBridge, director of the M.I.T.
Radiation Laboratory, wrote to the acting secretary of war on
behalf of the scientific community, suggesting that U.S.
scientists restore "at least Dr. Nishina's 60-inch [cyclotron]"
in view of the great loss to physics and the world, Acting
Secretary of War Kenneth C. Royall replied:
It is unsound to intimate that scientists are citizens of
the world alone, are internationalist and not loyal to
their native lands and are never willing participants in
the ambitions of dictators or tyrants. The evidence to the
contrary is too overwhelming for the American public to
accept this thesis, for modern war is scientific and total
war in toto. Without the scientist or the technical worker
the terrible instruments of destruction of the present day
would not have been possible.
In the interests of the country and of the American
scientists themselves, I believe you should exert your
influence to prevent any campaign for the restoration of a
cyclotron to the Japs at this time. ...
The Riken was dissolved "as a result of the defeat," although
Nishina later raised money to reestablish it on a different
footing. Elsewhere in Japan, physicists were restrained from
atomic research, and allowed only to work on applications to
biology and medicine. But without the big equipment to support
pioneering work, Japanese physics did not reattain the prominence
it had in the 1930's.
Could the Japanese have had an atomic bomb in World War II?
All the historians, Japanese and American, echo the conclusion of
the Physics Colloquium, that Japan did not have the uranium,
resources, or organization for a full-scale Manhattan-style
project. So the danger -- as turned out to be the case with the
Germans -- was not a real one.
But the historical importance of the project lies not in the
fact that Japan failed but that she tried, and that Japan's
postwar attitude that she, as the one nation victimized by atomic
weapons, is above seeking to acquire them for herself, is not
historically accurate. The historical record shows -- on the
basis of the eagerness of her military and the willing
cooperation of her scientists -- that if other factors had made a
bomb possible, the leadership -- which by the end of the war were
placing their own youth in torpedoes to home them on the
advancing U.S. fleet -- would not have hesitated to use the bomb
against the United States. -- Deborah Shapley

*G. Thomas and M.M. Witts, Enola Gay (Stein & Day, Briarcliff
Manor, N.Y., 1977). $11.95.

--------------------[First insert (p. 153:2)]--------------------
Derek de Solla Price, Avalon Professor of the History of Science
at Yale, with Eri Yagi Shizume, a Yale graduate student,
investigated Japan's wartime atomic bomb effort and published a
letter in the Bulletin of the Atomic Scientists in 1962, seeking
more information on the project. But none was forthcoming.
Price believes the effort was serious enough to "change the moral
and ethical relationship between Japan and the United States."

"Japan's attempt to acquire an atomic weapon during the World
War II changes the moral and ethical relationship between Japan
and the United States that has grown up over the use of the
atomic bomb against Japan. The story has been that the Americans
were guilty and the Japanese were innocent and blameless; that
the Americans developed this terrible new weapon and proceeded to
commit an atomic rape of the then-helpless Japanese."
"But the fact that the Japanese were trying to develop the
bomb, too, means that America was in an arms race with Japan as
much as she was with Germany."

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Post by DrG » 10 May 2004 16:56


Japanese Nuclear Weapons Program
Excerpted from The Making of the Atomic Bomb

(pp. 327, 346, 375, 457-459, 580-582, 612)

By Richard Rhodes

Japanese studies toward an atomic bomb began first within the military. The director of the Aviation Technology Research Institute of the Imperial Japanese Army, Takeo Yasuda, a lieutenant general and an alert electrical engineer, conscientiously followed the international scientific literature that related to his field; in the course of his reading in 1938 and 1939 he noticed and tracked the discovery of nuclear fission. In April 1940, foreseeing fission’s possible consequences, he ordered an aide who was scientifically trained, Lieutenant Colonel Tatsusaburo Suzuki, to prepare a full report. Suzuki went to work with a will.

Lieutenant Colonel Suzuki reported back to Lieutenant General Yasuda in October 1940. He confined his report to a basic issue: the availability to Japan of uranium deposits. He looked beyond Japan to Korea and Burma and concluded that his country had access to sufficient uranium. A bomb was therefore possible.

