Proceedings of the Fifth International
Symposium on Radiation Education
ISRE2016
第５回放射線教育に関する国際シンポジウム
論文集

December 16-19, 2016
Koriyama Chamber of Commerce and Industry
Koriyama, Fukushima, Japan

July 2017
NPO Radiation Education Forum

主催
NPO 法人放射線教育フォーラム後援
福島県、福島県教育委員会
郡山市、郡山市教育委員会
郡山商工会議所、郡山コンベンションビューロー
福島民報社、福島民友新聞社

ISRE2016 ScheduleMorning

AfternoonNight

Friday,11:00-

14:00-14:10

17:00-17:10

December 16, 2016

Registration

Opening AddressGroup Photo

14:10-17:00

17:10-18:10

Keynote Lectures

Welcome Reception

Saturday,8:30-11:50

13:00-15:50

16:00-17:30

December 17, 2016

Plenary Session

Plenary Session

Poster Session

Sunday,9:00-12:40

13:00-16:40

17:00-19:00

December 18, 2016

Tour:

Public Session

Symposium Dinner

Fukushima Environmental

13:00-14:20

19:00-19:10

Creative Center

Keynote Lecture

Closing Address

14:30-16:40
Plenary Session
Monday,9:00-18:00

December 19, 2016

Excursion:
Fukushima Daini Nuclear Power Plant

Venue: Koriyama Chamber of Commerce and Industry (KCCI)

Organizing Committee
K. Hasegawa

Chairperson

K. Horiuchi
Y. Hosobuchi
H. KudoVice-chairperson

K. KudoVice-chairperson

T. Nozaki
S. OhmoriS. OhnoS. Shibata
R. Tanaka

Secretary

M. Tsuji(Members of NPO Radiation Education Forum)i

ii

Preface
Radiation is an essential means to promote basic science research. In particular,radiation detectors and radiation research have made significant progress in the past
century. Furthermore, research and application of radiation in the medical field havegreatly developed in term of industry. X-ray applications in medicine, especiallydiagnostic CT scans are currently very common in hospitals. Some citizens do notrecognize the role of radiation and radioactivity and there are not a few who are afraidof them, but others are taking risks of excessive exposure to X-rays. We wish people tounderstand the nature and usefulness of radiation, and the dangers of its handling. It is
our duty as scientists and engineers to talk to citizens about how to use radiation andradioactivity safely in everyday life.
The 4th International Symposium on Radiation Education (ISRE2008) was held in
Hsinchu City, Taiwan 8 years ago, and this Symposium (ISRE2016) was held in
Koriyama City, Fukushima Prefecture. This symposium has been devoted to theradiation education for pupils and general citizens. Six major topics in this symposium
were discussed: (1) upbringing of human resources and securing the field of radiation
science、(2) radiation education, energy education and environmental education forschools and the general public, (3) effects of low-dose radiation on the human body,method of protecting the human body, (4) risks associated with the application scienceand technology, (5) natural radiation, (6) radiation literacy after the Fukushima nuclear
accident. There were 17 participants from Thailand and Taiwan, 4 keynote speakers,
14 oral presenters and 14 poster presenters, and a total of 95 participants in this
symposium. Thank you for letting us know about this unique experience.
The organizing committee of this symposium is very knowledgeable about the
purpose of this symposium and many companies, prominent lecturers and participants
cooperated in various ways to fruitful discussions. We sincerely welcome organizations
and individuals

Kunihiko Hasegawa
Chairperson of the Organizing Committee, The Fifth International Symposium on
Radiation Education (ISRE2016), and President of NPO Radiation Education Forumiii

Contents
Ⅰ. Keynote Lecture
1.1. Necessity of Education on Radiation and Radioactivity in Japan--------------------

1

Akito ARIMA
1.2. How to Explain Radiation Health Risk to The General Public: Lessons Learned from
Chernobyl and Fukushima Nuclear Power Plant Accidents---------------------------

10------------------------------------------------

15

Shunichi YAMASHITA
1.3. The Nuclear Energy Education in Taiwan
Keh-Shih CHUANG

Ⅱ. Oral Presentation
2.1. Patient-Specific Radiopharmaceutical Time Activity Curve Estimation Using External
Thermoluminescent Dosimeters------------------------------------------------------------

19

Hsin-Hon LIN, Cheng-Chang LU, Shang-Lung DONG, Yu-Ching NI, Meei-Ling JAN,
and Keh-Shih CHUANG
2.2. Risk of Natural Radiation of Japanese----------------------------------------------------

26

Michikuni SHIMO
2.3. Nuclear Technology Education at the Secondary Level in Thailand----------------

31

Thanakit LERDLU, Chuntana BOONMARK, Prayong PIYANART, Surat CHUMTHONG,
Mutita AODTON, and Khawee SUNTHORNOWARD
2.4. Radiation Education and Nuclear Power Plant in Taiwan-----------------------------

35

Chin-Wang HUANG
2.5. An Example of Lectures on the Nature of Radiation for General Public
Hiroshi KUDO-----------

39

2.6. Radiation Education Experiments and Other Science Education Experiments with a
Handmade GM Counter----------------------------------------------------------------------

Chizuo MORI
2.7. Development of Radiological Educational Program Using a Peltier-Cooling-Type Highiv

48

Performance Cloud Chamber --------------------------------------------------------------Masafumi AKIYOSHI, Hirokazu ANDO, Yasuki OKUNO, and Hiroto MATSUURA

54

2.8. Utilization of Small 68Ge/68Ga Generators as Experimental Tool in Wide Fields ofEducation----------------------------------------------------------------------------------------

63

Tadashi NOZAKI and Toru SASAKI

Ⅲ. Poster Presentation
3.1. Detection of Spatial Distribution of Dual Photon Emitters Using TOF Coincidence
Imaging Technique with Stochastic Origin Ensemble Approach---------------------

67

Chih-Chieh CHIANG, Keh-Shih CHUANG, and Hsin-Hon LIN
3.2. Post-311 Promotion Activities for Science & Disaster Literacy of Citizenry and SchoolStudents by Means of ‘Bulletin’, Symposium, and Summer School-----------------

72

Haruko NIHON’YANAGI, Tomie ISHIKAWA, Toshie KIKUCHI,
Toshi MATSUMOTO, Sachiko SAWAYA, Setsu OKAYAMA, Kaoru ENDA,
Kinue KANAZAWA, Hiromi TODOROKI, Kayoko YOKOYAMA,
Harumi OKUKAWA, Teruko UENO, Eiko NAKAYAMA, Kiriko MIYAMOTO,
Chikako ISHIKAWA, Hiroko HIRANO, Nobuko KUMANO, and Michi ARATANI
3.3. Mystery of Alpha Particle Track in Cloud Chamber!

----------------------------------

77

Chizuo MORI
3.4. The Image of Alpha Emitter Distribution on the Surface of Environmental Material with
CR-39---------------------------------------------------------------------------------------------

83

Chizuo MORI
3.5. Analysis of the Consciousness of University Students in Okinawa about the Radiation--------------------------------------------------------------------------------------------

88

Nanaho SAKASHITA and Eisaku HAMADA
3.6. Development of Teaching Materials for Radiation Education Using CR-39------

94

Yumeto NAKAHODO and Eisaku HAMADA
3.7. HATO Project / Practice of Radiation Education through Partnership of Teacher
Education Universities------------------------------------------------------------------------

Kazuko ONISHI, Akio HIRATA, and Masahiro KAMATAv

99

3.8. Effects of the Thoron Spa or Bath on the Anaplastic Carcinoma of Thyroid
Kimiko HORIUCHI, Atsuhiro KISHIMOTO, and Koji YAMAMOTO

----

103

Author Index------------------------------------------------------------------------------

107

ISRE2016 Photo--------------------------------------------------------------------------

108

Appendixvi

ISRE2016 (2017) 1-9

Necessity of Education on Radiation and Radioactivity inJapan
日本における放射線教育の必要性
Akito ARIMA
有馬朗人
President, Japan Radioisotope Association
日本アイソトープ協会会長
2011 年 3 月 11 日、東日本大震災・大津波によって東京電力福島第一原子力発電所の事故が発生した。津波によって外部電源も、非常用発電機も破壊され、原子炉の冷却が不可能になり、水素爆発が起きた。その結果福島第一原子力発電所より放射能物質が放出され、周辺の地帯が放射能に汚染され、多くの住民が疎開せざると得なくなった。
この事故によって福島県を始め日本全般に放射能・放射線への恐怖心が高まった。また福島県の農産物や海産物への不買運動が発生した。その恐怖心の中には正しいものも勿論あるが、必要以上に恐れるという面もある。そのような事態の発生した原因の一つに、日本において放射能・放射線教育が充分に行われていなかったことがある。
ここで日本の過去の放射能・放射線教育の問題を検討し、その現状を分析し、望ましい姿についての私の見解を以下の３項目に分けて述べたい。
１．日本の小中高生の理科力と成人の科学知識
２．日本の初中教育における放射能・放射線教育
３．放射能・放射線教育で教えて欲しいこと
１．日本の小中高生の理科力と成人の科学知識
小中高生の数学（算数）・理科の学力の国際的調査 TIMSS によると、日本の生徒の学力は高いことが分ります。そのうち理科の成績を表 1 に示しておきます。日本のみでなくシンガ
ポール、中国、韓国などアジアの国々の生徒も理科や数学などの学力が高いことが分ります。
それに反してアメリカやヨーロッパの生徒の理科力が低いこと（表 2）をよく見ておいて下さい。
高等学校の生徒の理科力はどうでしょうか。15 歳の人々に対する一般のリタラシーや数学、科学のリタラシーについての国際比較（PISA）が OECD で 2000 年以降数回行われています。そのうち科学についての成績を見てみましょう。
（表 3、図 1）ここでも日本の高校生の科学力が高いことが分ります。そしてまたやはりアジア諸国の高校生の科学力も高いことが示されました。
1991 年 OECD によって国民の科学知識についての調査が共通問題を用いて行われました。
私は、日本人は知識力が高いと思っていたのですが、その結果にがく然としました。日本人は 13 番目でした（表 4）。小中学生の時には日本よりずっと下の理科の学力であった国々、
例えばイタリアなどがずっと上でした。ギリシアやスペインよりも下です。そこでもう一度やってみようということで 2001 年に行ったのですが、どうでしょう（表 5）。ギリシアより
1

は上になりました。でも依然として上から数えると 13 番目。しかも EU 諸国の平均値より下でした。これは何を意味しているのでしょうか。子供のうちは理科好きであったのが、大人になると理科離れどころか、理科ぎらいになる傾向にあることを示しています。

2

3

4

２．日本における放射能・放射線教育
OECD による成人の科学知識の調査における共通問題の一つが「放射能には人工のものがありますか、天然のものはどうですか」です。日本人がこの問題に正しく答えなかった可能性があります。即ち日本の大人は科学知識が弱い。そして放射線・放射能の教育を充分に受けていないのです。
1989 年（平成元年）以降 2010 年迄、日本の中学校では放射線・放射能について教えませんでした。そもそも放射線・放射能の教育と言うと、原子力推進のためだと反対する人が昔から多く、2010 年に復活したときもそのような反対がありました。
原子力の利用に賛成反対どちらでも、医学などで放射線・放射能が使われていますし、ジャガイモの芽をガンマ線で処理して何時でもジャガイモが食べられるようにするなどで、放射線が利用されています。
アメリカなどでは牛肉なども放射線で処理してあります。それで腸管出血性大腸菌感染症を引き起す病原菌 O-157 の心配がありません。日本では時々生肉を食べて O-157 のため死亡することが良くありますから日本でも放射線で処理しておくと良いと思いますが、放射線利用に反対の人が多く実施されていません。また福島の原子炉の事故などの際、放射線・放射能に対してどう対応すべきかなど正しく判断できるように、きちっとした知識を持っていなければなりません。
しかし先程申しましたように、1989 年以来長年日本では中学における放射線・放射能教育が行われませんでした。高等学校では物理や化学を学べばそこで放射線・放射能について教育を受けることができますが、物理や化学は選択ですので、学ばない人が多いのです。理系でもそうですから、文系の人は大部分が物理や化学をとらず、従って放射能・放射線をきちっと学ぶことがなかったのです。
日本において義務教育段階の中学校で放射線・放射能をしっかりと教育すべきです。
３．放射能・放射線教育はいかにあるべきか
先ず放射能は何かを教えるべきです。歴史的には、フランスの物理学者ベクレルが 1896
年ウラン鉱からの放射線を発見しました。1895 年ドイツのレントゲンが X 線を発見したことに刺激されて、蛍光の研究などをしていたベクレルは、偶然ウラン鉱を置いた写真乾板を現像したらば、その鉱物の影のような不思議な像がうつっていたのです。その後ベクレルの弟子のピエール・キューリーとマリー・キューリーの 2 人がウラン鉱の放射能を追求しまたトリウムからも同じような放射能を発見し、その後ピッチブレンド中の放射能を追跡して、
1898 年更に新しい放射性元素ポロニウムとラジウムを発見したのです。
2 つの新しい放射性元素の一方はマリー・キューリーの母国ポーランドにちなんで、ポロニウムと名づけられたのです。
このポロニウムをキューリーからもらってイギリスのアーネスト・ラザフォードは、ポロニウムからの放射線に磁場を加えてみたところ、真直ぐに進むもの、かなり重い粒子らしい
少し曲がるもの、かなり軽い粒子らしいもので大きく曲るものの 3 種類あることを発見しました。真直ぐ進む軽いものは γ 線、ちょっと曲る放射線を α 線、大きく曲るものを β 線と名付けました。また曲り方からその電荷や、質量を測定し、α 線は正電荷のヘリウム He、β線は負電荷の電子であることをつきつめました。協同して研究したのは、ソディです。この5

γ 線は X 線や紫外線、可視光、赤外線、短波、長波などおなじみの光線の仲間で波長が最も短いものであることが分りました（図 2）。
光波も粒子、フォトンであり、そのエネルギーƐ は振動数νに比例します。νは波長λのhc

逆数でλν=c であり、Ɛ=hν= ですから、波長λが短い程大きなエネルギーを持ちます。でλすから紫外線や X 線そして γ 線はエネルギーが大きく、X 線や γ 線は人体に与える影響、場合によっては危険性が大きいのです。ですから X 線もあび過ぎると危険ですので注意しなければなりません。
現在は医師達も X 線で診断する時に極めて慎重なのはそのためです。
放射線の量を表わす単位に 2 種類あります。
照射線量、X 線や γ 線の放射線としての強さで単位はレントゲン。
吸収線量 物質 1 キログラム当りの吸収される放射線のエネルギー量、単位としてはグレイ（Gy）またはその 100 分の 1 のラド（rad）。グレイは物質 1 キログラム当り 1 ジュール吸収される放射線量、1 ラドはその 100 分の 1 です。
人間にとってもっとも重要なことは放射能が及ぼす影響です。放射線の生体吸収量の単位としてシーベルトが用いられます。1 Sv は 1 Gy（グレイ）の γ 線と生物学的効果がほぼ同等の線量として定義されています。1 Sv はあまりにも大きいので通常は 1 Sv の 1000 分の
1 のミリシーベルト mSv が用いられます。1 mSv は生体組織 1 g あたり 10 erg の γ 線のエネ
ルギー吸収に相当します。
地球上の人間は大地からの放射線、宇宙からの放射線、食物を採取することによる体内か
らの放射線、そして呼吸によってすい込む空気が持ち込むことによる放射線などがあります。
世界平均で人間は毎年宇宙から 0.39 mSv、大地から 0.48 mSv、食物から 0.29 mSv、呼吸から 1.26 mSv 自然放射能によって被爆しています。
です。平均して１年間に日本人は 1.5 mSv、世界平均は 2.4 mSv です。
自然放射能による被爆量は大地からの放射能は日本では 0.43 mSv/年、大きい所は、図 3の示すようにイランのラムサール 10.2 mSv/年、中国の陽江は 3.5 mSv/年です。
飛行機に乗ったり、医療などでどのくらいの放射線量をあびるかを示したのが 図 4 です。パイロットなどは飛行機に乗り過ぎないようにしなければなりません。
それでは放射線をどのくらい浴びれば、どんな病気が発生するか 図 5 に示しておきましょう。詳しくは山下先生がおられますので、山下先生など医学の専門家に聞いて下さい。
さて東電の福島第一原子力発電所の事故に伴う放射能汚染による放射線量を 1 mSv 以下にするという方針がありますが、これは以上述べた自然放射線量によるものに比べて、明らかに原子力発電所事故によって増加した線量の部分を取り除くことを意味しているのです。
もともとの宇宙線によるものとか、大地からのものは除きようはないのです。

6

7

8

結論
国民が正しい放射線・放射能の知識を持つべきです。正しく医療を受け、食料の殺菌などを理解するためです。更に原子炉事故等に伴う放射能汚染について正しく判断し、風聞に左右されないようにすべきです。そのためこういう客観的科学的知識をきちんと教育すべきでしょう。その上で恐れ過ぎず適切に行動すべきです。
御清聴有難う御座いました。

9

ISRE2016 (2017) 10-14

How to Explain Radiation Health Risk to The General
Public: Lessons Learned from Chernobyl and Fukushima
Nuclear Power Plant Accidents
Shunichi YAMASHITA, MD, PhD
Nagasaki University/Fukushima Medical University
Abstract
I have passed through many challenges and had a chance to actually realize the significance of
responsibilities from the nuclear power plant accidents in Chernobyl and Fukushima on accurate
evaluation of radiation risk and radiation health effects when communicating with the public. The
public has similar negative feelings about terror, tragedy of the atomic bombings and nuclear
accidents, frustration about the widely spread illusion of nuclear safety before the accidents. We
thus face many continuous difficulties when we have to perform crisis and post-crisis radiation risk
communications.
At first, we should realize that there are two types of radiation health effects: an acute radiation
syndrome, the so-called deterministic effect (tissue reaction) due to a high dose radiation exposure,and chronic radiation damages and possible genetic consequences, which underlie the stochastic
effects caused by the lower doses or low dose-rate radiation exposure. It is important to understandthat health effects of radiation may be very different depending on the level of the dose received.
Clearly, we naturally are surrounded by radiation exposures and radiological materials, even frominside our body. Therefore, we should learn comprehensively the effects of low dose and low
dose-rate radiation exposure at the standpoint of daily life and consider other health risk factors.
Introduction
I was one of the medical experts and advisors on radiation health risk management to commandthe emergency radiation medicine in Fukushima just after the accident. At first, we tried to mitigate
and block the radiation risk, especially overall health risk to the population in Fukushima in orderto calm down exaggerated anxiety and mental stress immediately after the forced evacuation andlater spontaneous evacuation. At present, we are meeting more challenges at the frontline of theindividual risk management far beyond the principal and conventional approach to radiation
protection. When we see people’s feelings and difficulties of the daily lives of evacuation, we
surely understand their deep damages and all negative consequences. If people could admit that “Itis no use crying over spilt milk“, it would be possible to forward positively radiation risk
communication. However, many still suffer from post-traumatic stresses, social discrimination andinequality, and from disruption of local communities and dramatic changes of daily lifestyle; theysometimes could not avoid individual self-stigmatization. We should keep in mind when we
implement a sound radiation education that the negative delayed impact of radiation exposure
always influences not only physical, but also psychosocial part of life.

10

In this presentation, on a basis of our knowledge and own experience of Chernobyl+30 andFukushima+5, an accurate and well-balanced way of education in radiation health risk, focusing on
thyroid problems, will be introduced.
Lessons learned from Chernobyl
Chernobyl nuclear power plant accident was of outstanding importance for the issues arising
after the Fukushima accident. The two accidents were different in terms of magnitude, with
Fukushima’s 10% of the radioactive materials released from Chernobyl. Large-scale releases ofradioactive materials including short-lived iodine-131 were widely diffused around Chernobyl andeven in the Northern Hemisphere around Europe. In particular, the critical problems for local
residents have been that iodine-131 was found in milk from cows that had grazed on contaminatedgrass in areas close to Chernobyl. Because of a lack of radiation protection and insufficient foodsafety control, many people including infants and children were likely ingesting iodine-131 in large
amounts. Iodine itself has the property to be selectively taken up by the thyroid gland and this also
fully applies to iodine-131. In addition, Chernobyl is an inland area poor in natural iodine, a factor
which contributed to exacerbating internal exposure of thyroids of children who were consuming
iodine-131 contaminated milk. These children were exposed to an estimated dose from tens toseveral thousand milliSievert of thyroidal radiation. As a result, infant and thyroid cancer incidence
increased rapidly in those who were children at the time of the accident. Eventually, the number ofthyroid cancers continues to increase even 30 years after the accident, and has amounted to ~6,000
as of 2005, and there may be additional 16,000 cases due to radiation in European countries by
2065.
Physical half-life of iodine-131 is around 8 days so it decays quickly, but radioactive cesium
remains in the environment. Physical half-lives of Cs-134 and Cs-137 are around 2 years and 30
years, respectively. Therefore, around Chernobyl, radioactive cesium was highly prevalent inanimals and plants in the forest as the food chains was polluted with it. Together with vigorous
efforts how to avoid internal exposure by contaminated food chain, the dose control under thesafety level is always challengeable. So far, besides thyroid cancer, the incidence of other malignant
tumors, leukemia and other radiation-associated diseases did not increase in the population as aresult of radiation exposure. Furthermore, there were no differences in congenital abnormalities rate
between cesium-contaminated and non-contaminated areas; however, the greatest health problems
were the mental and psychosocial issues due to the accident itself.
The difficulties we faced around Chernobyl were how to communicate radiation health risk to
the public and how to encourage their recovery from the accident given a problem of thyroid cancer.
It is of a big problem for us to encourage people overcome radiophobia as well as to help themrealize the accuracy of radiation health effects and risk estimates. We can explain the results of thepast epidemiological studies logically and comprehensibly describe the principles of radiation
protection, but far beyond from such approaches it takes time to reach the common and mutual
understanding of radiation health risks.
Therefore, one of the lessons learned from Chernobyl is that beyond the emotional reaction on
11

the event which is already in the past, we, especially experts in radiation protection, should honestly,
patiently and positively support and assist the public in gaining objective perception of radiation
risk. This needs to be done through the direct dialogue and various education materials because
public risk perception is easily influenced by other sources of information such as the unreliable
mass media and groundless rumors. Secondly, during the recovery and rehabilitation period after
the Chernobyl accident, the unnecessary threat of radiation as well as over- and under-estimation ofradiation risk among the residents of affected areas should be avoided. The community-based
recovery together with individual-based approach would be desirable for raising the radiation
protection culture in radio-contaminated areas of Chernobyl in addition to the governmental
support.
Lessons learned from Fukushima
Five years have passed since the Fukushima nuclear power plant accident, a multidimensional
disaster that combined to destroy, giving a serious impact to the world. Owing to the timely
emergency response and prompt countermeasures that included evacuation, sheltering and control
of food production and supply, the risk of radiation-associated physical consequences for residents
in Fukushima is quite different from that in Chernobyl. It is considerably lower or undetectablebased on the estimates of radiation doses the individuals received during the accident.
In contrast, however, there are striking similarities in the social, psychological and economic
impacts between the two accidents. For example, maternal concern is a very serious and importantconsideration, especially for children’s health and future. Wrong and misleading information of thesecond coming of Chernobyl evoked a profound mental damage, such as a radiophobia. Therefore,
in order to support people’s recovery, careful explaining radiation health risk in Fukushima is oneof the key issues to be solved. Indeed, it is difficult to understand the linear non-threshold (LNT)
cancer risk model used for radiation protection purposes, which does not reflect the real individual
health risk. Namely, the meaningfulness of the LNT model for and biological effects of low doseradiation exposure are insufficiently understood indicative of shortcomings in relevant scientificknowledge or of even possibly erroneous conception.
To overcome an endemic of fear of radiation, several concrete actions are now taking place inFukushima. These are a collaboration model in Kawauchi village, a series of dialogue seminars
organized by the International Commission for Radiological Protection (ICRP) and a courteous
explanation of the aims and results of the thyroid ultrasound examination (TUE) program to theaffected population by Fukushima Medical University.
Here is one example how to improve the TUE program. After the Fukushima accident, thegovernment established a wide-reaching health management survey in Fukushima in order topromote residents’ health for a long time. Strictly speaking, surveys are not primarily scientificstudies. Health and wellbeing is affected by a very large number of factors and to attribute any
health effect to a particular cause, careful scientific studies that involve control groups and take into
account various confounding factors are required, such as e.g. epidemiological investigations.
However, explaining the difference between surveys and scientific studies to the general public is
12not easy, particularly explanation about the TUE, which involves highly sophisticated andtechnologically advanced screening method.
In Fukushima, the results of TUE clearly indicate a high detection rate of childhood, adolescentand young adult thyroid cancer, which Fukushima residents sometimes tend to associate with theirradiation exposure. Accumulated health examination data, and repetitive examinations using highly
sensitive equipment and standardized diagnostic protocol result in the detection of increasing
number of thyroid cancer in young people. More than 140 papillary thyroid carcinomas wereoperated among the cohort of about 300,000 individuals aged less than 18 years at the time of theaccident in Fukushima. Although the thyroid doses from potential exposure to radioactive iodines
after the accident were very low compared to those around Chernobyl, misunderstanding andrumors suggesting a scenario similar to Chernobyl have evoked distress and anxiety about a rapid
increase of thyroid cancer in Fukushima. This has led to an epidemic of fear that exaggerates wrong
interpretation of an increase of thyroid cancer in Fukushima attributing it to radiation. Therefore, it
is important for physicians and public health workers to correctly understand the reasons of theincreased detection rate of thyroid cancer in Fukushima area. This is exactly due to mass screening.
To avoid misreading of the results of the TUE program, there is an urgent need to quantify themagnitude of the “screening effect” as well as the risk of potential overdiagnosis in young patients.
In addition, even though the Fukushima accident is likely to result in no discernible health effects
from radiation, our risk communication strategy and policy should be reconsidered and involve
various stakeholders. Especially during the post-crisis period, a common knowledge about radiation
protection and radiation health effects is essentially needed.
Summary
When we, medical and health care experts, challenge to tackle the difficulties, trying to find theways how to explain radiation health risk to the public, it is essential for all of us to clearly andmutually understand that expected radiation-associated health consequences in Fukushima are quite
different from Chernobyl. The risk is drastically lower or undetectable based on radiation dose
estimates. This is very fortunate; it gives us a strong confidence and encouraging background how
to communicate with local residents during the recovery phase. However, there are similarities
between the two accidents in the social, psychological and economic impacts. Therefore, thecontinuation of the Fukushima Health Management Survey is essential to monitor health conditionof the residents. It is also an important component of all recovery efforts to train and bring up the
specialists who can take responsibility for long-term risk management regarding health effect ofradiation. Our goals include overcoming and reforming the difficult and disordered situation totransform Fukushima in the future into the “Number one prefecture of longevity in Japan” based on
our common human spirit of “a happiness of lending a helping hand”. Academic responses to
Fukushima accident are now vital and in great demand to match the request for well-balanced
radiation risk communication from the public.

