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  3. The History of the Atomic Bomb On August 2, 1939, just before the beginning of World War II, Albert Einstein wrote to then

The History of the Atomic Bomb On August 2, 1939, just before the beginning of World War II, Albert Einstein wrote to then

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问题                                  The History of the Atomic Bomb
     On August 2, 1939, just before the beginning of World War II, Albert Einstein wrote to then President Franklin D.  Roosevelt. Einstein and several other scientists told Roosevelt of efforts in Nazi Germany to purify uranium-235, which could be used to build an atomic bomb. It was shortly thereafter that the United States Government began the serious undertaking known then only as "The Manhattan Project". Simply put, the Manhattan Project was committed to expediting research that would produce a viable atomic bomb.
     The most complicated issue to be addressed in making of an atomic bomb was the production of ample amounts of "enriched" uranium to sustain a chain reaction. At the time, uranium-235 was very hard to extract. In fact, the ratio of conversion from uranium ore to uranium metal is 500:1. Compounding this, the one part of uranium that is finally refined from the ore is over 99% uranium-238, which is practically useless for an atomic bomb. To make the task even more difficult, the useful U-235 and nearly uselessU-238 are isotopes(同位素), nearly identical in their chemical makeup. No ordinary chemical extraction method could separate them; only mechanical methods could work.
     A massive enrichment laboratory/plant was constructed at Oak Ridge, Tennessee. Harold C. Urey and his colleagues at Columbia University devised an extraction system that worked on the principle of gaseous diffusion, and Ernest O. Lawrence (inventor of the Cyclotron) at the University of California in Berkeley implemented a process involving magnetic separation of the two isotopes.
   Next, a gas centrifuge was used to further separate the lighter U-235 from the heavier, non-fissionable U-238. Once all of these procedures had been completed, all that needed to be done was to put to the test the entire concept behind atomic fission ("splitting the atom", in layman’s terms).
     Over the course of six years, from 1939 to 1945, more than $2 billion was spent during the history of the Manhattan Project. The formulas for refining uranium and putting together a working atomic bomb were created and seen to their logical ends by some of the greatest minds of our time. Chief among the people who unleashed the power of the atom was J. Robert Oppenheimer, who oversaw the project from conception to completion.
     Finally, the day came when all at Los Alamos would find out if "The Gadget" (code-named as such during its development) was going to be the colossal dud of the century or perhaps an end to the war. It all came down to a fateful morning in midsummer, 1945.
Which of the following does NOT help to separate the useful U-235 and nearly useless U-238?
选项 A、The principle of gaseous diffusion.
B、A process involving magnetic separation of the two isotopes.
C、A process nearly identical in the chemical makeup.
D、A gas centrifuge.
答案C
解析 问题是哪项不利于分离制造原子弹的铀。而选项C指的是铀235与铀238的相同化学结构。正是这个相同的结构造成了制造原子弹困难重重。选项A、B、D正好是后面几段提到的针对它们的相同的化学结构而采取的不同解决方法。
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