Photo/IllutrationPhysicist Hideki Yukawa’s diary entries dated Aug. 13 and 15, 1945 (Provided by Kyoto University’s Yukawa Institute for Theoretical Physics)

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KYOTO--Diary entries show how Japan’s first Nobel laureate started transforming from an atomic-bomb developer into an anti-nuclear peace advocate after World War II.

The entries include records of the lectures given by physicist Hideki Yukawa (1907-1981) at Kyoto Imperial University (current Kyoto University) as well as an entry dated Aug. 15, 1945, when the war ended.

Kyoto University released part of Yukawa’s diary on Dec. 21.

Yukawa, who was a professor at the university, wrote in the Aug. 15 entry: “I had my hair cut and tidied myself in the morning. There was an announcement from His Imperial Majesty at noon about Japan’s reluctant acceptance of the Potsdam Declaration. The Greater East Asia War finally came to a close.”

During the war, Yukawa was known to have been involved in the F-Go atomic bomb research project at Kyoto Imperial University.

Between February and July 1945, four diary entries included descriptions of the project, such as “there was a meeting on the F-Go research.”

An entry dated Aug. 7, the day after the U.S. atomic bombing of Hiroshima, indicates a change in Yukawa’s stance toward nuclear weapons.

“Newspaper reporters and others asked me to explain atomic weaponry in connection with the new type of bomb dropped on Hiroshima, but I declined to comment,” Yukawa wrote.

After the end of World War II, Yukawa initially kept silent to “spend days for reflection and meditation.” He later called for peace and the abolition of nuclear weapons.

The diary shows Yukawa met famous philosophers and writers on several occasions in late 1945.

Michiji Konuma, a professor emeritus of physics at Keio University, who was on friendly terms with Yukawa and analyzed the diary, said those experiences contributed greatly to Yukawa’s anti-nuclear stance.

“Dr. Yukawa drastically changed his stance around the end of the war that year (1945),” Konuma said at a news conference. “Taking into account both the content of the diary and his books, we can say his postwar thought was formed around that period.”

Yukawa’s diaries written in 1954 and between 1934 and 1949, the year he won the Nobel Prize in Physics, have been donated to Kyoto University’s Yukawa Institute for Theoretical Physics by his bereaved family.

Only a few entries of the diaries, including ones from 1934, have been disclosed to the public.