-JAERI Conf-

2005 001SESSI〇N 「VNATURALLY 〇CCURRING
RADIATl〇N/RADl〇ACTMTYAND
lTS USETUESDAY, AUGUST24-JAERI Conf

2005 -001

4.l Radioactivity of and exposure by the consumer's goods

containing N O R M
一般消費財中に含まれる放射性物質の存在量
M.Yoshida,T.0hhata,S.Sato,R.0hyama and H.Furuya
吉田昌弘,大畑勉,佐藤滋郎,大島柳太郎,古屋廣高---

Nuclear Safety Technology Center,Hakusan5 1 3,Bunkyo ku,Tokyo

原子力安全技術セン夕一「要旨」

自然起源の放射性物質 ( NoR M ) を 含 有 す る 2 0 種 類 の 一 般 消 費 財 を 、 多種多様な情報-源を用いて、 購 入 、 取 得 し た 。 これらの一般消費在中の放射能濃度をIcP Ms 及びGe(Li)
半導体検出器で測定した。 この結果を用いて、 NoRMを含む一般消費財が日常生活で使用される時の年間被ばく量を計算した。

この結果、 一般消費財の中には、 国際原子力機関が ク リ ア ラ ン ス レ ベ ル の 指 標 と す る 放 射 能 濃 度 ( U 、 T h で 1 B q/g ) を 超 え る 消 費 財 も あ っ
た が 、 そ の 年 間 被 ば く 量 は 、 E U ( ヨ ー ロッパ連合) の放射線防護委員会がNoR M に よ る
被ばくについて勧告した制限値(300µsv/y ) よ り 小 さ か っ た 。

1. Introduction-

There exist natura11y a number of long 1ived radioactive nuclides in the earth.The
materialcontaining these radioactive nuclides is ca11ed natura11y occurring radioactive
materials(NORM) ,and severalkinds of consumer's goods including NORM are circulated in
the usualdailylife environment.

Based on how to utilize NORM,these consumer's goods are classified into two types.In
the first type of consumer's goods,1owleve1of radiation emitted from NORM is important.As-

a typicalgood,the health enhancing product is famous.Many peoples who believe horm esis
use severalkinds of consumer's goods containing uranium and/or thorium such as underwear,

bedc1othes,body accessories,sma1lsize of hot spring source and so on in their daiI y l i f e . . I n
addition,the paint containing NORM is coated on the bottom of ship in order to protect theshe11from adhering to it.
In another type of consumer's good,the property characteristic of uranium or thorium isimportant.Uranium or thorium compounds have clearly beautifulco1or,depending the atomic
valence,because there are vacancies of electron in the5f shel1of inner orbitalin the atomic
core.Thus,NORM containing uranium and/or thorium are utilized as glazers on the pottery or
additions to uranium glass.[1]In addition the chemicalstabilities and consequently the melting

points of thorium dioxide are very high,and then they are utilized as one kind of refractory andan additive to tungsten electrode for the arc welding..
It is so important from the view of point of regulation to know the radioactive

concentration or radioactivity in the consumer's goods containing NORM and the radiation

exposure when they are used in the d a i l y l i v i n g l i f e . I n this study,20 consumer's goods

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1

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r ̲-

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2005 001

containing N〇RM were coliected. After chemica11y processingthem, the radioactive
concentrations in them were measured by an inductively coupled plasma attached with mass-

spectrometer(ICP M S ) a n d a γ 一 ray spectrometer of Ge(1i).In addition,theradiation

̲

exposures were calculated in four typicalcases where the consumer'goods are genera11y usedin the dailylivinglife.
2. Experimentalprocedures

2.1Co1lectionofspecimens
20 consumer's goods containing N〇RMwere co11ected,based on various inform ation

Kind of good

No.

1
2

-

bedclothunderwear

3

Specimen

Existing state1

upperbedcloth

fabric. c ottonllowerbedcloth

fabri c, cotton- IOP-M S

semisleeve underwear

fabrioIOP-MS

belly - warmer tie-A

fabricsocks

fabricshoes sheets- A

fabricshoes sheets-B

fabric(p rint)

shoes sheets-0

ceramics

1213

hot spring sourc
hot spring source

14
15

l

wal i paper
wallsheet paintceramios----

minus ion sheet

wallsheet paint

ll

̲

二
・ :
、

l: l l

'

.

paste

muffler catalyst

alloy

abbrasive

powderpowder(*1)ICP -MS:measurement of 2a 8 U and 232Th contents

γ: γ一ray spectrometryof 2o8T1,212pb,214p b , 2 1 4Bj and228Ac*2):ceramic botton attached on the fabric

206

s- i

IOP -MSl

1 ?1
M

I IOf:11:i MS
iOP:二-M
γ W
S -l I01MS
-

1

19

-

Iop-M

m e t l -商

ship bottom paint:I I0l;::MS l

0

18

1

T

ceramics -Th added W electrode20-

IOP -MS-17

1- lindustria1products

IOP - MS ̲,,

hot spring source B

16lbracelet-B︐

fabric(print)一

ICP-MSr-

IOP MSr

l 0P M Sr'wrist band︐

ceramic botton(#2)

bracelet A

bracelet

r

一

9o
1
一

1i

- l

r

belly -warmer tie B

socks

shoes sheets

IOP MSγ 田-

Analysis(*1)一

supporter

l

.

一
ss

1

・

一

Table1 l i s t of cosumer's goods containing NORM collected-

JAERI Conf-

2005 001

sources suchasthe commercialcatalogues,the inspection on the intemet by using key words'horm esis minus ion and others.
The consumer's goods containing N〇RM similar to each other were sold from di ffe rent

companies.Tablelshows thelist of consumer's goods containing N〇RM co11ected.These

goods can be divided into8kinds of goods used in the dailylivinglife and4kinds of goods
used in the industry.The bedc1othes are shownasatypicalexample in the Photo1.

Photo1 Bedc1othes
2.2Measurement of radioactivity

A p a r t o f each collected consumer's good was pulverized or burned i n air a n d thenwas chemically treated.The standard method was applied to the chemicaltreatment,
which has beenalready established a n d used for the analysis of environmental
specimen i n a number ofinstitutes or companies i n J a p a n.[2,3]Radioactivity i n the consumer's good w a s measured by two methods.First,theconcentration of u r a niu m and thorium were analyzed by a n inductively coupledplasma attached to mass spectrometer(ICP M S) a n d were converted to theie
radioactivities by using the value of specific radioactivity.Next,the radioactivities ofdaughter nuclides of uranium or thorium were measured by a GE L i semiconductor--

detector.

2.3 Calculation of exposure
From the results obtained i n the measurement ofradioactivity.the exposures were

calculated w h e n four kinds of consumer's were utilized i n the daily livinglife.A famous
computer code MCNP 4 C w a s applied to the calculation by using a relatively

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2005 0 0 lconservative boundaryas shown i n Table2.A schematic diagram of calculation systemi s shown i n Fig.1. T a b l e 2 s h o w s the boundaryconditions ofcalculation

Fig. 1 A schematic diagram of calculation sysytem

Table2Boundaryconditions used the calculation of exposure
N〇

NORM
goods

Radiation
sourceExposure
Scenarioa

Bedc1othes

0:210xlSOcm
U:210xl00cm

8h/d

b

Underwear

26 6 c m φ
65cm h24h/dc

H o t springsourcellx21cm

plane

30m/d
At10cm270x450cm
plane

At30cmd3.

Wallsheet̲

8h/dResults and discussion

3.1Radioactive concentration of uranium,thorium and their daughter nuclides
Table3shows the concentrations ofuranium and thorium in the consumer's goods,which were-analyzed by an ICP MS,together with the radioactive concentrations derived from the209 -a一﹁-

JAERI Conf

2005 -001-

measured results.Table4shows the radioactive concentrations of daughter nuclides measured

by the Ge(Li)semiconductor detector.
Table3Radioactive concentration of uranium and thorium in the consumer's goods

34

一

2

一

一

一

一

一

u

-

︐

一

:

±0.011
±0.3
±Q1
±0.5
±a002

3.3
l

232Th

02

± 01「 「 「e'
±001
±016
±012
±0.2
±00014±014±0.C12
±0012
±0.04
±02
±04

001
2.3

a8
a5

±001
±0.006
±0.04

094
5.4
0011
07
0.31
0.(B5
0.42
1.7
8.8

a

一

E

一

f成'

一

一

=

一

i一

-

w

n

'

．

1 .3
0ア7
21
20
52
017

1

Q

電

±0.4
±0.02

,,. l1l ltr,
, tlcn (Bcl/g)

l

±QCm7
±0.l)04

0.0,43
0.26

78
1
50
e 6
2
1

=

電

一

O CICl25 ±0lm04
0的±0.003
l
2.2
±004
l
2.1
±003
a 4 ±006
0.023 ±00003
1.5
± 00B
l
0.66
±Ql;ll5
0.16±0.(X)3
0.li8
±0009
3
±0.l:1,4
18
±0.1
l
67
±0.8

a

a

EE

組

5 6 7 8 9 2
0
1 1
1 1 1

0.00e5 ±0.0a)05
0a2±0.000B
0.082 ±0.Cm6
0076 ±00005
a43 ±000e
000093±0.0〔m20 ()57±0.0007
0a25 ±0.0004
0.(X169 ±0.0lX)120.C)34 ±0.0006014±0(1Cl2
0.71±0.003
2:8
±0.a2
0.83
±0014
0.054 ±0.0003
0047 ±0.0005
0.00096 ± 0.00008
a97 ±Q014
027±0(X)4
Q016 ±0.00a2

一
一
基
一

0 1u
l 2 3 4 5 6 7 8 9 1
1

Th

的

˜

Racioactive,

■

l 一1

器 装 差 器 萬︵登OcncerTtraticn (nrg/1g)

Specir日r 1

No-

0 P MS

34±000Cl2±0009±0.004±0.0015±0.008
±0.03
±0.04
士0.2
±02
±0.0Cl3±0.006±0.001±Q 2
士0.05±0.0030 ( )93

62
2.7
0.63
2:8
12
71
270
81
i
l

±3
±17
±0.1

5.4
31

86
81
l210
0.7
l

j

Table4Radioactive concentration of daughter nuclide in the consumer's goods

-一

一

l-

明 必

214日

-:l a me- nm
- D5
bell1 -v aTTgtie
:
±
250
は 的 電
:±02
Z
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162
±
07
5
im4
e -:l: D6
l 1 7 Th alded W M-±a009 6 i
1
1 1g mjf心商?
: -:l: m::ta:la calalystl dl d i l器
1 i

3 4
4 1
1

ll

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和

電

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oe -:l: alTm'l: aCm
Q9 ・:l: a(D4 l