13

References
1) Cardis E, Krewski D, Boniol M et al.: Estimates of the cancer burden in Europe fromradioactive fallout from the Chernobyl accident. Int J Cancer 119(6), 1224–1235, 2006
Saenko V, Thomas GA, Yamashita S. Meeting report: the 5th International expert symposium inFukushima on radiation and health. Environ Health 16(1): 3, 20172) Yasui K, Kimura Y, Kamiya K et al.: Academic responses to Fukushima disaster: three newradiation disaster curricula. Asia Pacific J Pub Health 29(2S): 99S-109S, 20173) Nagataki S: Minimizing the health effects of the nuclear accident in Fukushima on thyroid. Eur
Thyroid J 5(4): 219-223, 2016
4) Takamura N, Taira Y, Yosida K et al.: Communicating radiation risk to the population of
Fukushima. Rad Prot Dosimetry 171 (1): 23-26, 20165) Yamashita S, Takamura N: Post-crisis efforts towards recovery and resilience after the
Fukushima Daiichi Nuclear Power Plant accident. Jpn J Clin Oncol 45(8): 700-707, 20156) Ohtsuru A, Tanigawa K, Kumagai A et al.: Nuclear disasters and health: lessons learned,
challenges, and proposals. Lancet 386(9992): 489-497, 20157) Yamashita S: Tenth Warren k. Sinclair keynote address-the Fukushima nuclear power plant
accident and comprehensive health risk management. Health Phys 106(2): 166-180, 2014

Correspondence: Shunichi Yamashita
Atomic Bomb Disease Institute, Nagasaki University
1-12-4 Sakamoto, Nagasaki 8528523 JapanThe contents of this manuscript were presented in part at the Fifth International Symposium on
Radiation Education in Koriyama, on December 18, 2016.

14

ISRE2016 (2017) 15-18

The Nuclear Energy Education in Taiwan
Keh-Shih CHUANG
Department of Biomedical Engineering and Environmental Sciences
National Tsing-Hua University, Taiwan
Abstract
Tsing-Hua Open-pool Reactor (THOR), the first nuclear reactor built in Taiwan, reached its stateof criticality in 1961. THOR is a reactor dedicated for research and education in Nuclear Energy.
Since 1961, both College of Nuclear Science (CNS), National Tsing-Hua University (NTHU) andAtomic Energy Council (AEC) assumed the responsibility in the Nuclear Energy Education in
Taiwan. While CNS offers formal education and degree to the students in nuclear engineering andscience, AEC provides the general public information on atomic energy, nuclear power andradiation safety. Today, there are three commercial nuclear power plants commissioned: Chin-Shan
Nuclear Power Plant (1978, 636 MWe), Kuo-Sheng Nuclear Power Plant (1981, 985 MWe), and
Ma-An-Shan Nuclear Power Plant (1984, 951 MWe). The fourth nuclear power plant, Long-Men,
was licensed to build in 1999 but was deferral in 2015. During these years, the public opinion on
nuclear energy in Taiwan is similar to the riding of roller coaster. The society favored nuclear
energy during the global energy crisis but turned to downside due to the nuclear accident and the
problem in handling the nuclear waste. The Fukushima disaster in 2011 caused a significant impact
on the nuclear energy policy in Taiwan. The new government proposes a nuclear-free homeland at
2025, i.e. to phase out all the nuclear power plants. The college of Nuclear Science also adjusts its
structure to meet the rise and fall of the society favorite on nuclear energy. The original mission of
AEC was to foster peaceful applications of atomic energy, and to coordinate international
cooperation on nuclear energy. However, due to the non-nuclear policy AEC’s goal also changed.
In this talk, we will address the evolution of both Atomic Energy Council and College of Nuclear
Science, National Tsing-Hua University, Taiwan.
Introduction
College of Nuclear Science (CNS), National Tsing-Hua University (NTHU) and Atomic Energy
Council (AEC) are the two organizations responsible for Nuclear Energy Education in Taiwan.
CNS is mainly for the professional education in nuclear sciences. Tsing-Hua Open-pool Reactor(THOR) (Fig. 1), the first nuclear reactor built in Taiwan and also in Asia, reached its state ofcriticality in 1961. THOR is a reactor dedicated for research and education in Nuclear Energy. It
provided reactor operation training for Asia countries (supported by IAEA) during its early years. It
also undertook medical applications of nuclear reactor such as blackfoot disease in detecting
the levels of arsenic in hair and produced I-131, Na-24, and K-42 for medical examinations.
Recently THOR is under evaluation of Boron Neutron Capture Therapy (BNCT) in treatment ofpatients with head and neck cancer and gaining great successes.

15

The main task of AEC is to monitor environmental radiation induced by nuclear reactor andregulate the radiation dose by the radiation equipment for medical usage. It also provides thegeneral public information on atomic energy, nuclear power and radiation safety through internet,
flyers, advertisements, publications, press conferences, exhibitions, and media.
Nuclear Reactors in Taiwan
Today, there are three commercial nuclear power plants commissioned: Chin-Shan nuclear power
plant (1978, 636 MWe), Kuo-Sheng nuclear power plant (1981, 985 MWe), and Ma-An-Shannuclear power plant (1984, 951 MWe). The fourth nuclear power plant, Long-Men, was licensed tobuild in 1999 but was deferral in 2015.

Fig. 1. THOR is the first nuclear reactor in Asia. THOR is a 2 MW, light water moderated andcooled reactor of the TRIGA conversion type. License renewed in 2011.

Evolution
The society favored nuclear energy during the periods of global energy crisis and then turned todownside due to the nuclear reactor accident and the problem in handling the nuclear waste. The
Fukushima disaster in 2011 caused a significant impact on the nuclear energy policy in Taiwan. The
newly elected government (2016) proposes a nuclear-free homeland at 2025 policy: (1) suspensionof construction of the fourth nuclear power plant; (2) phasing out nuclear power plants; (3)searching for suitable site for the disposal of nuclear waste (3,575 tonnes of spent nuclear fuel); (4)promoting renewable energy; (5) improving power generation efficiency; (6) saving energy; (7)industrial structure adjustment; and (8) electricity liberalization.

16

During these years, the public opinion on nuclear energy in Taiwan is similar to the riding ofroller coaster. The College of Nuclear Science also adjusts its structure to meet the rise and fall of
the society attitude toward nuclear energy. In the following, we address the evolution of both
Atomic Energy Council and College of Nuclear Science.
College of Nuclear Sciences, National Tsing-Hua University
The evolution of College of Nuclear Science (CNS), NTHU can be classified into 5 periods:(1) Incubation (1956-1974)
During the Incubation period, the Institute of Nuclear Science (master program), the Departmentof Nuclear Engineering (undergraduate), and the Institute of Nuclear Engineering were founded in
1956, 1964, and 1970, respectively and the College of Nuclear Science was established in 1974. In
these years, several professors from Japan visited CNS and contributed their knowledge to enrich
the field of Nuclear Science in Taiwan. They were: 河野 宗治, 原島 鮮, 佐藤 德意, 影山 誠三郎, 小谷 正雄, 濱口 博, 齋藤 一夫, 真田 順平, 神原 富尚, 菊池 千尋, 赤石 準,
田中 重男, and 古田 悠. In the meantime, several faculties from CNS (楊末雄, 朱鐵吉, 許俊男,
王傳鍈) went to Japan and acquired their degrees. The frequent exchange of scholars between
Japan and Taiwan is not seen today as the Japanese in Taiwan is not so popular as before. The
younger generation is more fluent in English now and United States is their first choice for study.
(2) Development (1975-1994)
In the Development stage, the college continues to expand. During this time, the Institute ofRadiation Biology (Master Program), PhD program in the Institute of Nuclear Engineering, and theDepartment of Nuclear Science (undergraduate program) were added to CNS and undergraduate
program of NE Department expanded doubly.
(3) Paradigm Shift (1995-2006)
In these years, because of the anti-nuclear environment the Departments changed name to avoid“nuclear” in order to attract students. During the Paradigm Shift period, NE Department was firstrenamed as Department of Nuclear Engineering and Engineering Physics at 1995 and then to
Department of Engineering and System Science (ESS) in 1997. Nuclear Engineering became one ofthe programs in the ESS Department. In 1998, Institute of Radiation Biology was combined with
the Department of Life Science and became part of the College Life Science. In 2006, Departmentof Nuclear Science renamed to Department of Biomedical Engineering and Environmental
Sciences(4) Nuclear Renaissance (2007-2011)
Between the years 2007 to 2011, due to the Greenhouse effect (0.6oC temperature increasing andcaused sea level rising last century), Kyoto Protocol came into force, and rise in fossil fuel prices,
USA, England, Russia, Japan, and other industrial countries supported nuclear power stations.
Nuclear Renaissance term had been used to refer to a possible nuclear power industry revival. In
these years, the College continued to grow: re-establishment of Institute of Nuclear Engineeringand Science (master and doctoral program), establishment of Advanced Photo Source Program(with the corporation of Synchrotron Radiation Research Center), and establishment of17

Interdisciplinary Undergraduate Program of Nuclear Science.
(5) After Fukushima (2011~)
In March 2011, the nuclear disaster at Japan's Fukushima I Nuclear Power Plant raised questions
over the future of the nuclear energy. The nuclear-free homeland policy declared the end of nuclear
energy in Taiwan. The fourth nuclear power plant was in deferral state. It can be predicted that the
program of Nuclear Engineering will dwindle in the coming years. The research focus of theCollege gradually shifts from reactor design to nuclear waste disposal and medical applications.
The Department of Biomedical Engineering and Environmental Science is considering change
name to the Department of Biomedical Engineering and Medical Physics.
Atomic Energy Council
The Atomic Energy Council (AEC) was founded in 1955 at the ministerial level. Its original
missions during its initial establishment were: (1) to formulate the Atomic Energy Law; (2) to foster
peaceful applications of atomic energy; (3) to coordinate international cooperation on nuclear
energy; and (4) to help Tsing-Hua University in the construction of THOR.
After the construction of nuclear power plants, its missions became: (1) reactor safety regulation;(2) radiation protection; (3) radwaste administration; (4) environmental radiation monitoring; (5)R&D for technology development; and (6) other civilian nuclear applications.
After Fukushima Daiichi Nuclear Disaster, due to the non-nuclear policy AEC will undergo
reconstruction. Firstly, AEC will be included in the ministry of science and technology (MOST).
Then INER will be renamed as Institute of Energy Research (without nuclear) and moved to under
Ministry of Economic and Energy. Missions of AEC will be changed and be focused on: (1)ensuring safety during "nuclear power phase-out"; (2) regulating nuclear power plant
decommissioning; and (3) radioactive waste management.
Conclusion
The evolution of the nuclear education in Taiwan reflects the society attitude toward the nuclear
energy. The mission of College of Nuclear Science is to train professionals for nuclear power plant
when the society is for the nuclear energy. But when the society is against nuclear energy, thefocuses of the college researches switch to nuclear waste management, green energy, and medical
applications. Similarly, the mission of Atomic Energy Council switches from promoting of nuclear
energy to the safe decommission of nuclear power plants.

18

ISRE2016 (2017) 19-25

Patient-Specific Radiopharmaceutical Time Activity Curve
Estimation Using External Thermoluminescent Dosimeters
Hsin-Hon LIN1, Cheng-Chang LU2, Shang-Lung DONG2, Yu-Ching NI3,4, Meei-Ling JAN1,
and Keh-Shih CHUANG3
1Medical Physics Research Center, Institute for Radiological Research, Chang Gung

University/Chang Gung Memorial Hospital, Linkou, Taoyuan, Taiwan
2

Department of Medical Imaging and Radiological Sciences, Chung-Shan Medical University,
Taiwan3Department of Biomedical Engineering and Environmental Sciences, National Tsing-Hua

University, Taiwan
4

Health Physics Division, Institute of Nuclear Energy Research, Atomic Energy Council, Taiwan

Abstract
In this work, we proposed a novel method to estimate time activity curve in nuclear medicine
examination using serial timely measurements of thermoluminescent dosimeters (TLDs). The
approach is based on the combination of the measurement of surface dose using TLDs and Monte
Carlo simulations to estimate the patient-specific time activity data. Since the surface dose isconnected to the cumulated activities of source organs through the radiation transport from thehuman body which can be pre-calculated with the Monte Carlo simulations by inputting the patient
CT images, the organ cumulated activities can be estimated by solving the dose-activity equations.
Therefore, the activity of each organ at the time of measurement can be simply the cumulative
activity divided by the time span between measurements. Serial sets of TLDs to be read in asequential manner were employed and each TLD set measured a fraction of cumulative activity ineach organ. By connecting these timely fractional cumulative activities, the TAC can be constructed
for each source organ. Preliminary results indicate that it is an effective, robust, and simple method
to assess the TAC. The proposed method holds great potential for a range of applications in areas
such as targeted radionuclide therapy, pharmaceutical research, or patient specific dose estimation.

1. Introduction
The biodistribution of radioactive isotopes within the patient’s body is particularly useful for
calculating the cumulative activities and estimating the absorbed doses in the different organs of thepatient1, 2). Such information can be acquired by measuring the time–activity curve (TAC), a plot of
activity over time of a region of interest (ROI) drawn over a tissue. Biochemical or physiologicalmodels can be fitted to the time-activity curve (TAC) to produce parametric images and convey
more information than just the distribution of radioactivity in an organ3). However, themeasurement of TAC usually requires several repetitive scans by planar scintigraphy, positronemission tomography (PET) or single-photon emission computed tomography (SPECT) at different
time points. These repetitive procedures are usually time-consuming and not cost-effective. To this19

end, an alternative method to estimate TAC information by using external thermoluminescence
dosimetry (TLD) measurements is proposed in this work.

2. Methodology
Previously works4-6) suggested the uses of external TLD to measure organ dose. Let Sj←i be thedose to target j with the radiation from source i per unit cumulated activity. The total dose to anorgan is the summation of the dose delivered from all source organs. Their relation is characterized
by the following dose-activity equation:N

Dj  A S ( j  i)
~

i

(1)

i 1

~
where Ai is the cumulated activity occurred within the source organ i during the time interval of
study and Dj is the total dose delivered to target organ j. The S value representing the target–source
organ pair7) that can be obtained from the Monte Carlo (MC) simulation beforehand. In this study,
the MC simulation was based on our house-made patient-specific dosimetry system, namely
SimDOSE8, 9). Assuming N source organs distributed within the patient, as many as N TLDs placedon the surface around the subject should be sufficient to estimate the N source organ activities. The
N unknown cumulated activities of each organ can be calculated by solving the equation (1) using
the Jacobi method. Fig. 1 demonstrates the procedure example of estimating the

Fig. 1. The procedure of estimating the cumulative activities of each organ through the external
TLD measurement and Monte Carlo simulations.

20

cumulative activity of each organ using the combination of TLD measurements and MC
simulations. For obtaining the organ activity at different time points, one can leave the TLDs
untouched for a period of time. The cumulative activity in each organ during the period of time canbe calculated by performing the procedure in Fig. 1. Finally, the TAC of each source organ can beconstructed by connecting these timely fractional cumulative activities.

3. Results
The effectiveness of this method was studied using a Monte Carlo simulation based on an ORNL
mathematical phantom10) with TAC in six organs (lung, heart, urine, liver, head, and whole body)during an 18F-FDG study. Numerous TLDs were placed on different locations of the surface andwere repeatedly read and replaced as shown in Fig. 2 (b). The TACs presented in MIRD 19 reportused as input in 18F-FDG uptake simulation. Note that only lung, heart, urine, liver, head, andwhole body were selected as source organs and all the others (kidneys, pancreas, spleen, redmarrow, etc.) were grouped together with the whole body as one homogeneous background due totheir small activities from MIRD 19 report11). Simulations of dose measurements by using TLDs on
the ORNL phantom were performed at eight temporal frames (15, 30, 45, 60, 120, 180, 240, and
300 min) after the intravenous administration of 370 MBq 18F-FDG. Fig. 2(a) compares thereference TAC (solid lines) adapted from MIRD report 19 and calculated TAC (dash lines) using
the proposed method for decay-corrected FDG activity in the normal human brain, heart, lungs,
10 TLDs/ 10 organs

F-18 isotope

(a)

(b)

Fig. 2. Measurement of time–activity curves for decay-corrected 18F-FDG activity in normal humanbrain, heart, lungs, liver, and urine by placing the TLDs on the ORNL phantom. (a) The reference
TACs adapted from the MIRD 19 report (solid line) and calculated TAC using the proposed TLD
method (dash line). (b) The arrangement of TLDs on the ORNL phantom.

21

liver, and urine. A slight deviation was found between the calculated and reference TAC, but theirtrends were in close agreement in general. The percent sum of squared errors (PSSE) between thereference and calculated (decay-corrected) activities was 8.94%, 17.9%, 19.7%, 11.8%, 14.1%,
5.66%, 8.19%, and 5.93%, respectively, at the time of the TLD reading.
A proof of the concept–validation experiment using a physical phantom was performed. A
cylindrical water phantom (200 mm diameter with 168 mm height, AB) embedded with threecylindrical rods (A1-A3) (each with an inner diameter of 54 mm and an outer diameter of 58 mm)
was constructed for experimental validation of the proposed method. Various 99mTc activities wereadded to A1, A2, and AB while A3 remained empty with four Experimental scenarios. For eachscenario, four TLDs were attached to the surface of the physical phantom (D1–D3 and DB).

Fig. 3. Materials and devices used in physical phantom study. (a)TLD reader system, (b)TLD
annealing oven, (c)X-ray machine, (d)TLD plate, (e) RTI solid state detector, (f) TLD set, (g)dose
calibrator.

22

Fig. 3 depicted the materials and devices used for our dosimetric procedures of TLDs in thephantom study. A batch of Harshaw TLD-100H (LiF:Mg, Cu, P) (Fig. 3(f)) were used in this study.
All TLDs were annealed for 50 min by using a Barnstead/Thermolyne furnace (Fig. 3(b)) to remove
any previously stored energy. A diagnostic X-ray system (Siemens Axiom Aristos Vx Plus,
Germany) (Fig. 3(c)) was used to calibrate TLDs together with a solid-state detector (Fig. 3(e)).
The dose response (nC) was obtained for each TLD from a Harshaw model 3500 reader (Fig. 3(a)).
Then, the absorbed dose (mGy) can be calculated by multiplying the dose response (nC) with eachindividual calibration factor. To avoiding the non-uniformity of absorbed dose on the TLD plate(Fig. 3(d)) due to the heel effect and the scattered radiation, the absorbed dose for each TLD was
measured by placing the solid detector at its corresponding position on the TLD plate. The fading
effect of TLD within 24 h was assumed to be negligible. The energy-dependence correction of TLD
is not employed in the present study. A CRC-35R dose calibrator (Fig. 3(g)) was used to measure
the radioactivity of 99mTc before injection into the phantom.
Table 1. Comparison of calculated and reference 99mTc time–activity distribution in the source
organs with four experimental scenarios at different time points.
Experimental
scenarios

Exp 1

Exp 2

Exp 3

Exp 4

Compartments
Time points

A1

A2

AB

Ref

Calc

Ref

Calc

Ref

Calc

1st

426.2

426.7

0.0

0.0

0.0

0.0

2nd

390.1

415.4

0.0

0.0

0.0

0.0

3rd

347.6

340.3

0.0

1.1

0.0

0.0

4th

309.7

318.6

0.0

0.0

0.0

0.0

1st

27.0

20.6

501.2

497.6

0.0

0.0

2nd

24.4

17.9

446.6

442.8

0.0

0.0

3rd

21.7

12.0

397.8

400.4

0.0

0.0

4th

19.4

20.9

354.4

293.2

0.0

6.6

1st

0.0

61.5

0.0

66.8

499.7

371.5

2nd

0.0

76.4

0.0

83.9

445.2

269.4

3rd

0.0

39.4

0.0

42.6

396.6

325.0

4th

0.0

42.1

0.0

47.1

353.3

274.5

1st

264.0

288.4

180.2

179.2

52.2

0.0

2nd

235.1

259.1

160.6

164.2

46.5

0.0

3rd

209.5

240.4

143.0

146.7

41.5

0.0

4th

186.6

213.8

127.4

127.6

36.9

0.0

Table 1 compares the reference activities measured from the dose calibrator and the calculated
activities using the proposed method for each source compartment in the physical phantom withfour experimental scenarios. Due to the physical decay of 99mTc, the activity of all sources
decreased with time. The calculated TAC was found to be close to the calibrated TAC for each23source. The result demonstrates that the proposed method can be used to measure the TAC ofinternal organs based on timely external TLDs measurement. The largest error occurred for Exp. 4,
where three organs exhibited activities. As a result, background activity has a crucial impact on theaccuracy of estimating activities for the proposed method.

4. Conclusion
The proposed method generates TAC information of radionuclide in organs that can be further
used to estimate the total dose delivered to both cancer cell and critical organs. Simulations andexperiments were performed to validate the feasibility of estimating TACs using external TLD
dosimeters. The TAC curves of all source organs were successfully reconstructed and were quiteconsistent to the simulated for the ORNL phantom or the measured for the physical phantom.
Development of a prototype by integrating TLD and Monte Carlo computing for the time activity
curve estimation will be further investigated in future work. Such a design has great potential fordose evaluation of the treatment planning in radionuclide therapy.
References
1) S. Shcherbinin, J. Grimes, A. Bator, J. Cwikla, and A. Celler, "Three-dimensional personalized
dosimetry for

188Re

liver selective internal radiation therapy based on quantitative

post-treatment SPECT studies," Physics in medicine and biology, vol. 59, p. 119-134, 2014.
2) P. B. Zanzonico, "Internal radionuclide radiation dosimetry: a review of basic concepts andrecent developments," The Journal of Nuclear Medicine, vol. 41, p. 297-308, 2000.
3) P. Vicini, A. B. Brill, M. G. Stabin, and A. Rescigno, "Kinetic modeling in support ofradionuclide dose assessment," in Seminars in nuclear medicine, 2008, pp. 335-346.
4) T. Nakamura, Y. Hayashi, H. Watabe, M. Matsumoto, T. Horikawa, T. Fujiwara, et al.,"Estimation of organ cumulated activities and absorbed doses on intakes of several labelledradiopharmaceuticals from external measurement with thermoluminescent dosimeters," Physics
in medicine and biology, vol. 43, p. 389-405, 1998.
5) M. Matsumoto, T. Nakamura, H. Watabe, M. Itoh, and J. Hatazawa, "Estimation of organ
biodistribution and absorbed dose from external measurement with TLDs in PET studies,"
Medical and Biological Engineering and Computing, vol. 31, pp. S151-S156, 1993.
6) H. M. Deloar, T. Fujiwara, M. Shidahara, T. Nakamura, A. Yamadera, and M. Itoh, "Internal
absorbed dose estimation by a TLD method for-FDG and comparison with the dose estimatesfrom whole body PET," Physics in medicine and biology, vol. 44, p. 595-606, 1999.
7) W. S. Snyder, " S," Absorbed Dose Per Unit Cumulated Activity for Selected Radionuclides andOrgans: Society of Nuclear Medicine, 1975.
8) C.-C. Lu, H.-H. Lin, K.-S. Chuang, S.-L. Dong, J. Wu, Y.-C. Ni, et al., "Development andvalidation of a fast voxel-based dose evaluation system in nuclear medicine," Radiation
Physics and Chemistry, vol. 104, pp. 355-359, 2014.
9) K. Chuang, J. Lu, H. Lin, S. Dong, H. Yang, C. Shih, et al., "Improvements on apatient-specific dose estimation system in nuclear medicine examination," Radiation protection24

dosimetry, vol. 158, pp. 1-7, 2014.
10) E. Y. Han, W. E. Bolch, and K. F. Eckerman, "Revisions to the ORNL series of adult andpediatric computational phantoms for use with the MIRD schema," Health Physics, vol. 90, pp.
337-356, 2006.
11) M. T. Hays, E. E. Watson, S. R. Thomas, and M. Stabin, "MIRD dose estimate report no. 19:
radiation absorbed dose estimates from 18F-FDG," Journal of Nuclear Medicine, vol. 43, pp.
210-214, 2002.

