WWII Atom bomb survey

The atom bombs were very "war changing" weapons, maybe you should learn about when, where and why they were dropped?

 

Let's try to get something straight here, "heavy water" (deuterium) isn't a necessary ingredient to the production of a fission weapon. Neither of the American "atomics" used the stuff as a moderator to produce the fissile material. The Hanford Plant converted to a deuterium moderator/control system post war. Until then it used the Fermi graphite reactor design to make plutonium. "Heavy Water" isn't/wasn't an absolute required component.

Throughout the war Heisenberg continued to believe that many tons of the rare isotope uranium-235, or of plutonium (an impossible quantity for any country to obtain in his estimate) would be needed for a bomb, rather than the tens of kilograms actually required.

Upon hearing of the atomic bomb dropped on Hiroshima, Heisenberg dismissed the reports saying; "I consider it perfectly possible that they [the Allies] have about ten tons of enriched uranium," Heisenberg says, "but not that they can have ten tons of pure U-235." (the separated isotope)

This faulty estimate, apparently made early in the war and reiterated at Farm Hall, was an error of far-reaching consequence. With an exaggerated notion of the task, the Germans ruled out the possibility that a bomb could be built during the war and instead focused on reactors, which could also be used to generate plutonium for an eventual bomb. A further effect of the mistake was to encourage a false sense of security, which deprived the German project of the kind of urgency that drove the Allies.

To get a chain reaction in natural uranium you need a moderator to slow down the neutrons that are generated from fission. This was widely known in the world of physics. Two moderators were believed to be possible: carbon in the form of graphite, or "heavy water" (D2O, Deuterium) . Walter Bothe, the leading experimental nuclear physicist in Germany, did the crucial experiment and concluded that carbon in the form of graphite would not work. In America, Enrico Fermi did a similar experiment and concluded that graphite was marginal, but a possibility.

He (Fermi) suspected that an impurity in the graphite was responsible for the problem. Leo Szilard, who was working alongside Fermi, and had actually "patented" the concept of a fission bomb in the mid-thirties, had studied chemical engineering before going into physics. He remembered that electrodes of boron carbide were commonly used in the manufacture of commercial graphite. It was known that one atom of boron absorbs about as many slow neutrons as 100,000 atoms of carbon. Very small boron impurities would "poison" the graphite for use as a nuclear reaction moderator. Szilard therefore went around to the American graphite manufacturers and convinced one of them to make boron-free graphite.

Using this pure graphite as the moderator, the American group achieved a controlled chain reaction on December 2nd, 1942. The German team, however, felt they needed to use heavy water (Deuterium). Ordinary water contains heavy water at a rate of about 1 part in 5,000 to 10, 000. The two can be separated by repeated electrolysis, which requires large amounts of electric power in close proximity to a water source. The Germans had this at the Hydro Norsk hydroelectric plant in occupied Norway, since that plant had been the first (and only at the time) commercial producer of the Deuterium.

The British alerted the Norwegian underground that heavy water was useful for the war, without telling them why. The Norwegians had already suspected as much, and had smuggled their own "stockpile" of deuterium to France when the German orders multiplied exponentially. When the British SOE altered the underground, courageous Norwegians sabotaged production as best they could, by such diverse methods as adding cod liver oil to the process which cause excessive "foaming" in the plant and delayed the produciton. As a result the Germans had only about half the heavy water they needed by the end of the war.

Despite the shortage of heavy water, Heisenberg continued to work toward a controlled chain reaction using deuterium to the very end of the war. What else could he have done? Graphite was not an alternative; he had no reason to doubt Bothe's measurement. Bothe was the recognized authority in the field and Germans believed strongly in authority.

Even if another German scientist had repeated the experiment, the result would have been unchanged. No German physicist would have consulted a chemical engineer! The barrier between the two disciplines was too large and respect for "authorities" in the field too great. It would have been equally impossible to accelerate heavy water production. To do so would have required additional electric power sources in an already power-constrained economy. Germany's final attempt to build a nuclear reactor failed to go critical for lack of enough materials and time.

This was why he could tell Hitler with a straight face; "For the present I believe that the war will be over long before the first atom bomb is built." (Heisenberg, statement to Hitler in 1939)

As the head of German research (Heisenberg) could also honestly report to Hitler later, in July of 1943 that; "..though our work will not lead in a short time towards the production of practical useful engines or explosives, it gives on the other hand the certainty that in this field the enemy powers cannot have any surprise in store for us."

(OPPS)

 

Is that a reference to my post?

 

No telling? the above is about all I know about their nukes program. ;-))

 

Hi Clint, I think you missed your calling as a Nuclear Scientist? but great stuff and thanks for it.