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通

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A s shown in table3,the concentrations of uranium and thorium varies in severa1orders.That is,the concentrations of uranium ranges firom 0.00093to2.8mg/g,which co l Tespond to the range from

一

一

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2005 -001

J A E R I Conf

0.011 t o 3 4 B q/g. 〇 n the other hand,the concentrations of thorium scatters in the range from 0.0025

t o 6 7 m g/g , w h i c h correspond to the variation from 0.01to270 Bq /g. I t should be noted that theconcentration of thori um islarger than the one of uranium.This reasonlikely comes from the fact

the monazite including thorium is freq uently used in the consumer's goods and the Clark number is

1arger in thorium than in uranium.
It can be seen intable4thatthe radioactive concentration ofdaughter nuclides is approximately-

equalto the ones of uranium and thorium except the result ofT1 208.This agreement suggests thatthe secular equilibrium holds between the uranium or tho ri um and daughter nuclide.
In Japanese regulation on the raw nuclear materials, the upper limits of radioactive

concentration ofuranium and thorium approved in solid andliquid are370 and37Bq /g,respectively
Then,the results on the radioactive concentrations of uranium and thorium satisfy the regulation of

raw nuclearmaterials in Japan.However,the present data arelarger than the value,1Bq/g,cited in
the Basic SafetyStandard(BSS),which has been recommended as a basis of clearancelevelby

IntemationalAtomic Energy Agency(IAEA)[4].Thus,it is important to evaluate the exposure when
the consumer's goods are italicized in the dailylivinglife.
3.2

Evaluation ofexposure

T-

When the exposure is theoretically calculated during the utilization of consumer's good,it isnecessaryto certify the reliability of calculated value. Then,both experimenta11y measured andcalculated values were compared with each other in the water bath shown in.fig.2.The exposure
rates were measured at the distance of 16,32,64,85and90 cm from the radiation source,and then
一

̲

X

1

Fig.2

-

1

X:measuring point

1f

A schematic diagram of water bath for the comparison between the measured andcalculated values

210

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21 i --JAERI Conf

2005 -001

were compared with the calculated values.Fig.3shows the comparison between both measured

and calculated results. A s shown in this figure,both data agree with each other,and it can befound that the calculation ofexposure by MCNP 4C code wasreliable.

-

101

pO
l

︵1
/

u

A

︶-

S

rC

r
n

-

a

l

l

l

-

3

0

n

4

r0l

x
d
o
s

国

r

P
o
s
a

一 r:

2
r0

一

20

40

60

100

80

Distance from source ( c m )Fig.3Comparison between the measured and caleulated values

After certifying the reliabilityof calculation,the annualexposures were calculated when
the bedc1othes,underweaf,hot spring sourceused at home and wa1lsheetare used underthe
conditions described intable2.the results obtained are showntable5.
Table5Calculated results of annualexposures
N 0 NORM

goods

Radiation
sourceExposure
Scenario

Results(µ Sv /y)a

Bedclothes

0:210x150cm
U:210x100cm

8h/d

110

b

Underwear

26 .6 c m φ 24h 1/d
65cm h220c

Hot springsource11x21cm

110

plane

30m/d
At10cm270x450c
plane

8h/d
At30cm10d

Wa11sheet-J A E R I Conf

2005 -0 0 l

In the connection with the radiation protection in environment,thereare some kinds ofguidelines. I n Japan,the exposure ofpeopleliving around the nuclear facilityislimited to be be1ow
1 m Sv/y except the exposure due to naturalradiation,based on the ICRP recommendation[5].

Recently,EU radiation protection committee hasrecommended a value of 300µSv/y a s t h e

exposurelimit due to N〇RM goods[6].
As can be seen in table5,the annualexposures in four cases are in the range 1from10 to220ｵ
Sv/y.These values arelarger than10µ

Sv/y,which hasbeen recommendedasa guideline ofclearancelevelby IAEA,but are smallerthan t h e l m S v /y and300µ Sv/y described above.
4.

Conclusion

Twentykinds of consumer's goods containing N〇RMwere co11ected,based on various
information sources.The radioactive concentration were measured by ICP M S and Ge(Li)-semiconductor detector,and the annualexposure were evaluated in four cases of dailylivinglife-

based on the measured results by a computer code,MCNP 4C.The radioactive concentrations ofuranium ranged from 0 . 0 1 1 t o 3 4 B q /g. 〇 n the other hand,the radioactive concentrations ofthorium scatters in the range from 0.01to270 Bq /g. T h e annualexposure due to the utilization of

N〇RMgoods in the dailylivinglife ranged from10 to220µ Sv/y.They wee sma11er than300µSv/y,which hasbeen recommendedasthe exposurelimit due to N〇R M goods by EU radiation

protection committee.

Reference
1) K.Tomabechi 「Uranium Glass」Iwanami book service center(1995)
2) A Japanese standard on radioactivity measurement,series13「Specimen preparation method

for instrumentalanalysis including Ge(Li)semiconductor detector」(in Japanese),(1982)

・

ibid series16「Samplingmethodofenvironmentalspecimen」(in Japanese),(1983)
3) "RSIC COMPUTER CODE SELECTION,MCNP4,Monte Carlo Neutron and-PhotonTransportCode System,"CCC 200A/B(199l)
4) InternationalBasic Safety S tandards for Protection against Ionizing Radiation a n dfortheSafetyofRadiationSources Safety Series No.115(1996)
5) Japanese L a w [ L a w o n r a w nuclear material,nuclear materials,nuclear reactor]
6) European Commission,PracticalUse ofthe Concept of Clearance a n d Exemption Part II,Radiation protection 122(2001)

ーがある.

--JAERI C o n f 2 0 0 5 001

4.2 Hot Spring and Radioactivity
温泉と放射能Kimiko HORIUCHI
堀内公子

Otsuma Women's University
大妻女子大学

Karakida2-7- 1Tama,Tokyo206- 8540
Te1:042 -339 - 0089 Fax:042 - 339-0044 E - mail:horiuchi@otsuma ac jp〒206 8540

.

1.

はじめに

温 泉 と は 読 ん で 字 の 如 く 温 ( あ た た か ) い 泉 ( い ず み ) で あ る . しかし昔から温かくは感じな
いが色や臭い, 感 触 等 で 普 通 の 水 と 明 ら か に 区 別 の 出 来 る 水 が 地 中 か ら 湧 き 出 す こ と が 知 ら れ ていた. 現在では温度だけからではなくこれら特別の水を普通の水と区別して温泉と呼ぶことが温泉法 1) で 定 め ら れ て い る .

2. 温泉の成立要因 2)
温泉が湧出するためには, ①熱源, ②湧出径路, ③水源の三つが必要であって, こ の う ち 一 つが欠けても温泉は成立しない. 放射線は温泉成立の必要条件の総てに関係を持つている.

-2 1温泉の熱源
地球は宇宙の塵が重イオン反応や核融合反応を何十億年もの間繰り返し行つた末に誕生した
そ の た め , 誕生以来46億年経つた現在でも多種類の放射性元素が存在している.
地球内部は高温を示し, 地表へ向かって熱の流れがある. その熱源の一つに岩石中に含まれるウラン,

トリウム,放射性カリウム等の長寿命放射性元素の原子核崩壊に伴つて発生するェネルギ

一方地球内部からの熱の流出は①火山活動,②温泉・地熱,③地震波動,④地下から地表を通つ て 上 昇 す る 熱 (地殻熱流量) 等 に よ っ て い る . 従つて温泉の熱源の一部は地球の創成期から地殻に含まれる天然放射性元素に由来しているといえる. 地球誕生以来地球内部で岩石の中に貯えら れ た ウ ラ ン や ト リ ウ ム 等 放 射 性 元 素 の 崩 壊 熱 エ ネ ル ギ一 量 は か な り 大 き い と 見 積 ら れ て い る .

-2 2 . 温泉の湧出径路 2)
温 泉 が 地 表 ま で 上 昇 し て く る た め に は , 地 盤 に 開 ロ 割れ目が必要になる.地殻は地質時代より,
引つ張り,圧縮,火山,地震,隆起,陥没,その他の原因による変動が加えられ,断層や,大小の 割 れ 目 が 生 じ る . こ う し た 割 れ 目 (開口亀裂帯) は温泉の上昇に最も都合の良い径路となる.
こ の 割 れ 目 が 網 目 状 に 発 達 す る と , 多量の温泉を蓄える温泉貯留層の役目も果たす事が出来る.

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-J A E R I Conf

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開 ロ 亀裂帯は, 温 泉 の 上 昇 と 同 時 に 温 泉 の 熱 源 と な っ て い る 放 射 性 元 素 ウ ラ ン ,ト リ ウム等の崩壊生成物ラジウム, ラドン等が温泉水に溶解したり, 温泉水の移動によって運ばれるなどして地表部に到達し , 崩壊生成物の各種γ線を放出する.

-

2 3.温泉の水源

温泉水の大部分は, 天水が地下に浸透して地下深部で温められて, それが再び地表あるいは地
表近くにまで上昇して来た地下水と考えられている. よって地下水の動きを知る必要があるが,水 の 天 然 の ト レ ー サー と し て 水 素 の 放 射 性 同 位 体 ト リ チ ウ ム が 用 い ら れ て い る .

トリチウムを含んだ降水が地下に浸透し, 熱 源 に 近 い 所 で 加 熱 さ れ , 循 環 対 流 に よ っ て 他 の 開 口 亀 裂 帯 を 通 つ て

上 昇 し , 温 泉 と し て 湧 出 し た 時 , 温 泉 水 中 の ト リ チ ウ ム ( T 112 : 半 減 期 1 2 . 6 年 ) を 測 る 事 に よ り
水 循 環 の 速 度 を 知 る こ と が 出 来 る . ま た , 有望な温泉を得るにためには, 亀 裂 帯 な ど に よ っ て ,地下水の涵養機構が発達している循環性の地熱貯留層を探し出す必要がある.

3 . 温泉探査の手段としての放射能温泉の開発適地は地下からマグマや熱水が上昇し, 利用量が満足出来る水循環条件を持つことで あ る . 浅い位置でこの条件に合う場合は温徴が明瞭な地点で, 既 に 温 泉 開 発 が な さ れ て い る .

よって現在では地下1000m以上といった深い位置にこの条件を見出すことが課題とされている.

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31

ラドン

地層の開 ロ 割 れ 目 で は 揚 水 能 が 一 般 の 透 水 層 の 1 0 倍 以 上 に も な り , ま た 反 復 揚 水 に よ る 水 み ちの発達で降水や表層部からの水の浸入量は漸増する. 従つてまずは温度の十分な開口割れ目を見出すことが温泉探査の目的となる. 開口割れ目を通してラドンが上昇することは早くから知られて い て , 地表面にあけた小孔中の気体の放射能測定から埋没断層の位置を求める方法は数多く検討されて来た.

