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."
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....