The Great Gap in Nuclear Weapons Science and Technology between the U.S. and Japan in the 1940s:.
In the 1940s, Japan had an atomic bomb team led by Dr. Nishina.
In the U.S., the Manhattan Project was approved in the 1940s.
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On December 8, 1942, the day of the outbreak of war against the U.S. and Britain, Nishina invited Masashi Takeuchi, a researcher in RIKEN's Cosmic Ray Research Group, to work on the atomic bomb; on February 28, 1943, Takeuchi submitted a report on his numerical calculations, bringing the theory closer to realization. The Navy's atomic bomb research was disbanded, but around May 1943, the year after the development of the atomic bomb (Manhattan Project) began in the U.S., Nishina's laboratory presented the military with a report on the possibility of making an atomic bomb through the separation of uranium. The Army jumped on this report and continued the research under the direct control of the Army Aviation Headquarters.
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There is a big difference here.
Nishina and his team had only considered a uranium-type atomic bomb.
The Manhattan Project had also considered a plutonium atomic bomb from the beginning.
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The starting point for Japan's nuclear power development was the October 26, 1963 operation of the JPDR (BWR) power test reactor introduced from the United States.
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In other words, there were no reactors and no plutonium in Nishina's time.
Plutonium bombs should be detonation type, but to cause detonation
great computational power.
The Manhattan Project had
Von Neumann, the greatest human computing genius of all time, and his protégé
Richard Feyman, also a super-genius of computation, was waiting in the wings.
These two super-geniuses were able to calculate plutonium implosion by hand.
It took 10 months to complete the calculation though.
Plutonium was not available in Japan, and neither was the calculating genius of Neumann-Feyman.
The execution of the Nishina Group and the Manhattan Project is the difference between an adult and a nursery school child.
That's how much
There was such a gap in scientific capability between Japan and the United States.
It was not enough to study at a European institute.
Dr. Nishina had no way of knowing that.
Translated with www.DeepL.com/Translator (free version)