-32

γ線

1 9 5 0 年 代 の 末 に N a I ( T 1 ) 検 出 器 に よ る γ 線 ス ぺ ク ト ロ メ ト リ ーが 可 能 に な る と , ラ ド ン を 直 接 測
定 せ ず に ラ ド ン と 同 一 行 動 を し て い る 崩 壊 生 成 物 の 2 ] 4B i の γ 線 1 . 7 6 M e V の 計 測 が 行 な わ れ る よう に な っ た . 放 射 能 に よ る 温 泉 探 査 は 正 確 な 結 果 が 得 ら れ る と し て 信 頼 度 が 高 く , 次第に地表から 迅 速 に 検 出 し , 分 析 が 容 易 な ェ ネ ル ギ ー の 高 い 自 然 γ 線 2o8T1(2.61MeV),
4oK(1.46Me

214Bi(1.76MeV),v) 等 の 3 核 種 を 指 標 と し た 表 層 地 質 の 解 析 が 始 ま っ た 3-4).

次 い で こ の 3 核種の一次ガンマ線量は表層の核種の含有量に比例し, その含有量は地層毎に固有 値 を 持 つ と い う 現 象 が 見 出 さ れ る と , ア メ リ カ , カナダ, ヨ ー ロ ツ パ等の広い平坦な地域では
検 出 器 を ヘ リ コ プ タ ー に 乗 せ て 高 度 3 0 m を ゆ っ く り 飛 ぶ い わ ゆ る ェ ア ボ ー ン ( へ リ ボー ン) に よ

り , 表 層 地 質 の 解 析 が 行 わ れ る よ う に な っ た 5). し か し 地 形 の 起 伏 が 激 し く , 地 層 が 細 か に 変 わる我が国では自動車や携帯計測器を用いたカーボー ン や マ ン ボ ー ンでの精密な探査が極め手の鍵

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4. 温泉水中の放射能

4.1 ラ ジ ウ ム
我 が 国 の ラ ジ ウ ム 測 定 の 歴 史 は 古 く , 1 9 1 5 年 パ ナ マ 万 国 平 和 博 覧 会 を 契 機 に 刊 行 さ れ た 「TheMineralSprings ofJapan」 に 我 が 国 初 の 温 泉 の ラ ジ ウ ム 測 定 値 が 記 載 さ れ て い る . 全国477 ケ 所 の
温 ・ 鉱 泉 と 1 5 の 石 油 及 び 天 然 ガ ス 地 域 に 於 け る 試 料 水 の ラ ジ ウ ム 測 定 デー タ が 1 9 4 0 年 に 発 表 され た . こ れ は ラ ジ ウ ム 測 定 デー タ と し て 最 も ま と ま っ た も の で あ り , 時 節 柄 我 が 国 の ラ ジ ウ ム 資

源を鉱泉に求めるには経済的価値の低いことも述べられている.

液 体 シ ン チ レ ー シ ョ ン カ ウ ン タ ー( 以 下 L S C ) が 開 発 さ れ る と , 同 一 試 料 中 の ラ ジ ウ ム , ラ ド ン

を 測 定 し た 結 果 が 1 1 9 の 温 泉 に っ き 報 告 さ れ た . 従来, 温 泉 水 中 の ラ ド ン は , 親 核 種 ラ ジ ウ ム とは非平衡に多く存在することが知られているが, ここでもそれが証明されている.

-

42ラドン
温 泉 水 の 中 に は 主 と し て ラ ド ン ( R n : 222R n ) と そ の 同 位 体 ト ロ ン ( T n : 22oRn)が存在するが,半減

期 が 5 6 秒 と 短 い ト ロ ン の フ イ ール ド で の 検 出 は な か な か 困 難 で あ り , デー タ は あ ま り 多 く な い .

鉱泉水等環境試料中のラドンの存在は1903年に確認され,同時にラドンによる鉱泉水の治療効
果の可能性も示唆されている.

世界最初の鉱泉中のラ ドン測定器はェングラ ー ・ ジ ーべ キ ン グ 泉

効計で, 我が国でもこの泉効計により本邦最初の温泉の放射能値が報告された. よ っ て , 我が国の環境放射能の研究は温泉水中のラドン濃度の測定から始まったとも言えよう.

現在,温・鉱泉水中のラドンは温泉の分析項目の一つであり,温・鉱泉水中のラドン発見以来研究と利用との二つの面から測定され今日に至つている. ラ ド ン は , 放射性のガス成分であり,
温 ・ 鉱 泉 水 中 ほ と ん ど 他 の 溶 存 化 学 成 分 と の 相 関 は な く 単 独 に 存 在 し て い る . 我が国には多種類の泉質の温泉が湧出しているが, それらの中で放射能泉は溶存化学成分プラス放射能というかな

り特異的な存在と考えられる.

5 . 鉱 泉 の 定 義 1)
現在我が国の温泉は環境庁自然保護局の所管行政で, 国民の保健休養と同時に自然環境の保護
も 目 的 と し て い る . 長寿社会へと移行し, 余暇が増加し っ っ あ る 我 が 国 で 温 泉 の 果 た し う る 役 割

は 極 め て 大 き い も の と 期 待 さ れ て い る . 温泉は温泉法によって保護され利用の適正化と公共の福祉の増進が図られており,泉質は昭和26年制定され,53年に改定された鉱泉分析法指針により分析すべき項目と分析方法が定められている.
指 針 に よ れ ば , 放射能による鉱泉の定義はラドン(Rn)20x10- 1 oci 以 上 , 常 水 と の 区 別 , 鉱 泉 と 認 め る 濃 度 ( 5 . 5 マ ツ へ 単 位 以 上 )ラジウム塩(Raとして)ラドン(Rn)I X10-8mg以上

30x10- 1 oci 以 上 , 特 殊 成 分 を 含 む 療 養 泉 ( 放 射 能 泉 ) ( 8 . 2 5 マ ツ へ単位以上)で あ る . し か し 療 養 泉 (放射能泉) は温泉法の対象ではなく, 温泉医学に於ける臨床経験から医療効果の期待出来る温泉と言う考え方である.

我が国の鉱泉の基準は常水と区別する鉱水の限界値を定めたドイッのナウハイム決議(1911 年 )に 準 じ て お り , 温 泉 の 放 射 能 の 単 位 も H . M a c h e に よ り 提 案 さ れ た マ ツへ単位(1マツへ M . E .= 水

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1 1 に 含 ま れ る ラ ド ン に よ る 飽 和 電 離 電 流 が 1 0-3e. s . u. の と き ) が 用 い ら れ て 来 た . 放射能による 鉱 泉 ・ 放 射 能 泉 の 定 義 を べ ク レ ル 表 示 ( 1 B q = 2 7 p C i , 0 . 0 7 4 M . E . ) に 換 算 す る と , そ れ ぞ れ 7 4 B q /1

お よ び 1 1 1 B q/1以上となる.
6.

温 ・ 鉱 泉 分 布 図 に よ る , 我が国の放射能泉の特徴

我が国は世界で最も泉質の種類に富んでいる. 先 年 ま と め ら れ た 温 ・ 鉱 泉 分 布 図 6)に よ る と ,我 が 国 の 放 射 能 泉 は 全 体 の 7 . 7 3 % ( 泉 質 の 明 記 さ れ て い る も の : 総 数 3 , 6 5 9 ) に あ た り , 全国の放射能泉の数を都道府県別に集計すると花崗岩分布地帯の多いフオッサマグナの西側, 主 と し て 中 国
地 方 に 多 く 分 布 し て い る . また泉温にっいては25°C以下の冷鉱泉が多く全体の86.5%をしめている.中でも15˜20°Cが最も多く,地下水の温度領域に近い.
我 が 国 の 放 射 能 泉 の 特 徴 を ま と め て み る と , それ以外の泉質の温泉に比べて湧出量は 1/2 ˜ 1/3と 少 な く , 液 性 は 中 性 か ら 弱 い ア ル カ リ 性 を 示 し , ラドン以外ほとんど他の溶存化学成分を含まない単純冷鉱泉が主体である 7-9 ) .

7.

放射能泉の医療効果
古来, 放 射 能 泉 は リ ュ ー マチのリハビリや鎮痛作用等の医療効果が認められ, 温泉治療に利用されて来た.

温泉治療に利用されているのは, ほ と ん ど ラ ド ン 泉 で あ る . ガ ス 成 分 の ラ ド ン は 呼吸 に よ り 体 内 に 入 り , 体 内 に 入 つ た ラ ド ン の 一 部 は 崩 壊 し , 次々と半減期の短い別の核種に変化して体内に残る. ラ ドンの崩壊生成物はその濃度と体内にある時間に比例して多くなるが, や がて ラ ドンの崩壊生成物に固有の生物学的半減期によって排泄される.
ラドンの医学効果は臨床医学的に自律神経の鎮静, 内 分 泌 系 に 適 度 の 剌 激 を 与 え る こ と に よ る

ホルモンや代謝異常の調整,鎮痛,消炎作用などと言うことが出来る.ラドン濃度を増すと鎮痛
効 果 は あ が る が , 心血管や植物神経系統に反作用が起きるので, 他の温泉成分と同様, 適切な利用が大切である. また放射能泉の効果は単に放射能だけによるのではなく他の溶存化学成分や泉温等との相乗効果である.

8.終りに

,,

放射能泉は古くから多くの人達によっで農繁期の疲れを癒したり, リ ュ ーマ チ や 怪 我 の リ ハ ビ
リ 等 で 利 用 さ れ 続 け て き た . 世 界 に 誇 り う る 数 少 な い 天 然 の ェ ネ ル ギ一資 源 : 温 泉 は 限 り 在 る 資
源 で も あ る . 放射線関係の研究の進展に っれ, 放 射 能 泉 と 人 体 の 係 わ り 合 い の メ カ ニ ズ ム も 次 第に 明 ら か に さ れ っ つ あ る . 放射線の危険性を正しく理解した上で, 放射能泉が愛され有効利用されて行く事が期待される.

9.

