Documenting Hiroshima of 1945: September 4, hypocenter as observed by physicist
Sep. 4, 2024
by Kyosuke Mizukawa, Senior Staff Writer
On September 4, 1945, Hiroshima City’s Saiku-machi (in the city’s present-day Naka Ward), the location where Shima Hospital stood directly below the A-bomb’s detonation, was still covered in debris nearly one month after the atomic bombing. A photograph taken by Fumio Yamasaki, a researcher of nuclear physics at the Institute of Physical and Chemical Research (RIKEN) who died in 1981 at the age of 74, shows remnants of the walls of Shima Hospital amidst the ruins.
Mr. Yamasaki was 38 years old at the time. He worked in Dr. Yoshio Nishina’s laboratory, which had been entrusted with research on A-bomb development by the Japanese Army during the war. Mr. Yamasaki was engaged in research for the determination of whether uranium enrichment had been successfully carried out. To investigate the issue of residual radiation from the atomic bombing, he left Tokyo and entered Hiroshima on August 30 as a member of a joint survey team led by Masao Tsuzuki, a professor at Tokyo Imperial University (present-day University of Tokyo).
He was shocked when confronted with the area on which the atomic bomb had been used. He wrote in his journal in an entry dated August 30, “The roofs [of collapsed houses] looked as if they had been crushed by a giant walking over them.” In a journal entry dated September 1, he wrote, “What is so devastatingly different in Hiroshima compared with the ruins in Tokyo is that even all the stone buildings are destroyed, giving the impression that the city had been hit by a major earthquake, a massive storm, and a conflagration.”
Mr. Yamasaki and the other team members conducted measurements of residual radiation until September 5. They found that residual radiation measured near the hypocenter was higher than natural, background rates. Moreover, higher levels of radiation were observed in the areas of Takasu and Furue (both of which are in Hiroshima’s present-day Nishi Ward), located between three and four kilometers to the west of the hypocenter. The highest levels in this area were recorded in the eastern part of Furue and were roughly equivalent to those measured in the vicinity of the hypocenter. In these areas, where so-called “black rain” had fallen after the atomic bombing, particularly high levels of residual radiation were measured in the soil and sand accumulated in rain gutters.
Meanwhile, based on the measured radiation levels, members of the survey team refuted the theory that had spread with comments from U.S. scientists that “nothing would grow in Hiroshima for 70 years.” The Chugoku Shimbun published on September 4 carried an article with the headline “Living in Hiroshima is not dangerous” in which Mr. Tsuzuki’s rationale for the opinion was prominently reported.
Despite rejection of the idea of “biological infertility,” the fact remained that the atomic bombing had caused catastrophic devastation to the city and its inhabitants. Later, In an article he contributed to Fujin Koron (in English, ‘Women’s Review’), published in 1954, Mr. Yamasaki made the following appeal — “I think the banning of atomic weapons is an act of utmost urgency for humanity today.”
(Originally published on September 4, 2024)
On September 4, 1945, Hiroshima City’s Saiku-machi (in the city’s present-day Naka Ward), the location where Shima Hospital stood directly below the A-bomb’s detonation, was still covered in debris nearly one month after the atomic bombing. A photograph taken by Fumio Yamasaki, a researcher of nuclear physics at the Institute of Physical and Chemical Research (RIKEN) who died in 1981 at the age of 74, shows remnants of the walls of Shima Hospital amidst the ruins.
Mr. Yamasaki was 38 years old at the time. He worked in Dr. Yoshio Nishina’s laboratory, which had been entrusted with research on A-bomb development by the Japanese Army during the war. Mr. Yamasaki was engaged in research for the determination of whether uranium enrichment had been successfully carried out. To investigate the issue of residual radiation from the atomic bombing, he left Tokyo and entered Hiroshima on August 30 as a member of a joint survey team led by Masao Tsuzuki, a professor at Tokyo Imperial University (present-day University of Tokyo).
He was shocked when confronted with the area on which the atomic bomb had been used. He wrote in his journal in an entry dated August 30, “The roofs [of collapsed houses] looked as if they had been crushed by a giant walking over them.” In a journal entry dated September 1, he wrote, “What is so devastatingly different in Hiroshima compared with the ruins in Tokyo is that even all the stone buildings are destroyed, giving the impression that the city had been hit by a major earthquake, a massive storm, and a conflagration.”
Mr. Yamasaki and the other team members conducted measurements of residual radiation until September 5. They found that residual radiation measured near the hypocenter was higher than natural, background rates. Moreover, higher levels of radiation were observed in the areas of Takasu and Furue (both of which are in Hiroshima’s present-day Nishi Ward), located between three and four kilometers to the west of the hypocenter. The highest levels in this area were recorded in the eastern part of Furue and were roughly equivalent to those measured in the vicinity of the hypocenter. In these areas, where so-called “black rain” had fallen after the atomic bombing, particularly high levels of residual radiation were measured in the soil and sand accumulated in rain gutters.
Meanwhile, based on the measured radiation levels, members of the survey team refuted the theory that had spread with comments from U.S. scientists that “nothing would grow in Hiroshima for 70 years.” The Chugoku Shimbun published on September 4 carried an article with the headline “Living in Hiroshima is not dangerous” in which Mr. Tsuzuki’s rationale for the opinion was prominently reported.
Despite rejection of the idea of “biological infertility,” the fact remained that the atomic bombing had caused catastrophic devastation to the city and its inhabitants. Later, In an article he contributed to Fujin Koron (in English, ‘Women’s Review’), published in 1954, Mr. Yamasaki made the following appeal — “I think the banning of atomic weapons is an act of utmost urgency for humanity today.”
(Originally published on September 4, 2024)