Yasuda turned then to the director of Japan’s Physical and Chemical Research Institute, who passed the problem on to his country’s leading physicist, Yoshio Nishina. Nishina, born late in the Meiji era and fifty years old in 1940, known for theoretical work on the Compton Effect, had studied with Niels Bohr in Copenhagen, where he was remembered as a cosmopolitan and exceptional man. He had built a small cyclotron at his Tokyo laboratory, the Riken, and with help from an assistant who had trained at Berkeley was building in 1940 a 60-inch successor with a 250-ton magnet, the plans for which had been donated by Ernest Lawrence. More than one hundred young Japanese scientists, the cream of the crop, worked under Nishina at the Riken; to them he was oyabun, "the old man," and he ran his laboratory Western-style with warmth and informality.

The Riken began measuring cross sections in December. In April 1941 the official order came through: the Imperial Army Air Force authorized research toward the development of an atomic bomb.

Enrico Fermi and Edward Teller were not, however, the first to conceive of using a nuclear chain reaction to initiate a thermonuclear reaction in hydrogen. That distinction apparently belongs to Japanese physicist Tokutaro Hagiwara of the faculty of science of the University of Kyoto. Hagiwara had followed world fission research and had conducted studies of his own. In May 1941 he lectured on "Super-explosive U235," reviewing existing knowledge. He was aware that an explosive chain reaction depended on U235 and understood the necessity of isotope separation: "Because of the potential application of this explosive chain reaction a practical method of achieving this must be found. Immediately, it is very important that a means of manufacturing U235 on a large scale from natural uranium be found." He then discussed the linkage he saw between nuclear fission and thermonuclear fusion: "If by any chance U235 could be manufactured in a large quantity and of proper concentration, U235 has a great possibility of becoming useful as the initiating matter for a quantity of hydrogen. We have great expectations for this."

Both the Army Air Force and the Imperial Navy had moved separately since 1941 to promote atomic bomb research. The Riken, Yoshio Nishina’s prestigious Tokyo laboratory, primarily served the Army, exploring the theoretical possibilities of U235 separation by way of the gaseous barrier diffusion, gaseous thermal diffusion, electromagnetic and centrifuge processes. In the spring of 1942 the Navy committed itself to developing nuclear power for propulsion:

The study of nuclear physics is a national project. Research in this field is continuing on a broad scale in the United States, which has recently obtained the services of a number of Jewish scientists, and considerable progress has been made. The objective is the creation of tremendous amounts of energy through nuclear fission. Should this research prove successful, it would provide a stupendous and dependable source of power which could be used to activate ships and other large pieces of machinery. Although it is not expected that nuclear energy will be realized in the near future, the possibility of it must not be ignored. The Imperial Navy, accordingly, hereby affirms its determination to foster and assist studies in this field.

Soon after that nonviolent affirmation, however, the Naval Technological Research Institute appointed a secret committee of leading Japanese scientists–corresponding to the US National Academy of Sciences committee–to meet monthly to follow research progress until it could report decisively for or against a Japanese atomic bomb. The committee included Nishina, who was forthwith elected chairman. An elderly appointee was Hantaro Nagaoka, whose Saturnian atomic model had nearly anticipated Ernest Rutherford’s planetary model in the early years of the century.

The Navy committee met first on July 8 with the Navy’s chief technical officers at an officers’ club at Shiba Park in Tokyo. It noted that the United States was probably working on a bomb and agreed that whether and how soon Japan could produce such a weapon was as yet uncertain. To the task of answering those questions the Navy appropriated 2,000 yen, about $4,700, somewhat less than the Uranium Committee had summoned from the U.S. Treasury at Edward Teller’s request at the beginning of the American program in 1939.

Nishina hardly participated in the Navy committee meetings. The fact that he was already working for the Army probably constrained him; the two services, both of which were responsible directly to the Emperor without detour through the civilian government, operated far more independently than their American counterparts and were increasingly bitter rivals. Nishina was coming to conclusions of his own, however, and at the end of 1942, when the Navy committee began to report discouragement, he met privately with a young cosmic-ray physicist in his laboratory, Tadashi Takeuchi, told his young colleague he meant to carry forward isotope separation studies and asked him to help. Takeuchi agreed.