参考文献

1)

環境省自然環境局自然環境整備課:温泉,型 No.4/5 (2001)

2)

落 合 敏 郎 : 温 泉 開 発 , p. 2 0 3 リ ー べ ル 出 版 ,(1993)

3)

木 村 重 彦 , 小 前 隆 美 : 農 業 土 木 試 験 場 報 告 , A 1 4 , 17 26(1977)、

4)

J.N.Andrews:Geothermics,12,67 82(1983)

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A.B.Tanner:in The NaturalRaddiation Environment(J.A.S.Adams and WM.Lowder,eds), 161 l90-

Univ.ChicagoPress(1964)堀内公子:日本分析せんたー広報,No.28 23 30
6)金原啓司:日本温泉・鉱泉分布図及び一覧, 地質調査所(1992)

7)

堀 内 公 子 : 日 本 分 析 セ ン タ ー 広 報 , N o . 2 8 23 30

8)

堀内公子:放射線科学,

9)

堀 内 公 子 : 日 本 放 射 線 技 術 学 会 誌 5 7 No.12

41

No.10

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(1996)

420 4 28

(1998)-

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4.3 NaturalRadioactivityDistribution Images

and Their PracticalUses
自然放射能分布イメ ー ジ と そ の 活 用

Chizuo MORI
森千鶴夫
Aichi Institute of Technology
愛知工業大学--〒470 0392愛知県豊田市八草町八千草 1247 E mailcmori@sc.starcat.ne.jp
中部原子力懇談会-(ChubuAtomic Power Conference)-- -〒460 0 0 0 8 名 古 屋 市 中 区 栄 2 丁 目 1 0 19 Tel:052 223 6615

The generalpublics do not we11know that naturalradioactive substances arecontained i n al1 naturalmaterials including foods.We obtained the images of naturalradioactivity distributions i n vegetables,meat,stones,or ornaments by exposing themon the Imaging Plate deve1oped by Fuji Photo Film Co.Ltd. i n a l e a d shielding box forabout one m o n t h . W e made brochures named NaturalRadiations through Eyes orEnvironmentalRadiations through Figures ,etc. which include the images mentioned

above.We sometimesgivelectures a n d experiments o n radiations or energyto the
middle or high schoolstudents using the brochures. After t h e l e c t u r e s , m o s t of thestudents say that the images are effective to realize the presence of naturalradioactivity even i n our bodies.
1.はじめに

自然放射性物質は、 岩 石 は も ち ろ ん の こ と 、 野菜や肉などの食材、 装身具などの全ての材 料 に 含 ま れ て い る こ と は 、 一般人にはまだ十分に認識されていない場合が多い。 そ の よ
うなこともあって、放射線、放射性物質と聞くと、ただその言葉だけで、いたずらに恐怖
心 を 抱 く こ と が あ る 。 し か し 、 身近な食材などにおける自然放射能の分布状態を可視化した 像 が 得 ら れ れ ば 、 一 般 の 人 々 に と っ て 、 自然放射性物質、 自然放射線を実感的に理解する上で大いに役立つと思われる。 こ の よ う な 意 図 を も っ て 野 菜 や 肉 な ど に 含 ま れ る 自 然 放
射能分布の像を取得した。 本報告ではその取得の方法と取得したいくっかの像を紹介する

こと、および、これらの像を用いて学生や一般人に対して行なっているPA活動を紹介する。

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2 . 放射能分布像の取得

2. 1 露出時間の推定

Fig. 1 に 示 す よ う に 、 富 士 写 真 フ イ ル ム ㈱ が 開 発 し た イ メ ー ジ ン グ プ レ ー ト ( I P ) は 、 X
線 フ イ ル ム の 100˜1000倍の非常に高い感度を持つている ' ) 。 これだけの感度があれば私達の身の回りの品々に含まれている自然の放射能の分布状態が得られるのではないかと考えた。
自 然 放 射 能 イ メ ー ジングの取得に役立つ自然放射線は、 野菜などの食材においては、 ほ--と ん ど が K 4 0 か ら の β 線 で あ る 。 K 4 0 は 半 減 期 1 .2 X 1 0 9 年で、 β 壊変の割合は89 %

-

一

一

で あ る 。 K 40は食材や人体中には、0.02˜0, 1Bq/ g の 割 合 で 含 ま れ て い る 。 岩 石 や 装 身 具-に お い て は 、 や は り ほ と ん ど は K 4 0 で あ る が 、 ウ ラ ン や ト リ ウ ム 系 列 か ら の α 線 、 β線、γ線もイメージングの取得に役立つ。

-

Fig.1のIPの最低検出感度はC 1 4 に 対 し て 約 ( 0 1 5 d p m / m m2) X 6 0 分 X 1 8 時 間 = 1 6 0 β-/ m m2 で あ る 。 C 1 4 のβ線の平均エネルギーは約50keVであるか
n一-

一付与は 8 X:c︶起 集針表
︵
0
0
2
l

ネルギ

a

ら、単位面積当りのェ103keV/ m m2 と な る 。
このβ線の最大エネル

ギーは155keVで、その飛程はIPの厚さに換算すれば約 100µ m

であるので、IPの輝尽性発光体の厚さ 150µmの中で全てのェネルFig.1Comparison between the radiation sensitivity

ギー を 失 う こ と に な る 。

ofImaging P l a t e ( I P ) a n d that o f X ray fil m-

一方、 野菜などに含-

ま れ る K 40の含有率、 β線の平均エネルギ

一 440keV、飛程0.17g/cm2、等を考慮すれば、150µ mの厚さの輝尽性発光体の付与されるェネルギーは、 (0.26˜ 1.3) X 1 0 - 2 keV/mm2sと な る 。 したがって、 野菜などからのβ線を検出するのに必要な露出時間は 8 X

103keV/mm2 / ( 0.26˜1.3) X 1 0 - 2 keV/mm2s=7.2日 ˜ 8 6 日

2.2

となる。

遮蔽箱の必要性-

前 述 の K 40β線の輝尽性発光体(厚さ150µ m 、 密 度 3 ) へ の ェ ネ ル ギ 一付与は(0.92˜'4.6) x 10 - 2(J/kgs)である。一方、バックグラウンド放射線の単位時間当たりの吸収線量は、'

年 間 約 1 m G y で あ る こ と を 考 慮 し て 、 3.2 x 10 - 1(J/kgs)となる。 し た が っ て 、 バ ッ ク グ ラ
ウンド放射線を1桁以上低減する必要があることが分かる。

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鉛の厚さ 1 0 c m の 遮 蔽 箱 の 内 面 を カ ド ミ ウ ム と 銅 で 内 張 り し 、 さ ら に そ の 内 面 を 数 m mの厚さのアクリル樹脂で覆つた遮蔽箱はバックグラウンド放射線を約1/20に低減する。

2.3

潜像の減衰と長時間露出

IPに蓄えられた潜像が、読取た結果をFig.2に示す。

-

5日後の港像の強度をPSL(5)'特 性 を 、 いろんな放射線源で得

/

-

．

w
一
a
︶
一 1
︵0︶ ︵
-﹁
︐

て は 多 く の 報 告 が あ る 2)。 こ のm一一一

時間までに減衰する特性に関しとして、この値に対する相対強度をフイッティングによって求めれば、 次式が得られる。

PSL(t)/PSL(5)=0.48exp( - 0.32t)

f光後の時間, t・ (day)-+0.52exp( 0.0385t)≡R(t)
この曲線を図中に点線で示す。
露出が長時間Tにわたる場合

Fig.2 Fading characteristic ofthelatent image
stored i n Imaging Plateに蓄積された潜像が読取られる

強度I(T)は次式で表される。
1(
「) =

f

j[

] [ ; ][R(t )dt = : 1 - b1r1+j + 1 a l - c lr1;
lj

た だ し 、 a = 0 . 4 b =0.3, c = 0 . 0 3 、 T得られたI(T)の結果をFig.3に示す。
無限の長時間露出した場合に得られ]時間(h)である。

15

る で あ ろ う 強 度 の 約 7 5%が 3 0 日 の
露出時間で得られる。 したがって、実質的には1ヶ月以上の露出はあまり 意 味 が な い こ と が 分 か る 3 )。

3 . 得られた像の例

野菜や肉などの場合は遮蔽箱の中で ほ ぼー ケ月間の露出が必要である

0

ので、 腐敗や変形に注意する必要がある。 遮蔽箱から取り出したあとは出来るだけ早く潜像を読み取るのがFig.3

よ い 。 岩石などの場合の露出は数日

read out after1ong time exposure

でよく、場合によっては遮蔽箱を必220 -Effective intensity of the image-

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要としない。

-

Fig.4の左側に、豚肉、バナナのタテ切り、横切り、およびショウガからのK 40β線にFig.4 Naturalradioactivity distribution images of pork,banana,ginger(leftside)andleaves(right side)-

よる像を示す。 豚肉では、 たんぱく質の部分にK 40 が 多 く 、 脂肪の部分にはほとんど含まれない。バナナは皮の部分に多い。右側には木の葉の像を示す。葉脈の部分に多いが、葉の端に多く出ているのもある。

次に装飾品やめがねの像をFig.5に示す。陶磁器製のブローチやカリウムガラスにはカリ

Fig.5 Left:ornaments,glass ware,pottely w a r e . Right:glasses

221-

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ウムが多く含まれていることが分かる。 ナ ト リ ウ ム ガ ラ ス に は ほ と ん ど カ リ ウムは含まれていない。めがねでは、サングラスはナトリウムガラスらしくほとんど放射性物質がない。

-

し か し 、 近 眼 用 め が ね や 老 眼 鏡 な ど は カ リ ガ ラ ス で K 4 0 が 含 ま れ て い る 4 )。 し か し 。 既 知-の K 40含有量の試料による校正測定をし、計算によって眼の放射線被ばくを計算してみると 、 めがねから受ける放射線被ばくは、 日 本 の 低 地 に お け る 自 然 放 射 線 程 度 で あ る こ と が分かる。

-

Fig.6に花崗岩の小片の写真(左) と そ の 放 射 能 分 布 像 ( 右 ) を 示 す 。 黒 い 部 分 は K 40
か ら の β 線 に よ る も の で あ る 。 この白黒の像ではあまり見えないが、 カ ラ ー で は 、 雲母に含まれるウランやトリウムからのα線による強い点状の像が赤く見える。

4 . パンフレットの作成とその活用取得した像を含めて自然放射線に関するパンフレットを作成した。 F i g . 7 に パ ン フ レ ッ トの表紙を示すが、左側は「目で見る自然放射線」で、 自然放射線を可視化した様々な図を中心に編集している。右側は「図で見る環境放射線」で、環境放射線強度などを図にして編 集 し て い る 。 こ れ ら を 使 つ て 、 中学校や高等学校へ放射線やェネルギーなどをテーマにした出張授業を行なっている。 授業は講義と実験から成つている。 授業の最後にとる生徒の ア ン ケ ー ト に よ れ ば 、 野 菜 や 肉 の 中 に 放 射 性 物 質 が あ る こ と を 始 め て 知 つ た と か 、 直接

見 る こ と が 出 来 て 驚 い た と か が 述 べ ら れ て い て 、 像による視覚的な授業の効果は大きいとFig.6 Left:photograph of a piece of granite.Right:Radioactivity distribution
i m a g e ofthe granite .