25

ISRE2016 (2017) 26-30

Risk of Natural Radiation of JapaneseMichikuni SHIMO
Fujita Health University
1-98, Dengakugakubo, Kutsukake-cho, Toyoake, Aichi Pref. Japan
E-mail: shimomichikuni@sf.commufa.jp

Abstract
The cancer risk due to external and internal exposures by natural radiations was estimated using
the nominal risk factor 5.5×10-2 Sv-1 adapted by ICRP. Two hypotheses were taken in estimation.
One is that the health effect by radiation was caused by dose accumulated with time, without
reduction effect. Another is adaption of LNT (linear no-threshold) model. The accumulated
dose is taken from mean accumulated dose of each 5-years layer. The used data are the population
visual statistics of Japan that released by the Ministry of Health, Labor, and Welfare, and theJapanese annual dose due to natural radiation of 2.1 mSv that was estimated by the Atomic Safety
Research Association. The results are as follows; the mean dose is 95.6 mSv from mean age of
45.5, the lifetime dose is 175 mSv from lifetime of 83.5、and age-weighted mean lifetime dose is
160 mSv.
When we assume that every cancer leads to death with no-effect of treatment, the death rate ofcancer exposed by natural radiation is estimated to be 0.88%, the rate to all dead to be 0.29%, andthe rate to population to be 0.0029% (risk was 2.9×10-5), where Japan population, annual death ofJapanese and cancer death are 120,000,000, 1,200,000, 400,000, respectively.
１．はじめに自然放射線による外部被ばくは宇宙線と大地放射線に由来し、それらの 1 年間の合計線量の世界平均値は 0.87 mSv1)であり、日本平均は 0.63 mSv2)である。これらの値を参照して、
自然放射線による 1 年間の外部被ばくは、およそ 1 mSv であると言われることが多い。内部被ばくも入れた自然放射線による 1 年間の総線量は、世界平均値が 2.4 mSv、日本平均
値が 2.1 mSv である。
本稿では、自然放射線によるリスクはどれぐらいかに関心がある。自然放射線レベル程
度の低線量率の放射線を長期間継続的に被ばくした場合、放射線によって受けた損傷はかなり修復され、また排除されることが明らかになっているが、数量的には明らかでない。
そこで、ここでは修復や排除を考慮に入れず、また、線量はどれほど小さくても発がんをもたらすと仮定（LNT モデル）する。そのために、過大で大まかな評価になるであろうことを承知の上で、自然放射線によるがん死亡のリスクの上限値を試算することになる。

26

２．線量
(1) 累積被ばく線量
自然放射線の被ばくは途切れることなく連続している。この時、生体に与えられた影響は残り、累積すると考えると、長期間の被ばくのリスクは、累積線量で考えなければならない。つまり、ある 1 年間で受ける線量は、年齢に関係なく同じであるが、累積線量は年
齢とともに増加する。自然放射線を誰もが常に一定量を浴びていると考えると、線量は、
若年層ほど累積線量が少なく、また高齢者ほど累積線量は大きい。累積線量は「年齢に比例して直線的に増加する」と仮定すると、わが国の年間線量は 2.1 mSv であるから、0 歳
児の終わりでは 2.1 mSv であるが、9 歳児の累積線量は 21 mSv であり、99 歳の老人の累積線量は 210 mSv となる。
(2) 自然放射線によるリスク推定のための加重平均累積線量
自然放射線による発がんの影響を知る場合には、自然放射線による発がんで死亡した人の年齢分布データが必要であり、彼らの累積線量を知る必要がある。しかし、自然放射線のような低レベル被ばくでの発がんは、理論上考えられるが、臨床医学的に、疫学的に明らかにされないから、残念ながら、自然放射線による発がんで死亡した人に関するデータは望めない。ところで、がん死は、幼児から高齢者までの各層で見られる 3)。ここでは、若年層のがん死は実際には少ないが、自然放射線によるがん死がどの年齢層でも同じ割合で発生し、かつそれは累積線量に比例すると仮定する。これに基づけば、自然放射線によるがん死に寄与する線量、すなわちリスク評価のための線量は、各年齢層の累積線量を加重平均した「加重平均累積線量」でなければならない。

３．加重平均累積線量の算定(1) 算定式
加重平均累積線量 D を、次式で定義する。すなわち、
D＝Σ (kNi・Di)／ΣkNi(1)である。ここで、Ni は各年齢層の人口またはがん死亡者数で、Di は各年齢層の累積線量である。k は発がんのうち放射線が原因となる割合であるが、ここでは年齢層に関係なく一定と仮定しているので、分母分子で相殺される。D は、Ni に人口を取った時は生存者の加重平均累積線量を、がん死亡者数を取った時はがん死亡者の加重平均累積線量を表す。
(2) 算定値
厚生労働省から出されている「平成 25 年の人口とがん死亡者の年齢階層別（5 年刻み）に記された統計データ 3)」を使い、式(1)により加重平均累積線量を求めた。自然放射線による線量は 1 年に 2.1 mSv2) とし、年齢階層の線量には、たとえば、0-4 歳児の場合では 5
年の中間の 2.5 年分の 5.25 mSv とした。以下、同様に各年齢階層の中間年の値を取った。
これを人口、がん死亡者数などと共に表 1 にデータを示した。
同表 H 欄（生涯線量と表示）に、加重平均累積線量を示したが、この 160 mSv（159.6 mSv
を丸めた）が、自然放射線による発がんで死亡した個人の生涯線量の加重平均値を意味する。G 欄には各階層での被ばく線量を示した。F 欄（平均線量と表示）の 97 mSv（96.62 mSv
27

を丸めた）は、平成 25 年末に生きている人が、生まれてからその時までに被ばくした累積線量を階層の人口で重み付けした個人の平均線量である。

表１ 平成 25 年の生存者の平均線量とがん死亡者の生涯線量
E

F

G

H

(B*D)

ΣE/ΣB

(C*D)

ΣG/ΣC

A

B

C

D

年齢

人口

がん死亡者

線量

階層

(人)

(人)

(mSv)

(人・mSv)

0-4

5,239,000

83

5.25

2.75E+07

4.36E+02

5-9

5,361,000

104

15.8

8.47E+07

1.64E+03

10-14

5,790,000

97

26.3

1.52E+08

2.55E+03

15-19

6,047,000

149

36.8

2.23E+08

5.48E+03

20-24

6,205,000

176

47.3

2.93E+08

8.32E+03

25-29

6,869,000

301

57.8

3.97E+08

1.74E+04

30-34

7,623,000

635

68.3

5.21E+08

4.34E+04

35-39

9,060,000

1496

78.8

7.14E+08

1.18E+05

40-44

9,667,000

2871

89.3

8.63E+08

2.56E+05

45-49

8,406,000

4690

99.8

8.39E+08

4.68E+05

50-54

7,734,000

8206

110

8.51E+08

9.03E+05

55-59

7,731,000

14,252

121

9.35E+08

1.72E+06

60-64

9,666,000

30,891131

1.27E+09

4.05E+06

65-69

8,699,000

40,200142

1.24E+09

5.71E+06

70-74

7,596,000

49,260152

1.15E+09

7.49E+06

75-79

6,302,000

60,437163

1.03E+09

9.85E+06

80-84

4,762,000

65,554173

8.24E+08

1.13E+07

85-89

2,926,000

51,990184

5.38E+08

957 E+06

90-

1,614,000

33,292200

3.23E+08

6.66E+06

127,297,000

364684

合計

平均線量

1.23E+10

(mSv)

96.62

生涯線量
(人・mSv)

5.82E+07

(mSv)

159.6

すなわち、日本人は毎年 2.1 mSv を浴びているとすると、人口全体で見たときの累積の平均線量は 97 mSv である。これは生存者の平均線量である。他方、自然放射線による発がんで死亡したと想定した場合の人の自然放射線の生涯線量は 160 mSv とみられる。
４．自然放射線によるがんリスク(1) 名目リスク係数と前提条件
がん死亡リスクを求めるために、ここでは、放射線による発がんの名目リスク係数（nominal risk coefficient）として、ICRP Publication 103 の 5.5 ×10-2 Sv-1 4) を使う。これは高28

い生存率のがんも含んだ罹患率データに基づいているが、本稿では、先述したように、発がん者は治癒しないで全員死亡すると仮定する。
(2) がん死亡リスクの推定
平成 25 年は、わが国の総人口は 1.273 億人、同年の全死亡者は 126.8 万人であり、全死亡者の内、悪性新生物（がん）による死亡者が 36.47 万人であった。これを比率でみた場合、全死亡率は 0.996%で、がん死亡者に限ると 0.286%であり、死亡者の内のがんによる死亡者の割合は 28.8%である。これらを丸めた概数で見れば、それぞれ 1.0%、0.29%、29%である。
自然放射線が発がんを起こすとすると、自然放射線の加重平均生涯線量が 160 mSv（丸めた値）であるから、全がん死に占める自然放射線によるがん死の比率は、リスク係数 5.5×
10-2 Sv-1 を使って、8.8 ×10-3（0.88%）と見積もられる。
人口動態は年によって違いがあり、また経年の変動傾向も考慮すると、丸めた数値で概数として見るのが適切である。わが国の最近の人口動態の概略値として、総人口 1.2 億人、年間の死亡者 120 万人、そのうちのがん死亡者を 35 万人とすると、死亡率は 1%とみられ、死亡者のうちのがん死者の比率は 29%（人口に対するがん死亡率は 0.29%）とみられる。
さらに、がん死亡者のうちで自然放射線による発がんでの死亡率は 0.88%とみられるから、死亡者に対するその比率は 0.26%と見積もられる。わが国の人口全体でみた時のリスクは、
2.6 ×10-5（0.0026%）となり、この値がわが国における他のリスクと比較できる数値となる。
これらを表 2 にまとめた。ただし、リスク係数が高い生存率のがんも含んだ罹患率から出されていることや、低線量率で長期間継続して被ばくしている間に傷害を受けた細胞の修復や除去などを併せて考慮すると、2.6 ×10-5 はかなり大きめの値である。
がん死に対する様々な原因のリスクがハーバード大学レポートで評価されている 5)が、それによれば、「放射線・紫外線」のリスクは 2%である。両者の寄与の割合をそれぞれ 1％とすると、放射線のリスクは本稿で算出した 0.88%とほぼ一致する。日本と米国では、人種や生活習慣、食習慣、また線量など様々な面で違うにもかかわらず、発がん原因に対す
る自然放射線の割合は同程度と思われる。
表２ モデル人口・死亡者等による自然放射線によるがん死亡リスク
人数

人口

死亡者

がん死亡者

1.2 億人120 万人

35 万人

自然放射線のリスク
0.88%（対がん死亡者）*

率
1%

29%（対死亡者）

0.26%（対死亡者）

0.29%（対人口）0.0026%（対人口）2.6×10-5

リスク＊リスク係数（5.5×10-2 Sv-1）×加重平均生涯線量（160 mSv）

５．おわりに自然放射線による発がんがあると必ずしも明らかになっているわけではない。しかし、

29

自然放射線によるリスクがあるとすれば、上限値としてどれぐらいかを推定した。
わが国で毎日浴びている自然放射線（1 年で 2.1 mSv）に基づけば、生存している個人の加重平均累積線量は、97 mSv となり、これは年間線量 2.1 mSv にわが国の平均年齢 45.5
歳を掛けた値に等しい。放射線によるがん死という観点からみた場合、個人の加重平均生
涯線量は約 160 mSv に相当するが、これは年間線量に男女の平均寿命（男：80.21 歳；6,191
万人、女：86.61 歳；6,539 万人）を加重平均した 83.5 歳を乗じた値（175 mSv）よりも少し小さい。
自然放射線によるがん死があるとしても、それは全がん死の 1%未満と見積もられる。
また、わが国の人口からみた場合の自然放射線のリスクは 2.6 ×10-5 と算定された。この値
は、リスク評価の分野で概ね容認されるとみられているリスクの 10-5 6)と同じオ－ダーである。本稿で使用したリスク係数は、高い生存率のがんも含んだ罹患率から出されていること、また低線量率で長期間継続して被ばくしている間に傷害を受けた細胞の修復や排除のあることを考慮すると、実際の自然放射線によるリスクは本稿で求めたリスクよりもかなり小さいと考えられ、それゆえ、本稿で求めた値は上限値といえる。

参考文献
1) United Nations; Sources and Effects of Ionizing Radiation. UNSCEAR 2008 Report. 日本語版（放医研）第１巻 p.351, 2008.
2) 原子力安全研究協会；新版生活環境放射線（国民線量の算定）、p.73, 平成 23 年．
3) 厚生労働省：平成 26 年(2013)人口動態統計の年間推計、統計表第７表
4) ICRP; Annals of the ICRP, ICRP Publication 103, p.182, 2007.
5) Harvard Report on Cancer Prevention: Cancer Causes & Control 7, 55-58, 1996.
6) 辻本忠、草間朋子；放射線防護の基礎（第２版）、p.288, 日刊工業新聞社、1992.
要旨
外部被ばく及び内部被ばくに係る自然放射線による発がんリスクを算定した。名目リスク係数は、ICRP2003 の名目リスク係数 5.5×10-2 Sv-1 を使用した。算定では、2 つの仮定を置いた。すなわち、①放射線の生体への影響は単純な経年累積線量で、逓減効果はないとし、②しきい値のない直線仮定の LNT モデルの採用である。累積線量は、年齢 5 年刻みの加重平均累積線量を採用した。データには、わが国の平成 25 年の人口動態（厚生労働省）
を使用し、また、年間の放射線量は 2.1 mSv（原子力安全研究協会；新版生活環境放射線
2011）とした。わが国の平均年齢は 45.5 歳であるから、平均線量は 95.6 mSv となり、また、男女を平均した平均寿命は 83.5 歳であるから、生涯線量は 175 mSv となり、さらに、がん死亡者に限ると、年齢加重の平均生涯線量は 160 mSv となる。
仮に、放射線により発がんした人は、治癒がなくすべて死亡すると仮定すると、自然放射線による発がんによる死亡率は 0.88%、また死亡者に対する割合は 0.29%、全人口に対する割合は 0.0029%（リスク：2.9×10-5）となる。ただし、概数として、日本の総人口 1.2 億
人、年間の死亡者 120 万人、がん死亡者 40 万人としている。

30

ISRE2016 (2017) 31-34

Nuclear Technology Education at the Secondary Level in
ThailandThanakit LERDLU, Professional Level Teachers,
Hongsonsuksa school under the Patronage of HRH Princess Petcharat Rajsuda Sirisopaphannawadee.
E-mail: thanakit553@hotmail.com
Chuntana BOONMARK, Professional Level Teachers,
Sa-nguan Ying school, Suphanburi. E-mail: tippawan154@hotmail.com
Prayong PIYANART, Professional Level Teachers,
Princess Chulabhorn's College, Pathumthani. E-mail: prayongpccp@hotmail.com
Surat CHUMTHONG, Practitioner Level Teachers,
Sa-nguan Ying school, Suphanburi. E-mail: chedsurapatter@gmail.com
Mutita AODTON, Practitioner Level Teachers, Banchangkarnchanakulwittayaschool, Rayong. E-mail:mutita.maew@gmail.com
Khawee SUNTHORNOWARD, Practitioner Level Teachers, Banchangkarnchanakulwittayaschool,
Rayong. E-mail: Khaweekub@gmail.com

Abstract
The modern development of nuclear technology has both advantages and disadvantages. In Thailand,
an electric nuclear factory will be operational in 2020. Therefore, people should be informed about thepositive and negative effects of nuclear technology. An authorized organization should pass thisknowledge down to people. At the moment, there is no official science organization has incorporated
nuclear technology into its curriculum. In accordance to this problem, the researchers of this article
have discussed, surveyed, and collected data about nuclear technology education at the secondary levelin Thailand. This was done in order to present the various problems with nuclear education andidentify how to reform them.
The results of this study show that there are less informational resources for people or students toaccess. Additionally, it was found that people didn’t realize how important nuclear education is. Thiswas further reflected in the abysmal level of nuclear technology education at the secondary level.

31

1. BackgroundNowadays, a great number of countries benefit from nuclear energy and radiation in many aspects
such as agriculture, medicine, and industry. Although the modern development of nuclear technology isnecessary, this caused the crisis of fossil energy and pollution, one of the factors of severe global
warming and climate change. Also, the modern development of nuclear technology has both advantages
and disadvantages. In Thailand, an electric nuclear factory will be operational in 2020. Therefore,
people should be informed about the positive and negative effects of nuclear technology. An authorizedorganization should pass this knowledge down to people. At the moment, there is no official scienceorganization that has incorporated nuclear technology into its curriculum. Authorized organizations or
schools should realize the importance of passing this knowledge down to students by adding nuclear
information into the science curriculum at the secondary level. Students should be informed about theseissues before entering adulthood. In Thailand, there was less content about modern development of
nuclear technology in physics courses.
In accordance to this problem, the researchers of this article have discussed, surveyed, and collected
data about nuclear technology education at the secondary level in Thailand. This was done in order topresent the various problems of nuclear education and identify how to reform them. This study will also
be presented to the fifth international symposium on Radiation Education on the 16th through the 19th
December, 2016 in Japan.
Purposes
1. To study issues of nuclear education at the secondary level in Thailand.
2. To present the resolution of nuclear education issues at the secondary level in Thailand.
This article will discuss issues which were directly experienced by Physics teachers and researchedfrom other resources. The suggestions of this article were analyzed by only the authors and a
representative of Thai teachers. This article may not cover all the issues that were faced in Thailand.
2. Nuclear education at the secondary level in Thailand
The study of nuclear education in Thailand is normally a part of Physics course in higher secondary
level education. In Fundamental Physics courses, the content includes radioactivity and nuclear energy.
It is divided into three parts: radioactivity, radiation and human and nuclear energy. In Additional
Physics courses, the content is divided into eight parts containing the discovery of radioactivity, nuclear
transformation, isotope, nuclear stability, nuclear reaction, the advantages of radioactivity and nuclear
energy, natural radioactivity, and its disadvantages and prevention. Actually, these courses focus onmechanics, wave, dynamics, electricity rather than nuclear education.
Banchang Kanchanakulwittaya High School (2559), Muang, Rayong Province. There are threephysics teachers who teach at the higher secondary level (grade 10, 11 and 12). In grade 10, students
will only study mechanics. In grade 11, students will study mechanical wave, sound wave, light wave,
light qualitative physics, atomic physics, and nuclear physics. In grade 12, students will study dynamics,
electricity, electromagnetic wave. At each level students will spend three hours per week studying the32lesson. Additionally, all schools have holidays on which students do not attend class. Thus, teachers
have to shorten each unit to teach all of material. Teachers do not teach in deep detail about the positive
and negative effects of nuclear energy, but instead focus on calculation of energy because it importantfor student’s national test or university exams. Teachers do not teach in a deep detail about positive andnegative effect of nuclear energy but they focus on the calculation of energy because it is important for
students’ national test or university exam. Students know what the advantages and disadvantage of
nuclear energy are, but they are not informed how people can use it in the most beneficial ways. In a
survey where students were asked what they first thought about nuclear energy, 100 % of students said
that it could make nuclear bombs and was dangerous. Teachers need to teach more about how nuclear
energy can be beneficial when used in the right ways and how people can prevent the disadvantages
from nuclear energy.
Sa-nguan Ying High School (2015), Muang, Suphan Buri Province. This school opens to teachstudents grade 7-12 and there are three physics teachers in this school. Physics courses will be taught ingrade 10-12. There were two sections of physics course taught in this school. In the first section, 20082015, physics courses were based on the Thai national curriculum in 2008 and the Institute for the
Promotion of Teaching Science and Technology. The courses are divided into The Basics of Physics
and Physics 1-5. In grade 10, students study the Basics of Physics, including nuclear energy andPhysics 1 (mechanics, movement, momentum, mass, and force). In grade 11, students study Physics 2,
including work and energy, momentum, rotational motion, equilibrium and elasticity and Physics 3(mechanical wave, sound wave, light wave. In grade 12, student study Physics 4 and 5. The courses
includes dynamic, electricity, electromagnetic, fluid and heat, atomic physics and nuclear physics.
Students have three classes per week for all levels. During the second semester, in grade 12, teachers
always could never teach students the topic of physics nuclear because university exams would start
before the end of school semester. Thus grade 12 students had to take the national exam without
learning nuclear physics. This is the same problem that Ban Chang Wittaya School has faced. For thesecond section, in 2016, the Physics curriculum has been reformed. Grade 12 students have to study
Physics 1-5 by finishing the first semester of grade 12. Students study fundamental Physics in thesecond semester so they will have time to review the lessons before taking a national test and university
examination. In Thailand, at Kasetart University, there is a Department of Radiation and Isotope forstudents who are interested in this field. In 2015, a Sa-ngun Ying student studied in this field. At Sangun Ying School, the Physics lessons are based on the objectives of the national curriculum. As partof their teaching materials, teachers also use a book written by the Institute for the Promotion ofTeaching Science and Technology. In addition, teachers use a cartoon book written by the Office ofAtoms for Peace. Students also present and display informational boards about the modern
development of nuclear technology. As part of the National curriculum, students have to do anassessment, a basic operation, and a nuclear test.
Hongsorn Suksa High School (2016). Teachers will begin by teaching the topic of radioactivity
discovery, followed by the experiment of scientists, nuclear structure, Half Life Analog Kit, comparing
and radioactivity decay, analyzing isotope and mass of isotopes, nuclear forces, binding energy,
binding energy to nuclear, fission and fusion reaction of nuclear energy, the positive and negative33

effects of nuclear and radioactivity, and finally how to prevent the bad effects of nuclear energy andradioactivity. Teachers manage the class by focusing on the scientific processes including researching,surveying, checking, recording data, discussion and data cluttering.
Conclusion
The finding demonstrates that there were problems of nuclear education in Thailand including thefollowing:
1. There were less informational resources for students to access.
2. It was found that people did not realize the importance of nuclear education is.
3. This was further reflected in the abysmal level of nuclear technology education at thesecondary level.
Implementation
1. Add more informational resources for students for access readily in anyplace.
2. Physics Teachers should help students to realize how important and beneficial nuclear
energy is.
3. Add more ways to inform students about positive and negative effects of the modern
development of nuclear technology.

References
1) The Institute for the Promotion of Teaching Science and Technology, Ministry of Education, 2011.
Basics Physics. Bangkok.
2) The Institute for the Promotion of Teaching Science and Technology, Ministry of Education, 2011.
Physics 5. Bangkok.

34

ISRE2016 (2017) 35-38

Radiation Education and Nuclear Power Plant in Taiwan
台湾における放射線教育と原子力発電所について
Chin-Wang HUANG
黄金旺

Emeritus Prof., Chung Yuan Christian University,
台湾中原大学栄誉教授
200, Chung Pei Rd,Chung Li,Taiwan 32023,RO.C.
台湾桃園市中壢区中北路 200 號
E-mail: yt_huang@cycu.edu.tw

Abstract
Radiation education at school and the current state of the nuclear power plant in
Taiwan are described. In compulsory education, radiation education and radioactivity
education are not so much accomplished. The explanation of radioactive materials
using a periodic law table is mentioned during "natural life and science technology” byscience of a junior high school. Safety of radiation, division chain reaction and nuclear
fusion reaction are mentioned about an X-ray at a high school. A chapter of nuclear
physics and nuclear chemistry is in the general physics and the chemistry texts of auniversity, but the majority teachers actually do not lecture.
There are four nuclear power plants and six nuclear power plants are working atpresent in Taiwan. A problem describes some facts to administrative correspondence ofa government in a safety management side in a nuclear power plant.
１.はじめに
台湾における学校での放射線教育と原子力発電所の現状について述べます。
義務教育では、放射線教育及び放射能教育はあまりなされていません。中学校の理科で、「自然の生活と科技」の中に周期律表を用いた放射性物質の説明が載っています。高校では X 線について放射線の安全性、核分裂連鎖反応及び核融合反応が記載されています。大学の一般物理と化学の中に、核物理と核化学の章がありますが、大部分の教員は講義していないのが現状です。
台湾には 4 つの原子力発電所があり、現在 6 基の原発が稼動しています。原発の安全管
理面で、政府の行政的な対応に問題があることなど述べます。
２．学校における放射線教育について
台湾の小・中学校の義務教育の就学率は、95％以上に達成されています。義務教育における、放射線と放射能に関する教育は、あまりなされていないのが実情です。小学校の理科に「自然と生活科技」がありますが、その主な内容は太陽の光のエネルギーを利用した
35

電球の発光について述べているだけです。
2011 年 3 月 11 日、東日本に大地震と大津波が発生し、莫大な被害が起こりその結果、東京電力福島第一原子力発電所の原子炉が水素爆発し、放射性物質による汚染おこしたことが、台湾で特別に注目されています。今まで、中学校の授業が軽視している、放射線の知識の内容を改めて、少しばかり充実されています。最近の中学校理科「自然の生活と科技」の中に、周期表の発明者とともに原子番号が 92 より大きい超ウラン元素は人工的に造られ、原子核の性質が不安定なため短時間で安定な元素に変化する、との紹介があります。
また、このような性質をもった元素が放射性物質で、マリー・キュリーが放射能の研究でノーベル物理学賞（1903 年）とラジウムとポロニウムの発見でノーベル化学賞（1911 年）と 2 回受賞したこと、同位元素（同位体）は原子構造が異なっているが、化学的性質は同じであるとの説明があり、例として、11H および 21H が挙げられています。
高校の理科に「基礎物理と基礎化学」があります。基礎物理のエネルギーの項目に、X線の発見とその応用について、X 線の性質は電気および磁力に影響されないが、感光性があることが載っています。また、その応用は、結晶構造の解析、生物の品種改良、医学的な診断、そして空港の手荷物検査などに利用されていることが書かれています。放射線の安全に関しては、α、β、γ 線それぞれの放射線強度の比較、放射線の強さは、距離の二乗に反比例し、時間に正比例の関係にあるなどが記されています。また、日常生活中での放射線量について、台湾一般居住民の自然放射線量の平均値は年間 2 mSv、また日常生活中の放射線量の図が掲載されています。コバルト-60 による局部照射（全治療）の放射線量は、60.000 mSv 、テレビジョンから 3 m の距離で毎日 1 時間見るとすると、年間の放射線量が 0.01 mSv と述べられています。
核分裂連鎖反応については、ウラン-235 に熱中性子を照射すると核反応が起こると説明されています。その核反応のときに放出された熱を、原子力発電所で発電に利用しています。火力発電所は大量の二酸化炭素ガスを排出して、酸性雨が発生し環境に悪影響を及ぼすことがあります。そのほかに、核融合についても触れていますが、簡単な紹介に留まっています。
基礎化学の化学とエネルギーの項目では、核反応前後の質量数の変化によるエネルギーの算出は、アインシュタインが提出したエネルギーと質量の式（E = mc2 ） から求めます。
核分裂反応は、熱中性子による反応で、235 U + 1 n → 141 Ba + 52 Kr + 3 1 n,
92
0
56
36
0

235 U + 1 n → 141 Xe + 90 Sr + 3 1 n
92
0
54
38
0

235 U + 1 n → 140 Cs + 93 Rb + 3 1 n,
92
0
57
37
0

235 U + 1 n → 140 Xe + 90 Sr + 3 1 n
92
0
54
38
0

などの式から核反応により放出されるエネルギーを算出します。
核融合は二つの軽い原子核が、超高温度の条件下において核反応を起こし、より重い原子核に変わる際に大量のエネルギーを放出します。たとえば、21H + 31H → 42He + 10n +エネ
ルギーで、太陽の中では核融合反応が引き起こされています。また、東京電力福島第一原
子力発電所事故も紹介されています。

36

３.台湾の原子力発電所について
大学の一般物理と化学には、英文版と中文版の教科書が多数あります。その中には、核物理と核化学が関連している章がありますが、大部分の教員はこれらを講義していません。ただし、ラジオアイソトープ(RI) と放射線の使用者
は、国家試験をパスして初めて使用の資格が得られます。
政府は、原子能委員会を設置し、RI と放射線を全国統一して管理を行っています。原子力発電所は、経済部（通産省）に付属しておりますので、安全管理については、スムースに統括することが困難であると感じています。また、県政
府には放射性物質の管理組織制がなく、一般大衆は RI、放射線に対して無知の状況です。
台湾には、四つの原子力発電所が設置されています。原
Fig. 1. Atomic power station

発Ⅰ、原発Ⅱ、原発Ⅲは運転中、原発Ⅳは近いうちに建設が完了し、安全審査がなされます。Fig. 1 と Table 1 から、原発Ⅰ、原発Ⅱ、原発Ⅳは台湾の北部にあり、原発Ⅲは南部にあります。原子力発電所を設置する地域の選択には、まず活断層がある地震帯と人口密度の高い場所を回避することが先決と考えます(Fig. 2)。

Table 1. Atomic nuclear power stations
原発Ⅰ

原発Ⅱ

原発Ⅲ

原発Ⅳ

新北市

新北市

屏東県

新北市

石門区

萬里区

恒春鎮

貢寮区

*1. 1978.12

1981.12

1984.7＿＿＿*2 1979.7

1983.3

1985.5＿＿＿

容量

1,272 kw

1.970 kw

1.902 kw

2,750 kw

型式

BWR

BWR

PWR

BWR

停止

2019.72023.32025.5場所

運転しかし台湾の原発Ⅰ、Ⅱ、Ⅳの原発は、いずれも設置条件に合致しておりません。今までは、原子力発電所の事故演習は、毎年 1 回おこなわれています。原発から半径 5 km 圏内の少数市民が事故演習に参加していましたが、最近やっと 9 km 圏内に拡大されました(Fig. 3)。
福島第一原子力発電所事故を考えると、台湾でこのような状況は、政府経済部の非常に無責任なやり方であると思います。

37

Fig. 2.

Fig. 3.

