Was Japan building a nuclear bomb? Notebooks uncovered in Kyoto show how far wartime scientists had got

Previously unseen documents have been discovered in a university library in Japan that will shed new light on just how close Japanese scientists were to developing a nuclear weapon during the second world war.

As the nation prepares to mark the 70th anniversary of the attacks on Hiroshima and Nagasaki this year, three notebooks, containing hand-written calculations by a scientist working on equipment to produce enriched uranium for a weapon, have been found at Kyoto University.

Previously known as Kyoto Imperial University, the institute was at the forefront of research into nuclear physics during the war and had been charged by the Japanese navy with studying the feasibility of developing an atomic weapon.

The notebooks are dated October and November 1944 and were apparently the findings of Sakae Shimizu, a researcher who worked for Bunsaku Arakatsu, known as the foremost nuclear scientist in Japan in the 1940s.

Arakutsu had studied in Cambridge and under Einstein at Berlin University and in 1943 was tasked with achieving the separation of Uranium-235 with centrifuges. The research was given the code-name F-Go Project.

Due to a chronic shortage of raw materials, progress on the project, as well as a parallel scheme by the army, was slow. It was also disrupted by air raids on Japan as the war wore on, although the Allies were not apparently aware of the nuclear programmes and did not target the research centres.

In April 1945, the army's project was abandoned when the research facility in Tokyo was badly damaged in air raids.