WASHINGTON – The U.S. Library of Congress has two books of notes written by two scientists involved in Japan’s unsuccessful attempt to develop atomic bombs during the war, it was learned recently.

Sakae Shimizu and Yoshiaki Uemura worked under Bunsaku Arakatsu, a professor at Kyoto Imperial University — now Kyoto University — ordered by the Imperial Japanese Navy to develop atomic bombs, according to the two notebooks, copies of which were obtained by Kyodo News.

The notebooks were seized by the General Headquarters of the Allied Forces during the postwar Occupation. They have been kept with other wartime Japanese documents and not sorted and indexed to date at the library in the U.S. capital.

Discovered 61 years after the United States dropped the atomic bomb on Hiroshima, the notebooks likely will give significant insight into Japan’s wartime nuclear program, about which little is known. There are few notes left written by scientists involved at such a high level in Japan’s A-bomb program.

The library has more than 10,000 wartime Japanese documents that have not been cataloged, according to research by Kyodo News and Keiichi Tsuneishi, a professor at Kanagawa University.

Among them are the two notebooks — one with about 220 pages of notes written by Shimizu and the other with about 75 pages written by Uemura. The notes date from before Japan began full-fledged efforts to develop atomic bombs.

Shimizu, who later was named a professor emeritus at Kyoto University, was involved in the production of a cyclotron, an accelerator used for experiments on nuclear reactions.

His notebook, with the title “Laboratory Notes 2,” details the development of the high-voltage accelerator from 1942.

Shimizu, who died in 2003 at 88, visited Hiroshima soon after the atomic bomb was dropped there as part of an academic survey mission.

He also is known for his analysis of dust on the Japanese fishing boat Fukuryu Maru No. 5 that proved the vessel had been exposed to radiation in 1954 from a U.S. hydrogen-bomb test at Bikini Atoll, part of the Marshall Islands.

Uemura, who later became a professor at Kyoto University, made notes on the research he did in his notebook, “Research Diary,” starting in 1941, including research on nuclear reactions when metal is exposed to gamma rays.

His notes show that it was decided on June 14, 1941, to build a cyclotron and that a comparison was made with the results of testing done by Danish physicist Niels Bohr, who worked on the Manhattan Project, Washington’s secret atomic-bomb project.

The U.S. succeeded in developing the first atomic bomb and was the first to use one, on Hiroshima on Aug. 6, 1945, and another one on Nagasaki three days later.

Japanese scientists recognized the potential of using atomic energy to develop a powerful new bomb even before the war.

While the navy commissioned the Arakatsu laboratory to undertake research, the Imperial Japanese Army also ordered a laboratory headed by Yoshio Nishina at Riken, a national research institute for physical and chemical sciences, to develop an atomic bomb.

The Arakatsu laboratory tried to enrich uranium using a centrifuge but was not successful before the war ended. However, both programs failed.