Fault of north in Taiwan

Distance from atomic nuclear power station

４．最後に
以上、台湾の一般市民の放射線・放射能の知識不足、さらには管理者の放射線に対する
安心・安全思考の軽視の傾向があり、いろいろな課題が山積しています。このような情況から今後益々、放射線教育の充実を図っていくことが重要と考えています。

38

ISRE2016 (2017) 39-47

An Example of Lectures on the Nature of Radiation
for General Public
Hiroshi KUDO
Professor Emeritus of Tohoku University
Tohoku Radiation Science Center, Chuo 2-8-13, Aoba-ku, Sendai 980-0021, Japan
E-mail: kudo.hrs@nifty.com
Abstract
To make general public interested in and familiar to radiation, the author has given lectures on the basic
science of radiation for more than a decade. Because scientific literacy of general public is limited, it was
sometimes hard to let people understand what radiation is and how it interacts with matter, within a limited
time available for the lecture. After the FUKUSHIMA nuclear accident in 2011, however, the situation has
dramatically changed: a lot of Japanese people worried about health hazards of radiation, stirred up mainly
by mass media that emphasized only risks of radiation even at the dose as low as 1 mSv. Variety of news
put the society into confusion for a while. At present, more than 5 years since the nuclear disaster, theconfusion has almost settled down and most of the people fairly accept not only the risk, but also the benefitof radiation. The author presents an example of his lecture, by which the audience could understand thenature of radiation. To know fundamental features of radiation such as the origin and interactions withmatter would help the audience to feel safe from danger of radiation in their daily life.
1. Introduction
Many Japanese vaguely fear radiation and think that they will not be exposed to radiation if there is no
nuclear power station. On the other hand, however, many Japanese are pleased to visit hospital for diagnosis
using radiation. Their contradictory behavior would come from a lack of radiation literacy due to a limited
chance of radiation education. In fact, the teaching of radiation in a Japanese junior high school has restored
in 2012 for the first time in 30 years.
From experience of giving lectures about radiation to general public for more than a decade, the author
found some key factors of letting them interested and understood what radiation is and how it interacts withmatter. One of the significant factors is to give a lesson of radiation as a “science class”, not only for pupils
in school, but also for general public. The learning of basic science of radiation can make an audience feelsecure for a low level of radiation, although they would probably like to know definite radiation effects on
living bodies, particularly for the people living in Fukushima.
In the present paper, the author will introduce a science talk on the nature of radiation with emphasis laidon its origin and interactions with matter. It is stressed that radiation is not necessarily special, but ubiquitousin the environment. Knowing its origin and nature, people would be able to express reasonable fear about arisk caused by radiation.

39

2. An example of the talk “The nature of radiation: Its origin and interactions with matter”
Two years after the nuclear accident of Fukushima Daiichi Nuclear Power Station, Fukushima Prefecture,
Japan, the author was invited to talk about radiation to people evacuated from Katsurao-mura that is avillage where all residents left after the nuclear accident in 2011. That was his first occasion to talk in frontof the evacuees from the nuclear accident. The big confusion stirred up mainly by mass media immediately
after the accident excluded the talk on real nature of radiation. Scientists who told that the exposure ofradiation as low as 1 mSv had no risk were hardly trusted and did not invited to talk in front of the evacuees
immediately after the accident. But after the talk on that day, the author was pleased to hear from audiencesthat the talk helped them to understand the real risk of radiation and they were encouraged to be back totheir home as soon as possible. “We should have heard today’s talk earlier,” they added.
In the following described are the main subjects of the talk.
2.1 Introductory remarks
Someone believes that there is no radiation if we have no nuclear power plant. But this is
misunderstanding with prejudice. Huge doses of radiation, like in a core of nuclear reactors, causes a big
risk for health, but radiation itself is ubiquitous in the environment, albeit low in dose. Knowing its origin
and nature as well as its interaction with matter, we will be able to express reasonable fear about radiation.
This is a basis of the lecture, and the author gave the lecture in an atmosphere making the audience feelthemselves to be attending in a “science class” of high school.
2.2 The origin of radiation
The source of radiation is a nucleus in the atom as illustrated in Fig. 1. And radiation is ubiquitous in theenvironment, because everything in our world is ultimately composed of various atoms. The atomcomprises of a nucleus with positive charges and electrons (e–) with a negative charge. The size of an atom
is around a few ångström (Å) or ~100 picometers [pm, 10–12 m] and that of the nucleus is in a order of
femtometers [fm, 10–15 m]. The nucleus is composed of protons with a positive charge and chargelessneutrons. The mass of both particles is about 1 atomic mass unit [u] and that of an electron is 1/1840 of a
proton or a neutron.
2.3 The mass number and nuclear
structure
Immediately after the nuclear accident inFukushima, 2011, we have frequently readsuch words as “Radioactive iodine-131 andradioactive caecium-137” in newspapers oron TV. These digits 131 for iodine-131(131I) and 137 for ceasium-137 (137Cs) arecalled the mass number, and indicate

Fig. 1. A model of the structures of an atom and a

directly the feature of nuclei. The mass

nucleus.

number means the sum of protons and40neutrons in a nucleus, and we can understand that 137Cs with the atomic number 55, for instance, has 82
neutrons in the nucleus (Fig. 2). The number of neutrons is of importance, because there are many isotopes
in the same element; the isotope means nuclear
species with the same number of protons but
different in the number of neutrons such that133

Cs, 134Cs and 137Cs. Of these isotopes; 133Cs is

not radioactive but stable, while both 134Cs and137

Cs are radioactive. The difference between

134

Cs and 137Cs are in the nuclear character suchas the half-life, ~2 years for 134Cs and ~30 years
for 137Cs, as well as the energy of emitted

137

Fig. 2. The nuclear structure of caesium-137 ( Cs) radiation.
consisting of 55 protons and 82 neutrons.
The atomic number is equal to the number ofprotons in the nucleus. We usually place the mass number on the left shoulder of the symbol of an element,
like 137Cs, but we do not need to put the atomic number because the symbol of a chemical element holds theatomic number as shown in Fig. 3. We use another term “nuclide”, that represents every nuclear species
with the mass number to the symbol of an element like 2H, 4He, 137Cs and 235U regardless of elements.
More than 3000 nuclides are known until now and 90% of which is radioactive nuclides with a variety ofhalf-1ife from picoseconds to 14 Giga years (232Th).
2.4

The

real

natureofradiation
The radiation is defined as“moving energetic particles orphotons” emitted from nuclei,
but it sounds a little bit difficultfor general public to understand.
Although

such

names

of

radiation as  rays, rays and 
rays are popular, most people
do not know what the radiationis, because it is difficult to see
on eyes. The first radiation was
X ray, which was discovered inFig. 3. The terms element, isotope and nuclide.

1895 by German physicist W. C. Röntgen. He named it as X rays because of the faint nature of it at thattime, albeit supposed to be unseen light. But the use of X rays spread rapidly all over Europe to takephotographs inside the living body, and Röntgen received the first Nobel Prize in physics in 1901. Hearing
the Röntgen’s discovery of strange rays, French physicist A. H. Becquerel noticed that something unknown
was emitted from uranium ore, and named it as alpha radiation later. At the same time, French physicists
Pierr Curie and Marie Curie found so called  rays emitted from newly discovered radium. And these three41

scientists received the Nobel Prize in discovery of spontaneous radioactivity and radiation phenomena in
1903.
At the present time of morethan 120 years since discoveriesof radiation, we know the realnature of radiation: X ray is thephoton (a few keV in energy)
emitted from atomic shells, 
ray the bunch of 2 protons and2 neutrons (i.e. 4He2+) emitted
from

Fig. 4. A variety of radiation that defined as moving energetic
particles or photons emitted from nuclei; the X ray is emitted fromatomic shells.

nucleiheavier

bismuth (Bi),–high-energy

electronthan

ray the(e–)

emitted from nuclei and  ray
the high-energy photon emitted
from nuclei, as summarized inFig. 4.

2.5 Interaction of radiation
with matter
Radiation interacts mainlywith electrons in atoms
comprisingmaterials

including living bodies, andthe interaction occurs whenradiation is absorbed in thematerial, because the energy
carriedbyradiationistransferred to or deposited inconstituent atoms of thematerial. The main processes
are ionization and excitation

Fig. 5. Interactions of radiation with matter.

of the electron shells, resulting in production of active chemical species such as ions, radicals and solvatedelectrons (Fig. 5). The term “active chemical species” sounds rather difficult, but the audience would befamiliar to “active oxygen.” If such active species play hazardous roles in living bodies, the radiation is arisk to health. On the contrary, if such active species play therapeutic roles for cancer, for instance, theradiation is of a great benefit to our life.
When radiation interacts with gaseous species, electrons (e–) are emitted through the ionization processes.
And we can use such electrons to detect the radiation; e.g. a G-M (Geiger-Müller) counter and an NaI
scintillation survey meter.
42

Radiation penetrates through matter and can be used for medical diagnosis such as an X-ray photographtaken by using X rays, as most of us have experienced. The X ray is widely used also in industries as asignificant mean of a nondestructive
inspection and we are familiar to abaggage inspection at airports.
The penetrability of radiation
varies depending on the kind ofradiation. As illustrated in Fig. 6, 
rays do not penetrate a sheet of paper,
while  rays penetrate a sheet ofpaper but stop at a thin plate ofaluminum. The X rays as well as rays stop at a thick plate of heavier
metals like iron and lead. Neutron
beams are somewhat strange and stopin water as well as in concrete blocks

Fig. 6. Depiction of penetrability of ,  and  rays as well
as neutrons. When the particles or photons are stopped, they
are not radiation anymore.

through elastic collisions with protons in the water (H2O). Radiation is defined as “moving energetic
particles or photons”, and it is not radiation anymore when these particles or photons stop at such shielding
materials as paper, metals and concrete. It is instructive to note that helium gas filled in balloons, forinstance, is an underground resource resulting from energetic 4He2+ particles; i.e. the origin was  rays
emitted from uranium and thorium ores in the earth’s crust.
2.6 Radiation and radioactivity
Confusion is seen in the use of technical terms “radiation” and “radioactivity.” It should be clarified asfollows: Radiation like ,  and  rays are substantial because they are moving energetic particles orphotons emitted from radioactive materials or radionuclides, albeit unseen. On the other hand, theradioactivity is a concept or definition. One of the concepts is a natural character of spontaneous emission ofradiation from matter; used by A. H. Becquerel for the first time in 1896. At present, the radioactivity isdefined as the number of atoms
decaying every second and its
unit is becquerel [Bq] in the SI
system. Namely, the meaningof radioactivity is the amount ofradioactive

materials

orradionuclides, although most ofJapanese mass media use itwith a meaning of radioactive
materials in confusion.
The unit of the radiation dose

Fig. 7. The terms radiation and radioactivity.
43

or equivalent dose is sievert

[Sv],

which

is

used

for

assessing radiation effects on aliving body, derived from theenergy absorbed in matter(kJ/kg) by exposure to radiation,
expressed in the unit of grey
[Gy].

The

comparisonofradiation and radioactivity issummarized in Fig. 7.
The radioactivity decreases
at a constant rate specific to anuclide, and the reciprocal of
the rate is called a half-life (T1/2)

Fig. 8. A feature of 8-days half-life of iodine-131 (131I) and a list ofwhich is the amount of time

half-lives for some nuclides.

that it takes to lose half its radioactivity
as shown in Fig. 8, and the inset of thisTable 1. Biological half-life and physical half-life.

figure lists half-lives of popular nuclides
such as 131I (T1/2 = 8 days) and 137Cs (T1/2= 30 years). The shortest half-life listed
here is 15 hours for 24Na and the longest
is 4.5x109 years for 238U.
In addition to the “physical half-life”
of radionuclides mentioned above, wesometimes use another half-life called a“biological half-life” as shown in Table
1, that is used when we discuss a risk of internal exposure of radiation from ingested radioactive materials.
2.7 Exposure to radiation in daily life
As shown in Fig. 9, we are exposed to
2.4 mSv of radiation a year on world
average. That is the sum of 0.4 mSv fromcosmic rays, 0.4 mSv from the groundcontaining uranium (238U) and thorium(232Th), 1.3 mSv from radon gas (220Rn,
222Rn) inhaled from indoor air and 0.3 mSv

from daily ingestion (40K). Potassium is
one of the essential elements for living
things and our muscle contains 0.2% ofFig. 9. World average doses a year for living bodies in potassium. Although the natural abundanceof 40K (T1/2 = 1.3 x 109 years) is as low asdaily life on the earth.
440.01%, the equilibrium radioactivity of 40K in our body resulting from ingestion through everyday life iscalculated to be around 4000 Bq for a person with 60 kg of weight as shown in Fig. 10, and the equivalentdose from 40K is estimated to be about 0.3 mSv a year. This figure also depicts the typical radioactivity of40

K in a kilogram of foods (Bq/kg) such as rice, spinach, fish, seaweed and milk. The value is clearly high inthe potassium chloride (KCl) fertilizer widely used in agricultural fields.
2.8

Typicalaffairs

associated with exposure toradiation
To discuss a health risk
caused by radiation, it isinstructive to pick up typicalaffairs associated with theexposure to radiation. Table
2 lists the related affairs as afunction of the equivalentdose (mSv). Although it isdifficult to make clear theclinical

symptomatexposure to radiation below
200

mSv,

a

Fig.10. Radioactivity of potassium-40 (40K) in muscle of living bodytaken from foods we ingest in daily life.

temporarydecrease in the number

Table 2. Typical affairs associated with exposure to radiation.

of leucocyte in blood
becomes clear around
500

mSv.

In

this

respect, a twice a yearof blood tests are
obliged in Japan for
persons working in acontrolled

area

for

radiation, in addition tothe official dose limitof 50 mSv a year and
100 mSv in very five
years. Above4000

mSv of exposure for awhole body is so
dangerous as 50% of
persons will die within
30 days. In Japan, a huge number of persons were killed in exposure to terribly huge doses of radiation45

induced by the explosion of nuclear bombs in Hiroshima and Nagasaki in 1945.
Figure11

summarizes

dose

limits in respects ofour daily life andthe obligation for
professional
workers. We should
feel

safe

for

exposure as low as
1

mSv

a

year,

although we should
always be careful toFig. 11. A dose limit recommended for general public by ICRP (International
Committee on Radiation Protection) and the official dose limits applied toprofessionals working in controlled areas.

be exposed to ahigherdoseofradiation. Here, it is to
be pointed out thatJapanese people are receiving about 4 mSv a year of radiation on average through medical diagnosis. Thisvalue is the highest in the world, and the availability of such a medical diagnosis makes Japanese thelongest life in the world.
2.9 Applications of radiation and benefits for daily life
In developed countries, radiation is used in a variety of fields such as medicine, engineering andagriculture as well as in research. Figure 12 shows examples of the application of radiation in Japan. In
addition to the medical use of radiation for diagnosis and therapy, we would recognize that the radiation
sterilization of medical device — e.g. sterilization of medical needles and syringes by -ray irradiation — isof great benefit to medical safety. In the field of materials modification, on the other hand, radiation is used
to produce foamed polyethylene to be used for a dashboard of vehicles and heat-resistant cables used forwiring around a high-temperature engine.

Fig. 12. Beneficial useof radiation in medicine,
agriculture, engineeringandresearchdevelopment.
46&

The above-mentioned is the essentials of the one-hour lecture for general public. The tables and figuresattached here are copies of the slides selected for a handout distributed to the audience.
3. Summary
From the experience of giving lectures for general public including evacuees from the nuclear accident inFukushima, the present author has recognized that it is effective to give a lecture with emphasis laid on thebasic science of radiation rather than on the influence of exposure to radiation. Although it seemed first aroundabout way for the audience, the learning of the basic nature of radiation was eventually a shortcut tounderstand a real risk of radiation even if any special case occurs.

47

ISRE2016 (2017) 48-53

Radiation Education Experiments and Other Science
Education Experiments with a Handmade GM Counter
手作り GM 管計数器による放射線教育実験と他の理科教育実験
Chizuo MORI
森 千鶴夫
Chubu Atomic Conference, Adviser
中部原子力懇談会 顧問
2-10-19 Sakae, Naka-ku, Nagoya, Aichi Pref., 460-0008, Japan〒460-0008 愛知県名古屋市中区栄2-10-19 商工会議所ビル6F
E-mail: moric@wh.commufa.jp
The seminar on radiation education experiment named “Radiation watching” has been held overmany years by Chubu Atomic Conference for high school students and teachers. The participants
fabricate GM counter and counting equipment by themselves. We recently developed air-filled GM
counter with a darning needle as an anode. The counter is very easy to fabricate and the counting
performance is stable. The usual radiation measurement experiments are possible. Moreover, since
this counter can open the widow, alpha-particle source is able to be put inside the counter andalpha-particle absorption experiment is possible. When a small metal plate such as aluminum or zinc
is put into the counter and irradiated with light, photoelectrons can be counted, and hence theexperiment of metal surface oxidation is possible. When optical films are inserted between the lightemitter and GM counter, the absorption of ultraviolet ray can be evaluated. The air-filled GM
counter would be useful for science education experiments as well as for radiation education
experiments at school teaching.
“放射線ウオッチング”と名付けた放射線教育実験を、中部原子力懇談会が中学・高校の生徒や先生を対象として長年開催してきた。受講者がＧＭ管や計数器を自ら組み立て、放射線実験をする。最近我々は、とじ針を陽極にした組立ての極めて簡単な空気ＧＭ管を開発した。通常の放射線実験は可能であるが、ＧＭ管の窓を容易に開くことができるため、中にアルファ線源を入れたアルファ線の吸収実験、薄い金属板を入れて外から光を照射す
る光電子放出実験、紫外線吸収実験、金属表面の酸化やエキゾ電子放出などの放射線実験
以外の実験ができるので、中学・高校の先生がこれらの実験に活用することができる。

Key words: radiation education, experiment, GM counter, handmade, photoelectric effect,
ultra-violet ray, oxidization, exo-electron, electrostatic experiment48

1. Introduction
Radiation education experiment is a part of radiation education. However, experiment needs
experimental instruments and is generally time consuming. It is therefore not so easy to carry out
experiments in the class work. The author considered that school teachers might hesitate to performthe experiments only for radiation education. They might be interested in using the radiation
education experimental instruments for other science experiments or in carrying out radiation
experiments combined with other general science experiments.
The author and his collaborators developed handmade GM counter filled with air with a version
of a GM counter 1). Since it is possible to open the window of the counter, various specimens can beinserted in it and some general science experiments other than radiation experiments became
possible.

If radiation education experiments orexperimental equipment can be related to other(A)

science education experiments, it would be(B)more attractive and educational. Teachers inhigh schools and even in elementally schools
would be interested in such experiments.
2.

Counting

equipment

andradiation

experimentFig. 1(A) shows a handmade GM counterand some metal plates to be put inside thecounter. The GM counter had a darning needle(C)

as an anode and electric conductive paper lined
inside a plastic cup as cathode. The window
was covered with thin plastic film. Butane gas
from cigarette lighter was blown into GM

Fig. 1. (A) Handmade GM counter with metal
plates, (B) cross sectional view of the counter,(C) light shield box covering GM counter andcounting equipment.

counter for about 10 seconds as quenching gas.
(B) shows the cross-sectional view of thecounter, and (C) the whole view of theequipment with a light shielding box including
GM counter in it.
Fig. 2 shows Plateau curve of the counter.
The applied voltage was decided to be 4.2 kV.
Fig. 3 shows absorption curves of alphaparticles emitted from a monazite source 2) andso-called mantle source. The absorber was
cooking aluminum foil with thickness of 12 μm.

Fig. 2. Plateau curve of the counter

Experiment on alpha particle absorption is not

so easy because of very short penetration range of the particles.

49

3. Experiments other than radiation experiment
3.1 Photoelectric effectFig. 4 shows the experimental setup (left) and thephotoelectron count rate for various materials (right).
Fluorescent light tube emits visible light andultra-violet light (UV) which enter into the GM
counter through a diaphragm aperture of the lightshielding cup and through the transparent back ofplastic GM counter cup and irradiate the surface ofspecimen put inside the counter. Photoelectrons are

Fig. 3. Absorption curves of alphaparticles from two different sources

emitted when the energy of UV is larger than theworkfunctionofthematerial. The work functionof aluminum is 3.3-4.2 eV
depending on the surface

Diaphragm
aperturecondition and that of zinc is
4.08

eV.

The

other

materials in the figure havelarger work function. Evenaluminum,surface

when
is

the

oxidized,photoelectron emission issmall.

Incandescent light

Fig. 4. Experimental setup for photoelectric effect (left) andphotoelectron count rate for various materials (right)

showed almost the same photoelectron emission to fluorescent light, whereas ordinary LED (lightemitting diode) light did not emit photoelectrons.
Photoelectric effect caused by γ-rays and X-rays is physically the same phenomenon to thatcaused by UV light mentioned here.
3.2 Absorption of ultra-violet rays by
various materials
UV rays emitted from fluorescent lighttube are absorbed by thin plate etc. Fig. 5
shows the count rate of photoelectrons
emitted from the oxidized surface ofaluminum when thin film etc. wereplaced on the diaphragm aperture shownin Fig. 4. When UV cut film was put on
the diaphragm the photoelectron countrate was very small compared with theFig. 5. Absorption of ultra-violet rays by thin film andglass plate, etc.

50

case of no film. Thin polyethylene film coated with sun block cream absorbed UV, whereas the film
coated with ordinary cream did not so much. Plastic glasses made with CR-39 coated with UV block
material absorbed UV, whereas pure CR-39 did not so much.
Absorption of γ-rays and X-rays is similar to that of UV, but not to that of visible light.
3.3 Decrease of photoelectron emission
with elapsed time
The surface of zinc plate was fully
polished

with

emery

paper

and

immediately inserted inside the counter.
The count rates shown by circles ●in Fig.6 gradually decrease with elapsed
time due to the oxidization of thesurface. Background count rate andexo-electron count rates (mentioned
later) were subtracted.
When zinc plate was heated in a
toaster 80 ℃ for 10 second, the countrates shown by triangles▲ suddenly

decreased. The count rates for gamma
rays shown by ■ irradiated from theFig. 6. Decrease of count rate of photoelectrons
emitted from the fully polished zinc plate surface
with elapsed time after polishing. When the plate washeated in a toaster for 10 seconds, the count rates
suddenly decrease due to the increase of oxidization.

outside of the counter with light
aperture closed were almost constantwhich showed the stable performance of the counter throughout the measurement time.
3.4 Exo-electron emission
When material surface was fully polishedor

irradiatedwithnuclearradiations,exo-electrons are emitted (Fig. 7). The
surfaces of three metals were fully polishedwith emery paper and immediately inserted
inside the GM counter. In this case, thediaphragm aperture was closed not to enter
any light. Exo-electron emission strongly
depended on the degree of polishing andlasted only for a few tens of minutes.
4. Utilization of high voltage supply

Fig. 7. Exo-electron emission from the heavily
polished surface of metal plates. In this case, thediaphragm aperture was closed not to enter any
light.

51

The handmade counting instrument proposed here contains high voltage supply up to 5 kV with
output resistance of 1 GΩ for safety. The resistance makes it possible even to touch on the highvoltage terminal. In our surroundings, there is no such safe high voltage supply, which is very usefulfor electrostatic experiment. Fig. 8 shows tissue paper cut into strips, which is connected to the highvoltage terminal. When the power switch was off, the strips were closed (left). Whereas the switch

Fig. 8. High voltage was not supplied tothe strips of tissue paper (left). The voltage
was supplied (right) and the strips opened.

Fig. 9.
Measurementof very highresistance R

was on, the strips opened.
As shown in Fig. 9, the high voltage was supplied to a handmade leaf electroscope through very
high resistance R which was a strip of thick paper with a resistance of 1011-1012Ω. Measurement ofsuch a high resistance is usually is not so easy. Measurement of the time (T1/2) to decrease the angleof the leaf to the half of the maximum angle gives the resistance R as follows when the capacitanceis known. The measurement of capacitance C is usually possible by using digital circuit multi-meter(tester).
R = T1/2/(C*ln2)
5. Conclusion
The handmade GM counter presented here is able to open its window, it is then possible to insert
various specimens inside the counter. When alpha particle source was put inside, alpha particle
absorption curve was easily obtained.
Science education experiments other than radiation experiment were proposed. When metal plates
were inserted inside the counter, the experiments on photoelectric effect by ultra-violet rays included
in fluorescent light, absorption of ultra-violet rays, oxidation of metal surface, and exo-electron
emission were possible.
The high voltage supply to the GM counter was able to utilize for electrostatic experiments.
Measurement of very high resistance 1011-1012Ω was possible.
Utilization of the instruments for radiation education experiments to other science education
experiments is not only economically effective but also effective to understand the similarity and thedifference between radiations and light through the experiment of, for example, photoelectric effector photon absorption.
52

References
1) Aoyama T., Mori C., Kamiya H., Sagou Y., Hayakawa I., Iida T., and Goi S., Handmade
Air-filled GM Counter with Needle Anode and Ethanol Quenching Gas, Isotope News, No.744,
22-25 (2016) (in Japanese)2) Mori C., Hayakawa I. and Sagou Y., Theoretical Calculation of the Number of α-ray Track in a
Petri Dish-type Cloud Chamber with Monazite Source, RADIOISOTOPES, 61, 399-406(2012)(in Japanese)

53

ISRE2016 (2017) 54-62

Development of Radiological Educational Program Usinga Peltier-Cooling-Type High Performance Cloud Chamber
ペルチェ冷却式高性能霧箱を用いた放射線教育プログラムの開発
Masafumi AKIYOSHI1, Hirokazu ANDO2, Yasuki Okuno2, and Hiroto MATSUURA1
秋吉優史 1、安藤太一 2、奥野泰希 2、松浦寛人 1
Radiation Research Center, Osaka Prefecture Univ. 大阪府立大学・放射線研究センター
2
Quantum Rad. Eng., Osaka Prefecture Univ. 大阪府立大学・量子放射線系専攻

1

Abstract
A Peltier-cooling-type high performance cloud chamber was developed which is very effective
equipment for performing radiological education. Observation in a few tens of seconds after a
power supply is possible without dry ice, and not only simple observation of alpha-rays track, butalso observations of beta-rays track or a delta-rays track arisen from gamma rays are possible. It
enables us to perform far deep radiological education. In this paper, the technical features for the
hardware of this equipment and the educational program as software using this equipment are
introduced.