Between December 1942 and March 1943 the Navy committee organized a ten-session physics colloquium to work through to a decision. By then it was understood that a bomb would necessitate locating, mining and processing hundreds of tons of uranium ore and that U235 separation would require a tenth of the annual Japanese electrical capacity and half the nation’s copper output. The colloquium concluded that while an atomic bomb was certainly possible, Japan might need ten years to build one. The scientists believed that neither Germany nor the United States had sufficient spare industrial capacity to produce atomic bombs in time to be of use in the war.

After the final March 6 meeting the Navy representative at the colloquium reported discouragement: "The best minds of Japan, studying the subject from the point of view of their respective fields of endeavor as well as from that of national defense, came to a conclusion that can only be regarded as correct. The more they considered and discussed the problem, the more pessimistic became the atmosphere of the meeting." As a result the Navy dissolved the committee and asked its members to devote themselves to more immediately valuable research, particularly radar.

Nishina continued isotope studies for the Army, deciding on March 19 to focuses on thermal diffusion as the only practical separation technology at a time of increasing national shortages. He spoke to his staff of processing several hundred tons of uranium after first building laboratory-scale diffusion apparatus. He envisioned a major program run in parallel, as the Manhattan Project was beginning to be, with weapon design and development proceeding simultaneously with U235 production.

Meanwhile a different branch of the Navy, the Fleet Administration Center, sponsored a new project in atomic bomb development at the University of Kyoto, where Tokutaro Hagiwara had made his startling early prediction of the possibility of a thermonuclear explosive. The university won support in 1943 to the extent of 600,000 yen–nearly $1.5 million–much of which it budgeted to build a cyclotron.

Progress towards a Japanese atomic bomb, never rapid, slowed to frustration and futility across the middle years of the Pacific war. After the Imperial Navy had bowed out of atomic energy research Yoshio Nishina had continued patriotically to pursue it even though he privately believed that Japan in challenging the United States had invited certain disaster. On July 2, 1943, Nishina had met with his Army liaison, a Major General Nobuuji, to report that he had "great expectations" for success. He noted that the Air Force had asked him to study uranium as a possible aircraft fuel, as an explosive and as a source of power, and he had recently received a request for assistance from another Army laboratory, which had contributed 2,000 yen to his expenses. Nobuuji promptly discouraged such consultations. "The main point," Nishina agreed, "is to complete the project as rapidly as possible." His calculations, he told Nobuuji, indicated that 10 kilograms of U235 of at least 50 percent purity should make a bomb, although cyclotron experiments would be necessary to determine "whether 10 kg. Will be sufficient, or whether it will require 20 kg. Or even 50kg." He wanted help finishing his 60-inch cyclotron:

The 250-ton, 1.5 meter accelerator is ready for operation except for certain components which are unavailable as they are being used in the construction of munitions. If this accelerator is completed we believe we can accomplish a great deal. At this moment the U.S. plans to construct an accelerator ten times as great but we are unsure as to whether they can accomplish this.

The previous March Nishina had discarded as impractical under wartime conditions in Japan all methods of isotope separation except gaseous thermal diffusion. Otto Frisch had tried gaseous thermal diffusion (differing from Philip Abelson’s liquid thermal diffusion) at Birmingham early in 1941 and proved it inadequate for separating uranium isotopes, but Nishina had no knowledge of that secret work. The Riken team had designed a thermal column much like the laboratory-scale column Abelson had built at the Naval Research Laboratory in Washington: of concentric 17-foot pipes, the inner pipe heated to 750 F—electrically heated in the Riken configuration—and the outer pipe cooled with water.

Nishina did not meet again with Nobuuji until seven months later, in February 1944, when he reported difficulty producing uranium hexafluoride. His team had managed to develop a method for generating elemental fluorine but had not yet been able to combine the gas with uranium using an old an inefficient process that Abelson in the United States had discarded before he began his thermal diffusion studies. Nishina also had a problem with his diffusion column that Abelson would have appreciated: it leaked. "To achieve an airtight system," Nishina told Nobuuji, "we used [sealing] wax and finally achieved our goal. Solder could not be used because of the corrosive properties of the fluorine." He was "in the middle of developing this [hexafluoride-generating] process but can see the end in sight." His 1.5 meter cyclotron was now in operation but only at low energy; his explanation for that compromise comments pointedly on the condition of the Japanese industrial economy by 1944:

We have been unable to obtain any superior, high-frequency-generating vacuum tubes…for the cyclotron… As a result of this constraint, the low operating voltages limit the population of neutrons we can produce…. In order to liberate many high-energy neutrons, a high-voltage vacuum tube is required. But, unfortunately, they are difficult to acquire.

