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Professor at Hiroshima University seeks soil under floors to discern area of "black rainfall"

by Uzaemonnaotsuka Tokai, Staff Writer

A group led by Professor Masaharu Hoshi at the Hiroshima University Research Institute for Radiation Biology and Medicine is pursuing research on residual radiation in the soil under floors of private houses that were built in and around the city of Hiroshima between the end of the war and 1949. Based on this research, conducted on the radiation level of soil minimally impacted by post-war nuclear tests, the group will seek to discern the area where "black rain" fell immediately after the atomic bombing. The project will be completed in fiscal 2011 and the results may lead to the expansion of the designated area of the black rainfall, which is cited in the Atomic Bomb Survivors Relief Law.

In February 2009, the group embarked on its research in the area within 50 kilometers of the hypocenter. The group is conducting the research in the designated area exposed to the black rain and the "light rain area," the latter of which is not included in the designated area despite testimony that the black rain fell there. The group is looking for buildings that were built between 1945 and 1949, or between when the atomic bomb was dropped and when the former Soviet Union began its nuclear tests. With the permission of the owners of the buildings, they seek to confirm the presence of Cesium 137, a product of fission, in the soil under the floors.

The group has already collected soil from 13 sites, including sites in Kamiyasu in Asaminami Ward and Yuki Town in Saeki Ward. They will look for sites to collect soil in Kitahiroshima Town and in other locales.

The team will ask the Low Level Radioactivity Laboratory at Kanazawa University in the city of Nomi, Ishikawa Prefecture, to analyze the soil samples and the results will be used to shed light on the area exposed to the black rain and estimate radiation doses at each site immediately after the bombing.

Regarding the black rain, the former Ministry of Welfare announced the results of its research on the soil within 30 kilometers of the hypocenter in 1976. However, the ministry said, "The research results showed no significant differences between the area exposed to the black rain and other areas," partly due to the effects of radioactive fallout caused by post-war nuclear tests by the United States, the former Soviet Union and China.

Following the United States, the former Soviet Union began its nuclear tests in 1949 and China in 1964. Professor Hoshi said, "The effects of the nuclear tests on the soil under floors of the houses targeted for research are limited. We can illuminate the black rain scientifically."

Keywords

Area of black rainfall
In 1976, the Japanese government designated the oval area stretching for 19 kilometers from north to south and 11 kilometers from east to west as the "Health Examination Special Designated Area" in the Atomic Bomb Survivors Relief Law. If an A-bomb survivor is suffering from one or some of the 11 government-designated diseases, the survivor can be granted the Atomic Bomb Survivor's Certificate. There is a move to seek the expansion of the "Health Examination Special Designated Area" in the "light rain area," including Asakita Ward and many parts of Saeki Ward and Asaminami Ward, which is not included within the designated area of black rainfall despite testimony that black rain fell there, too.

(Originally published on January 9, 2010)

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