1. はじめに各地で行われている放射線に関するオープンスクール活動において、霧箱工作は世代を問わず大変人気があり、目で見て直感的に放射線の存在を知ることが出来るため教育的効
果が大変大きく、様々な研究・教育者が霧箱の改良に携わってきた。近年多く行われるようになった工作を中心とせず、測定などを中心とした放射線セミナーなどでも、工作は行
わなくても展示物として設置が望まれている。
しかしながら、従来は霧箱の展示を行うためにドライアイスの準備が必要であり、遠隔地でのオープンスクールや、小規模な展示の場合ドライアイスを準備することをためらうことも少なくない。エチレングリコールを用いた高温拡散型の霧箱も販売されているが、電源を投入してから安定して観察できるまで時間がかかり、観察途中の線源の交換などが難しい、大勢の子供が来るオープンスクールではヤケドに対する注意が必要、価格も高価で、展示中のメンテナンスの際に有害なエチレングリコールの蒸気を吸ってしまう可能性があるなどの問題があり、余り推奨できない。さらに、これまで用いられてきた霧箱では、天候などにより飛跡が観察できないことも多かった。また、内容としても「α 線の飛跡が見えた」に留まっていた。
そこで、簡単に-20℃以下の低温を得る手段として、ペルチェ素子を使用した高性能霧箱を開発した（http://bigbird.riast.osakafu-u.ac.jp/~akiyoshi/Works/index.htm#CloudChamber）。最大の特徴はドライアイスが不要であることに加えて、長時間安定してクリアな飛跡の観察が可能であるため、一般的な霧箱での α 線の飛跡の観察に加えて β 線の飛跡の観察も可能
であり、さらには γ 線により放出された光電子なども観察可能なことである。これにより、
放射線の種類による物質との相互作用の違いを直感的に学習することが出来るため、ただ単に飛んでいるのが見えた、に留まらない奥が深い放射線の世界を紹介することが可能である。
54

既に当初の開発から一年以上が経過し、試験的な販売を行いながらの改良を繰り返すことにより十分な耐久性と信頼性を得ることが出来ており、多数の大学や中学校などの教育機関、放射線に関連した研究所などへの導入実績を得るに至っている。本論文に於いて、このペルチェ冷却式高性能霧箱の技術的な情報を公開することで、各地の研究・教育者が自分でペルチェ冷却式霧箱を製作し、よりすぐれた装置の製作、改良が行われることを期待する。
さらに、放射線の種類により生体への影響がどう異なるのか（4000 Bq の K-40 と 20 Bqの Po-210 による実効線量の違い）を実習の結果を交えて説明できる。そのことからベクレ
ルだけでは生体への影響（シーベルト）は評価できないこと、さらに、どういった核種がどのような放射線を出しているかという情報から、身の回りの放射線と福島の事故で放出された核種からの放射線について、同じ土俵で比較する力を付けることが出来るような教育プログラムを作成し、実践を行ったので紹介する。

2. ペルチェ冷却式高性能霧箱の技術的特徴
・ペルチェ素子とヒートシンク
一番の心臓部であるペルチェ素子は、電流を流すと素子の片側から反対側に熱を輸送するという働き（ペルチェ効果）を持つ。熱を輸送する際に仕事をするため素子自体の発熱も伴い、闇雲に電流を流せばよく冷えるというわけではないことに注意する必要がある。
TEC1-12708 素子単体を Shuriken Rev.B CPU クーラーに載せて（銀ペーストは後述の
MX-4）、アルインコ DM-330MV 安定化電源で入力電圧を変えたときの電流と素子表面の到達温度の関係を図 1 に示す。電流は単純に電圧に比例している。ペルチェ効果による熱輸送量は電流量に比例するが、ジュール発熱量は電流の二乗に比例するため、12 V 程度を境に温度が上昇してきている。ペルチェ素子は様々な業者を通じて広く一般的に販売されている商品であり、40 mm 角の大きさで、結露水に対する防水加工済のものを一枚 800 円
以下で入手可能であり（図 2）、TEC1-127xx の型番で消費電力、吸熱能力が異なる様々な製品が販売されている（http://www.everredtronics.com/thermoelectric.TEC1.html）。

図 2. ペルチェ素子の例 型番の図 1. TEC1-12708 ペルチェ素子単体で入力電圧を変えた際の到達温度

ペルチェ効果による熱輸送は電流に比例するが、ジュール発熱は電流の二乗に比例する。
55

印字面が冷却側である。結露水に対応するため防水処理がされている。

いずれの素子も単体では霧箱として観察可能な-20℃以下に冷却することは出来ないた
め、二段重ねのカスケードを形成することで十分な冷却能力を達成する必要がある。一段目と二段目の組み合わせによっては到達可能な温度が異なり、下段の素子に 12 V、上段の素子に 5 V 印加という条件で素子の組み合わせを検証した結果（表 1）、TEC-12705 を上段に、TEC1-12708 を下段に配置すると最も到達温度が低くなることが確認された。
表 1. 上段と下段のペルチェ素子の組み合わせを変えた際の到達温度（℃）の変化
測定時気温は 25℃

下段(12V)
なし

12703

12705

12706

12708

12709

12710

12715

25

-13

-15

-14

-15

-10

-9

4

12703

0

-20

-22

-24

-25

-24

-22

-4

12705

0

-17

-23

-21

-26

-21

-20

-4

上段

12706

0

-17

-23

-20

-25

-21

-17

-4

(5V)

12708

-2

-12

-19

-17

-23

-17

-12

0

12709

0

-12

-22

-18

-25

-19

-14

-1

12710

1

-6

-15

-13

-19

-13

-7

-6

12715

13

なし

使用上の注意点としては、150℃以上に素子の温度が上がると、内部で素子を固定しているハンダが溶けてしまい、使用不能になってしまうという点が挙げられる。ヒートシンクとの間に異物が挟まるなどして素子背面の冷却が上手くいっていないと簡単に破損するた
め、到達温度が不十分な場合どちらかの素子が破損していないか確認する必要がある。
ペルチェ素子はあくまでも熱を輸送する素子であり、吸収してしまうわけではないので、必ず高温側の熱を放熱するヒートシンクが必要となり、PC 用の CPU クーラーを使用する。
現在の CPU は高集積化、高クロック化が進んだ結果、発熱量が非常に上昇しており、最新の製品では TDP（熱設計電力） が 140 W にも達しているため、ヒートパイプを使用した高性能な CPU ファンが開発されている。なお、ヒートパイプは開発当初は設置する向きが決められており傾けたり回転したりすると熱輸送を行う事が出来なかったが、現在のCPU ファンなどに用いられている製品ではその心配はなく、どの向きでも使用することが可能である。現在販売している霧箱では、Scythe 社の Shuriken Rev.B という、トップフ
ロー型であるが十分な性能を持つ CPU クーラーを使用している。
CPU クーラー同様に、大きな発熱量を処理するために様々な熱伝導グリスが PC 用に市販されている。高性能の熱伝導グリスとして銀の微粒子を使用した製品が数多く売られており、定番と言われている物に、熱伝導率 9.0 W/m・K の Arctic Silver 社の AS-5、熱伝導率 8.5 W/m・K の ZAWARD 社 MX-4 が挙げられる。MX-4 は長期間高温で使用してもグリスのオイルが抜けず硬化しにくいと言われており、現在販売している霧箱ではこの
MX-4 を使用している。銀以外では、JouJye Computer 社のナノ・ダイヤモンドサーマルグ
リス OC7 は、20 nm の人工ダイヤを 40%使用していると謳っており、12.6 W/m・K に達

56

する。
なお、ペルチェ素子を二段重ねにして CPU ヘッドに乗せる際に、熱伝導接着剤（ワイドワーク社製 2 剤混合の高熱伝導性シリコーン系接着剤 J-Thermo-14C (14 W/m・K) や、
Arctic Silver 社の熱伝導製エポキシ接着剤 Thermal Adhesive(7.5 W/m・K) など）を開発の初期に使用していたが、当初は良好な性能を示すものの使用したペルチェ素子が次々と使用不能となる（導通が無くなる）トラブルが多発したため、それ以降使用していない。
・ATX 電源
ペルチェ素子 2 枚、CPU クーラー、LED ライト、高電圧回路を駆動するために、電源が必要となる。+5 V と、+12 V の二種類の出力を使用する。実験用の安定化電源などを使用しても良いが、一台につき 12 V で 5 A 程度とかなりの容量が必要で高価な電源となるため、PC で使用する ATX 電源を使用する。容量は、一台だけの駆動であれば 150 W 程度、同時に二台並べて使用する場合は 300 W 以上の物を選ぶ必要がある。ペリフェラル 4 ピンコネクタ（大）などと呼ばれる、コマーシャルメイテンロック ソケットハウジング
1-480426-0（図 3）があれば十分で、最新のマザーボードに対応するためのコネクタなどは一切必要ないため、不要になった古いデスクトップ PC から抜き出して調達が可能である。
なお ATX 電源は PC 用のマザーボードに挿して使用することを前提としているため、そのまま電源を入れても動作しない。そのため、マザーボードに接続する 20 pin もしくは
24 pin のコネクタのうち、緑の線が繋がっている PS_ON を、黒い線が繋がった適当なCOM（左右どちらでも良い）に Y 端子などを使用して短絡して単体で動作するようにする必要がある。

図 3. ペリフェラル 4 ピンコネクタ大図 4. ダイソーのコレクション（左）と FDD4 ピンコネクタ（右）ケース（ミニ）・観察用チャンバーと LED ライト
観察用のチャンバーとして、ダイソーのコレクションケース（ミニ）が非常に優れている（図 4）。底面が黒色で、9.3 cm 角×高さ 8.7 cm と手頃な大きさであり、LED ライトの貼付けの際に円筒状のケースでは加工が困難であるので四角いケースが望ましく、材質的にもアクリルはアルコールに徐々に侵されてひび割れなどが入ってしまうが、このコレクションケースは台座もフタもポリスチレン製であり全く問題無く使用することが出来る。なお、ペルチェ冷却式の霧箱作成のパーツとしてだけでなく、ドライアイスを用いた従来型の霧箱を作成する際にも、台座が最初から黒く、薄く熱伝導が良いため、スポンジテープ
57

を付けるだけの短時間の作業で極めて安価で高性能な霧箱が出来るため、最適な選択支と言える。300 円程度のより大型のケースも販売されており、これを用いた大型の展示用の霧箱も実証済である。これらのケースのチャンバーは薄いプラスチックであるため、天板にマントル線源を載せれば α 線は透過せずに、β 線・γ 線だけをチャンバー内に入れることが可能であり、特殊な線源無しに β 線観察を可能としている。ガラス製のチャンバーでは不可能であり、大きな特徴となっている。
照明としては、普通の室内程度の明るさでも飛跡を明確に観察可能とするため、電飾用に市販されている 12 V タイプの高輝度 LED モジュールを使用している。現在は SMD 5730 3-LED モジュール（図 5）を使用しているが、抵抗などもモジュールに組み込まれておりそのまま 12 V 電源に繋ぐだけで終端処 図 5. SMD 5730 3-LED モジュール
20 個単位で入手可能
理等せずに使用することが出来る。
・UV レジン
コレクションケースとペルチェ素子の接合には UV レジンを使用している。エポキシ接着剤などでも構わないが、仕上がりの綺麗さと 2 分程度で固まる作業性、接着強度で UV
レジンは非常に優れている。通販や手芸店でネイルアート用やアクセサリー製作用などで多数売られている。製品によっては臭いがきつかったり表面がべたついたりするが、硬化後にアルコールで拭き取ることで概ね解決可能である。硬化には日光に当てるか UV ライトを使用するが、LED 式の UV ライトは 375 nm LED を使用していると明記していないと硬化に必要な波長と合わず、多灯式の物でも役にたたないため注意を要する。
UV レジンの硬化は、放射線による重合反応の説明に応用することが出来る。また、紫外線自体も、電波や可視光線から続く光の仲間として、X 線やガンマ線を説明する際に理解の助けとなる。近年 UV レジンを使用したアクセサリー工作は極めて人気が高く、母親層を含めた広い年齢層に対してアピールすることが出来る新しい放射線教育のツールとして現在ソフトウェアを開発中である。
・線源
容易に入手できる線源としては、トリウムを含んだランタン用のマントルが最も適しているが、近年ほとんどの製品がトリウムを含んでいない。現在手に入るトリウム含有マントルとして、サウスフィールドブランドの SF-2000 用マントル SF-2000MT と D-X ハイパワーランタ
ン 3000 用の D-X ハイパワーマントルが挙げられる（図 6）。しかし、同社の似たような製品でも SF 200MT や SF-DX400MT と言う製品は全く放射線を出しておらず、前述の製品も産地によってはトリウムを含んでいないという情報もあるため、返品が可能かなど注意が必要である。
なお、元々がキャンプ用品であるため、冬場はほとんど市場に出回っておらず、入手しにくくなるため、夏場に購入しておく必要がある。
次に入手しやすいのは、ラジウムセラミックボール（図 6 下）で 100 g 2000 円程度で入手可
能だが、マントルに比べるとやや線量率が低く、丸いボールなので、ワッシャーのような物を58

台座にする必要がある。
最も簡単に α 線源を入手するには、空気中のラドン娘
核種を掃除機で捕集するのがよい。掃除機は一般的な物
で十分であるが、オープンスクールや授業など、限られたスペース、時間で捕集を行う場合は、Electrolux 社製のエルゴスリーマルチフロアという極めて静粛性が高い製品が適している。捕集する際にろ紙のような目の詰まったフィルターを用いると、非常に捕集効率が悪く時間がかかるため、ベンコットなどのようなガーゼを使用するという点に注意する。掃除機の吸い込み口にガーゼを当てて輪ゴムで止め 10 分程度吸引するだけでよい（図 7）。
建物の素材（鉄筋コンクリートかどうか）や空調の状況などによって異なるが、地下室などがあればマントルに匹敵する強度の線源も作成可能である。半減期 40 分程度で減衰するため霧箱工作教室などでの配布の際にも安心である。USB 接続して PC に計数値を取込可能な高感度のパンケーキ型の広窓 GM サーベイメーターである SE
International 社製インスペクターUSB などの製品を用いれば、授業時間内程度で半減期を明確に評価可能であり、減衰挙動を直接学習することが出来る貴重な線源となる。

・高圧電源
通常の霧箱では、雨天時など α 線の飛跡がよく観察できない事態が頻繁に発生する。これは、空気中の雑イオンが多すぎるため、放射線が通らなくてもアルコールが核生成してしまい過飽和蒸気圧が低下するため

図 6. サウスフィールドブランド
D-X ハイパワーマントル（左）とSF-2000MT （右）、ラジウムセラ
ミックスボール（下）である。この雑イオンを、高電圧を印加することで除去する必要がある。
最も簡単には、化学繊維の布などでチャンバーを直接こすることで静電気を発生させるが、飛跡が見えない悪天候時は静電気も発生しにく
く、上手くいかないことも多い。小型のバンデ
グラーフ起電機なども利用可能であるが、長時間の運転には向かず、電圧のコントロールも容易ではない。
そこでコッククロフト・ウォルトン回路（図8）を用いた高電圧発生装置を利用する。冷陰極管（CCFL）用のインバータ回路（図 9）が安価で入手できるため、これを 1 kV 程度までの交流

図 7. ベンコットと掃除機を用いて空気中のラドントロン娘核種を捕集している様子の高圧電源としてコッククロフト・ウォルトン回路に入れて、昇圧・整流を行う。余り電59

図 8.コッククロフト回路の例
ダイオードを直列に繋いでい図 9. 冷陰極管用インバータ回路の例

るのは耐圧を上げるため。図では 4 段であるが製品では 2 段に留めている。
圧を上げすぎると、逆にイオンを加速して雑イオンを増やしまうことが、これまでの研究で明らかになっている。インバータに入れる電圧を 50 Ω の半固定抵抗器を用いてコントロールすることで出力電圧を可変としているが、最適な電圧を評価したところ 500 V 程度であった。これは放射線検出器の電離箱領域上限に相当し、それ以上になると比例計数領域
から GM 領域となることから、印加電圧の妥当性が説明される。ただし、今後より適切な電極形状などの検討を行う必要があり、より厳しい条件でのクリアな観察を可能とすることを目指す。
・素子表面の塗装
霧箱中のペルチェ素子表面は観察しやすくするために黒く塗る必要があるが、室温から-40℃以下への温度変化を繰り返し受け、さらにアルコールに曝され続けるため、その双方に耐えうる塗装は非常に困難である。当初はアサヒペンの高耐久性ラッカースプレーを使用していたが、エタノールに徐々に侵されたため、同じくアサヒペンの弱溶剤 2 液ウレタ
ンスプレーに変更した。塗膜は非常に強靱であり、イソプロパノールにも全く侵されなかったが、温度変化によりひび割れ・素子表面からの剥離が発生した。このため素子表面をシリコンオフ（ヘプタンが主成分）でしっかりと脱脂し、密着性の良いプライマー剤を塗布した後に弱溶剤 2 液ウレタンスプレーを使用することで、温度変化にも溶剤にも強い塗膜を得ることが出来た。2 液ウレタンスプレーは 1 回使い切りであり、補修なども困難なため、一般向けには車の補修用のタッチペンなどが手頃である。

3. ペルチェ冷却式高性能霧箱を用いた放射線教育プログラム
2016/8/18 に福井県立若狭高校から、および 2016/12/13、15 には京都府立桃山高校から、大阪府立大学放射線研究センターへの訪問研修があり、ペルチェ冷却式高性能霧箱を用いた放射線観察実習を行ったので、その内容を以下に紹介する。

60

・熱電対を用いたペルチェ素子表面温度の測定
熱電対式のデジタル温度計により霧箱表面温度（-30℃程度）を測定する。熱電対とは、温度差があると電流が流れる、ゼーベック効果を利用しているが、ペルチェ素子は逆に電流を流すと温度差が発生する、吸熱している訳ではなく熱を裏面に輸送している事などを説明する。点接触では正確な温度測定は出来ず、アルミテープでしっかりと熱接触を取って測定する事に注意する。
・空の霧箱とポリパックに入れたマントル線源を入れた霧箱の観察
スポンジテープへエタノール（イソプロパノール入りの安価な消毒液で構わない）を注
入して線源を入れずにチャンバーを閉じ電源を入れる。ペルチェ素子によりアルコールの蒸気が冷やされ過飽和となり、空気中の雑イオンなどにアルコール分子が集まって核生成してうっすらと霧状の液滴が漂っていることを観察する。もう一つのチャンバー中にはポリパックに入れたマントル線源を入れておき、ビニール一枚で α 線は遮蔽されていることを確認する。また、いずれのチャンバー中でもよく観察を続けると空気中のラドンなどからの α 線や、バックグラウンドの β 線などが観察される。
・ポリパックから取りだしたマントル線源を入れた霧箱での α 線の観察
一般的な霧箱観察同様に、マントルからの α 線の飛跡を観察する。飛行機雲と同じく、粒子自体は見えなくても飛跡が見えている（原子の小ささを説明する）、空気中での飛程はせいぜい数 cm だが、はっきりと直線的に飛ぶことから、後述する β 線に比べ α 粒子はずっと重たく、空気との相互作用によるイオンの生成も激しいことを説明する。なお、線源からの α 線は上下方向にも飛んでいるが、過飽和層が層状になっているため水平方向に飛んだ α 線だけが観測できている。
・空の霧箱の上にマントル線源を置いての β 線の観察
α 線はチャンバー天板のプラスチック板を透過できないが、β 線は薄いプラスチック板
程度は透過できる上に、非常に軽く散乱されやすいので、上から入射しても空気や素子表面で散乱されて素子に平行に走る電子線が観察できる。相互作用は α 線よりもずっと小さくうっすらとしか観察されない、平行に走っている間にも散乱されて糸くずのように曲がりくねる、と言う点に注意して観察する。
・空の霧箱とマントルの間にアルミ板を載せての γ 線 （からの光電子など）の観察
ウラン系列核種からの β 線のアルミ中での最大飛程は、Bi-214 からの 3.27 MeV の β 線
による 6.1 mm であるため、6 mm のアルミ板をマントル線源とチャンバー天板の間に入れて β 線を遮蔽し、γ 線のみをチャンバー内に入射する。すると、非常にイベント数は落ちるが、γ 線によって放出された光電子などが電離作用を示す、δ 線が観察される。見た目は
β 線と同様であり、γ 線が最終的には β 線と同じような作用を示すことが分かる。
・α 線、β 線、γ 線の物質との相互作用との違いと、生体影響の違いを説明
α 線、β 線、γ 線それぞれ物質との相互作用が異なり、それによって霧箱での見え方が異なる。紙一枚で遮蔽されてしまう α 線は、実は短い距離で強烈な相互作用をしており、内部被ばくを考えると非常に危険。透過力の強い γ 線は逆に体をほとんど素通りしており、時々δ 線を出して β 線と同じような作用をする、などが理解できる。このことから何発出61

たかのベクレルだけでは生体影響は評価できず、αβγ の種類の違いやエネルギーの違いも考えなくてはならないこと、それによってたった 20 Bq の Po-210 が年間 800 μSv の実効線量を与えるのに対して、4000 Bq の K-40 は年間 170 μSv にしかならない訳が説明できる。

4. 結言
放射線教育を行う場で極めて有効な装置であるペルチェ冷却式高性能霧箱の開発を行い、ハードウェアとしての技術的特徴と、それを用いたソフトウェアとしての教育プログラムを紹介した。販売されている製品のユーザーのみならず、これから開発を行う研究・教育者にとって、製作・運用上の参考となれば幸いである。
運用を行う上で、ガスストーブを使用している部屋では観察が非常に困難であるという情報をユーザーから得ているが、実際にその通りであった。様々な環境の現場での使用報告は非常に参考となり、今後の開発の助けとなるため、ユーザー間の ML を作成して情報交換を行い、より確実な観察を可能とするよう、ハード面と運用面からの改良を、また様々な層の受講者に対してより効果的な学習が出来るよう教育プログラムの開発を行っていく予定である。
また、低予算で授業を行う小・中学校の教育現場に必要なハードウェアを供給できるよ
う、ふるさと納税制度を用いた大阪府立大学つばさ基金でのプロジェクトを立ち上げている。大阪府立大学は公立学校という特殊な立場であるため、この制度が利用可能であり、既に数件の受入と僻地や福島の中学への霧箱提供の実績がある。今後全国的にこの仕組みを活用したシステムを展開できないか検討を行う予定である。

62

ISRE2016 (2017) 63-66

Utilization of Small 68Ge/68Ga Generators as Experimental
Tool in Wide Fields of Education
Tadashi NOZAKI1 and Toru SASAKI2
1

Kitasato University, School of Sciences; 1-1 Kitasato, Minami-ku, Sagamihara, Japan

2

Kitasato University, School of Allied Health Sciences; 1-1 Kitasato, Minami-ku, Sagamihara, Japan

Abstract
Regarding small 68Ge/68Ga generator as highly useful main tools in experiments for education ofvarious fields, we first made possible the self-manufacture of the generator. We then selected about 20
kinds of suitable experiments and have tested them for the preparation of their manuals. We intend tocontribute to arouse interest of citizens in various fields of sciences by wide use of the generator.
Introduction
In Japan at present, study and use of radioisotopes are declining, and opinions concerning promotion
or refusal of atomic power are based either on “safety myth” or on “radiation allergy”. We now need
Renaissance to replace these religious situations by scientific discussions. Unique properties ofradioisotopes, i.e., decay characteristics, highly sensitive, continuous and nondestructive detectability,and equal behavior with stable isotopes, are thought to be useful in experiments for education ofvarious categories. Isotope generators are the best supply of radio-isotopes to the experiments, and, of
all generators shown in Table 1, small 68Ge/68Ga generator is probably the most useful. First, we looked
for a simple method of manufacturing small types of the generator, and now “manufacture of thegenerator” is ranked in the titles of experiments. We selected about 20 experiments based on thegenerator, and have tested them following trial procedures for publishing a guide book of experimental
manuals.
In this presentation, first the superiority of this generator is explained, then the title and main aim
are shown for each of the experiments together with the stage of progress in our work. Some comments
not directly scientific but inevitable in the achievement of our task are added.
Superior Properties of the small 68Ge/68Ga Generator
Decay properties of 68Ge (271 d; EC 100 %; no γ) and 68Ga (67.7 m; β+ 90 % and EC 10 %; γ weak)
are quite suitable, making it possible to milk easily the daughter, 68Ga, several times every day formore than a year, and to observe clearly the growth of 68Ga in the generator just after milking without
any interference from radiations of 68Ge. The milked carrier-free 68Ga can be used for a variety oftracer studies.

Fig. 1 shows our self-made generator, which is simply a column chromato-graphic set,with the column being 1 mL plastic disposable syringe and the adsorbent SnO2 powder prepared byour method. Attendants to the class of experiments will be able to select a course involving selfmanufacturing of generator, though ready-made adsorbent powder, requiring a long time of
preparation, is offered. Fig. 2 shows the milking and column-washing stages. Experiments based on
68Ga milked from such a generator surely gives stronger impressions to the attendants.

63

Still smallergenerators can be manufactured similarly
and used also as nearly point sources ofannihilation radiations. The highest 68Ge
radio-activity treatable free of the law
restriction is 100 kBq, by which several
experiments

shown

below

undertakenbyseveralcanbegroupssimultaneously.
Attendants to the course of experiments
are regarded as learning more about
radioisotopes and radiations than about its
main/nominal aims. This fact is really a
two-bird-one-stone solution.

Fig. 1. Manufactured generator assembly with
its parts. From bottom to up: adsorbent
SnO2 powder (before HNO3 treatment);
Generator connected with eluent syringe; andporous plastic diskette and short end of plastic
tube (see text for more detail).
Experiments: Title, Main Aim, and Stage of Manual Preparation
Table 2 shows the title, the main aim and thestage of manual preparation for each of theexperiments. The total experiments can bedivided into three categories: (A) manufacture
andproperties

of

the

generator,(B)experiments by 68Ga, and (C) measurement anduse of annihilation radiation.
In (A), the treatment of the results of decay
and growth measurements can be a valuable
exercise of differential equation. In tracer
experiments

withcarrier-free

68Ga,

characteristic behavior of ultra-minute amountor hyper-low concentration substances arelearned to become some knowledge valuable
for understanding entropy of mixing and thesecond law of thermodynamics.
Fig. 3 shows the adsorption of the 68Ga fromacetate buffer solutions of various pH in a

Fig. 2. Milking by ordinal procedure (right), andColumn washing by intravenous drip system(left).
64

single pass through a sheet of filter paper 4A. Some ill reproducibility is inevitable for these kinds ofexperiments.

Table 2. Title, aim and present stage of manual preparation for each experiment
Title

Aim

Present stage*

A. Manufacture and properties of generator
1. Manufacture of 68Ge/68Ga generator

Self-manufacture of tool for experimentEnd

2. Milking and half-life measurement of 68Ga

Relation among exponential, real number and logarithm

End

3. Growth of 68Ga in generator after milking

Intimacy with differential equation

End

4. Milking yield and breakthrough of 68Ge

Properties of generator

End

B. Experiments by 68Ga
1. Adsorption, coprecipitation and solvent
extraction

Behavior of ultra-low concentration and ultra-minuteamount materials

Near end

Entropy of mixing and the second law of thermodynamics
2. Ion exchange and chromatography

Chemical separation and analytical chemistry

3. Isotope exchangeIntermolecular atomic exchange without chemicalchange4. Chelate chemistry, and synthesis of

Near end

MidwayRadiopharmaceutical chemistry

Before starting

Positron radiopharmaceuticals
5. Uptake by plants

6. Contamination and decontamination, andNondestructive, continuous measurement of RI
taken up by plants

MidwayAdvantageous utilization of short-lived RI

MidwayLeak hunting

C. Measurement and use of annihilation radiation
1. Absorption by various substances

Absorption mechanism ofγ-ray

End

2. Dependence of coincidence counting

Principle and utilization of coincidence countingEnd

3. Low background counting of β＋ emitters

Naturally existing RI and radiations

Near end

4. Principle of PET and image

Nuclear medicine

efficiency on geometrical arrangement

Some new idea needed

reconstruction* Present stage of test experiments for manual preparation.

Without isotopes, isotope exchange cannot be observed. Isotope exchange between Ga-EDTA
complex and 68Ga3+ can be recognized to occur by solvent extraction as oxinate, though correct
analysis of its rate seems to be too difficult for the attendants except chemists. The milked 68Ga canbe obtained as citrate complex in a neutral solution by an on-line treatment in a cation exchange
column. This 68Ga is often taken up by some plants, e.g., Eulalia (Susuki) with the rate enough for65being followed by coincidence measurement ofannihilation radiation. However, the uptake by any
plant changes so remarkably, depending on
conditions of both the plants and environments, thatnext experiment time often cannot be scheduled.
Safety Guarantee and other Problems for our
TaskInternal exposures caused by 18F and 68Ga areroughly the same when these possess the same firstactivity (in Bq) and decay away in the body. We
have planned to use 10 to 100 kBq 68Ge/68Ga

Fig. 3. Dependence on pH in the adsorptionof carrier-free 68Ga on filter paper 4A

generator, while about 100 MBq of 18F is injected in usual FDG PET diagnosis. The dose (in Gy) from
68Ge is clearly smaller than from the 68Ga. Hence, the radiation exposure in our experiments can be

regarded as being negligible. The fact that about 4 kBq/person of 40K always exists in our body also
gives the same result.
More and more expensive modern apparatus will be needed for science education in future, butthese will be used less frequently in each school. This will be of considerable similarity with ourgenerator experiment. Rental system or round-robin use will be unique and profitable solution.

