Editors:
Michio AOYAMA and Yutaka OOCHI

Revisit
The Hiroshima A-bombwith a Database
Latest Scientific View
on Local Fallout and Black Rain

Hiroshima City 2011

Copyright© 2011 by Hiroshima CityAll rights reserved.

International Standard Book Number: 978-4-9905935-0-6

Bibliographical Note
This book contains 11 articles based on studies by members of HiSoF, The
Hiroshima Study Group on Re-construction of Local Fallout from A-bomb in
1945, and 3 articles by the contributors.

National Diet Library of Japan Cataloging-in-Publication Data
Catalog record is available from the National Diet Library of Japan
Hiroshima City publication data
Revisit The Hiroshima A-Bomb with a Database（広 H8-2011-133）
Research Division, Atomic Bomb Survivors Relief Department
Health and Welfare Bureau, The City of Hiroshima
Telephone：082-504-2191

Editors
Michio Aoyama
Meteorological Research Institute
1-1 Nagamine, Tsukuba, Ibaraki, 305-0052 Japan

Yutaka Oochi
Atomic Bomb Survivors Relief Department
Health and Welfare Bureau, The City of Hiroshima
6-34 Kokutaiji-machi 1-chome Naka-Ku, Hiroshima, 730-8586 Japan

This book is dedicated to huge number* victimsby the Hiroshima A-bomb in 1945

* The exact number of the death at the instance of explosion of the Hiroshima A-bomb

in 1945 has not been cleared. Approximately 140,000 (error of ±10,000) are estimatedto have died by the end of December 1945.
269,446 names are registered in Hiroshima Peace Memorial Park as the A-Bombvictims at of August 6, 2010.

iPreface

Nearly sixty-six years have passed since that fateful summer when Hiroshima wascompletely destroyed by the first atomic bombing in history. Today more than ever, weneed to keep working to convey the devastating reality of the bombing to people aroundthe world and pass on our legacy to future generations – this is Hiroshima’s mission.
Although many studies have been done on Hiroshima’s radioactive fallout and theblack rain that fell after the bombing, we have yet to fully understand its impact. As such,in 2010 we established the Hiroshima Study Group on Re-construction of Local Fallout
from A-bomb in 1945 (HiSoF) to bring together experts in geochemistry, radiation
biophysics, nuclear engineering, and other fields to further evaluate the extent and effectsof Hiroshima’s black rain and other radioactive fallout.
We created this book, which includes HiSoF’s latest findings and data on the conditions
right after the bombing, to facilitate collaborative research with experts in Japan andabroad. We sincerely hope it will become the basis for future studies on Hiroshima’sradioactive fallout and damage, and that in turn, many more people will come to realize
the A-bomb’s disastrous effects and feel compelled to work for a peaceful world without
nuclear weapons.
In closing, I would like to thank all the members of HiSoF and everyone whose
contributions made this book possible, and I ask for your continued cooperation andsupport for our city’s initiatives for peace.

July 2011
MATSUI Kazumi
Mayor
The City of Hiroshima

ii

iii

序みぞう

広島が人類史上初めての原子爆弾による未曾有の大惨禍を被ってから、６６年目の夏を迎えようとしています。
被爆から長い年月が経過した今日、原爆被害の実相を広く世界に発信し、次世代に継承していくことが、被爆地広島の使命となっています。
こうした中、原子爆弾投下直後に降った黒い雨などの放射性降下物については、これまでも様々な研究が行われてきましたが、未だにその実態は、十分に解明されていません。
このため、本市では、平成２２年（２０１０年）から、広島の原爆による放射性降下物などの実態を解明することを目的として、地球化学、放射線物理学、原子力工学などの様々な分野の専門家で構成された「広島原爆による放射性降下物等実態検証に係る関係者協議会（Hiroshima Study Group on Re-construction of Local Fallout from A-bomb in 1945（HiSoF））」を設置し、黒い雨を始めとする放射性降下物などについての研究や最新の知見の収集に取り組んできました。
この取組の成果として、これまでの研究結果や収集した知見を、今後の国際的な研究の基礎となる初期条件や検証データとしてまとめたものが本書です。
本書を読まれた国内外の研究者の方々の手により広島の原爆による放射性降下物などの実態解明が進み、原爆被害の実相について、多くの人々の理解が深まることにより、核兵器廃絶や世界恒久平和の実現につながることを心から期待します。
最後に、HiSoF のメンバーの皆様を始め、本書の製作に携わられた方々の御協力に改めて深く感謝の意を表しますとともに、本市の平和行政に対する一層の御協力をお願いいたします。