By summer Nishina’s group had manufactured some 170 grams of uranium hexafluoride— in the United States hex was now being produced by the ton—and in July attempted a first thermal separation. Gauges at the top and bottom of the column, intended to measure a difference in pressure—showing that separation was taking place—indicated no difference at all. "Well, don’t worry," Nishina told his team. "Just keep on with it, just keep giving it more gas."

He reconvened with Nobuuji on November 17, 1944, to report that "since February of this year there has not been a great deal of progress." He was losing as much as half his hexafluoride to corrosion effects:

We thought the materials we had used to make this apparatus for working with the [hexafluoride] were made of impure metals. Therefore we next used the most highly-refined metals available for the system. However, they were still eaten away. It was therefore necessary to reduce the pressure of the system…to compensate for this erosion.

The cyclotron was operating at a higher but not yet full power; Nishina was using it, he told Nobuuji, "to assay the concentrated, separated material." Significantly missing from the November 17 conference report is any mention of measurable separation of U235 from U238. Nishina’s staff had understood for more than a year that he did not believe his country could build an atomic bomb in time to affect the outcome of the war. Whether he continued research out of loyalty, or because he thought such knowledge would be valuable after the war, or to win support for his laboratory and deferment from military service for his young men, the bare record does not reveal. On the occasion of the November 17 conference he once again complained of the lack of sufficiently powerful vacuum tubes for his cyclotron and told Nobuuji, contrary to the evidence of the experiment, that the Riken’s efforts at isotope separation were "now at a midpoint in their practical solution." Nobuuji might have been more helpful if he had understood even the most basic facts of the work. An exchange between the tow men late in the meeting indicates the military liaison was as innocent of nuclear physics as a stone:

Nobuuji: If uranium is to be used as an explosive, 10kg is required. Why not use 10kg of a conventional explosive?

Nishina: That’s nonsense.

Friday April 13 [1945], and on the night of that unlucky day B-29’s bombing Tokyo bombed the Riken. The wooden building housing Yosio Nishina’s unsuccessful gaseous thermal diffusion experiment did not immediately burn; firemen and staff managed to extinguish the fires that threatened it. But after the other fires were out the building suddenly burst into flame. It burned to the ground and took the Japanese atomic bomb project with it.

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Post by DrG » 10 May 2004 17:04

In this article there is also a passage about Hungnam.


Japan's A-bomb goal still long way off in '45

The Associated Press

The night the American B-29 warplanes came, Ryohei Nakane had been enriching uranium for Japan's "super bomb."

Ryohei Nakane, a former scientist at Riken Institute, speaks about Japan's wartime A-bomb project.

By the next morning -- April 13, 1945 -- all that remained of his samples and his laboratory at Riken Institute was charred, splintered wood and broken glass.

For nearly six decades, historians have been unable to solve one of the mysteries of Japan's World War II A-bomb project: How close were Japanese scientists to building the bomb before the U.S. air raid stopped them?

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.

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."

Nakane has been telling a similar story for years.

Yoji Shimada, a public relations worker at Riken, displays handwritten notes that form part of the only surviving record of that research.

"We were carrying out our research so leisurely. None of us thought we would finish before the war ended," Nakane, 83, said in a recent interview at his Tokyo home.

More than a half-century after the war, Japan's A-bomb project is only a historical footnote. Few Japanese have even heard of their government's wartime nuclear program.

Scientists and military officers who were there have written memoirs and talked publicly about their work. But over the years, speculation and conspiracy theories have clouded the facts and raised doubts about the participants' accounts.

Japan's own efforts to build a bomb are difficult for many here to accept because of the bombings of Hiroshima and Nagasaki, and the widespread feeling that Japan would never have even considered such a brutal attack.

Every year, the two cities honor more than 200,000 people killed or wounded by the two U.S. atomic bombs, and the ceremonies are nationally televised.

As the only nation to have suffered a nuclear attack, Japan has been one of the most outspoken advocates for a global ban on nuclear weapons. It has vowed never to possess, build or trade nuclear weapons and has used this stance to upbraid countries with nuclear ambitions, including North Korea.