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Fig.7 Brochures containing naturalradioactivityimages. Left: Natura1

radiations looking through eyes .

Right:

Environmental naturalradiations understanding through figures

5. まとめ放射線に対して極めて感度の高いイメージングプレートを用いて、遮蔽箱の中で野菜、肉、木の葉、装飾品、岩石などを露出し、これらに含まれる自然放射能の分布像を得た。
こ れ ら を 使 つ て パ ン フ レ ッ ト を 作 成 し 、 中学校、 高等学校、 ならびに一般の人々に自然放射性物質が、 私達の身体を含む全ての物質に存在し、 ど の よ う に 分 布 し て い る か を 可 視 的に 示 す こ と に 役 立 て て い る 。 ア ン ケ ー ト の 結 果 で は 、 生 徒 や一般の方々において、放射線に対する無理解に伴う必要以上の恐怖感を少なくすることができていると思われる。
謝辞
中部原子力懇談会放射線部会の委員の方々には、 パ ン フ レ ッ ト の 作 成 に お い て 多 大 の 御協力を得た。 ここに謝意を表する。
文献1 ) 富士写真フイルム㈱パンフレット:FUJI X バイオイメージアナライザー
2)小井戸伸吾:名古屋大学大学院工学研究科原子核工学専攻修士論文(1996)

3)Suzuki,T.,Mori,C.,eta1.: J.Nucl.Sci.Technol.,34,461(1997)4)鈴木智博:名古屋大学大学院工学研究科原子核工学専攻学位論文(l998)

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4.4 Radon variations i n an activelandslide zone from Himalaya: A
preliminary study
V.M. Choubey, S.K.Bartarya and R.C.Ramola1
Wadia Institute ofHimalayan Geo1ogy,
33GeneralMahadeo Singh Road,Dehradun- 249001,India
Emai1:vchoubey l @rediffmai1.com
1

Physics Department,HNB GarhwalUniversity,Badshahi ThaulCampus,Tehri
Garhwal 249199,India-

Abstract
The radon concentration was measured in soiland water samplesfrom an active
1andslide zone in the GarhwalHimalaya. Thelandslide is compound innature i.e. slump
in the crown portion and debris slide in the 1o wer part. The measured radon
concentration v a r i e s f r o m 3 . 1 t o l 8.3 B q/1 i n water whereas in soi1/debris samples it
variesfrom2.3to12.2 k B q/m3. The crown portion(upperportion)show higher radonvalues in comparison to distalportion. The higher radon concentration in crown portion
may be because of the failure plane of landslide associated with highfracturing andcrushing whereas,increased porosity o f debris of slide does not a11ow radon toaccumulate in soiland water in the1ower portion.
Introduction:
Radon is omnipresent radioactive gas and used as a naturaltracer in hydrology,
geology and geophysics.Dynamic phenomena occurring in the rock mass due toearthquake,volcanic activities,tremors,rock blasting andlandslide may be related to
outbursts of gas and changing radon concentration(Triquel999;Wysockal999;Kies
et a1.,2002).Schmid and Wiegand,1998have suggested that due to traffic vibration the
topmost soi11ayers1ose radon to the atmosphere and as a result the upwardmigration
increased.High radon concentration is genera11y considered with uranium deposits orwith highly sheared fault/thrust zone(Choubey and Ramola,1997;Purtsche1ler et a1.,
1995;Steele et al.,1982).

The investigations in Himalayan region shows that the concentrations of radonin soiland groundwater arelargely contro11ed by the tectonic processes,types o f rocks
and geohydro1ogicalcharacteristics ofthe rock mass(Choubey et.a1.,1999,2001). The
Himalayan area is prone tolandslides due to geodynamic processes,which have been
considered as a source ofradon(Partsche1ler et.a1.,1995).The indoor measurement in
Koefelslandslide(Tyro1,Austria)shows high concentration ofradon in houses1ocatedon oldlandslide deposits(Ennemoser et.al.,1994). However,more study is needed to
fiind out the relationship between radon emanation in soiland water withlandslide
activities.The use ofradon as a precursor of landslides is also yet to be investigated indetails.
The aim of this study is to analyze the radon characteristics o f soiland water inan activelandslide zone in relation to its applicability in the study of geo1ogica1
disasters.Keeping in view this,radon was measured in the soiland spring water in and- 2 2 4

1b).

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around an activelandslide zone1ocateda1ong PindarRiver between Hirmani and Matheravi11ages inthe Chamoli District of Uttaranchal,]lndia.The relationship betweenlandslide
activityand observedradon concentration in soiland spring water isreported inthis paper.

Radon Measurement Technique:
The radon wasmeasured in water(spring and seepage)and soii/ debris in an active
1andslide zone. About750mlofwater sample wastaken inradon tight reagentbottle of 1
1itl e capacityconnectedin a c1osecircuitwitha ZnS coated detection chamberthrougha
hand operated rubber pump and a glass bulb containing CaC12 to absorbthe moisture(Fig.

-

-

(a)

Pump

(b)

「 一 ]
Countin,g syslem

Fig. l (a)B1ock diagramof c1osecircuit technique forradon measu],1ements i n soil(b)Apparatusforthe measurement ofradon in water.
Airwasthen circulatedin c1ose circuit 1for aperiod often minutes ti11theradon foms
a uniformmixturewiththeairandthe resultingalpha activitywasrecorded.The detector
wasthen isolated by clainpingboththe ends and observations weretaken after four hours.A
time gap of four hoursis necessarytoa1lowalphaemittingdaughtersofradonRaA and RaC,
to come in equilibriumwiththeir own daughters.Resulting countswerethen converted in
Bq/1 by using an appropriate calibration factor(Choubey eta1.,2000).

225

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For soilgas radon measurement,auger holes each50 cm in depth a n d 6 c m indiameter wereleftcovered for24hours so that the amount ofradon and thoron became
stable. The soi1 gas probe was fixed in the auger hole and formed an airtightcompartment(Ghosh and Bha11a,1981). The rubber pump,soi1 gas probe and alphadetector were connected in a c1ose circuit(Fig. 1a).

--

Air was circulated through a ZnS coated chamber for a period of ten m inutes tiii
the radon formed a uniform mixture with the air. The detector ends are clamped andcounts are recorded after a time gap o f four hours.The resulting number of the alphacounts is then converted into Bq/m3byusing the calibration factorlcount/m i n = 6 6.30
Bq/m3,determined by Choubey et a1. (2000)under similar conditions.
Gneissic rock samples c1ose to thelandslide zone were also analyzed for theirtrace elements,including uranium using the sequentialX ray spectrometer(Siemens
SRS 3000) .

--Results and Discussion

Thelandslide is1ocated on theleftbankofthe Pindar river in Chamoli district of
GarhwalHimalaya. The slide is compound one i.e. slump in the upperportion and slidein middle part ofthe slide. The slide consists ofthree parts: cro ,1レ,n portion (slide scararea consist offractured and jointed freshly exposed rock mass),the rruddle slide massand toe portion having accumulated slide debris(Fig. 2). The radon concentration wasmeasured in waters o f spring and seepages and fro m soi1ofthe crown,middle portionand toe portion ofthe slide. The main rock mass consist predominantly o f schist andalternating bands o f gneiss ofthe Saryuformation o f Almora Group ofPrecambrian age(Valdiya,1980). The rocks exposed in the scar area are highlyfractured, jointed andsheared. The intensity of fracturing inlandslide zone diff el rsfrom place to place but
was high in upper portion ofthe slide.

、The observed radon concentrations in soiland groundwater o f theland slide
zone are given in Table1 . Soilgas and groundwater radon concentrations were found tovaryfrom2.3 B q/m3 to12.2Bq/m3 a nd 3. l Bq/1 t o 1 8 . 3 B ,q/ l,respectively(Table1) . It
was observed that for both the cases radon concentration is higher in crown area and1ower in the toe area ofthelandslide.

-

The most important pre requisite for high radon concentrations in soilair andwater are uranium and radium contents,permeability of the soi1or rock and thepossibility for high emanation rates,determined by certain moisture content as one of
the most important factors(Gundersen et a1.,1992) . Nearly a11these factors are c1osely
related with deformations. Sincelandslide are1ocalized phenomenon and no fault has
been recorded withinthelandslide zone other possible sources for the enhanced radonin crown area are need to consider. Surbeck(1992)related radon distribution in rockslides to permeabilties but not as source. The otherlandslides which have shown highradon concentration are those of Langtang Hima1of Nepaland Koef 1a lslide o f Tyro1(Austria) . The present slide show somewhat similarity to the above slides. Though,radon concentrations are far be1ow the values reported in these slide but the present
slide show enhanced radon towards crown portion. The high degree of fracturing in
the crown portion near the base o f the slide scar where possibilities of emanation and

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circulation pathways are best exist result in relatively high radon towards slide scar incrown portion. According to Putsche11er(1995)the materia1ofthelandslide meet a11
the prerequisites for an elevated emanating power and diffusion coefficient by theirheavyfi acturing and crushing down to grain and sub grain size,resulting in an increase
ofactive surface porosity.

-

Figure2. Map of thelandslide zone showing geomorphic features andlocation o f thesamples for radon measurement. (open circle=water,solid circle=soilsamples)
Table1 . Radon concentration in soiland water in theland slide area

Sample No ,Location o f sample inslide area

Soilsamt)les
SL1,2,3 .4,4a,5,SL6,7,8,9,10,11,12

Water samples
SW7,8
SW4,5,6
SW1,2

Crown area
(upper po rtion of slide)Toe area(1ower portiono f slide)

Crown area
(upper po rtion of slide)
Middle portion of slide
Toe area(1ower portiono f slide

-

227

-

Radon
kBq/m」
10.3,9. 1,12.2,
11.7,4. 7,12.1
2. 8 2.3 6. 3
5.7 1 0. 5
Bq/1
15 .3,18.3l

l

1

8 . l,9. 8,8.4
18 .3 3 . 1
1

l

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The recorded high value o f radon in crown area(slide scar)of the present slide
is mainly because o f the steeply dipping crosscutting and partly open joints which
provide good permeabilities and circulation pathways for soilair.
Therefore,thehighest radon emanations in thelandslide zone occur withinlandslide scar area wherestronglyfi acturedgneisses and schist are exposed.The contribution o f radon due topresence ofuraniurn/radium in the debris materialis almost negligible. This is reflectedin the geochemicalanalysis o f gneisses rocks which are present c1ose to thelandslidezone. The uranium concentration v a r i e d f r o m 1 . 8 t o maximum o f 3 . 9 p p m. The
m in imum,maximum and average values oftrace elements are giveninTable2.