66

ISRE2016 (2017) 67-71

Detection of Spatial Distribution of Dual Photon Emitters
Using TOF Coincidence Imaging Technique with Stochastic
Origin Ensemble Approach
Chih-Chieh CHIANG, Keh-Shih CHUANG, and Hsin-Hon LIN
Department of Biomedical Engineering and Environmental Sciences, National Tsing-Hua
University, Hsinchu, Taiwan.
Introduction
The nuclear waste classification is an important issue in the process of nuclear waste disposal. In
this study, the time of flight (TOF) coincidence imaging technique is employed to obtain the spatial
distribution of dual photon emitters. Co-60 is a dual photon emitter (1.17 and 1.33 MeV) and plays
an important role in the process of nuclear waste disposal. The proposed technique can be applied
to Waste Inspection Tomography (WIT) system for nuclear waste drum characterization and activity
measurement in the future.
MethodDual photon emitters emit two directionally uncorrelated photons simultaneously. If both photons
are detected in the same time, the possible location of decay could be determined by TOF
information and the coordinates of detectors. By detecting the gamma rays with TOF information incoincidence, the hyperbolic response curve can be described on the space (Fig. 1). Actually, theconcept of TOF coincidence imaging technique is the same as time difference of arrival (TDOA)
technique, which is an electronic technique used in direction finding and navigations1-3).
D

Equation of hyperbola:

D

1

2

P

Fig. 1. The illustration of TOF coincidence imaging technique.
Due to the complexity of the spatial distribution, the activity map was reconstructed by using
stochastic origin ensemble (SOE) algorithm. Stochastic origin ensemble algorithm, fist proposed by
Sitek in 2008, is one of iterative reconstruction method, which is based on Markov chain and use
Metropolis–Hastings algorithm4,5). In the proposed SOE reconstruction, the origins of each eventare randomly assigned to locations on hyperbolic response curve. After a sufficient number of
iterations, the possible origins can converge to actual position of emitters.

67

In order to validate the proposed concept an algorithm, a full-ring PET-like detection system wasbuilt to detect the dual-photon emitters (e.g. Co-60, Se-75, or In-111). The system was built
referring to the geometry of Siemens Biograph 6 PET scanner and the detail geometric parameters
are shown in Fig. 2.

Geometry of the scanner LSO crystals
 48 detector modules
 39 detection rings
 13x13 array of 4x4x20 mm3
 Total of 24,336 crystals
 Diameter of 83 cm
 Dual Energy window:
108-164 keV and 211-318 keV
 Time window: 2.0 ns
Fig. 2. The full-ring PET-like detection system.
An in-house developed GATE/MPHG Monte Carlo software was used for the simulation study ofselenium-75. In this study, Se-75 was used as preliminary test and its decay scheme was shown in
Fig. 3. A point source and two phantoms (contrast and Jaszczak-like array phantom) were built insimulation for assessment of performance (shown in Fig. 4 and Fig. 5). Five different CRT of
detectors (0, 50, 100, 150, and 200 ps) were set to estimate the system spatial resolution under
different conditions in point source measurements. In all cases, the activity of Se-75 was set to 1
mCi.

Fig. 3. Decay scheme of Se-75.

68

cm

Fig. 4. The phantom configuration of Contrast phantom that was used in Monte Carlo simulation.
The phantom was a 30 cm diameter uniform cylinder containing 10 cm diameters hot/cold rods andplaced on the center of system. The ratio of activity concentration was 5:1:0.

Fig. 5. The phantom configuration of Jaszczak-like phantom that was used in Monte Carlosimulation. The phantom was 25.6 cm diameter and contained 19 independent rods with varying
diameters (15.4, 19.1, 25.4 mm).
Results
We have simulated and reconstructed three different objects: a point source, contrast phantom
and Jaszczak-like array phantom. Fig. 6 shows the point spread functions evaluated along thecentral x-axis of reconstructed images with varying CRT and its corresponding reconstructed
images. The figure illustrates the relationship between the spatial resolution and the coincidence
resolving time. It shows that as the coincidence resolving time decreases the resolution improves.
The reconstructed FWHMs as function of iteration numbers for different CRT are shown in Fig. 7.
Following the iterative process, the number of event origins per voxel reaches steady state after 50
iterations. The results show that the value for the FWHM of the PSF in the central field-of-view canachieve about 25 mm when CRT is under 100 ps. Fig. 8 displays the reconstructed images ofcontrast and Jaszczak-like phantoms. For the final image made with SOE after running for 500
iterations, the spatial distribution of dual photon emitters is reconstructed successfully. We
demonstrate that the SOE seems practical for proposed system and can obtain acceptable image
quality.

69

x-direction
1000

PSF function
row data

CRT=0 ps
800

counts

600

400

200

0
0

10

20

30
bins
x-direction

40

50

1000

countsPSF function
row data

CRT=50 ps

800

60

600

Evaluation of spatial resolution

400

200

0
0

10

20

30
bins
x-direction

40

50

500

60

PSF function
row data

CRT=100 ps
counts

400

300

200

100

0
0

10

20

30
bins
x-direction

40

50

400

CRT=150 ps

350

60

PSF function
row data

300

counts

250
200
150
100
50
0
0
200

10

20

30
bins
x-direction40

50

CRT=200 ps

60

PSF function
row data

counts

150

100

50

0
0

10

20

30
bins

40

50

60

Fig. 6. The point spread function evaluated along the central x-axis of reconstructed images withvarying CRT and its corresponding reconstructed images.

200
0 ps
50 ps
100 ps150 ps200 ps175

FWHM (mm)

150
125
100
75
50
25
0

50

100
SOE iterations

150

200

Fig. 7. FWHM as function of iteration number for different CRT

70

Fig. 8. Results of the phantom studies: (a) initial event density images for the contrast phantom (b)reconstructed images of contrast phantom with 500 iterations (c) initial event density images for the
Jaszczak-like phantom (d) reconstructed images of Jaszczak-like phantom with 500 iterations
Conclusion
The TOF coincidence imaging technique can locate radioactive sources, provide internal activity
approximations, and provide the data needed for waste classification. Our results show that TOF
coincidence imaging technique combined with SOE reconstruction technique is feasible and might
open other avenues that can be used for the existing multimodality WIT system to acquire thespatial activity distribution of nuclear waste inside the drum. By using the technique, theclassification accuracy and quantification accuracy may be enhanced as well.
References
1) Spirito, M. A., & Mattioli, A. G. (1998, September). On the hyperbolic positioning of GSM
mobile stations. In Signals, Systems, and Electronics, 1998. ISSSE 98. 1998 URSIInternational Symposium on (pp. 173-177). IEEE.
2) Misra, P., & Enge, P. (2006). Global Positioning System: Signals, Measurements andPerformance Second Edition. Massachusetts: Ganga-Jamuna Press.
3) Powell, M. D. (1989). Multiphoton, time‐of‐flight three‐dimensional radionuclide imaging.
Medical physics, 16(5), 809-812.
4) Andreyev, A., Sitek, A., & Celler, A. (2009, October). Stochastic image reconstruction method
for compton camera. In Nuclear Science Symposium Conference Record (NSS/MIC), 2009
IEEE (pp. 2985-2988). IEEE.
5) Sitek, A. (2008). Representation of photon limited data in emission tomography using origin
ensembles. Physics in medicine and biology, 53(12), 3201.

71

ISRE2016 (2017) 72-76

Post-311 Promotion Activities for Science & Disaster Literacyof Citizenry and School Students by Means of ‘Bulletin’,
Symposium, and Summer School
都市圏市民・中高生の科学・災害リテラシー向上に向けた文書および実践による 3・11 後の活動
Haruko NIHON’YANAGI1, Tomie ISHIKAWA1, Toshie KIKUCHI1, Toshi MATSUMOTO1,
Sachiko SAWAYA1, Setsu OKAYAMA1, Kaoru ENDA1, Kinue KANAZAWA1,
Hiromi TODOROKI1, Kayoko YOKOYAMA1, Harumi OKUKAWA1, Teruko UENO1,
Eiko NAKAYAMA2, Kiriko MIYAMOTO2, Chikako ISHIKAWA2, Hiroko HIRANO2,
Nobuko KUMANO1, and Michi ARATANI3
1
二本柳晴子 , 石川とみゑ 1, 菊池トシエ 1, 松本とし 1, 澤谷幸子 1, 岡山せつ 1,
遠田薫 1, 金澤きぬゑ 1, 轟博美 1, 横山香代子 1, 奥川春美 1, 上野照子 1,中山榮子 2, 宮本霧子 2, 石川稚佳子 2, 平野浩子 2, 熊野伸子 1, 荒谷美智 3
1 Reading Circle, Rokkasho Culture Association

六ヶ所村文化協会読書愛好会
Cultural Assoc. Address: 1-8 Nozuki, Obuchi, Rokkasho, Aomori, 0393212 Japan〒039-3212 青森県上北郡六ヶ所村尾駮野附 1-8、六ヶ所村文化交流プラザ内
E-mail: suwany97@jomon.ne.jp
2 The Society of Japanese Women Scientists

一般社団法人 日本女性科学者の会
Nakayama, E. Address: Graduate school, Showa Women University
1-7-57 Taishido, Setagaya, Tokyo, 1548533 Japan
〒154-8533 東京都世田谷区太子堂 1-7-57 昭和女子大学大学院
E-mail: enaka@swu.ac.jp
3 Radiation Education Forum

NPO 法人 放射線教育フォーラム
1-8 Nozuki, Obuchi, Rokkasho, Aomori, 0393212 Japan〒039-3212 青森県上北郡六ヶ所村尾駮野附 1-8
E-mail: rks00031@rokkasho.jp
Abstract
At Rokkasho, the site of reprocessing facilities of spent nuclear fuels, members of Reading
Circle, an affiliate of Rokkasho Culture Association (RCRCA, since 1995, Represetative: H.
Nihon’yanagi) have been promoting Science Literacy for themselves under support of the Societyof Japan Women Scientists (SJWS), mostly Northeast Block (Head: M. Suzuki). After the 311
catastrophe, promotion was extended to Science & Disaster Literacy for themselves, and citizenry
and high school students.
The members of RCRCA were apprehensive about the public sentiment of “No More Genpatsu(Nuclear Power Station)” accompanied by the government policy at that time. In view of thesituation of such an island country with no natural energy resources, it seemed unwise andimpolitic for Japan and for residents of Rokkasho as well.
The highlights of our activities are: 1) publication of the first English version of our ‘Bulletin’(selected articles of 1995-2011) “Women’s Messages from the Village of Rokkasho to the World”(2012), 2) Holding Symposia entitled ‘Messages from Rokkasho Women’ in Rokkasho (2013), in
Tokyo and Sendai (2014) and in Mutsu (2015), and 3) Carrying out Summer School for junior &senior high school girls at National Women Education Center (NWEC), Ranzan, Saitama Pref.
(2012-16).
72

General view of our principal activities
In 1995, the villagers of Rokkasho, the site of reprocessing facilities of spent nuclear fuel, took
first step of Rokkasho Reading Circle, an affiliate of Rokkasho Cultural Assoc. (RCRCA,
Representative: H. Nihon’yanagi, one member of SJWS in addition). The aim was to improve ourown literacy in radiation and science, while sending messages through Nos. of ‘Bulletin’1, 2).
Things went favorably by working together 3) of SJWS, Soloptimist Intl. Aomori (SIA, comprisedof leading businesswomen), and RCRCA.
Circumstances changed suddenly by an unbelievable criticality accident of JCO in Tokai (30
Sept. 1999). From necessity, our activities had to be more extensive, and socially evaluated as aresult; Aoi-Mori Science BBL (Founder: Y. Osanai 4-7), a member of both SJWS & SIA) was
selected as a promotion program (2007), while RCRCA won Grand Prix ‘Nourishing Seedlings inScience’ (2007).
Situation turned out more serious after the nuclear catastrophe 9) following the East Japan
Earthquake 8-11) and Tsunami 11, 12) (11 March 2011). A nationwide mood ‘Ex Nuclear Power’
prevailed throughout, even coupled with national policy at that time. In aware of what to do, we
extended our activities; “Women’s Messages from the Village of Rokkasho to the world” waspublished (2012), symposia were held successively in Rokkasho (2013), Tokyo (2014), Sendai(2014), and in Mutsu (2015), for instance.
Featured further is the Summer School of NWEC for students (junior & senior high) we
participated for 5 years (2012-16), as an extension of our ‘Science School for Parent-Child’ (led by
M. Kazuno, the then President of SJWS): Experiment/Practice: ‘Learning energy from cosmic
stars---Fundamentals of the nuclear accident in Fukushima’, for instance. This program is forstudents, parents and teachers across the country (from Okinawa was the longest way off so far).
Timelines of our activities after March 20112011
Mar. 11The East Japan triple disaster (earthquake, tsunami & nuclear accident)

July 24“On the ‘natural nuclear reactor’ by Prof. Dr. P. K Kuroda”, ‘Bulletin’ No. 251.

Aug. 23“What can we do on the basis of correct understanding of radiations and observationof the stricken areas?” SJWS (Soc. of Jap. Women Scientists) Lecture Meeting (E.
Nakayama, K. Miyamoto, N. Kumano), Visitor Center of JNFL, Rokkasho.

Oct. 01“Radiation-related hands-on” Aoi-mori Science BBL, “Life-long Learning Fair 2011”,
Aomori Pref. Social Education Center, Aomori.

Oct. 26“What can we do on the basis of correct understanding of radiations and observationof the stricken areas?” Mini Symposium to support Fukushima, Cultural Exchange
Plaza (Swany), Rokkasho.

2012
Aug. 10

Experiment/Practice.“Learning energy from cosmic stars---Fundamentals of thenuclear accident of Fukushima”, Summer School 2012~for budding scientists and73

engineers~, Natl. Women Education Center (NWEC), Ranzan.
Oct. 08

M. Aratani, E. Nakayama. K. Miyamoto: Report, The 9 th Science Conference of
SJWS, “NWEC Summer School 2012, Experiment/Practice, Learning energy fromcosmic stars---Fundamentals of the nuclear accident of Fukushima”, Arcadia Ichigaya,
Tokyo.

Oct. 12

K. Yokoyama: “From my living right in the way of Dan (cut)-Sha (dump)-Ri (goaway)” ‘Bulletin’ No. 267.

Dec. 12Published “Women’s Messages from the Village of Rokkasho to the World”.

2013
Mar. 28

M. Aratani: On the circumstances of publishing “Women’s Messages from the Villageof Rokkasho to the World”, Study Association for Revitalization of Peninsula
Shimokita, Masakari Plaza, Mutsu.

July 08

Study visit: Recycle Fuel Stock Co. Ltd., Mutsu.

Aug. 09

Experiment/Practice “Learning energy from cosmic stars---Fundamentals of thenuclear accident of Fukushima”, Summer School 2013~for budding scientists andengineers~, NWEC, Ranzan.

Sept. 22

The 20th year Commemorative Round-table Symposium of Rokkasho Reading Circle
on the Vitrified High-level Radioactive Waste, N. Kumano: Science lecture “We are
made of stardusts”, Swany, Rokkasho.

Dec. 03

H. Nihon’yanagi: “Activities in Yokohama Town”, T. Ishikawa: “The way I havecome”, M. Aratani: “Geothermal energy (hot spring) and radiation”, Senior School of
Yokohama Town Public Hall, Community Center, Yokohama.

2014
Jan. 31

K. Yokoyama: Let’s begin the ‘Fuk (u) kou (reconstruction and happiness) Egg’ from
Fukushima, ‘Bulletin’ No.289.

Feb. 02

E. Nakayama, K. Miyamoto, M. Aratani: “Career choice in Science~for you, future
creators”, Poster session, Korasse Fukushima, Fukushima.

Feb. 02

E. Nakayama, M. Aratani as facilitators of discussion around the lecturers (M.
Takahashi, commentator of the Asahi, K. Abe, Prof. emer., Dept. Agriculture, Univ. ofTokyo), M. Katsuyama (Shiseido Res. Lab.).

May 30

Messages from Rokkasho “Nuclear energy and the way we have come” Tokyo
Symposium, Vision Center Nihonbashi, N. Kumano: Science lecture “Nature’s gifts ina long history of our planet”, Tokyo.

Aug. 08

Experiment/Practice “Learning energy from cosmic stars---World of science spreadingfrom Fukushima”, NWEC Summer School 2014 for girls’ students~Meet with
Science, Technology and Human~, NWEC, Ranzan.

Oct. 05

Messages from Rokkasho “Nuclear energy and the way we have come” Sendai
Symposium, El-sola Sendai, K. Yokoyama: Art display “Egg art”, N. kumano: Science74

lecture“CigarLakeuraniummine---anaturalanalogueofgeologicaldisposal”/Display & Experiment “Zeolite”, Sendai.
Nov. 12

K. Yokoyama: “Profile of K. Yokoyama, the leader of Circle “Ka (fragrance)-Ri(Lapis Lazuli)-Mu (dream)”, ‘Bulletin’ No.293.

Nov. 19

K. Yokoyama: “Being compelled to be on endless branch road”, ‘Bulletin’ No. 294.

Nov. 22

Messages from Rokkasho “Nuclear energy and the way we have come” Exchange
meeting with Higashidori, K.Yokoyama: Art school & display “Let’s begin the‘Fuk(u)kou (reconstruction and happiness) Egg’ art (Ukrinian egg art) from
Fukushima”, N. Kumano: Poster & display “Volcanic ashes as Nature’s gift”, Tomari
Community Center, Rokkasho.

2015
July 30

Published the “Bulletin” No. 300 of Rokkasho Reading Circle.

Aug. 07

Experiment/Practice “Learning energy from cosmic stars---World of science spreadingfrom Fukushima”, NWEC Summer School for girls’ students~Meet with Science,
Technology and Human~, NWEC, Ranzan.

Aug. 30

Messages from Rokkasho 2015 “Future Shimokita and women’s role”, Mutsu
Symposium, K.Yokoyama: Display “Nami’e Town Now”, N. Kumano: Sciencedisplay 1) Interior of the earth, 2) “Boreholes for Hot wastes” (Science 10 July 2015),
Kasamai Hall, Mutsu.

Sept. 13

Exchange Meeting of Omaezaki Energy Group, Nagoya Energy-Ecology Wing, andRokkasho Reading Circle, Hamaoka Power Station, Omaezaki.

Oct. 11“Detoxification of radiation (experiment) and play school children with seashells”,
Tomari Community Center Festival, Rokkasho.

2016
Feb. 28

Published the “Messages” Vol. 12 (Part I & II, Nos.236-308 of the “Bulletin”).

Aug. 07

Experiment/Practice “Know more and manage cosmic gifts, won’t you?”, NWEC
Summer School 2016 for girls’ students~Meet with Science, Technology and
Human~, NWEC, Ranzan.

Sept. 25

Opinion-exchange Meeting with NPO HSE-Risk C-Cube (Tokai village), Crystal
Palace, Hitachinaka.

Nov. 06“Enjoy with seashells from Rokkasho/Radiations close to us”, Apio-Aomori Fall
Festival, Aomori.

Dec. 17

ISRE2016 Poster session, Koriyama.

Although the present authors are mostly nonmember of REF, we have been favored withoccasional opportunity to be close to the then secretariat Prof. Dr. T. Matsuura and the then Chairof the board of directors Prof. Dr. A. Arima in either Aomori or Rokkasho.
Once Tohoku branch of REF was established indeed (Head: S. Tsushima, the then member of75

Soloptimist International Aomori). We will be pleased to present our activities here in Koriyama,
Fukushima Pref., and grateful for any comments or suggestions you could give for.
Acknowledgments
Continuous Nos. of our ‘Bulletin’1) never be realizable without all those thoughtful contributions.
The budgetary support of the Town Coordinate Conference of Rokkasho was indispensable for the
publication of “Messages” 2) (combined Nos. of ‘Bulletin’). All those symposia listed were held in
support of the subsidy of the Japan Atomic Energy Relations Organization (JAERO). We also owe
the continuous support of those capable office staffs of the Rokkasho Cultural Exchange Plaza(Swany). We are obliged to all of the Rokkasho Public Hall in providing the booth for RCRCA.

References
1) The ‘Bulletin’ of Rokkasho Reading Circle, No. 246 (Mar.26, 2011) ~ No.334 (Nov.10, 2016)(in Japanese).
2) Messages from Rokkasho Women, 12 Part I & II, Kyodo Insatsu-kogyo Inc., Mutsu, 2015 (inJapanese).
3) Sasagawa S., Aratani, M: Women Scientists Joining Rokkasho Women to Sciences,
Proceedings of the 1st International symposium on Radiation Education, Hayama,1999.
4) Osanai, Y., Aratani, M: Science Literacy Promotion Activities by Citizens in Aomori Pref., J.
Soc. Jpn. Women Scientists, 2, 75 (2001) (in Japanese).
5) Osanai, Y., Kudo, M, Kamayachi, T., Tsushima, K., Uchiumi, F., Aratani, M.: Science
Education in the Life-long Education II, J. Soc. Jpn. Women Scientists, 5, (2004) (in Japanese).
6) Osanai, Y., Aratani, M., Kudo, M., Kamayachi, T., Tsushima, K., Uchiumi, F.: Periodic Table
as a Powerful Tool for Radiation Education, Proceeding of the 3rd International Symposium on
Radiation Education, 407, Nagasaki, 2004.
7) Osanai, Y., Tsushima, K., Hosokawa, S., Uchiumi, F., Aratani, M.: Science Education in theLife-long Education II, J. Soc. Jpn. Women Scientists, 6, 29, (2005) (in Japanese).
8) Aratani, M.: Contribution of Fundamental Science to Reconstruction of Human Beings andRegion -Development of the idea of Nucleus and Earthquake Disaster-, Earth Science (Chikyu
Kagaku) 61,401 (2007) (in Japanese).
9) Aratani, M.: An Interpretation on the ‘Natural Nuclear Reactor’ of P.K. Kuroda: Radiation
Education, 15, 41 (2011) (in Japanese).
10) Kumano, N. edited: “Women’s Messages from the Village of Rokkasho to the World”,
Kyodo-insatsu, Mutsu, 201211) Aratani, M.: Literature and Science---On Terada Torahiko, Proceedings of the 21st Century
Unions Symposium, Nihon Kagaku Miraikan, Tokyo, 2003 (in Japanese).
12) Aratani, M.: Led by Terada Torahiko, To’ohnippo Column-kosaten, Oct.10, 2003 (in Japanese).

76

ISRE2016 (2017) 77-82

Mystery of Alpha Particle Track in Cloud Chamber!
霧箱におけるアルファ線の飛跡の謎
Chizuo MORI
森 千鶴夫
Aichi Institute of Technology
愛知工業大学
Yachigusa 1247, Yagusa-cho, Toyota, Aichi Pref., 470-0392, Japan〒470-0392

愛知県豊田市八草町八千草1247

E-mail: moric@wh.commufa.jp
The track length of alpha particle with 6 MeV in air with the atmospheric pressure is about 4.7
cm and the flight time is only 7.3 ns. Then ion pairs are produced almost simultaneously
throughout the track and therefore the white track in a cloud chamber with ethanol vapor is
supposed to appear simultaneously. However, the white track of alpha particle is clearly seen toextend from the alpha particle source to the end of the track. This is mystery! The specific energy
loss of alpha particle along the track is expressed by the Bragg curve. The track is visible only
when the liquid drops of ethanol have grown to about 3 μm in diameter and then Mie scattering oflight has appeared. At the beginning of the track, 2-3 ion pairs per 1μm of the track are produced
and they are able to grow to the liquid drops with 3 μm diameter by the diffusion of supersaturated
ethanol vapor diffused through about 0.3 mm distance. However, near the end of the track, 6-8 ionpairs per 1μm are produced and they need the ethanol vapor diffused through 0.46 mm distance togrow each of the drops to 3 μm diameter. Therefore, the end of the track appears later than the
beginning of the track. Beta ray track, on the contrary, appears simultaneously throughout the track
length because of very low density of ion pairs per unit length.
6 MeV のアルファ線の１気圧の空気中の飛程は 4.7 cm で飛行時間は 7.3 ns である。すな
わち、全飛程にわたってほとんど同時にイオン対を作る。したがって霧箱中では飛程の全ての場所に白い飛跡（霧）が同時に現れると思われるが、飛跡は線源から遠方へと伸びて行く。これはまさに謎である。飛跡が白く見えるためには、霧滴は直径約 3 μm 程度に大きくなって Mie 散乱が生じなければならない。アルファ線のエネルギー損失はブラッグ曲線で表され、飛程の最初の位置では、飛跡の長さ 1 μm 当たりのイオン対の数は 2～3 個で、これらは、約 0.3 mm の離れた位置からのエタノールの過飽和蒸気の拡散によって直径 3 μmに育つ。しかし飛程の最後の方では 6～8 個のイオン対ができ、これらが直径 3 μm に育つには、0.46 mm のより遠方の過飽和蒸気が拡散して来なければならない。従って飛跡の終わりの方は最初の方よりも遅く現れる。対照的に、ベータ線の飛跡は飛跡長さ全長にわたって同時に現れるが、これは単位長さ当たりのイオン対の密度が非常に小さいからである。
Key words: extension direction, alpha-particle, cloud chamber, track, diffusion, energy loss
77

1. Introduction
Since Wilson invented the expansion cloud chamber 1, 2), these chambers have frequently beenused to find new particles. In 1939, Langsdorf developed diffusion cloud chamber 3). However,
because of the development of new electronic radiation detectors, cloud chambers are little used
today, excepting for radiation education purposes.
Large expansion cloud chambers were used mainly to study cosmic rays. After expanding thechamber, the droplets grew to a few micrometers in diameter and a strobe light was flashed tophotograph them. In the study of cosmic rays, researchers observed comparatively light particles
such as positrons, muons, and pions. Because the ion density created along the path of these lightparticles is very less and almost constant throughout the path, the liquid droplets appear almost
simultaneously along the entire particle path. Therefore, the direction of the track extension was
not accessible for researchers. Actually, in large diffusion cloud chambers, beta-ray tracks appear
simultaneously throughout the path and we are not able to see the extension direction. Conversely,
the direction of the tracks of alpha-particles can be determined with human eyes, even with small
diffusion cloud chambers for educational purpose.
However, the flight time of alpha-particles in air is less than 10 nano-seconds. The author
noticed there was a contradiction between the visibility of the extension direction of alpha-particle
track and the flight time of alpha-particles. In this paper, the reason why the direction of theextension of alpha-particle track is visible will be described.
2. Extension time of alpha-particle track and flight time of alpha particle in air
Diffusion cloud chamber used in the present experiment was 12 cm×12 cm×7 cm(height) withethanol sink at the upper part of the chamber. The temperature of the upper part was about 20℃.
The chamber was put on dry ice so that the temperature of the bottom of the chamber was about-40℃. The saturated vapor pressures of ethanol at 20℃ and -40℃ were 44.0 Torr (5780 Pa) and7.5 Torr (1000 Pa), respectively. Alpha-particle source was
232ThO

2 attached at the tip of a thin bar.