平成２３年（２０１１年）７月

広島市長

松 井一 實iv

v

ContentsPreface ········································································································· i
序 ················································································································ iii
Introduction ································································································ vii
1. Initial Conditions
1.1 Initial process of atomic bomb cloud formation and radioactivity distribution ·················· 1
Tetsuji Imanaka
1.2 Mapping the Fire Field near the Hypocenter of the Hiroshima A-bomb ························· 15
Noriyuki Kawano, Megu Ohtaki, Takao Okada
1.3 Digital mapping of Hiroshima just before and after the atomic Bombing ······················· 25
Toshio Koizumi
1.4 Resources of heat, water and carbon fluxs for an induced urban fire in 1945
Hiroshima based on field research of Japanese traditional houses ····································· 37
Yoshihiro Okada and Michio Aoyama
1.5 Estimation of heat, water, and black carbon fluxs during the fire induced by theHiroshima A-bomb ··································································································· 43
Michio Aoyama, Yoshihiro Okada, Toshio Koizumi, Takahiro Tanikawa, Noriyuki Kawano
1.6 Height Estimation of Hiroshima A-bomb Mushroom Cloud from Photos······················· 55
Masashi Baba, Fumio Ogawa, Shinsaku Hiura, Naoki Asada

2. Validation Data

2.1 Radiation survey activities in the early stages after the atomic bombing inHiroshima ··············································································································· 69Tetsuji Imanaka
2.2 137Cs concentration in Soil Samples Collected in an Early Survey of Hiroshima
Atomic Bomb and 235U/238U Ratios in Black Rain Streaks on a Plaster Wall·························· 83
Kiyoshi Shizuma
2.3 Preliminary results on 137Cs in soil core samples collected from the under-floorsof houses built within 1-4 years after the Hiroshima Atomic Bomb···································· 93
Aya Sakaguchi, Haruka Chiga, Kiyoshi Shizuma, Masaharu Hoshi, Masayoshi Yamamoto
2.4 Geospatial Analysis of 137Cs in Hiroshima Soil Cores Collected in 1976 and 1978 ············ 97
Harry M. Cullings
2.5 A review of Masuda’s re-investigation of ‘black rain’ after the Hiroshima
A-bomb ·················································································································· 125
Yoshinobu Masuda

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2.6 Re-construction of spatial-time distribution of ‘black rain’ in Hiroshima basedon statistical analysis of witness of survivors from atomic bomb ······································ 131
Megu Ohtaki
2.7 Feasibility of using 236U to reconstruct close-in fallout deposition from theHiroshima atomic bomb ···························································································· 145
Aya Sakaguchi, Kenta Kawai, Peter Steier, Tetsuji Imanaka, Masaharu Hoshi, Satoru Endo,
Kassym Zhumadilov, Masayoshi Yamamoto

3. Databases

Sources and a structure of database for numerical model simulation of theHiroshima A-bomb in 1945 ························································································ 153
Michio Aoyama and HiSoF members

Appendix I
State and spread of fires in Hiroshima City ····················································· 157
Appendix II
Meteorological Conditions Relating to the Atomic Bomb Explosion in Hiroshima
City (1947, Synopsis) ································································································ 169

Appendix III
History of Rainfall Areas··························································································· 177