But Tokyo hasn't always escaped its own criticism.

Last May, Prime Minister Junichiro Koizumi's top aide, Chief Cabinet Secretary Yasuo Fukuda, appeared to signal a shift away from the antinuclear doctrine by saying Japan was not legally prohibited from having atomic arms.

China, South Korea and Russia immediately protested, prompting Koizumi to reiterate Tokyo's long-standing policy against nuclear weapons. Fukuda later complained that he had been misquoted.

Surprisingly, the reaction in Japan was muted.

"I think younger Japanese might not be that strongly opposed since they were born after the war and probably have never even heard about their government's wartime atomic program," said Yuzo Fukai, an atomic energy expert and former Nihon University professor.

The treasure-trove of wartime papers could change that.

Sneaked out of the country just after the war by former University of Tokyo professor Kazuo Kuroda, who left for the United States, the papers were sent to Riken Institute, north of Tokyo, by Kuroda's widow months after his death in Las Vegas in 2001.

The documents -- the only surviving record of Japan's A-bomb research -- read like a blueprint for the bomb.

Among the papers are several pages of handwritten notes taken by an army officer during a June 1943 interview with Yoshio Nishina, the country's leading physicist. Nishina, who had once worked with atomic pioneer and Nobel laureate Niels Bohr in Copenhagen, headed the project's 100 scientists beginning in the early 1940s.

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.

But making U-235 proved to be no easy task.

By early 1945, Nishina's team was still struggling to make U-235 from uranium hexafluoride gas in a leaky chamber using a technique known as gaseous thermal diffusion, said Yamazaki of the Tokyo Institute of Technology. In the United States, scientists years earlier had ruled out the technique as too unwieldy.

"Given the inefficiencies of that method, Nishina would have needed thousands of tons of ore," Yamazaki said.

Years later, one of the project's physicists, Tatsusaburo Suzuki, said they had managed to make only about 5 kg of impure U-235 -- far short of what they needed for an atomic weapon.

Uranium wasn't their only concern. Wartime rationing made equipment scarce and money even harder to come by, and scientists had to make do with only one industrial-size cyclotron and four smaller ones to purify fissionable uranium.

Scholars estimate that the army spent the equivalent of $500,000 -- a pittance compared with the roughly $2 billion the United States shelled out for the Manhattan Project. A parallel Japanese navy project, which had no chance of success, cost $150,000.

So stretched were the country's resources that, at one point, military leaders considered scrapping a battleship to supply steel to the army's A-bomb team, said Nakane, the former scientist, who is now an honorary director at Riken.

But at the root of Japan's failure was Nishina's flawed theory about an atomic blast.

To generate an atomic explosion, Nishina knew he had to trigger a chain reaction of U-235. Experts agree that has to occur within 1/200th to 1/300th of a second. In the documents, Nishina says he thought he could do it in 1/20th to 1/30th of a second.

"That's equivalent to the slow-fission reaction in an out-of-control nuclear reactor. An explosion of that magnitude wouldn't be very strong at all," Yamazaki said. "Only years after the war did he realize that his calculations were wrong."

Not everyone believed the Japanese were so far off.

Beginning in the late 1940s, speculative reports citing U.S. and Japanese military intelligence sources concluded that Japan's wartime government had successfully completed an atomic test explosion in August 1945 near a uranium ore processing plant in Hungnam, Korea.

However, postwar U.S. scientific missions to Korea, which was under Japanese colonial rule from 1910 to 1945, found no evidence to back those claims, said Walter Grunden, a professor at Bowling Green State University in Ohio who is finishing a book on the topic.

Grunden said neither U.S. spy photographs of the site nor corporate records from Nihon Chisso, the Japanese company that owned most of the plants in Korea during the war, reveal any A-bomb research activity.

Nakane agrees. When U.S. warplanes destroyed the Riken labs, Japan still hadn't done any work on bombshell design or conducted a single experimental explosion, he said.

"Completing the bomb wasn't Nishina's priority. Advancing Japan's scientific research and saving scientists from the war were more pressing concerns," Nakane said.

The Japan Times: March 7, 2003
Last edited by DrG on 10 May 2004 17:20, edited 2 times in total.

