Ni-Go Nuclear Research Project

The Ni-Go project (also called the Nishina project) was the Imperial Japanese Army's effort to develop a nuclear weapon; the name comes from the first syllable of the surname of its leader, Yoshio Nishina. Its origins go back to 1940, when Lt. Gen. Yasuda Takeo, head of the Army Aviation Technical Research Institute, ordered a study of the feasibility of an atomic bomb. In 1941 the institute formally commissioned RIKEN's director Okochi Masatoshi to study 'the possibility of manufacturing a uranium bomb' (20 June 1941 according to Japanese Wikipedia; April 1941 according to English Wikipedia). After Nishina reported in 1943 that a bomb was technically feasible, the work was placed directly under Army Air Headquarters and formally launched as 'Ni-Go research'; RIKEN's own history dates the start to January 1943, Japanese Wikipedia to May 1943.

Led by physicist Yoshio Nishina at RIKEN in Komagome, Tokyo, the project ran from 1943 to 1945 with about thirty members; Takeuchi Masa was in charge of separating uranium-235 by thermal diffusion and Iimori Satoyasu of the search for uranium ore. A thermal-diffusion separation column, a double copper cylinder about 5 metres tall, was completed in RIKEN's Building 49 in March 1944, and separation experiments with uranium hexafluoride began that July, but six runs failed to yield enriched uranium, partly because of corrosion. Uranium itself was scarce: prospecting was carried out in Korea, Manchuria and elsewhere from 1944, and from April 1945 pupils of Ishikawa Middle School in Ishikawa, Fukushima Prefecture, were mobilised to dig ore.

Building 49 and the separation column were burned out in the Tokyo air raids of mid-April 1945. Plans to rebuild columns at Osaka Imperial University, at a Sumitomo Metal plant in Amagasaki and in Kanazawa were not realised, and the Army decided to stop the research in June 1945; Japanese Wikipedia cites an official document dated 28 June 1945 stating that research on the use of uranium nuclear energy 'has been discontinued'. Japan never achieved a self-sustaining chain reaction due to shortages of uranium, resources, and the destruction of equipment in bombing raids; about 20 million yen is said to have been spent. A separate Navy-funded project (F-Go) ran at Kyoto Imperial University under Arakatsu Bunsaku, centred on centrifugal separation and involving Yukawa Hideki among others; a joint meeting of the university and the Navy at the Biwako Hotel on 21 July 1945 was its first and last.

After Hiroshima was bombed in August 1945, Nishina was sent to investigate and confirmed that the weapon was an atomic bomb. In November 1945 the occupation forces dismantled the cyclotrons at RIKEN and Kyoto Imperial University, dumping RIKEN's in Tokyo Bay, an act later acknowledged on the US side as a mistake. The Ishikawa Town Museum of History and Folklore preserves photographs and other material on the pupils' wartime ore digging.