Rainer Karlsch, author of Hitler’s Bombe, reveals “a previously unpublished diagram of a German nuclear weapon”:
Shortly after the end of the war in Europe, an unknown German or Austrian scientist wrote a report that describes work on nuclear weapons during the war. This report, which RK discovered after Hitlers Bombe was published, contains both accurate information and less accurate speculation about nuclear weapons, and may well include some information from the Manhattan Project – the word “plutonium” is used, for example. Unfortunately, the title page is not included and there is no other evidence of who composed it. However, this individual does not appear to have been a member of either the mainstream German uranium project or the group working under Diebner.
What the report does demonstrate is that the knowledge that uranium could be used to make powerful new weapons was fairly widespread in the German technical community during the war, and it contains the only known German diagram of a nuclear weapon (figure 2). This diagram is schematic and is far removed from a practical blueprint for an “atomic bomb”.
The diagram appears in a Physics World article co-authored by Union College historian Mark Walker.
The BBC notes the report appears to have drawn on the official history of the Manhattan Project by Henry De Wolf Smyth, entitled Atomic Energy for Military Purposes: The Official Report on the Development of the Atomic Bomb Under the Auspices of the United States Government (The Smyth Report). That report revealed the word “plutonium” (coined under wartime secrecy of the Manhattan Project) and the concept of a “tamper” to reduce the critical mass necessary for a chain reaction—both appear in the report discovered by Karlsch.
Karlsch and Walker note the estimate of a critical mass of slightly more than 5 kg for a plutonium bomb could not have been derived from the Smyth Report because “such detailed information was not included in the Smyth report.”
Maybe I am missing something here, but the Smyth Report does explain the role of tampers in Chapter XII:
In a uranium-graphite chain-reacting pile the critical size may be considerably reduced by surrounding the pile with a layer of graphite, since such an envelope “reflects” many neu-trons back into the pile. A similar envelope can be used to reduce the critical size of the bomb, but here the envelope has an addi-tional role: its very inertia delays the expansion of the reacting material. For this reason such an envelope is often called a tamper. Use of a tamper clearly makes for a longer lasting, more energetic, and more efficient explosion. The most effective tamper is the one having the highest density; high tensile strength turns out to be unimportant. It is a fortunate coincidence that mate-rials of high density are also excellent as reflectors of neutrons.
It seems to me the drawing is not really all that revealing.
The one interesting thing—to me at least—is that the design looks like a gun-type assembly using plutonium, which is infeasible. But I don’t read German and the image is fuzzy.