Index ·········································································································· 183
List of reprint permissions ············································································· 187

viiIntroduction
Hiroshima City has been carrying out a series of surveys in an effort to draw acomplete and more realistic picture of the A-bombing and its impact on the people there at
the time of the explosion. As a part of its efforts, the City set up the Hiroshima Study
Group on Re-construction of Local Fallout from A-bomb in 1945, HiSoF, to facilitate
further studies and discussion on this issue.
HiSoF is a group of researchers including meteorologists, radiobiologists, nuclearengineers, as well as experts in statistics, computer graphics and other related fields.
Hiroshima City also invited researchers who were essential to perform studies on theeffects of radioactive fallout and ‘black rain’ resulting from the explosion of the Hiroshima
atomic bomb, and to compile data into this book.
Incorporating the latest data and modelling, Hiroshima City is planning to conduct theinter-laboratory comparison experiment of model simulations of local fallout and blackrain, if some modellers agree to do this.
The main objectives of this book are to provide results of the latest studies and acomprehensive database on the local fallout and black rain from the A-bomb explosion atHiroshima on 6 August 1945.
This book contains 11 articles based on studies by members of HiSoF and 3 articles bycontributors. It consists of three parts: Initial Conditions, Validation Data and Databases.
Part I begins with a review of current knowledge about the process of atomic bombcloud formation and radioactivity distribution. The case of the Hiroshima atomic bomb isdiscussed here (1.1). In order to show the development of the fire field, mapping ofinduced fires near the hypocenter is created (1.2). Also a digital mapping of the wholeurban area of the city just before and after the atomic bombing is produced in an attempt
to illustrate accurate damage distribution (1.3). For re-construction of the atomic cloud andrainfalls in Hiroshima, the amount of flammable materials in traditional Japanese housesin the region is estimated (1.4). Then based on those data, heat, water and carbon fluxes areestimated (1.5). Also the height and width of the mushroom cloud is estimated using
geometric camera calibration methods (1.6).
In Part II, the results of radiation survey activities during the early stages areoverviewed (2.1). Also the previous studies regarding the measurement of 137Cs deposition(2.2) and ‘black rain’ (2.5) are reviewed. In addition, the book carries a geospatial analysisof 137Cs in soil core collected in Hiroshima (2.4) and a preliminary report on measurementof 137Cs in soil core collected from under floors of houses (2.3). Also re-construction of theviii

spatial-time distribution of rainfall is produced based on statistical analysis of thewitnesses among the survivors of the Hiroshima A-bomb (2.6). Those can be used asvalidation data for model simulation when conducted. The feasibility of using 236U tore-construct close-in fallout deposition is included (2.7).
In Part III, sources and a structure of a database are outlined for numerical model
simulation of the radioactive fallout and ’black rain’.
For reference, the book carries a synopsis of a preceding study by Mititaka Uda in 1947,
and lists a history of ‘rainfall areas’ in the appendix.
We believe that all articles in this book as well as the database attached would be
beneficial to all researchers and modellers in this field, and of use for further developmentof the study toward elucidation of the effects due to local radioactive fallout by the atomic
bombing in Hiroshima.

AOYAMA, Michio
Meteorological Research Institute, Tsukuba
BABA, Masashi
Graduate School of Information Sciences, Hiroshima City University
CHIBA, Masaru
Meteorological Research Institute, Tsukuba
ENDO, Satoru
Graduate School of Engineering, Hiroshima University
HOSHI, Masaharu
Research Institute of Radiation Biology and Medicine, Hiroshima University
IMANAKA, Tetsuji
Research Reactor Institute, Kyoto University
KAWANO, Noriyuki
Institute for Peace Science, Hiroshima University
KOIZUMI, Toshio
Architecture and Civil Engineering, Chiba Institute of Technology
KUDO, YozoTokuyama College of Technology
OHTAKI, Megu
Research Institute for Radiation Biology and Medicine, Hiroshima University
SAKAGUCHI, Aya
Graduate School of Science, Hiroshima University
SUZUKI, Manami
Coordinator of HiSoF