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Newly released logs of Nobel laureate Yukawa chronicle reaction to Bikini fallout incident

Yukawa's contribution on nuclear power, which appeared on the front page of the Mainichi Shimbun on March 30, 1954, and then in the English-language Mainichi the next day. (Mainichi)

KYOTO -- Previously unreleased diary entries written by Japan's first Nobel physics prize laureate Hideki Yukawa (1907-1981) on a hydrogen bomb test by the United States near Bikini Atoll in 1954 went on public display on May 11 at Kyoto University.

The entries chronicle Yukawa's reaction to the Japanese fishing vessel Daigo Fukuryu Maru's exposure to the South Pacific nuclear test's radioactive fallout, his contribution to newspapers, and his nationwide speeches on nuclear power. The Bikini incident drove Yukawa to seek the elimination of nuclear weapons for the rest of his life as an activist, and experts view the diary as an important document linked to the physicist's turnaround.

Yukawa's journal, written in a student diary, was kept by his family. Officials at the Yukawa Hall Archival Library at Kyoto University's Yukawa Institute for Theoretical Physics read the handwritten manuscript and selected for display entries related to the Bikini incident, dating from March to December 1954.

The first entry on the fallout incident appears on March 16, two days after the Daigo Fukuryu Maru returned to its home port in Yaizu, Shizuoka Prefecture. "The tuna fishing boat Daigo Fukuryu Maru, covered by pure white fallout from a hydrogen bomb test blast, came home. Shipmates with burns were examined and were presumed to have hydrogen bomb syndrome," the entry reads.

Yukawa had remained silent about the incident until his contribution titled "Nuclear power and humankind at a crossroads" appeared on the front page of the Mainichi Shimbun newspaper on March 30, 1954, and then in the English-language Mainichi the next day under the headline "Work Out Way To Protect Mankind From Threat Of A-Energy, Urges Yukawa." In the diary, Yukawa wrote on March 28 that he had written a contribution to the Mainichi at home.

He then embarked on a nationwide tour to warn the public about the dangers of nuclear power. An April 2 entry in the diary says, "At the Diet. Spoke about nuclear power at the Liberal Party general affairs committee." Yukawa wrote on Dec. 6 that a speech in Fukuoka Prefecture in southern Japan attracted "an audience of almost 3,000," indicating the general public's high interest in the issue.

In an entry dated Sept. 23, Yukawa recorded the death of the Daigo Fukuryu Maru's chief radioman. "A victim of the deadly fallout from Bikini, Mr. Aikichi Kuboyama, reportedly passed away," he wrote.

Yukawa in 1955 became a joint signatory to the Russell-Einstein Manifesto, which highlighted the dangers of nuclear weapons and called for a resolution to international conflicts. The document was authored by European and American intellectuals including philosopher Bertrand Russell and Albert Einstein, who won the Nobel Prize in physics.

Michiji Konuma, 87, a professor emeritus of particle physics at Keio University who had contact with Yukawa and deciphered Yukawa's handwriting, recalls Yukawa saying that "writing the contribution (to the Mainichi) was a turning point for me."

According to Kyoto University, extant documents related to Yukawa include diaries and research records spanning from 1934 through 1954. In December 2017, entries from 1945 mentioning "F Research" on atomic bombs -- a reference to nuclear fission -- and the atomic bombing of Hiroshima were made public.

(Japanese original by Mai Suganuma, Kyoto Bureau)

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