physics

Japanese nuclear weapons programs

Japanese nuclear weapons programs is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Japanese nuclear weapons programs rather than just read about it. In short: During World War II, the Empire of Japan had several programs exploring the use of nuclear fission for military technology, including nuclear reactors and nuclear weapons. Like the similar wartime programs in Nazi Germany, they were comparatively small, suffered from Allied air raids, shortages, disarray, and did not progress beyond the laboratory stage.

Key takeaways

Japanese nuclear weapons programs belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Japanese nuclear weapons programs to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Japanese nuclear weapons programs from memory before moving on to harder problems.

Reference excerpt

During World War II, the Empire of Japan had several programs exploring the use of nuclear fission for military technology, including nuclear reactors and nuclear weapons. Like the similar wartime programs in Nazi Germany, they were comparatively small, suffered from Allied air raids, shortages, disarray, and did not progress beyond the laboratory stage. The Imperial Japanese Army initiated the "Ni-Go Project" for nuclear weapons at the RIKEN institute, led by physicist Yoshio Nishina. Work was limited to cyclotron research, production of small quantities of uranium hexafluoride, and an unsuccessful attempt to enrich it via thermal diffusion in a Clusius tube. The Imperial Japanese Navy also supported the "F-Go Project", at Kyoto Imperial University, led by physicist Bunsaku Arakatsu and involving Hideki Yukawa. This group focused on designing an ultracentrifuge to enrich uranium hexafluoride, but did not construct any before the end of the war. Japan has not since had a nuclear weapons program. Its postwar constitution is interpreted to forbid its possession of weapons of mass destruction. It is party to the Nuclear Non-Proliferation Treaty, and has enacted laws affirming its Three Non-Nuclear Principles: to not possess, manufacture, or permit the introduction of nuclear weapons. However, the United States stationed nuclear weapons in Japan and in the Ryukyu Islands from the 1950s until 1972. Today, Japan is considered to be an exemplar latent or threshold nuclear state, capable of developing weapons in a short timespan. It is unique among non-nuclear weapons states in that it possesses a full nuclear fuel cycle and plutonium stockpile, as part of its civilian nuclear energy industry, and advanced developments in the industries necessary to make nuclear weapons.

Background

In 1934, Tohoku University professor Hikosaka Tadayoshi's "atomic physics theory" was released. Hikosaka pointed out the huge energy contained by nuclei and the possibility that both nuclear power generation and weapons could be created. In December 1938, the German chemists Otto Hahn and Fritz Strassmann sent a manuscript to Naturwissenschaften reporting that they had detected the element barium after bombarding uranium with neutrons; simultaneously, they communicated these results to Lise Meitner. Meitner, and her nephew Otto Robert Frisch, correctly interpreted these results as being nuclear fission and Frisch confirmed this experimentally on 13 January 1939. Physicists around the world immediately realized that chain reactions could be produced and notified their governments of the possibility of developing nuclear weapons.

World War II

The leading figure in the Japanese atomic program was Yoshio Nishina, a close associate of Niels Bohr and a contemporary of Albert Einstein. Nishina had co-authored the Klein–Nishina formula. Nishina had established his own Nuclear Research Laboratory to study high-energy physics in 1931 at RIKEN Institute (the Institute for Physical and Chemical Research), which had been established in 1917 in Tokyo to promote basic research. Nishina had built his first 26-inch (660 mm) cyclotron in 1936, and another 60-inch (1,500 mm), 220-ton cyclotron in 1937. In 1938 Japan also purchased a cyclotron from the University of California, Berkeley.

Due to the German-Japanese alliance resulting from Germany's Four Year Plan, Japan and its military had already been pursuing nuclear science to catch up to the West in nuclear technology. This allowed for Nishina to introduce quantum mechanics to Japan. In 1939, Nishina recognized the military potential of nuclear fission, and was worried that the Americans were working on a nuclear weapon which might be used against Japan. In August 1939, Hungarian-born physicists Leo Szilard and Eugene Wigner drafted the Einstein–Szilard letter, which warned of the potential development of "extremely powerful bombs of a new type". The United States started the investigations into fission weapons in the United States, which eventually evolved into the massive Manhattan Project, and the laboratory from which Japan purchased a cyclotron became one of the major sites for weapons research.

In the early summer of 1940, Nishina met Lieutenant-General Takeo Yasuda on a train. Yasuda was at the time director of the Army Aeronautical Department's Technical Research Institute. Nishina told Yasuda about the possibility of building nuclear weapons. However, the Japanese fission project did not formally begin until April 1941 when Yasuda acted on Army Minister Hideki Tōjō's order to investigate the possibilities of nuclear weapons. Yasuda passed the order down the chain of command to Viscount Masatoshi Ōkōchi, director of the RIKEN Institute, who in turn passed it to Nishina, whose Nuclear Research Laboratory by 1941 had over 100 researchers.

B-Research Meanwhile, the Imperial Japanese Navy's Technology Research Institute had been pursuing its own separate investigations, and had engaged professors from the Imperial University, Tokyo, for advice on nuclear weapons. Before the Attack on Pearl Harbor in 1941, Captain Yoji Ito of the Naval Technical Research Institution of Japan initiated a study that would allow for the Japanese Navy to use nuclear fission. After consulting with Professor Sagane at Tokyo Imperial University, his research showed that nuclear fission would be a potential power source for the Navy. This resulted in the formation of the Committee on Research in the Application of Nuclear Physics, chaired by Nishina, that met ten times between July 1942 and March 1943. After the Japanese Navy lost at Midway, Captain Ito proposed a new type of nuclear weapons development designated as "B-Research" (also called "Jin Project", Japanese: 仁計画, lit. "Nuclear Project") by the end of June 1942. By December, deep in the project, it became evident that while an atomic bomb was feasible in principle, "Japanese scientists believed that it would be difficult for even the United States to realize the application of atomic energy in time to influence the outcome of the war." This caused the Navy to lose interest and to concentrate instead on research into radar.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Japanese nuclear weapons programs

Start with the simplest possible case. Write down what Japanese nuclear weapons programs claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Japanese nuclear weapons programs before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Japanese nuclear weapons programs ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Japanese nuclear weapons programs

In research: Japanese nuclear weapons programs appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Japanese nuclear weapons programs in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Japanese nuclear weapons programs is common in secondary-school and first-year university syllabi. It links to neighbouring topics Military history of Japan, Military history of Japan during World War II, Nuclear history of Japan, so understanding it makes those chapters shorter.
In everyday life: Look for Japanese nuclear weapons programs outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Japanese nuclear weapons programs in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Japanese nuclear weapons programs means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Japanese nuclear weapons programs out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Japanese nuclear weapons programs in simple terms?

Why does Japanese nuclear weapons programs matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Japanese nuclear weapons programs?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Japanese nuclear weapons programs.