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Post by DrG » 10 May 2004 17:08

This article deals also with research made in Hungnam.


San Diego Union-Tribune
(Page A-25)

New evidence tracks Japan's efforts to create atomic bomb

Richard Benke
01-Jun-1997 Sunday

LOS ALAMOS, N.M. -- When a captured Nazi U-boat arrived at Portsmouth, N.H., toward the end of World War II, the American public was never told the significance of what was on board.

The German submarine was carrying 1,200 pounds of uranium oxide, an ingredient for an atomic bomb, bound for Japan. Two Japanese officers on board were allowed to commit suicide.

Two months later, in the New Mexico desert, the United States detonated the first atomic bomb, a prelude to the obliteration of two Japanese cities.

Unknown to many of the people who built those bombs, not to mention the public, Japan was scrambling to build its own nuclear weapon.

Some of the evidence was the uranium aboard the U-boat that surrendered in the North Atlantic on May 19, 1945, shortly after Adolf Hitler committed suicide.

Documents now declassified, including the sub's manifest, show there were 560 kilograms of uranium oxide in 10 cases destined for the Japanese army, and two Japanese officers were aboard, accompanying the cargo.

`This crazy idea'

"Germany was collapsing. They had a lot of good uranium. Somebody got this crazy idea of taking it to Japan," says physicist Herbert York, director emeritus of the University of California's Institute on Global Conflict and Cooperation.

"The Japanese officers insisted on being given the right to commit suicide."

Germany's Zeit-TV has aired interviews with crewmen recalling the Japanese officers who killed themselves and were buried at sea.

The uranium oxide is believed to have gone to Oak Ridge, Tenn., bolstering supplies for the Manhattan Project, the U.S. bomb-building program.

It was even possible -- but not probable -- that some of the uranium headed for Japan reached there aboard the Enola Gay, the B-29 that dropped the atomic bomb on Hiroshima on Aug. 6, 1945, says U.S. Energy Department archivist Skip Gosling. The bomb dropped on Nagasaki on Aug. 9 used plutonium, not uranium.

No secret

The fact that Japan had been struggling to produce a bomb has been known for decades. How far Japan got remains unclear.

It's also unclear whether President Truman knew about Japan's program when he ordered the bomb dropped on Japan. Several Manhattan Project scientists said in interviews they knew nothing of Japan's atomic bomb program until after the war.

"I don't think anybody knew," York said in San Diego. "We didn't think the Japanese were doing anything. We were worried about the Germans."

Would knowledge of Japan's nuclear program have changed the minds of people critical of Truman's decision to drop the bomb?

"I think if there were clear evidence of this, it would indeed help to mollify in some way some of the people who are coming out with criticism of our government in using the bomb," says Steve Stoddard, an engineer who worked 30 years at Los Alamos.

Greg Mello of the anti-nuclear Los Alamos Study Group counters, "It's incredibly irrelevant."

U.S. bombings

The bomb dropped on Hiroshima left almost 130,000 people dead or wounded and leveled 90 percent of the city. The Nagasaki bomb left about 75,000 casualties.

Military leaders at the time estimated an invasion of Japan would have cost the invaders 2 million lives.

Mello contends Japan's atomic bomb efforts were never a threat. But Robert Wilcox, author of "Japan's Secret War" (Marlowe & Co.), a book about Japan's bomb project, says documentary evidence suggests Japan may have gotten further on the bomb than did Germany.

"I know the Japanese were trying to make a bomb all through the war and would have done so had we not ended the war," Wilcox said by phone from his Los Angeles home. "I have documents showing one of the ways they were going to use it was to put it in kamikaze bombers and send it against the invasion fleets."

After Japan surrendered on Aug. 15, 1945, the occupying U.S. Army found five Japanese cyclotrons, which could separate fissionable material from ordinary uranium. The Americans smashed the cyclotrons and dumped them in Tokyo Harbor.

Wilcox, who updated his book in 1995 with newly declassified material, says the Japanese also built six large separators.

Some doubts

Most historians and scientists, including York, say Japan never came close to producing an atomic bomb.

"We had hundreds and hundreds of separators," says John Hopkins, a retired Los Alamos scientist. "We used silver bars out of Fort Knox to make the low-resistance coils and made hundreds of these mass separators in lines in big banks in buildings. Those were run day and night to separate U-235 from natural uranium. This was separated one atom at a time."