-

The1ow concentration o f radon both in soiland water in the toe portion o f the
1andslide may be due to the high porosity and permeability ofthe debris materia1,which
does not a11ow radon to accumulate in the soiland water. Wu et a1.,2003observed thatthe permeability/porosity o f the subsurface materialandfracture network plays animportant role in escape ofradon to the atmosphere.
.
Table2. Trace element data of rock samples(ali values in ppm)

Minimumoi u n0 0 0 0 0 3 9 0 8 04 0 8
69 7 8 389
98
1 1 57 1 77 1 3 1 9 4C

Elements

N

aG
Z
C
bP

h
T

U
b
R

S

Maximum

Average

21 .0
65.0
39.0
89.0
l6.8
34.7
22. 1
219.0
3 .9
104.0
42. 1
351 .016 3

13 . 9
34.6
28. 8
74.7
12.7
24.5
14.2
l33.0
2. 9
7 l .6
33.3
218 . 9
11 .5

̲

r

Y
rZ
b
N

The preliminary results o f the radon measurement in an activelandslide zone
? o m the Lesser Himalayan region suggests that the enhance radon concentration in the
1andslide zone may be indicative of instability of the s1ope. Possibly thelandslide scarand failure plane of an activelandslide may be the source of enhanced emanation ofradon in an activelandslide zone(Figure2). The enhanced radon emanation is becauseof the high active surface area and circulation pathways due tofracturing and crushingof rocks near thelandslide scar. However in the toe portion increased porosity of thecolluvialdebris increased the diffusion ofradon in the atmosphere and thus resulting in
low radon concentration.However,more measurementsfi・om other activelandslide
would confirm the above inference.

The continuous monitoring of radon in thelandslide prone area may also be
helpfulto predict the occurrence of landslides in the area. Keeping in view the active

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J A E R I Confnature of GarhwalHimalayas,the measurement o f radon in soii and groundwater wi11be
helpfulto1ocate thelandslide prone areas and thus to minimize the risk to the1oca1
habitants.

Acknowledgements
We are thankf u l t o the Director,Wadia Institute of Himalayan Geo1ogy,Dehradun forproviding the necessaryresearch facilities to carryout the present studies.

References

Choubey,V.M. and Ramola,R.C 1997. Correlation between geo1ogy and radonlevels
in ground water,soiland indoor air in Bhilangana va11ey,GarhwalHimalaya,
India. EnvironmentalGeo1ogy,32(4),258 262.

-

,

-

Choubey,V M., B i s t , K. S.,Saini,N.K. & R a m o l a , R.C l999. Relation between soii gas
radon variation and the differentlithotectonic units ofGarhwalHimalaya,India
Jour. Applied Radiation and Isotopes,51(5),587 592.

--

Choubey,V.M.,Ramachandran,T. V., N e g i , M . S. and Ramola,R.C. 2000. Calibration
ofradon emanometer.IJEP.2095),329 331.
Choubey,V.M.,Bartarya , S.K., S a i n i , N. K . , a n d R a m o l a , R . C . 2 0 0 1 . I m p a c t o fgeohy,dro1ogy and neotectonic activity on radon concentration in groundwaterof intermontane Doon Va11ey,0uter Himalaya,India.EnvironmentalGeo1ogy,
40(3),257 266.

-,

Ennemoser,〇, Ambach. W, Brunner.P, Schneider.P,0beraigner. W, Purtsch11er.F,
Stingl.V,Keller . G , l 9 9 4 . Unusua1ly high indoor radon concentrations from a
giant rockslide. The science ofthe TotalEnvironment,15l,235 240.
,-

Ghosh,P.C. and Bha11a,N.S .,1981. 0 n the behaviour and measurement o f thoron( 22oRn)insoi1.Ind. J. EarthSci. 8,1 9.

-

Gundersen L.C. S,Schumann R.R,0tton J.K. D u b i e l R.F . , 0 w e n D.E,and Dickinson
K. A. , l992. Geo1ogy o f radon in the United States. I n : G a t e s A E a n dGundersonsen L.C.S. (Eds),Geo1ogic controls onradon. Geo1ogicalSocietyof
America SpecialPaper271
Kies,A.,Massen,F. and Tosheva,Z. 2002. Influence o f variable stress on undergroundradon concentrations. Geofisica Intemationa1.41(3),325 329.

-

Purtsch11er.F.,Pirch1.P .,Sieder.G.,StingLV.,Tessadri. T., Brunner.P.,Ennemoser,0.
and Schneider.P . 1995.Radon emanationfrom giantlandslides of Koe;fels(Tyro1,Austria)and Langtang Hima1(Nepa1) . EnvironmentalGeo1ogy,26,32-

Schmid,S. and Wiegand, J. 1998 . The influence o f traffic vibrations on the radon
potentia1. HealthPhysics.74(2),231 236.

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Steele,S.R., H o o d , W.C a n d Sexton, J.L. 1982. Radon emanation in the N e w Madrid
seismic zone. Geo1.Surv. Prof paper1236:191 201 .

-Surbek,H., l992. Das nationale Schweizer Radonprogramm. In: Tagungsber14 th
Jahrestagg. V i enna : 〇 S R A D . P p 6 14.

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Trique,M., R i c h e n , P., P e r r i e r , F.,Avouac, J.P and J .P . Sabroux. 1999.Radonemanation and electrica1 potentia1 variation associated with transient
deformation near reservoirlakes.Nature399,137 141 .

-Valdiya,K.S . 1980. G eo1ogy (1f K u mau n H im alaya, Wadia Institute of Himalayan
Geo1ogy,Dehradun. India271p.

Wu Y,Wang W , X u Y,Liu H,Zhou X,Wang L and Titus R.2003.Radononcentration:
A toolfor assessing thefi・acture network at Guanyinyan study area,China. water-

S A 2 9 ( 1 ) , 4 9 53.

Wysocka,M.,Skovronek, J.,Chalu pr1 i k , S and Sl(ubacz,K. l '09ll). Changcs o f radon
concentration in soi1over so me fault in upper Silesian coalbasin . Proc.5 th Int.
conf on rare gas geochemistry,Debrecen Hungary,61 70.

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4.5 Cosmic rays in space
宇 宙 空 間 と 能t線
Kazunobu FU;fllAKA
藤高和信

NationalInstituteofRadiological Scien1ces
独立行政法人放9、ll 線医業合研究所

ProjectLeader,SpaceRadiationProtection
宇宙放射線防護プロジェクトリ ーダー

ABSTRACT

Cosrnos is a mysteriousspace by whichmanyresearchersarefascinatedformany years. Bn
going intospacemeans thatwewi11receive extraexposuredue to existenceofcosmic rays.Cosmic
rays aremainlycomposedofhiglhly energetic protons.lt wasbom int1,?elaststage ofste11arlife.
Understandingof cosmoswi11certainly bring ri?t understanding of radiation ene1rgy,or energy
itselfAs rlo onecouldseethe veryearly stage ofcosmic rays,thel1eis only a speculation.Butit isbettertospeculatesomething basedon certainside ,evidences thanto give upthe 的ole.Such
attitl.lde sha11be welcomedinthespace researches.
,

Arryway,cosmicrayswerebominthelastexp1osionofastar.vl1tlichiscaliedasSuperNova.Aftercosmic raysareemittedfromthe SuperNova,itvl1illreachtot:] l1e1olu manL surroundings.To indifate
itsintensity1,specialunit of doserate is used . W],1en a m an climbs a mountain,cosmic rayintensitysurelyincreases.It doublesas11le goesupevery1500melevation. It wasascertainedby ourown measurements . Then vldlathappensvv,hen he goes up more?At avialionaltitude, wlhere
airplanes fty1, the doseratewi11beincreasedupto100timesthehiglh mountaincases.Andwhatis
expected 的en he goesupfur1:hermore,up tospaceorbitaltitude?]lnthiscase, the doserate
iricreasesup to1()timestheairplanecases.
Geomi1gnetismaffectsthe doserateverymuch.Asprimarycosmic ray particlesarecharged
particles,they cannot do we11withexistenceofthe magnetic field.In eff ect,cosmic rays canpenetrateintothepolaratmospherea1ong geomagnetic linesof forces whichstandalmostvertica1,
but1:)el11,fil nil lon of 1ow energycosmic rayswi11bebanned v1henthey intend topenetratecrossing
the geomagnetic linesof fofces inequatorialregion.Therefore,exposuredue tocosmic rays wil1
becomelarge inpolarregion,while itremainssmallin equatorialregion. ]ln effect,airplanes whichfyt overthepolewillreceivelargerdosethantofly overtheequator.

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Only,we have to knowthatthecosmos hasitsown lifetime, Iln other words,1ifetime of cosmos isfinite.Aftera11,atleast human beinが Teooncemed,wecannot ignorethis.
誰しも宇宙がどのようなものか、なぜ宇宙が存在し、これから宇宙はどうなるのか、を考えてみたことがあるに違いない。 宇宙の来し方行く末を考えるのは字宙論という分野だが、 宇宙論の端くれを理解しておくことが、 放射線という エ ネ ルギーの形態に理解を深めることになると信じる。

そもそもなぜ宇宙に エネ ルギーがあるのか、は誰も答えられない疑問である。大昔に、誰かが投け込んだのが、 エ ネ ルギーの束だったとしか言いようがない。 何ごとにも必然性を求め、 それを説明するのが自然科学の当然の方法だが、 宇宙開闢だけはどうにも説明できない。 あるものしかなく、 現実にそれは存在する、 としか言いようがない。 それで不安を感じるなら、 自然科学以外の世界で安心を得るべきである。 もともと自然科学とは自然現象の説明学だったのである。ある一定条件の下に、どのような法則性があり、従つてそれから先々何が起きるかを予想することを目的としていた。 その条件そのものが変わってしまうなら、 話は別なのである。 宇宙ではそのような変化もあり得るのである。 また宇宙という容器がなければ何も無く、 何も起きようが無い。 その意味で、 宇宙論とは万物の根本を扱う分野である。 ただ、 シニカルな こ と を 言 う な ら 、 役に立つことをしたいという人には勧められない。 どうにも役に立ちそうもないからである。

役に立つ分野の代表は医学である。誰も病気になりたくなく、病気から 一瞬でも早く解放されたいはずである。 その技術を持つのが医者であり、 だからこそ医者は特別扱いされても当然とされる。 最近航空機医学の雑誌に 「良きサマ リヤ人」 の話がよく出るが、それは医学の本質を付いていると思う。 良き医療l1表術者に過ぎなくても、 それでいいのである。 看護師も同様であるが、 彼らは心理分析家かもしれず、 親しい相談相手かも知れない。 一方宇宙を扱う物理学では、なぜ、に答えることは出来ないが、どのような形で起きそうかは答えられる。 また宇宙の今後を占うことも、 或る程度可能である。