The extension of an alpha-particle track was observed inmovie mode with 60 frames per second of a digital camera. As
shown in Fig. 1, there was no track in the first frame (0 s), thenthe beginning of a track appeared in the second frame (17 ms)
and it grew in the third frame (34 ms). Finally, the trackcompleted in the fourth frame (51 ms).
Fig. 2 shows the relation between travelling time andtravelling distance of alpha-particles in air. The maximum
energy of a natural alpha-particle is 8.785 MeV (for 212Pb in thethorium series). The travel time is, therefore, less than 10 ns for
all natural alpha-particles. There is the discrepancy between theFig. 1. The extension ofan alpha-particle track

extension time of the track (about 50 ms) and the travelling time (less than 10 ns) of analpha-particle. This would be “mystery”.
78

3. Visibility of the direction of alpha-particle
track
Fig. 3 shows the energy loss and the number ofion pairs per 1μm of alpha-particle track in air
against the travelling distance of alpha particle.
At the beginning of the track, 2-3 ion pairs per
1μm of are produced and they are able to grow totheliquid

drops

by

the

attachmentofsupersaturated ethanol vapor. However, near theFig.2. Travelling time against
travelling distance of α-particles

end of the track, 6-8 ion pairs per 1μm areproduced.

Electrons of ion pairs quickly combine with oxygen molecules forming negative ions O 2－.
When low electric voltage is applied on an ionization chamber, it is known that the ionization
current is small due to the recombination of the ion pairs. When the applied voltage is zero, thecurrent is zero. Similar phenomenon would appear on a cloud chamber without electric applied
voltage. However, since the droplets actually appear, not all of the ion pairs recombine. It isdifficult to determine the degree of the recombination. Here, it is supposed that the half of the ion
pairs recombine. It means that the initial n ion pairs leave n ions.
Ions collect the supersaturated ethanol vapor and the liquid drops grow. The droplets scatter lightby Mie scattering, and they are visible to humaneyes when they grow to over about 3μm in
diameter 4, 5). Droplet with 3μm in diametercontains about 1.5×1011 ethanol molecules. The
temperature at the upper part of the diffusion
cloud chamber is about 20 ℃ (saturated vapor
pressure of ethanol is 5,870 Pa) and thetemperature at the lower part is about -40 ℃(saturated vapor pressure of ethanol is 1,000 Pa).
Therefore, the degree of super saturation (supersaturation ratio) is 5.8 which satisfies theFig. 3. Number of ion pairs per 1μm
in alpha-particle track

condition that the degree of super saturation isgreater than 4 6) to grow ethanol droplets in air. In saturated vapor at 20 ℃, the density of alcohol
molecules is 1.55×1018 cm-3. Thus, three droplets correspond to three ions per 1μm at the beginningof the track require 3×1.5×1011 (=4.5×1011) molecules to grow to droplets with diameter of 3μm.
These alcohol molecules are contained in a volume of 2.9×10－7 cm3 of air, which corresponds to acircular disk with a thickness of 1μm and a radius of 0.30 mm as shown in Fig. 4. For sevendroplets (seven ions) near the end of the track, the disk radius must be 0.46 mm.

79

We expect that the diffusion time ofalcohol molecules in the larger disk
diameter required to grow seven dropletswith 3μm in diameter near the end of the
track would be longer than the diffusion
time required to grow three droplets with
3μm diameter near the beginning of the
track. This would be the reason why wecan see the direction of the extension of
the track of alpha-particle in a cloud
chamber.
4.

Comparison

betweencalculated

Fig.4 Number of ion pairs per 1μm on the path ofalpha-particle in air and the distance from where
ethanol molecules must diffuse to make each
droplets to 3μm in diameter.

diffusion time and experimental result
To calculate the diffusion time of the required ethanol molecules to make an ethanol liquid
droplet by being attached to a N 2 or O2 ions, it is important to find the region where the ion pairs
are created by an alpha-particle travelling in air. Although little information is available on thismatter, it is considered that most ion pairs are substantially produced in a distance less than about
50μm by simple calculation.
Positive and negative ions rather quickly gather alcohol molecules forming droplets of ethanol
and the diffusion coefficient of the droplets is very small compared with that of ethanol molecules.
For this reason, only the diffusion of ethanol molecules is taken into account in what follows.
Owing to the geometry shown in Fig. 4, the diffusion equation is expressed in cylindricalcoordinates 7).
𝛿𝐶(𝑟)
𝛿𝑡

=

1 𝛿
𝑟 𝛿𝑟

(𝑟𝐷

𝛿𝐶(𝑟)
𝛿𝑟

(1)

)

In Equation (1), C(r) is the density of ethanol molecules at radius r, t is the time and D is the
diffusion coefficient of ethanol molecule in air. In the steady state, the flow rate Q(molecules/(sec×unit axial length）) from radius b with density C(b) to radius a with density C(a) isexpressed by the following equation 7).
𝑄=

2𝜋𝐷(𝐶(𝑏)−𝐶(𝑎))𝑙𝑛(𝑏⁄𝑎)(2)where C(b)=1.55×1018 cm-3 and C(a)=0 in the present case. Several ions are distributed within thedisk of radius 50μm, so it is appropriate to consider the radius a=50μm. The diffusion coefficient D
for an ethanol molecule in air is 0.088 cm2/s which is the average value of the experimental value
and the theoretically determined value extended to -40 ℃ by using values from the literature 8).
The total number of diffused molecules that is the current Q×10-4(molecules/s*μm) times
diffusion time t must be 4.5×1011 molecules/μm for 3 drops/μm and 10.5×1011 molecules/μm for 7
drops/μm under the simple assumption that the molecules are supplied by a steady state current
from radius b to radius 50μm, although the actual diffusion is not a steady state current but a80

transient current. The author has to admitthat the above assumption is the first
approximation.

Table 1. Comparison between the calculated
diffusion time and experimental result
Number of
Calculated Experimental
droplets

Table 1 shows the comparison between
thecalculated

diffusion

time

and

3 at the beginning

experimental result (obtained by Fig. 1)of the track

for the number of droplets at the

6 at the end of

beginning of the track and at the end of

the track

the track. The both agreed each other,

8 at the most endof the track

though under the rough assumption.

time (ms)time (ms)

18

17

35

34

48

51

5. Conclusion
We examined why it is possible to see the extension direction of an alpha-particle track in adiffusion cloud chamber with human eyes despite alpha-particle travel time of less than 10 ns.
Ethanol droplets must grow to a diameter of about 3μm to become visible by Mie scattering oflight. The energy loss (-dE/dx) of alpha-particle and thus the number of ions per unit length ofalpha-particle path are very large compared with the corresponding quantities for beta-particles. In
addition, the number of ions produced by alpha-particle per unit length near the end of the path islarger than that near the beginning of the path. Therefore, near the end of the path, a larger numberof ethanol molecules have to diffuse from farther distance than that near the beginning of the path.
The time required to grow droplets to a diameter of about 3μｍ near the end of the path is longer
than that near the beginning of the path. For this reason, the alpha-particle track appears first at the
beginning of the path and then at the end of the path, and thereby the direction of the extension canbe seen with human eyes.
Acknowledgements
The author acknowledges Radiation Education Forum (NPO), Chubu Atomic Power Conference
and Japan Atomic Energy Relations Organization, which have allowed him to attend various
radiation seminars where he could find some interesting phenomena such as the subject of thispaper.
References
1) Wilson C. T. R.: On the method of making visible the paths of ionizing particles through a gas,
Proc. Roy. Soc. 85, 285 (1911).
2) Wilson J. G.: The Principles of Cloud-Chamber Technique, Cambridge Univ. Press, London(1951).
3) Langsdorf A.: A Continuously Sensitive Diffusion Cloud Chamber, Rev. Sci. Instr. 10,91(1939).
4) Barret and Germain L.: Growth of Drops Formed in a Cloud Chamber, Rev. Sci. Instr. 18, 84(1947).
815) H. C. van de Hulst : Light Scattering by Small Particles, John Wiley & Sons, Inc. (1957) p.119.
6) Mori C., Shirakawa Y., Fujinami M.: Growth of Cloud Drops in Diffusion Cloud Chamber,
Isotope News, No.7, 25 (2006) [in Japanese].
7) Crank J.: The Mathematics of Diffusion, second ed., Clarendon Press, Oxford, (1975) p.69.
8) The Society of Chemical Engineers, Japan , Bussei Jousuu, Maruzen, (1964) p.248
Japanese].

82

[in

ISRE2016 (2017) 83-87

The Image of Alpha Emitter Distribution on the Surface ofEnvironmental Material with CR-39
身の回りの物品表面のアルファ放射体分布像を CR-39 で取得
Chizuo MORI
森 千鶴夫
Aichi Institute of Technology
愛知工業大学
Yachigusa 1247, Yagusa-cho, Toyota, Aichi Pref., 470-0392, Japan〒470-0392 愛知県豊田市八草町八千草1247
E-mail: moric@wh.commufa.jp

Abstract
Some environmental materials, such as stone, brooch and ornament made of pottery, lead, solder, etc.
contain Th-232 or U-238 and emit alpha-particles. The images of the distribution of alpha emitters on
the surface of such materials are able to simply obtain using nuclear track detector CR-39 used forheavy particle radiations. The obtained images are very clear, because the penetration ranges ofalpha-particles in solid are very short such as a few tens micro-meter. Since the method is simple andinexpensive, it can be used at science clubs at senior and junior high schools. From the etch pit density
obtained by microscopic observation, the radioactivity density of materials can be determined with thehelp of some theoretical calculations.
身の回りの物品、例えば岩石、陶磁器でできたブローチ、徽章、鉛板、鉛を含む半田など
は Th-232 や U-238 などを含んでいて、物品の表面からアルファ線を放出している。そのような物品表面のアルファ線放出核種の分布像を核放射線の飛跡固体検出器である CR-39 を使って簡単に取得することができる。アルファ線の飛程が固体中では数十ミクロンで極めて短いので、鮮明な像を得ることができる。この方法は簡単で安価なので、高校や中学校の科学クラブなどには適していると思われる。顕微鏡で CR-39 の表面を観察することによって、固体中に含まれる放射能強度を求めることもできる。

Key words: alpha emitter, distribution image, nuclear track detector, CR-39, environmental material,radioactivity,83

1. Introduction
Geometrical distribution images of radioactivity on the surface of environmental materials are very
helpful to understand natural radioactivity and natural radiations. With this intention, so far images ofbeta-ray emission from 40K, which is naturally present in vegetables, meat, and other environmental
materials, have been obtained using an imaging plate 1). These images have been widely used in public
education. However, an expensive image reader is necessary to obtain such images.
A unique method to obtain macro-autoradiographs of alpha emitters was developed by N. Ishigure 2)
who used a solid-state track detector CR-39 plate to obtain plutonium distribution image with verystrong radioactivity in a mouse’s body after the injection of plutonium in a vein. The author consideredthat this method could be adaptable to obtain the image of natural alpha particle emission on thesurface of environmental materials such as stone, and ceramics 3), although a very long exposure time
would be necessary for these environmental materials. Such images would be very useful tounderstand natural radioactivity and naturalradiations. Since this method is inexpensive and(A)simple, it would easily be used even at the highschools.
2. Procedure to obtain alpha particle images(B)with CR-39
An inexpensive solid-state track detector
CR-39 plate, 280 mm×280 mm×0.9 mm in size,
known

as

BARYOTRAK

iscommerciallyavailable through Nagase Landauar Ltd, Japan.
For the present study, this plate was cut into 15(C)pieces. The detector is sensitive to alpha particles
and insensitive to beta- and gamma-rays. Stone,
ceramic ware, lead plate, etc. are appropriate
specimens, because they emit natural alphaparticles.
The

exposure

processisvery

simple.

Fig. 1. (A) Alpha emitter specimens are
exposed on a piece of CR-39, (B) pieces of
CR-39 are chemically etched in sodiumhydroxide solution, and (C) the photograph of
the image was taken under the illumination oflight through only one side of the plate as
shown in (C).

Specimens are simply placed on a CR-39 plate as
shown in Fig. 1 (A). It is not necessary to shieldenvironmental radiations or light. However, theexposure time is very long as 2-3 months,
because the alpha-radioactivity of environmental
specimens is very small. It is important to makethe specimen surface contact with the plate surface to obtain a sharp image.
Alpha particle leaves a radiation damage trail called a latent track. The chemical etching enlarges it
to be visible size under the microscope or human eyes. In the present case, the CR-39 plate was
immersed in sodium hydroxide solution (7.5N, 80℃) for 5 hours as shown in Fig. 1 (B). Cone-shaped84etch pits with diameter in the range of 10-100 micrometers appear on the plate surface. Since theexposure time is as long as 2-3 months, the surface density of the number of etch pits is large and thereflection of light by these dense etch pits allows to observe the image with human eyes. If theobservation with an optical microscope is desired, the etch pit density must be small. Therefore, in thiscase, the exposure time was chosen to be as short as several days depending on the radioactivity
density of the specimen.
After chemical etching, the CR-39 plate was washed with water. The etch pit density image can bedirectly seen with the eyes. To obtain the photograph of the image, the plate was put in a dark box so
as to face having etched pits downward and the plate was illuminated with light only through one sideof the plate as shown in Fig. 1 (C). The photograph was taken and exhibited on the personal computer
screen.
3. Some examples of alpha-particle emission distribution images
Fig.

2

(A)

shows

a

photograph of a piece ofgranite with a flat surface. The
granite was placed on the
CR-39 plate for 3 months and(B) is the obtained image
shown

pseudo

by

(A)

(B)

color

treatment. The radionuclides
present in granite are thorium,
uranium and their daughter
nuclides. Therefore, the etchpits caused by alpha particles
emitted from the radon gas

(C)

(D)

(E)

(F)

emanated from granite and its
daughter nuclides can be seenat outside the granite surface
area. The black points (biotite
containing

232Th,

238U

andtheir daughters) shown in (A)coincide with bright points
shown in (B).
Fig. 2 (C) shows two
broaches, an emblem with apigeon pattern, and an IC(integrated circuit) part in a
brokenelectronic

Fig. 2. Photograph of the flat surface of granite (A) and its
image of alpha-emitter distribution (B). Two broaches, anemblem, and an IC part (C) and their images (D). Various lead
specimens, two emblems, two monazite spheres and uranium
glass (E) and their images (F).

deskcalculator. Fig. 2 (D) shows the distribution images of alpha emitters of these materials. The wirings of85

the IC were attached with solder containing lead. Lead contains natural alpha emitters, although
recently manufactured solder does not contain lead. Fig. 2 (E) shows the photograph of a leadcontainer and the cap, from upper left to right, uranium glass, two emblems of the Atomic Energy
Society of Japan, two monazite spheres with a diameter of 2.5 mm, and three different lead plates. Fig.
2 (F) shows the auto-radiographs obtained by the exposure of (E) for two months. Different three small
lead plates showed different lead contents depending on the content of 210Pb (half-life is 138.4 days) of
the daughter nuclide of 238U. Two monazite alpha sources have been used for small cloud chamber at
the radiation seminars held by
Chubu Atomic Conference andtheir alpha-particle emission rate is
only about 0.8 particle /second 4).
However, the exposure time was solong as 5.2×106s that the densityof the pits was extremely large as
about 100 pits per the area of 100

Fig. 3. Three dried sardines (left) and their alpha emitter
distribution images (right)

μm×100 μm.
Fig. 3 gives the case of dried sardines (left) and their alpha-particle pit image (right) which showsalpha-emitters were included in special internal organs. The author obtained the image of the same
specimens after about one year to confirm whether the alpha emitter was 210Po with the half-life of
138.4 day or not. The image of alpha emitters was faint, so that the emitter was estimated to be 210Po.
From the etch pit density obtained by microscopic observation, the radioactivity density of materials
can be determined with the help of some theoretical calculations 5). In this case, however, the exposure
time should be much shorter than 2-3 months not to overlap the pits depending on the radioactivity
density in the specimen.
4. Conclusions
By using solid state track detector CR-39, very sharp alpha particle macro-autoradiographs can beobtained which are very useful for understanding natural radioactivity and natural radiations. Since
this method is very simple and inexpensive, it can be adapted in extra-curricular activities under thesupervision of a teacher at high schools or junior high schools. At universities or research institutes,
this method can be used for studying petrology. Radioactivity density in a specimen is able to obtainfrom the pit density observed by microscope.
Acknowledgements
The author would like to express his sincere thanks to Prof. Takao Iida and Assoc. Prof. Jun
Moriizumi of Nagoya University for their valuable advice on chemical etching of CR-39.
References

1) Mori C.: Measurement of extremely low level radioactivity distributions with imaging plate,Radioisotopes, 48, 589 (1999) (In Japanese).
862) Ishigure N.: Application of CR-39 plastic to rapid and quantitative macro-autoradiography of
α-emitters in a whole body section of an experimental animal, Radioisotopes, 34, 101 (1985)(In Japanese).
3) Mori C.: Obtaining alpha-ray image of surrounding material with CR-39, Proc. 2011 Annual
Meeting of the Atomic Energy Society of Japan, Fukui Univ., Japan, March 28-30, (2011),
M20 p617, ISBN 978-4-89047-151-5 [CD-ROM]. (In Japanese)4) Mori C.: Theoretical calculation of the number of α-ray track in a Petri dish-type cloud
chamber with monazite source, Radioisotopes 61, 399 (2012)(In Japanese)5) Mori C.: Macro-autoradiographs of alpha emitters in environmental materials observed withsolid-state track detector CR-39, J. Nucl. Sci. and Technol., 50, 891 (2013)

87

ISRE2016 (2017) 88-93

Analysis of the Consciousness of University Students in
Okinawa about the Radiation
沖縄県の若者の放射線に対する意識分析
Nanaho SAKASHITA and Eisaku HAMADA
坂下 奈奈穂，濱田 栄作
Faculty of Education, University of the Ryukyus
琉球大学 教育学部
1 Senbaru, Nishihara-cho, Nakagami-gun, Okinawa 903-0213, Japan
〒903-0213 沖縄県中頭郡西原町字千原１番地
E-mail: e-hamada@edu.u-ryukyu.ac.jp
Abstract
By revising curriculum guidelines for junior high school in 2008, radiation was added to thethird grade science. Most of the students who enrolled in the university in last year (2015) were thefirst student who learned a radiation at the age of the junior high school. In this study, we compared
the awareness of radiation of undergraduate students who received the new curriculum versus theold curriculum by survey. The revision of the curriculum has brought about improvement of someknowledge of radiation. However, no significant difference was found in many other question items.
Since the awareness of the topics of radiation related to Okinawa was low, we should develop
familiar teaching materials for students.
1. はじめに
学習指導要領の改訂に伴い，平成 23 年度から放射線に関する内容が中学校理科第三学年に復活し，「放射線の性質と利用にも触れること」と明記された。また，中学校学習指導要
領解説理科編においては，その取扱いについて「原子力発電ではウランなどの核燃料からエネルギーを取り出していること，核燃料は放射線を出していることや放射線は自然界にも存在すること，放射線は透過性などをもち，医療や製造業などで利用されていることなどにも触れる」と記載されている 1)。平成 27 年度に入学した大学生の多くは，中学校で放射線を学習した第一期生となった。そこで，本研究では学習指導要領の変更に伴う学生の理解度の変化を明らかにするために，大学生を対象とした放射線に関するアンケート調査を実施した。
2. 学生の放射線に関する認知度調査
2.1 アンケート調査の概要
本研究では，中学校第三学年で放射線を学んだ第一期生となる平成 27 年度の大学一年生と，学習指導要領改訂前の内容を学習した大学二年生以降を対象にアンケート調査を実施
し，学生の放射線に関する知識の定着度合いを調査・分析した。なお，学生によっては，入学年度が同じであっても年齢が異なる場合もあり，学習指導要領の新旧の属性は生年月88日で判断した。質問項目は以下の通りである。Q1 放射線の種類に関する認知度，Q2 放射線の性質に関する認知度，Q3 放射線の利用に関する認知度，Q4 放射線の透過力と危険認知。
平成 27 年 7 月から 8 月にかけて記入式アンケートを 342 枚配布し，335 枚を回収した。
その内，323 枚の有効回答があった。有効回答者の属性から以下のグループに分け集計し比較した。Ⅰ 新課程履修者（N=99）
・旧課程履修者（N=224）
（以下，
「新課程」
「旧課程」），
Ⅱ 男性（N=177）・女性（N=146），Ⅲ 出身高校県内（N=263）・県外（N=60），Ⅳ （教育学部を除く）理系学生（N=128）
・文系学生（N=73），Ⅵ 教育理系（N=48）
・教育文系（N=74），
Ⅶ 男性新課程（N=54）
・男性旧課程（N=123），Ⅷ 女性新課程（N=45）
・女性旧課程（N=101），
Ⅸ 理系学生新課程（N=41）
・理系学生旧課程（N=87），Ⅹ 文系学生新課程（N=28）・文系
学生旧課程（N=45），Ⅺ 教育学部理系新課程（N=10）
・教育理系旧課程（N=38），Ⅻ 教
育文系新課程（N=20）・教育文系旧課程（N=54）。なお，教育学部を除く理系の学部（医学部，工学部，農学部，理学部）に在籍している学生を理系学生，文系の学部（観光産業
科学部，法文学部）に在籍している学生を文系学生とした。また，教育学部に在籍している学生の内，理系教科に属する学生を教育理系，その他を教育文系とした。Q1，Q3 については，イェーツの連続補正を行ったカイ二乗検定を基本としたが，期待度数が 5 未満のセルが 20%あるとき，または期待度数が 1 未満のセルが存在するときにはフィッシャーの正確検定（Fisher’s exact test）を用いた。また，Q2，Q4 については Mann-Whitney の U 検定を用いた。何れも有意水準は P＜0.05 とした。
2.2 アンケート分析結果
2.2.1 放射線の種類に関する認知度
最も認知度が高かったのはエ

表 1.

放射線の種類に関する認知度（新課程・旧課程）ックス線で，次いでガンマ線，
アルファ線，ベータ線，中性子

Method ofQuestion

Know
Curriculum

AnalysisP-value(%)の順となった（表 1）
。新課程を

alpha

New

75.76

履修した学生の方が，全ての放

ray

Old

64.73

New

71.72

Old

58.98

Chi-squared

New

94.95

test

Old

92.86

0.067

射線種に対する認知度が高かったが，統計的に有意な差がみら

beta ray

れたのはベータ線と中性子のみであり，学習指導要領の改訂の0.038*

X-ray

0.138

明確な効果は確認出来なかった。

gamma

New

78.79

その他の属性間の比較では，学

ray

Old

70.09

New

40.4

Old

23.66

0.646

生理系の方が学生文系に比べア
ルファ線，ベータ線，ガンマ線

neutron0.003**

について有意に認知度が高かっ*p<.05た。学生理系の新課程・旧課程**p<.01***p<.001

については，アルファ線，ベータ線，中性子で，新課程の方が有意に高かった。一方で，文系学生，教育理系，教育文系の新課程・旧課程については，全ての線種について有意な差は見られなかった。

89

2.2.2 放射線の性質に関する認知度

図 1.

放射線の性質に関する認知度（新課程・旧課程）

放射線の透過力や不可視性，シーベルトや人体への影響に関する認知が高かったが，イオン化や，自然放射線の存在およびその起源については低かった。また，ラドンに関する
項目も低かった。新課程と旧課程で有意差が確認されたのは透過力とイオン化に関する項
90

目のみで，何れも新課程で学んだ学生の方の認知度が高かった。なお，理系学生と文系学生，県内と県外で，多くの項目で有意差が確認され，理系学生と県外の高校出身者の方が認知度は高かった（図 1）。
2.2.3 放射線の利用に関する認知度
放射線の利用についてはエックス線撮影やがん治療，空港の手荷物検査に関する認知度は約 7 割を超えた。しかしながら，その他の放射線利用に関する認知度は低く，沖縄県の農業に多大な恩恵をもたらした害虫駆除 2)ですら，認知度は僅かであった。属性間比較を行ったところ，全ての利用について，新課程と旧課程に有意な差はみられず，学習指導要
領の改訂による効果は確認できなかった。一方で，出身高校の県内・県外については，県外出身者の方が農作物の品種改良，タイヤの強度改良，医療用器具の滅菌，文化財の調査に関する認知度が有意に高かった（表 2）。
表 2. 放射線の利用に関する認知度（新課程・旧課程）
Question

Method of Analysis

Curriculum

Know (%)

Unknown (%)

New

10.10

89.90

Old

14.73

85.27

New

15.15

84.85

Old

15.18

84.82

New

24.24

75.76

Old

19.20

80.80

New

1.01

98.99

Old

2.23

97.77

Chi-squared

New

92.93

7.07

test

Old

97.77

2.23

New

85.86

14.14

Old

83.93

16.07

New

30.30

69.70

Old

31.25

68.75

New

27.27

72.73

Old

33.48

66.52

New

68.37

31.63

Old

66.96

33.04

1.じゃがいもの発芽防止

n.s.

2.害虫駆除n.s.

3.農作物の品種改良

n.s.

4.タイヤの強度改良

5.X 線撮影

P-value

n.s.

n.s.

6.がん治療n.s.

7.医療用器具の滅菌

n.s.

8.文化財の調査

n.s.

9.空港の手荷物検査

n.s.

2.2.4 放射線の透過力と危険認知
放射線の透過力を説明する図を提示し（図 2），5 段階で危険度の評価を問うたところ，すべての属性においてアルファ線，ベータ線，ガンマ線・エックス線の順に危険度認知（平均値）が高くなった（表 3）。なお，危険度の評価は「危なくない」を 0 とし，「危ない」
を 4 とし，数値化した。

91

放射線被ばくには外部被ばくと内部被ばくがあるが，放射線の透過力を示す図は外部被ばくからの影響を無意識にイメージさせ，透過力の高いガンマ線やエックス線に対する危険認知を高めたと考えられる。アルファ線の放射線荷重係数は光子の 20 倍もあり，放射線被ばくを議論する際には，アルファ線による内部被ばくを無視することはできない。放射線の透過力だけではなく，放射線被ばくの形態と放射線種の関係を示す適切な解説が必原子力・エネルギー図面集 2015

要である。

図 2. 放射線の透過力
表 3. 放射線の透過力と危険認知（新課程・旧課程）
Question

Method of Analysis

Curriculum

Average

New

1.79

Old

1.28

New

3.29

Old

3.56

New

3.00

Old

3.49

P-valuealpha raybeta rayn.s.

Chi-squared testn.s.

gamma, X-rayn.s.

