Let's Look at the Special Exhibit
Atomic Physics and Radiation Research in Japan
on the Eve of the Bombing

The discovery of nuclear fission in 1938 by the German national Otto Hahn et. al. attracted the intense attention from physicists around the world. The atom was supposed to be solid, impossible to split. Suddenly, the field of atomic physics gave rise to highly competitive research and a rapid series of discoveries. Furthermore, nuclear fission generated enormous energy. If this reaction could be harnessed for military purposes, it could lead to a weapon the likes of which had never been seen. With the war looming, the major powers-the US, UK, Germany, and Japan- were all working on atomic bombs, though the scale of the projects differed considerably. The US, which made this project a high national priority, succeeded in testing the world's first atomic bomb in July 1945, a mere seven years after Otto Hahn first discovered nuclear fission. Atomic bomb development in Japan was pursued separately by both the army and the navy. The war ended with no concrete achievements, but the researchers who investigated the damage after the atomic bombing saw with their own eyes in Hiroshima the stunning consequences of the destructive power unleashed by the atomic bomb, which they had envisioned only in the laboratory and literature.

Atomic physics research worldwide
Otto Hahn's Discovery of Nuclear Fission

In 1932 when Fermi discovered the neutron, he predicted that if the world's heaviest element, uranium, were bombarded by neutrons, an even heavier element (transuranium) would be produced. Otto Hahn, on the other hand, thought that part of the uranium nucleus would be knocked away so the result would be the lighter element radium. He performed a series of experiments, but all he produced was barium, which is about half the weight of uranium. On hearing this, the Austrian Lise Meitner believed that that the uranium nucleus must have been split almost in half (nuclear fission). Based on the change in mass after the reaction, she concluded that, compared to chemical reactions, energy was released at an entirely different level of magnitude (about 100 million times greater). Soon, many scientists noted the possibility that the neutrons released by nuclear fission could strike other uranium nuclei leading to more nuclear fission (a nuclear chain reaction). The first nuclear chain reaction was achieved in the world's first experimental nuclear reactor at University of Chicago in 1942. The development of an atomic bomb had become a practical reality.

Otto Hahn (right) and Lise Meitner (left) 1913
Atomic physics and radiation research in Japan
Institute of Physical and Chemical Research led atomic physics research before the war

The Institute of Physical and Chemical Research was established in 1917 to contribute to Japanese industrialization by promoting science and technology. It conducted a wide range of research, including synthetic sake and vitamin A. The Institute was at the vanguard of atomic physics research in Japan and in the world before the war; among its projects was the building of Japan's first cyclotron. The cyclotron accelerates atomic nuclei through its coils in a magnetic field. When the accelerated nuclei strike nuclei in a target substance, both nuclei are split. Before the war, scientists were attempting to get the neutrons released from split nuclei to strike various other substances and create entirely new elements.
The Nishina Laboratory became the center for atomic physics research at the Institute of Physical and Chemical Research. Until Chief Scientist Yoshio Nishina returned to Japan in 1928, he was working at the Copenhagen University Bohr Laboratory where he had become a world-renowned atomic physicist conducting vanguard research with the world's leading scientists in the field.

A-bomb Research by the Japanese Army and Navy
In 1942, the Navy created a Nuclear Physics Applications Committee that included Hantaro Nagaoka, Yoshio Nishina (chairman), Masashi Kikuchi, and Ryokichi Sagane. However, this group concluded that "Even the US will be unable to develop an atomic bomb for this war," and the group disbanded in 1943. However, in May 1943, they requested that Bunsaku Arakatsu of Kyoto Imperial University began the F Project, an effort to develop an atomic bomb. The army began its internal consideration of the subject in 1939. In April 1941, the Army Air Engineering Institute requested the Institute of Physical and Chemical Research to develop an atomic bomb. In early 1943, they began a program called the Ni Project, that is, concrete research into producing enriched uranium through thermal diffusion. However, the war came to an end before Japanese A-bomb research produced any concrete results.

Japan's first cyclotron at the Institute of Physical and Chemical Research 1937
Courtesy of Institute of Physical and Chemical Research

Progress report on the Ni Project (A-bomb development) February 2, 1944
Courtesy of Institute of Physical and Chemical Research

  "It was an atomic bomb."
- A History of A-bomb Investigations -

 *Atomic Physics and Radiation Research in Japan on the Eve of the Bombing
 *The Great Tragedy: a "New Type of Bomb" Out of the Blue
 *First surveys: looking through the confusion to confirm an "atomic bomb"
 *Damage surveys in the post-war turmoil
 *The Special Committee for the Investigation of A-bomb Damages
and Japan-US Joint Commission

 *A-bomb documentary film by Japan Film Corporation
 *A-bomb Investigations after the Occupation
 *The Role of A-bomb Research Today

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