それでは宇宙を最も卑近な所から眺める事から始めたい。下部では地殼に含まれる放射性核種から出る放射線が強く出るが、 地表面から高い方へ向かって上昇すると、 線源から離れるため放射線量は減少し 、 それが 150m程度から上昇に転じる。 これは航空機で実測したし 、 また高い鉄塔に上つても確かめた。 このようにして、 現在なら、 宇宙線のせい、 と言える。 しかしこれは90年前にはどうしてそうなるのか、分からなかった。 この 「上方にある線源」はオー ストリアの探検家のHess が予想し、それから約30年後にノ ーベル賞を受賞した。 これを分かり易く言うと、 地上から航空機高度へ上 る と 1 0 0 倍に増え、それが宇宙空間に出るとさらに10倍(つまり地表の1000倍)になる。 これは放射線の線量率を計測した場合である。結論から先に言うと、世の中で「宇宙線」と称するものは、 実は多くの粒子群の集合体である。 実はそれらは大半が荷電粒子であり、故に磁場の影響を受けている。 ところが地球磁場は荷電粒子と仲が惡く、 磁場の強い所
を荷電粒子は避けたいのである。 太陽は一種のプラ ズマ発生源 (荷電粒子群) だから、・-

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この流れの中にある地球は、地球磁気圏という独特な形を保つようになる(Fig.1)。このように、 宇宙にあるのは線源に違いないが、 それは通常の線源ではない。 そもそもそれは約100億年前の線源である。 だ か ら 宇 能 を コ ン ト ロ ー ル し よ う と し て も 出 来 な い のである。 これは各所にある放射線施設を監視する機器に関連して、 常に頭を悩ました点だったが、 それを理解するには天体物理学の情報が必要だった。

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MagnetosphereFig.l R,ough sketch of magnt如sphere
今日の知識で言えば、 一般環境にある宇宙線とは、 実は宇宙空間にある宇宙線そのものでなく、 それらが大気と相互作用してできた2次宇由線のことである。 余りに種l貢;が多いため、 これらを総称して宇'ili線と呼ぶ。 宇宙ではほとんどが陽了であるが、 これが大気粒子と衝突してそれを破壊すると、 構成粒子がバラバラになって飛び出t。 この過程のことを「核カスケード」と称する。飛び出すのが 場了かも知れず、あるは中性子、または中間子かもしれない。

:

このうち、中間子というのはπ粒子であって、それは電荷を帯びないπo粒子と、電荷を帯びたπ±粒子とからなる。 電荷を帯びないπoは即2個の光子になってしまう。 光子は動くと電子対を生み、 その電子対が動くとが光子が生まれる。 これは交互に起きること
で、実際間題として区別しにくいため、単に「電子カスケード」と称している。航空機
高度では電子による被ばくが問題になるが、 それはこの理由による。一方、電荷を帯びたπ±粒子からは、 もう一つの中間子たるµ :'粒子が生まれる。 ただしπ+ はより寿命が長 い ( 1 0 5 秒のオ、ー ダー) ので、地表やもっと深部まで達してから、µ 粒子に転換される。 今まで最も深い所で見つかったのはインドのコラ鉱山の中である。 結果的に地表面

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では全体の被ばく源の80%がµ 粒子であり、 残りが電子である。 要するに地表の環境において、 我々がi管通する宇能はほとんどµ 粒子である。
すると最初に生じた宇宙線はどうやってできた力、,,。 これは星の進化に伴う超新星el )爆発だろうと推定されている。 ,「面 星 は 始 め 表 面 に あ る 水 素 を 核 融 合 前 能 行 が 、 それが尽きるとその内側にあるヘリ ウムが燃え出す。我々の太陽はまだそこまで達していない。
ヘリウムに点火するとこれは燃焼効率が高いので巨大に膨らみ、 太陽系を例にとって説明すると、地球軌道を呑込む程度まで膨らむ。 ところが後が続かない。 そして太陽は燃
焼による膨張圧力と、 結ti重力が競い合い、 ついには後者が勝つ。 そして星は中心に向かって急激に落ち込み、 これが大変な圧力を生む。 元々の星の質量が太陽の3倍以下しかない場合は、 白 能 星 を 残 し 、 太陽の3倍を越える時は、 中心部に中性子星が残される。元々の星がさらに大きく太陽の30倍もあった時は、中央にブラックホールが生まれると言われる。

いずれも落ち込みが激しく、その際に中性子を含む様々な粒子群が生まれ、それが四方八 方 に 飛 散 る 。 そ れ が 宇 宙 線 の 誕 生 で あ る 。 な ぜ 様 々 な 重 さ の 自ス解があるのか、 その訳はこの中性子を考えれは説明できる。 この減少は平均して100億年の寿命があるとされるが、我々の太陽はまだその半分程度し力?肖耗していない。 しかし、 いずれ
どうにもならない時が来る。 天体物理を知り過ぎるとシニカルになるわけである

Energy spectrum in space

Fig.2Enegyspectraofcosmicrays
宇宙線を両対数グラフ用紙にプロ ツトしてみると、全貌が良く分かる(lFig.2)。 ここには太陽風という極めて穏やかなプラズマ流から、 太陽フレアと呼ばれる実発的な現象、 また普通に宇宙線と呼ぶ高エネルギーの現象の各フラックス分布を示してある。 そして太陽起源のものも、 銀河起源のものも宇能の能に入れてある。 そしてこの銀河で生まれる最大エネルギーは1013MeV/1核子とされる。我々の銀河の外で生まれた超高エネルギ- 2 3 4 -- 235 --JAERI Conf

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ーのものも無いわけではないが、それは星雲同士の衝突に起源を持つと考えられている。

分 か り 易 く す る と 、 放医研が誇る加速器HIMACの最大出力が800MeV/核子だから、 その100億倍のェネルギーが、銀河内部で生まれる最大エネルギーである。人智の作り出す技術の小ささを感じさせる。

それでも地球は磁気圏の存在によって護られていることに触れたい。地球は全体として天然の棒磁石だが、そのモー メントは少しだけ回転軸から傾いている。我々はその中にいる限り、 太陽フレアのような実発的な現象の時を除いて、 かなり護られているのである。これが最も顕著に現れるのが、航空機で北回り路線と南回り路線のどちらを選ぶか、という問題が起きた時である。 同じ欧州に行くとしても、 南回りの方が時間がかかる。
では線量はどう力,,,。

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ここにモンテカルロ計算コードCali 6を用いて計算した結果がある。 仮想的な飛行ルー
トで、片方は成田→プラハぺ飛び、 もう片方はシンガポーノレ→アテネに飛ぶノレートである。モンテカルロ計算だから、色々な仮定に左右されるので、限界は自明だが、ここでは370000 フイートの一定高度で飛ぶ場合を考えた。但し上昇時と下降時には各30分づ
つ時間をかけて移行するとした。 明らかに成田→プラハの方がシンガポーノレ→アテネ ょ

り被ばく線量が大きい (F ig.3)。 ほとんど2倍の差がある。 モンテカルロ計算は便利だか
ら、色々高度を変えた計算もしてみた。すると37000フイートと3l000フイートでは、前者が約55µ sv浴び、後者は約34µ Svを浴びることが分かった。 さらに太陽活動の影
響を調べるため、Helio,centric Potentialという磁場のインデックスを計算したところ、成田発ではニューヨーク便が最大40%の変化を見せ、ベルリンやモスクワもそれに準じた。

ところがホノルルやシンガポールでは殆ど変化しなかったCFig.4)。 ここに描いていない
国内便のグラフはもっと下になり、 形も寝ている。 繰り返すが、 あくまでこれはモデル

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計算なので鵜呑みにはできない。

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太陽と言えば昨年のフレアの時どうなったの力 ,興味あるだろう。これは太陽からの圧力で地球磁気圈が圧縮されて磁場が強くなり、 もっと外側からくる銀河宇宙線が跳ね返さ- 、

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れて、地球近傍の宇宙線は減つたのである。 これはForbush減少と呼ばれる現象であ り 、
日 本 の よ う な イ 解 解 前 測 さ れ た こ と は 珍 し い 。 その計測データを持つている。
どこまで飛んだらどれだけ被ばくすることになるかのデータも持つているが、 これは簡易型のポケット線量計の結果であり、 その限りにおいて、 また中性子の評価法もその限- 2 3 6 -- 237 --JAERI Conf

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りにおいて、とにかく校正してある。成田から各地で飛ぶ時の片道線量で、ニュ ー ヨ ー
ク行きが最も大きく、 ア ジ ア 必 で は 小 さ い 。 ただし経験から言うと、 同じパリ行でもルートが大きく異なったり、 また飛行高度が大きく異なったりした例があった。 従つて
一般的にこうなる保証はないかもしれない。

-

Dose rate of Space Shuttle in1981 198
.

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そして宇宙である。 我々の所では、 その被ばく 線量計測を調べている。 米国NASAのミッションが中断中なので、ロシアに頼み、プログレス・ロケットで打ち上げて貰つている。 また中国からも長征6号に能して貰う話が進められているところである。 今までのところ、磁気圏なし 宇 宙 空 間 で は 1 dY/日というのが線量の値として、世界中電用されている。 図はその内訳と簡略化の方法
i を示す (F'ig.lS)。
.