3. まとめ学習指導要領の改訂後に中学校で放射線教育を受けた学生の方が，放射線に関する知識が高い傾向が一部を除き見られたが，統計学的に明確な効果は見られなかった。また，学習指導要領で明記された放射線の利用については，新旧課程の有意差が全ての項目で見られなかった。福島第一原子力発電所事故が収束しない状況で，社会の関心が放射線の環境や人体への影響に集まる中，放射線利用が授業でどの程度扱われたのか，疑問が残る。特に，害虫駆除や建物内のラドン 3)など，沖縄と関係が深い項目について，県内出身の学生の認知度は極めて低かった。地域の実情に合わせた放射線教育が今後求められるとともに，放射線を教える教師への支援も必要と思われる。他方，放射線の透過力を表す図のみの説
明では，自然放射線による被ばくの約半分を占めるラドンガス（アルファ線）の影響を過小評価する可能性もある。放射線被ばくの形態と放射線種の関係を示す適切な解説が必要である。今回の調査では，理系と文系で放射線に関する認知に有意差が多くみられた。調
査時点では，新課程の学生は 1 年前期の講義を履修中であり，大学での学習ではなく高校での学習が影響したと思われる。中学校のみでなく，継続的な放射線教育が必要と考えられる。
謝辞
本研究の一部は，JSPS 科研費 26350239 の助成を受けて行われた。

92

参考文献
1)

文部科学省: 中学校学習指導要領解説理科編. 大日本図書 2008

2)

Kakazu Hiroshi, A new frontier of Okinawa’s Agriculture: An economic evaluation of themelon fly eradication project. Journal of Agricultural Development Studies 17, 21 (2006)3)

沖縄県農林水産部病害虫防除技術センター: ウリミバエ根絶防除事業概要 2008

4)

Inspector General U.S. Department of Defense: Military Housing Inspections–Japan. Report
No. DODIG-2014-121 2014

93

ISRE2016 (2017) 94-98

Development of Teaching Materials for Radiation Education
Using CR-39
固体飛跡検出器 CR-39 を用いた放射線教育教材の開発
Yumeto NAKAHODO and Eisaku HAMADA
仲程 夢斗，濱田 栄作
Faculty of Education, University of the Ryukyus
琉球大学 教育学部
1 Senbaru, Nishihara-cho, Nakagami-gun, Okinawa 903-0213, Japan
〒903-0213 沖縄県中頭郡西原町字千原 1 番地
E-mail: e-hamada@edu.u-ryukyu.ac.jp
Abstract
For visualization of radiation damage to the solid track detector, it must be etched with a high concentration of
sodium hydroxide solution or potassium hydroxide solution. Since the use of these solutions is accompanied bydanger, it is difficult to do in elementary and junior high school. In order to use the solid track detector CR-39 in the
education field, we have investigated a safe etching method for CR-39.
When a low concentration sodium hydroxide solution (5%) was used for etching at room temperature, etched pits
could be observed by etching for 3 days. If etching could be performed at 90 ºC using a hot water bath, the etch pit
on CR-39 appeared in just a few hours. By irradiating CR-39 with UV, it became easy to observe the etch pits. In
particular, the size of the etch pits of CR-39 irradiated with UV before and after α-ray irradiation has expanded. By
partially irradiating alpha particles, we were able to observe the presence or absence of radiation damage without
using a microscope. By combining these methods, it can be safely utilized CR-39 in the school.
1. はじめに現行の中学校学習指導要領理科に「放射線の性質と利用にも触れること」が明記され 1)，学校現場では放射線に対する理解を高めるために，霧箱や放射線測定器の利用など様々な工夫がされてきた 2 – 4)。
一方で，医療，農業，工業分野での放射線利用や，放射線の人体への影響を理解するためには，放射線と物質の相互作用，すなわち放射線が持つエネルギーを実感し，理解することが重要であり，放射線損
傷を眼で確認できる固体飛跡検出器の放射線教育教材としての活用が望まれる。
固体飛跡検出器は，荷電粒子が入射した際に形成される放射線損傷を化学薬品によるエッチングで拡大し，光学的に観察できる検出器である 5)。特に，
プラスチック材料の PADC（Poly-Allyl-Diglycol-Carbonate，
CR-39）は荷電粒子に対して高い感度を持ち，放射線損傷を観察しやすく，宇宙飛行士の線量評価など，
その取扱い性から様々な分野で利用されている 6)。また，軽量で衝撃に強く割れにくい一般的な CR-39
は優れた光学性能も有していることから，偏光レンズや溶接カバーとしても利用されており，生徒にとっても馴染みのある材料である。

94

プラスチック板 CR-39 に荷電粒子が入射すると，飛跡に沿って放射線損傷（潜在飛跡）を与える。その損傷は極めて小さいが，化学薬品でエッチングすることで，損傷された場所の方が損傷を受けていない場所よりもエッチング速度が速い
ため損傷が拡大され，光学顕微鏡で観察できるよ
うになる（図 1）。このように，放射線による損傷を観察できる CR-39 は，学校現場での教材として

図 1. エッチピットの形成過程の活用が期待されるが，CR-39 の放射線損傷の可視化には，高濃度（30 %）の水酸化ナトリウム水溶液や水酸化カリウム水溶液によるエッチングが一般的で，教育現場で使用するためには取扱いに注意が必要となる。また，昨今の放射線教育のニーズの高まりから，簡単に放射線損傷を可視化できる実験キット（サンルックス，Sun9）も市販されているが，30 %の水酸化ナトリウムを沸騰させ，徐冷しながらエッチングしており，中学生の生徒実験としては，
安全面から特段の配慮が必要である 7)。
そこで，本研究では CR-39 の教育現場での活用を目的に，エッチング溶液の低濃度化を中心に検討を行った。
2. 教材化のための検討
本研究では，市販の CR-39（長瀬ランダウア，BARYOTRAK，t = 0.9 mm）を用いた。また，教育現場での活用を考慮し，「毒物及び劇物取締法」に該当しない 5%の水酸化ナトリウム水溶液をエッチング溶液として主に利用した。なお，放射線源（アルファ線）には，硝酸トリウムを含侵させたマントルの芯を用いた。以下，①エッチング溶液の低濃度化，②紫外線照射効果，③超音波照射効果について述べ，
最後に④光学顕微鏡を利用しない方法について述べる。
2.1 エッチング溶液の低濃度化
一般的に，エッチング溶液の液温を上昇させることで，エッチピット
をより早く拡大できる。しかしながら，教育現場ではウォーターバス等の恒温装置が無いのが現状である。
そこで，低濃度エッチング溶液による室温でのエッチングを試みた。図
2 に，高濃度（30% NaOH (aq)）および低濃度（5% NaOH (aq)）エッチン
グによる，エッチピット径の時間変化を示す。高濃度エッチングの場合，

図 2. エッチング時間とエッチピット径の関係（室温，NaOH (aq)）

数時間後にはエッチピットを観察できたが，低濃度エッチングでは，3 日目から小さなエッチピットが観察でき，20 日目に明瞭なエッチピットを観察することができた。

95

2.2 紫外線照射効果
CR-39 に放射線を照射する前または後に，紫外線を照射することでエッチング速度が大きくなることが報告されている 8)。そこで，本研究では，
波長 254 nm の紫外線（UVP，3UV-34，4 W）を以下の条件で照射し，エッチピットの拡大について調べた。
【pre-UV】予め紫外線を照射した CR-39に放射線を照射し，その後エッチングを実施。
【post-UV】放射線を照射した CR-39 に紫外線を照射し，エッチングを実施。
【pre-post-UV】放射線を照射する前と後に紫外線をそれぞれ照射し，エッチングを実施。
図 3 は，紫外線照射によるエッチピットサイズ

図 3. エッチピット画像の変化を示したもので，紫外線を照射することでエッチピットの拡大が確認できた。図 4，5 は紫外線をそれぞれ 1 時間（図 4）又は 3 時間（図 5）照射した際のエッチピットサイズの時間変化である。両条件とも，エッチング時間が 3 時間を超えると，エッチピットの大きさに変化が現れ，特に，放射線照射の前後に紫外線を照射すると，その効果は顕著であった【pre-post-UV】。

図 4. 紫外線を 1 時間照射したときのエッチピット

図 5. 紫外線を 3 時間照射したときのエッチピットの時間変化（90 ℃，5 % NaOH (aq) )の時間変化（90 ℃，5 % NaOH (aq) )2.3 超音波照射効果
エッチング反応の効果を高めるために超音波（本多電子，HM-303N，超音波発振周波数 2.4 MHz）を照射しながらエッチングを行ったところ（室温，5% NaOH (aq)）， 24 時間後には直径約 2.3 μm のエッチピットを観察することができ，5 日目には 17 μm となり，エッチピットの拡大が確認された（図 6，7）。
しかし，超音波発生時に，溶液温度の上昇（50℃）も確認されており，更なる研究が必要である。

96

図 6. 超音波照射時のエッチング時間とエッチピットの関図 7. 超音波照射時のエッチピットの例 （5 日目）

係（室温，5 % NaOH (aq)）

2.4 顕微鏡を使用しない観察手法
CR-39 の損傷から放射能分布を肉眼で観察する方法が報告されている 2, 9)。本研究でも，約 4cm 四方に切った CR-39 に放射線を遮蔽するための紙を置き，その上から放射線源としてマントルを 1 日静置した。その後，30 % NaOH 水溶液を使用し 90 ℃で 20 分間エッチングを行った結果，放射線を遮蔽していない部分のみが白く濁り，模様を観察することができた（図 8）。同様の実験について，低濃度のエッチング溶液（室温，5% NaOH (aq)）でも試みたが，観察可能な大きさまでエッチピットが拡大するためには長時間（30 日超）のエッチングが必要であった。

図 8. 放射線の遮蔽方法と結果

3．まとめ
本研究では，固体飛跡検出器である CR-39 を放射線教育用教材として，安全に利用するための手法について検討した。
「毒物及び劇物取締法」に該当しない 5 %程度の NaOH 水溶液を使用する場合，90 ℃
で液温を一定にできれば，1 時間のエッチングでエッチピットを観察することができた。また，液温を室温にし，5 %濃度で長時間エッチングを行えば観察も可能であった。さらに，紫外線照射や，エッチン
グ中に超音波照射することで，エッチング速度の増加が確認された。顕微鏡を使用しない観察手法では，放射線照射による損傷部分とそうでない部分の状態の違いを肉眼で観察できるので，放射線がエネルギーを持つことについての理解が容易になる。これらの手法を組み合わせることで，より安全に CR-39 を教育現場で活用できると思われる。
謝辞
本研究の一部は，JSPS 科研費 26350239 の助成を受けて行われた。
97

参考文献
1) 文部科学省: 中学校学習指導要領解説 理科編. 大日本図書 20082) 森千鶴夫: 学校教育における放射線実験に関する提言. 放射線教育 16, 3 (2012)3) 佐伯英人，宇宿公紀: 秋芳洞，大正洞，景清洞の放射線に関する基礎研究と教材化に関する一考察. 理科教育学研究 56，355 (2015)4) 濱田栄作，松田翔: WebGIS を活用した放射線教育実践. 放射線教育 17 , 3 (2013)5) G. F. NOLL: 放射線計測ハンドブック. 日刊工業新聞社 1982
6) B. G. Cartwright, E. K. Shirk, P. B. Price: A nuclear-track-recording polymer of unique sensitivity andresolution. Nuclear instruments and methods 153, 457 (1978)
7) 石川一平, 清原修二: 放射線飛跡を可視化するプラスチック教材を用いた教育方法の実践, 応用物理
教 40, 101 (2016)8) K. C. C. Tse, D. Nikezic, K. N. Yu: Effects of UVC irradiation on alpha-particle track parameters in CR-39.
Radiation Measurements 43, 98 (2008)
9) Nobuhito Ishigure: Application of CR-39 plastic to rapid and quantitative macroautoradiography ofalpha-emitters in a whole body section of an experimental animal. Radioisotopes 34, 101 (1985)

98

ISRE2016 (2017) 99-102

HATO Project / Practice of Radiation Education throughPartnership of Teacher Education Universities
HATO プロジェクト/大学間連携による放射線教育の実践
Kazuko ONISHI1, Akio HIRATA2, and Masahiro KAMATA2
大西和子 1、平田昭雄 2、鎌田正裕 2
1Center for Teacher Education Development through Partnerships, Tokyo Gakugei University
東京学芸大学 教員養成開発連携センター
2
Faculty of Education, Tokyo Gakugei University
東京学芸大学 教育学部
4-1-1, Nukuikitamachi, Koganeishi, Tokyo 184-8501, Japan〒184-8501 東京都小金井市貫井北町 4-1-1
E-mail: onishi@u-gakugei.ac.jp
Abstract
Teacher training to produce junior high school science teachers who can teachradiation/radioactivity based on scientific perspective has become an urgent task in Japan. Since
2012, four Teacher Education Universities (Hokkaido University of Education, Aichi University of
Education, Tokyo Gakugei University（TGU）, Osaka Kyoiku University) have been engaged in the“HATO Project”. Under this big project, Tokyo Gakugei University (TGU) has managed a
sub-project; “HATO Radiation Education Project” whose objective is pre-service teacher training ofradiation education for junior high school science. In this project, we started two new subjects“Radiation Education I” and “Radiation Education II” in TGU from 2014. The former one is for the
students of the four universities, and is made of lectures and educational experiments. The latter“Radiation Education II” is for the students of TGU, and is made of lectures and practical work
such as practice teaching at junior high school. In addition, we have developed teaching materialsof radiation education (Video contents and “Teaching Materials Package for teachers”).
Outline of “HATO Project”
In Japan, curriculum guideline(Course of Study) for junior highschool science was revised in 2008,
and radiation education was added in
the guideline of school science. After
Fukushima Daiichi nuclear power
plants accident of 2011, scientific
literacy on radiation/radioactivity isFig. 1. The Organization of HATO

socially demanded.

Project

Under the circumstance described above, teacher training to produce junior high school scienceteachers who can teach radiation/radioactivity based on scientific perspective has become anurgent task in Japan.
The HATO Project is implemented to build a support system for advanced teacher education99

through university partnership. The project was established in 2012. Four Teacher Education
Universities (Hokkaido University of Education (H), Aichi University of Education (A), Tokyo
Gakugei University (T), Osaka Kyoiku University (O)) have been engaged in the “HATO Project”(Fig. 1). Under this big project, Tokyo Gakugei University (TGU) has managed a subproject;
Radiation education project. The objective of this project is to develop junior high school teachersof science who can teach radiation and radioactivity based on scientific perspective.
Radiation Education Curriculum
In this project, we have developed a curriculum and materials for radiation education, and havestarted two new subjects “Radiation Education I” and “Radiation Education II” for university
students since 2014.

Table 1.
Day
2016
9/2(Fri.)

Curriculum of “Radiation Education I” （2016）

Sc h e du leN o. Title
9:00

Te ac h e r

01 Guidance

10:40 02 Basics of radiation physics
13:00
9/3(Sat.)14:40 04 Nuclear fission and nuclear reactor
9:00 05 Natural nuclear fission reactor, uranium deposits and deep geological
10:40

9/5(Mon.)
9/6(Tue.)

13:00
14:40
16:00
16:20
9:00

13:00
9/7(Wed.)

9:00
12:50
9:00

9/8(Thu.)
9/9(Fri.)

03 Science of Radiation

10:40
13:00

repository
06 Separation of radionuclides using ion exchange and solvent extraction
method07 Effects of radiation on living organism
08 Molecular mechanism of Cs specific adsorption
09 Guidance(for students of three other universities)
Basics of radiation physics
10, Measurement of natural radiation,
11 Visualization of radiation by cloud chamber
12 Experiment of model waste fluid processing using ICP and AAS (1)
13 The effect of radiation on biological systems (1)Model experiments using ultraviolet light
The effect of ultraviolet light on E. coli and Drosophila
14 Principles of IP, CT, and radiation detectors
15 Elementary particles observed in Photographic Emulsion
16 Experiment of model waste fluid processing using ICP and AAS (2)17 Radiation effect of foods
18, Measurement of the natural radioactivity of mineral rocks
19 Identification of radionuclides in mineral rocks
20 The effect of radiation on biological systems (2)Model experiments using ultraviolet light
The effect of ultraviolet light on E. coli and Drosophila

Masahiro Kamata(TGU),
Akio Hirata(TGU)
Masahiro Kamata(TGU)
Masahiro Kamata(TGU),
Kazuko Onishi(TGU)
Shu Matsuura(TGU)
Masataka Nakata(TGU)
Hisao Kokusen(TGU)
Fumi Nakanishi(TGU)
Kiminori Sato(TGU)
Masahiro Kamata(TGU),
Akio Hirata(TGU)
Masahiro Kamata(TGU),
Kazuko Onishi(TGU)
Hisao Kokusen(TGU)
Kazuo Harada(TGU),
Hisaki Takamori(TGU)
Etsuo Arakawa(TGU)
Koichi Kodama(AUE)
Hisao Kokusen(TGU)
Hideo Nakamura(hue)Masataka Nakata(TGU),
Akio Hirata(TGU)
Kazuo Harada(TGU),
Hisaki Takamori(TGU)

In “Radiation Education I” (Table 1), students learn about radiation systematically throughlectures and experiments. In “Radiation Education II”, students design some classes of radiation forjunior high school science. They actually try in junior high school what they designed, and confirm
the responses from the junior high school students.
Since “Radiation Education I” was held intensively for four days (16 school hours) in September,
students of three other universities came to TGU and learned about the basic of radiation, radiation
measurement, radiation effects on living things through experiments with TGU students. In 2016,
professors from Hokkaido and Aichi University of Education participated in the class as lectures,and the students’ impressions were very positive (Photo 1).
100

1)

2)

3)

4)

Photo 1. Scenes from “Radiation Education I” (2016)
1) The effect of radiation on biological systems （1）2) Elementary particles observation using Photographic Emulsion3) Experiment of model waste fluid processing using ICP and AAS(2)4) Students from four universities.

Class questionnaire
Before and after the class “Radiation Education I”, we asked 26 students of the four universities
to answer our questionnaire. Before the class, we asked the reason why they took part in the class.
The results indicate that they could not find enough opportunities to learn about radiation while
they understood the knowledge is important when they become teachers in future.
After the class, we asked them if the contents of “Radiation Education I” were useful forteaching science classes in future. The students who choose “Very useful” and “Useful a little”,
were 96% (Fig. 2).
Students’ opinions- In future, we will teach science in junior high school. But we have not learned about radiation. So
I think the class is very useful.
- Although radiation is harmful to a human body, it is used for various purposes in our lives. In
future, I would like to teach correct knowledge about radiation to my students.

101

Fig. 2. Results of questionnaire before
and after “Radiation Education I”

Developed materials
In 2016, we developed teaching materials for radiation education; “Video contents” and“Teaching Materials Package for teacher training”. The materials have been uploaded on thewebsite of HATO Project, and can be used for free in any university for preservice and in-service
teacher training.

(Top page)(Contents)

http://hato-project.jp/index.html

http://hato-project.jp/product/post_10.html(2017/2/16)*This research was supported by the Japanese Ministry of Education, Culture, Sports, Science andTechnology through the Grant for Strengthening National University Reforms for the “HATO
Project/Teacher Training Renaissance: Building a Support System to Advance Teacher Education
through University Partnership”.

102

ISRE2016 (2017) 103-106

Effects of the Thoron Spa or Bath on the Anaplastic
Carcinoma of Thyroid
Kimiko HORIUCHI, Atsuhiro KISHIMOTO, and Koji YAMAMOTO
Healthypeople Co.,Ltd1. Introduction
It is generally received that the low dose irradiation emitted by the radioisotope such as radon
222( Rn) and thoron (220Rn) is effective for the improvement of the condition of the lifestyle diseases
such as cancers and diabetes. In this meeting, we reported about the effects of the thoron spa or bathon the anaplastic carcinoma of thyroid.
2. Materials and Methods
The thoron hot water was prepared using our devices based on the weak acid leaching method. The
cancer patient took a bath in the thoron hot water from six to eight times a day for each ten minutes
every day. We judged the evaluation from a blood test and so on.
3. Results
Comparison of the thoron and the radon hot spring
The thoron is an isotope of the radon. The radon is a member of the Uranium-238 decay series andis the α decay product of Radium-226 then becomes stable Lead. On the other hand, the thoron is amember of the Thorium-232 decay series and is the α decay product of Radium-224 then becomesstable Lead (Fig. 1).

Fig. 1. Summary of the Uranium-238 and the Thorium-232 decay series. The Uranium-238 and theThorium-232 become radon (222Rn) and thoron (220Rn) each.
As the radioactive material, the half-life of radon is about 3.8 days, and it takes more than 20 years
for the radon to become the Lead. On the other hand, the half-life of thoron is about 55.6 seconds, and103

it takes around 11 hours for the thoron to become stable Lead. Thus, because the period when thethoron exists as radioactive material is shorter than that of the radon, it is thought that the negative
effect of thoron on human body is small. For the thoron hot water, it is easy to obtain the radioactive
effects stably and to investigate various conditions such as the concentration and the component of thewater because of preparing artificially. On the other hand, for the radon hot water, it is difficult tomaintain the radioactive effects and to study more effective conditions because of the natural hot water.
As the location of the radon hot spring, it is difficult to move the place of spa facility because of thenatural hot spring. As the location of the thoron hot spring, it is easy to build the spa facilities in thevarious places because of the artificial hot spring. Thus, the thoron hot spring is useful as theradioactive spring (Table 1).
Table 1. Comparison of the thoron and the radon hot spring
Item
Safety ofradioactive
material

Radon hot spring

The half-life of radon is about 3.8 days, and The half-life of thoron is about 55.6 seconds,
it requires more than 20 years until it
and it requires around 11 hours until it
206
becomes stable Pb.
becomes stable 208Pb.

Radiation
intensity

Hot water

Thoron hot spring

5.4 x 106 MeV

6.3 x 106 MeV

Because of natural hot water, it is difficult
To prepare hot water artificially, it is easy
to maintain the radioactive effects and toto obtain the radioactive effects stably. It isstudy more effective conditions. It iseasy to build the spa facilities in the various
difficult to move the place of spa facility
places because of the artificial hot spring.
because of the natural hot spring.

Radioactive component of the thoron hot water
A stock solution immediately after the thoron preparation was measured by the liquid scintillation
counter. We could detect the thoron even after 4 hours of elution. (Table 2).
Table 2. Radioactive component of thoron hot water
Elapsed tim e（ h）
0
0.24
2.4
4.0

228

Ra (bq/ l)
7.43
7.43
7.43
7.43

228

Ac (bq/ l)
0
0.19
1.76
2.74

224

Ra (bq/ l)
9.70
9.68
9.52
9.39

220

Rn (bq/ l)
0
9.68
9.52
9.39

Total radioactivity (Bq/ l)
17.13
26.78
28.23
28.95

Case
The patient was diagnosed with undifferentiated carcinoma of thyroid, which is a high grade ofmalignancy and is one of intractable cancers, in June 2014, and the surgery was performed in the same
year on August. The treatment of taxol, which is an antitumor agent to prevent the microtubuleorganizing and produces the serious side effects, was started from September of the same year. Bathing
in the thoron hot spring (every day, 6 to 8 times a day, and bathing of each ten minutes) began justbefore the second taxol treatment (Fig. 2).
104

Fig. 2. Time table of the therapy of the patient
The number of white blood cells sharply decreased after the 1st time of taxol treatment, and it has
become less than the normal value. Thus, the 2nd taxol treatment was canceled. But it recovered after
the thoron bathing, and it was fall within the normal range. It was possible the administration of 11
consecutive weeks. The peripheral neuropathy, which is observed generally in the taxol treatment did
not appeared (Fig. 3). On the other hand, the recurrences of the thyroidal anaplastic carcinoma werecaused four times by August 2016. However, only the removal operation was carried out because theprogress was very slow unlike normal anaplastic carcinoma.

Fig. 3. Data of blood test. These graphs show the white blood cell count, the red blood cell count, theplatelet count, AST, ALT and gamma-GTP from September 16, 2014 to January 7, 2015.
Discussion
It was suggested that the thoron hot spring possibly reduced the side effect of the anticancer drugs.
Furthermore, the possibility that the thoron hot water affected the malignancy of cancer was suggested.
The mechanism of the effectiveness of the thoron spa or bath was still unknown, but it would besuggested of the good results for the improvement of the cancer.
References
1) Atsuhiro Kishimoto, Kimiko Horiuchi, Koji Yamamoto. Effects of the Thoron spa or bath on the105anaplastic carcinoma of thyroid. The 49th Annual Meeting of Japanese Society of Thyroid
Surgery (October 2016, Kofu)
2) Atsuhiro Kishimoto, Kimiko Horiuchi, Koji Yamamoto. Effects of the Thoron spa or bath oncancer patients. The 41th ISMH World Congress (May 2016, Bucharest)
3) Atsuhiro Kishimoto, Kimiko Horiuchi, Koji Yamamoto. Effects of the Thoron spa or bath oncancer patients. The 81st Annual Meeting of The Japanese Society of Balneology, Climatology
and Physical Medicine (May 2016, Shibukawa)106

Appendix
Author Index
Name

Page

Name

AKIYOSHI, Masafumi

54

LIN, Hsin-Hon

19, 67

ANDO, Hirokazu

54

LU, Cheng-Chang

19

AODTON, Mutita

31

MATSUMOTO, Toshi

72

ARATANI, Michi

72

MATSUURA, Hiroto

54

ARIMA, Akito

1

MIYAMOTO, Kiriko

72

BOONMARK, Chuntana

31

MORI, Chizuo

48, 77, 83

CHIANG, Chih-Chieh

67

NAKAHODO, Yumeto

94

CHUANG, Keh-Shih

15, 19, 67

NAKAYAMA, Eiko72

CHUMTHONG, Surat

31

NI, Yu-Ching

19

DONG, Shang-Lung

19

NIHON’YANAGI, Haruko

72

ENDA, Kaoru

72

NOZAKI, Tadashi

63

HAMADA, Eisaku

88, 94

OKAYAMA, Setsu

72

HIRANO, Hiroko

72

OKUKAWA, Harumi

72

HIRATA, Akio

99

OKUNO, Yasuki

54

HORIUCHI, Kimiko103

ONISHI, Kazuko

99

HUANG, Chin-Wang

35

PIYANART, Prayong

31

ISHIKAWA, Chikako

72

SAKASHITA, Nanaho

88

ISHIKAWA, Tomie

72

SASAKI, Toru

63

JAN, Meei-Ling

19

SAWAYA, Sachiko

72

KAMATA, Masahiro

99

SHIMO, Michikuni

26

KANAZAWA, Kinue

72

SUNTHORNOWARD, Khawee

31

KIKUCHI, Toshie

72

TODOROKI, Hiromi

72

KISHIMOTO, Atsuhiro

103

UENO, Teruko

72

KUDO, Hiroshi

39

YAMAMOTO, Koji

103

KUMANO, Nobuko

72

YAMASHITA, Shunichi

10

LERDLU, Thanakit

31

YOKOYAMA, Kayoko

72

107

Page

ISRE2016 Photo

Opening Address by Prof. Hasegawa (President of NPO Radiation Education Forum)

Group Photo of Symposium Participants

108Keynote Lecture by Prof. Arima (President of Japan Radioisotope Association)

Keynote Lecture by Prof. Yamashita (Vice President of Nagasaki University)109Oral Presentation by Prof. Horiuchi (The Jikei University School of Medicine)

Poster Session

110Tour to Fukushima Environmental Creative Center

Group Photo at Fukushima Environmental Creative Center

111