For all that, he says, America produced only four bombs' worth of U-235, a > fissionable uranium isotope.

"So I would be very surprised if the Japanese had enough uranium," says Hopkins, who joined Los Alamos National Laboratory in 1960 and was associate director for nuclear weapons. He is now a member of the Los Alamos Education Group, established to counter what it considers nuclear misconceptions.

"To suggest the Japanese were close to a nuclear capability is nonsense," he says.

Program under way

But there was a program, Hopkins acknowledges.

By most accounts, Japan's wartime atomic bomb efforts were headed by Yoshio Nishina, who had earlier worked in Copenhagen, Denmark, with atomic pioneer Niels Bohr.

The diary of Masa Takeuchi, a worker assigned to Nishina's thermal diffusion separation project, says Nishina wanted to process hundreds of tons of uranium at the rate of 300 milligrams per day, according to the U.S. journal Science.

According to Japanese science historian Tetsu Hiroshige, preliminary research for a Japanese bomb program began in 1940, and the program called F-Go, or No. F (for fission), began at Kyoto in 1942.

However, a memoir by Kyoto physicist Bunsabe Arakatsu says the military commitment wasn't backed up with resources, and the 1978 Science article concluded the danger of a Japanese atomic bomb "was not a real one."

Wilcox says documents suggest Japan's military took over the program late in the war with help from Japanese industry and built the separators. He says Japan searched for uranium, buying $25 million worth in China.

Facilities moved

Wilcox and Washington, D.C., researcher Charles W. Stone have documents suggesting Japan might have moved its nuclear operations to Korea after U.S. B-29 raids dropped conventional bombs on Japan.

Postwar documents show U.S. concern about a Japanese plant in Hungnam, now part of North Korea, which was captured by Soviet troops at war's end.

"Consistent rumors from the Hungnam area have dealt with the possibility of atomic research being conducted there," says a U.S. Army 24th Corps document.

It says the mysterious output of the Hungnam plant was collected every other month by Soviet submarines.

The document seems to partly corroborate an Oct. 3, 1946, report by The Atlanta Constitution describing a plant in Konan, the Japanese name for Hungnam.

The Constitution writer, David Snell, reported he was a 24th Corps investigator when he learned of the Hungnam plant from a Japanese officer.

Japanese success?

Snell said the officer, whom he wouldn't identify, claimed Japan detonated a small atomic device Aug. 12 on an island off Hungnam three days before Japan's surrender.

He said the Japanese destroyed the plant, including incomplete bombs, hours before the Soviets arrived.

Immediately after Snell's article, U.S. investigators began reinterviewing Japanese sources about Hungnam, documents show. At least two sources said the plant had nothing to do with atomic research, interrogation reports say.

Snell said his source told him the Japanese moved their atomic operations there because of the B-29 raids.

"We lost three months in the transfer," Snell quoted him as saying. "We would have had (the bomb) three months earlier if it had not been for the B-29."

Akira Yamada, a leading World War II historian who teaches at Tokyo's Meiji University, said he doubts there was a Japanese atomic bomb program at Hungnam.

Not a word

Yamada says he has seen no documentary evidence of it, nobody associated with any atomic research there has ever come forward, and no wartime leader ever mentioned atomic research at Hungnam, although other secret research -- into chemical and biological weapons -- came to light.

However, it is clear that Japan's nuclear efforts were interrupted in April 1945 when a B-29 raid damaged Nishina's thermal diffusion separation apparatus.

After the Hiroshima bombing four months later, the Science report said, Nishina was summoned by Japanese commanders who asked about the atomic bomb and "whether Japan could have one in six months."

But it was just a few days after the Nagasaki bombing that Japan surrendered.

While many people around the world were horrified by the bombings, many were overjoyed. An unidentified man from West Australia, writing in a guest book at the science museum at the Los Alamos National Laboratory, had this to say:

"My mother, sister and I were in a POW camp in Java (Djakarta) when the first bomb went off. As a reprisal, the Japanese were going to place all the camp residents in barges and sink them in the Java Sea. The second bomb saved our lives -- and all those innocent women and children held in POW camps all over Java and Sumatra and no doubt elsewhere.

"I am grateful."

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