pdf - WHALE

contains billions of micro-pores or holes of specific and tiny size,
through which the atoms of different isotopes diffuse at slightly
different rates of speed. "The original estimate was that 5,00 of
these barriers would be needed for nearly complete separation, as
opposed to 22,000 centrifuges." 21 The other process was thermal
diffusion that was already examined more closely in chapter 7.
The thermal diffusion method is mentioned briefly in the
published Farm Hall transcripts during the conversations of the
German scientists on the day of the Hiroshima bombing by
Weizsacker. 24 Bernstein notes of this method that it was being tried
by Korsching, and that it consisted of a "glass tube and heating coil
to separate isotopes. It never worked well for uranium." 25 But what
Bernstein has described is the original Clusius-Dickel tube for
thermal diffusion, a process that was not efficient, as Bernstein
correctly indicates. However, a different method of Clusius tubes
was described by Wilcox in reference to the Japanese program:
What the Nishina group finally did settle on was a process called
thermal diffusion. This had been one of the first isotope separation
processes devised. Bu until it was perfected by two German scientists,
Klaus Clusius and Gerhard Dickel, in 1938, it had not been practical.
Stated simply, thermal diffusion relied on the fact that light gas moves
toward heat. Clusius and Dickel constructed a simple device consisting
chiefly of two metal tubes placed one inside the other. The inner tube
was heated; the outer tube was cooled. When the apparatus was turned
on, the lighter U-235 moved to the heat wall; the U-238, to the cold
wall. Convex currents created by this movement sent the U-235
upward; the U-238 downward. The result was something like a heated
house in winter; hot air rising, cold air staying at the bottom. At a
certain point the U-235 at the top could be collected, and new gas
pumped in. It was a simple and rapid way to get relatively large
concentrations of U-235. 26
And with repeated passes through a series of such vessels, purity
would be increased. In any case, there is some discrepancy in the
23
Bernstein, op. cit., p. 119, n. 28.
24
Ibid., p. 199.
25
Ibid., p. 83, n. 27.
26
Robert K. Wilcox, Japan's Secret War, p. 95, emphasis added.
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