、

一方 J AXA(旧NASDA)の計画している宇宙飛行士の受ける被ばく線量限度が発表されている。これをみると、火星に行くのは、40歳にならないと1Sv(シーベルト)を越すよ
うな被ばく線量を受け入れられないことになる。 こ の S v という単位は発がんを意識した単位である。 比較すると、 如何に火星ミッションが大きな被ばく源になるかが分かる

CFig.7)。 この1Svという被ばく限界も法的な面でどうなるかは不明だが、 その数値に頼って色々な星までの線量を距離から推定してみると、 ど う も 人 類 は 冥 f̲星を越えられないようである。すなわち、太陽系から脱出できなし 。がんの治療線量になるからである。
がん治療では合計15回程度に分割して患者に与え、 その合計線量が約70Svになるが、宇宙でも太陽系の境界まで行くと 、 その値に近づく 。 がん系田胞を箱iす事を期待していたが、 同様の線量で正常細胞も死ぬかも知れないのである。 これをさらに他の,t百是に惑星系があったとして、アルファ・ケンタウルス星まで行くと、10万Svとなって到底無理なことが分かる。この線量をどうするか、という税がさらに深まることを期待したい。

、

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Estimated dose in various missions (mS

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字由線は約 92%の陽了 と、7%の重粒子、1%の重粒子の合計からなる。 これが人体に当たった時、何が起きるだろう力、,,。 体の特定系田胞を考えるなら 、 陽子は2˜3日に1回ぶSame cel i has a rare opportunity to be hi 1

Fig.8CoIlisionofsamecells
ぶっかるし、アルファ粒子(ヘリウム原子物イオンは1ヶ月に1度ぶっか り 、 ま た 数
子に至つては 100年に一度しかぶっからなし 、(F'ig.8)。 一生涯当たらない人もいるはずである。 ところが体のどこかの細胞にぶっかれば良いとして1報肇率重を計算すると、 この部系は大きく変わる。即ち陽了 は1秒に3.3億回、ヘリウム原子核イオンは1秒に2300万回、

238 -

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動立子は 1.8 万回衝突するのである(Fig.9)。 人体には60 兆個もの細胞があるためだが、特定系田胞でなく、そこから外れた細胞でも可、 という所に興味が持たれる。放射線生物学では「バイスタンダ一効果(当たっていなし 、細胞が影響を受ける)」 が昨今話觀 を集めているからである。
・Some cells have got opportunities to be hFig.9Collision of dif fierentcelis
も う 一つ指摘しておきたいのは、 宇宙が微小重力だという点である。 現在違心分離器の原理に基づき、大型の装置を計画中だが、実際問題として人工重力を作らないと、長期間宇宙へ人間を送ることは困難だと思う。 3ヶ月間軌道にあったスカイラブ4号の宇宙飛行士の骨を観察すると、 脱カルシウムが 5%程度見られたからである。 永久に地球に戻らないなら、タコみたいになっても良いと言うなら、影響を無視li一 ることも可能だが、元に戻ることを想定するなら、 この微小重力対策は重要と思う。 今までロシアで行われたボランティアによる長期間の寝たきりテスト結果や、過去にあった1年を越すような
長期間宇宙滯在の際の記録を点検する必要があると考えている。
今のところ、 宇宙に行くのはある種のボランティアのような、 使命感のある人たちだろう と 思 う 。 彼らはパイオニアであり、 大切にされなければならないと思う。 そして地上でも理論研究や加速器lJ用研究をもっと進めるなど、 色々な方面の研究をしないと、 宇
宙の余りの巨大さに太刀打ちできないだろうと考える。

n[参考文献]NAsDA:有人サポー ト委員会放射線被ばく管理分科会報告書 13.12等

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4.6

Utilization ofTechnologyRelevant to Radiation and Isotope
in the ArchaeologicalResearch
考古学における放射線及び同位体技術の応用
Nobuaki Matsuoka and Hidehisa Kawamura
松岡信明、川村秀久

Kyushu EnvironmentalEvaluation Association
九州環境管理協会

Abstract

Many kinds of scientific technology have been used in the archaeologicalresearch.Especia11y
the methodo1ogies relevant to radiation and isotope have contributed toarchaeo1ogy,giving a1ot ofscientific information.Among these methodologies,the radiocarbon dating,proposed by Wi11ard

Libby,hasthe greatest contribution since1950.In Japan some scientists introduced this dating
method immediately after Libby 's proposa1.As the result,the start ofthe Jomon period,in which
the rope pattern wasapplied for decoration of earthenware,wasreconsidered to be about10,000

years ago.Yoshimasa Takashima mastered this technique and did the dendrochrono1ogicalstudy at
Universityof Washington,Seattle,from1960 to1961.After that he started the radiocarbon datingin Kyushu University,Fukuoka.First he employed the proportionalgascounter to measure 14C,--

requiring the complicated and time consuming preparation of sample.When he restarted the radio
carbon dating with the authors in1994at Kyushu EnvironmentalEvaluation Association(KEEA),-

he adopted theliquid scintillation counting method combined with the benzene synthesis fromsample.Because this method is so convenient,manylaboratories have adopted it as the conventionalmethod in Japan.Since1994,almost100 samples have been treated everyyearin KEEA by
this method.However this requires considerably much amount of sample,for example20g in thecase o f w o o d . S o that,in case ofonl y sma11amount ofsample can be obtained or a valuable sample-

is subjected to measurement,this method cannot be applicable. T o resolve this problem,the accel

erator mass spectrometer(AMS)hasbeen used widely. I n this method the atoms of 14C are counted

directly,getting the high sensitivity and requiring very sma11amount of sample(order of mg).Re

cently, i n KEEA,the radiocarbon dating using A M S was started under the cooperation with Center

forApplied Isotope Studies(CAIS),University ofGeorgia.
Another work o f K E E A is the measurement of lead isotope ratios in the archaeo1ogicaland en-

vironmentalresearch.Thelead isotope ratios, 2o7Pb/2o6Pb and 2o8Pb/2o6pb,give usefulinformatjon

to understand the place or age in which an archaeo1ogicalrelic wasproduced.For example,as the

1ead isotope ratios are changeable depending on the diffierence of lead mine,it becomes possible toestimate the origin ofrelic containingleadasa component.Especia11y the origin ofancient bronze

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mirror can be estimated by this method.Thelead isotope ratios are measured by ICP M S easii y. I n
addition,the source estimation of lead po11ution in the environment can be done in the same man

1.Introduction

Although archaeo1ogy is class面ed into
the category of culturalor socialscience,

many scienti fic technologies are applied
for investigation in this field.Especia11y

in recent years,new technologies havebeen introduced into the archaeo1ogica1

research one after another,and participa-

tion of scientists has been increasingl y-

req uested.In Table1,scienti fic technolo
gies,which have been introduced into thearchaeology in Japan, are listed. As
shown in Table 1, many techno1ogies
relevant to radiation and isotope,i. e . r a-

diocarbon dating, therm oluminescence-・

TablelScienti fic technologies appIied in archaeoIogy-

Scie n tific technologies

PurposeDatingRadiocarbon dating

Estimation o f rel ic
producing center-A p p n四l o f l h
n i ljueand , erial-・App l a i a I o「1 red
pjgment

Thermoluminescencedating

relatedrela回

ch tn l a l a n a l、・sis

Measu l 'ement o f lead isotope

relatedX ra , lluo rol11l1・nce analysis

related-,-t tl i Tl a Tlt lSSiOn

E X P IO「atiOn of

G e o h slcalexln
P yPora onC 0 l ial' V allO n 0 f

conSe a tiOn menC.
erelltand n m a l n s

lt

Chemical analysis
X ra1l fluor fsl l ence analysis

Investigation of life Poli en a nalysis
and occupatjon
Plantopalanalysis
Fattyacid analysis
Measurement of car h on andrema1ns

Rtlation

related˜--dating,electron spin resonance dating,activation analysis,X ray fluorescence spectroscopy andothers,have been applied in the archaeology.

Especia11y the radiocarbon dating,proposed by Wi11ard Libby (1),has the greatest contribution a]1
over the world.For example,it wasrevealed by the radiocarbon dating that the monuments such as

Stonehenge were earlier than the Mycenae civilization.Also in Japan,the start ofJomon age(ropesentence age,10000 - 400 BC),when the rope pattern wasapplied for decoration of earthenware,

was reconsidered to be about12,000 years ago through the radiocarbon dating. T h i s is several
thousands years earlier than previously believed.〇n the early stage of investigation,the gas

counting method was mainly used to measure radiocarbon.In the next stage,since the gascounting
method is so complicated,theliquid scinti11ation counting method(LSC)hasbeen introduced andwidely used in theworld due to its convenient property. I n recent years,however,the veryhighprecision is required to evaluate the accurate chrono1ogicalage,and it is also required to use thevery sma11amount ofsample for the test.For these reasons,now the accelerator mass spectroscopy( A M S ) i s commonly used to measure radiocarbon (2).

The natura11y occurringlead has the four isotopes, 2o4Pb, 2o 6Pb, 2o7Pb and 2o 8Pb.Thelead isotope

ratios provide the information regarding to the producing center andage of ancient bronze relics
excavated in Japan,in particular bronze mirrors.That is,the bronze relics contain a trace amount of

1ead and the Iead isotope ratios are changeable depending on the diff el rence of lead mine.Consid--

ering this propertyit becomes possible to estimate the producing center and age of relics.Com
monly thelead isotope ratios are measured by the thermalionization mass spectrometry(TI MS)toachieve high precision.〇n the other hand,the inductively coupIed plasma mass spectrometry--

J A E R I Conf-

2005 0 0 l-(ICP M S ) h a s come into wide use for trace analysis in the environmentalresearch and can be usedalso to measure isotope ratios with the sufficient precision.This technique also can be applied tosource estimation ofenvironmentalpollution.Thelead,existing in the environmentasthe pollutant,

has the same isotope ratiosasthose ofsource materials.

And genera11y thelead isotope ratios ofsurrounding environmentalmaterials are different from those ofpo11utants.

So the source estima-tion of lead po11ution can be done e as ily by comparing the isotope ratios of surrounding materials,

po11utants and source materials.
Kyushu EnvironmentalEvaluation Association(KEEA)is the research institution that has been
doing the analysis ofenvironmentalpo1lutants,radioactivity,isotope ratios a 1nd so o n . l n its actlvity.,
there are many opportunities in which the analyses o f archaeo1ogicalsamples are done.In this pa-

per,some examples regarding to the radiocarbon dating and thelead isotope ratios of ancientbronze mirrors are presented.
2.Radiocarbon Dating in KEEA
2.1Principle

Carbon has the three naturally occurring isotopes,that is, ] 2C, l 3C and 14 C.It consists of 9 9 % o f
12C a n d 1 % o f 13C,but about one part in a 1 0 12 o f m o d e m carbon is t4C.Unlike 12C and 13C, 14C is

unstable and therefore radioactive,emitting β一ray with the energy of 186keV.

As shown in

Fig.1,the earth is always exposed to the primarycosmic rays. I n the upper atmosphere the primarycosmic rays react with the atmospheric materials,

producing the secondarycosmic rays.Neutron is
one of the secondary cosmic rays and produces
the radiocarbon( 14C)through the nuclear reac--tion of 14N ( n , p )14C.Carbon 1 4 i s oxidized into
carbon dioxide( 14C〇2) a n d distributed uniformlyon the earth through circulation and mixing ofuted in hydrosphere through dissolution of car -atmosphere.Furthermore l 4C would be distrib

bon dioxide into fresh and ocean water,and in

biosphereasthe results ofphotosynthesis.Thus a

Fig. 1 14 C cycle in the enviromlentslight amount of l4C exists in our surrounding
environment.

-

While 14C decays with the half 1 ife of 5730 y,it is newly produced in the upper atmosphere asshown above.So the equilibrium between decay and production of 14C hasbeen established in theenvironment. In the radiocarbon dating, i t is the principalcondition that the atmospheric concentra--tion of l 4C ( B q/g C)hasbeen constant through the earth history, w h i l e actua11y slight variations
due to some reasons,that is,fluctuations of earth's magnetic field strength,variations in sunspot

activity and so on,have been confirm ed.In principle,there is a constant 14C l e v e l i n the atmos
phere and a1lliving organisms.

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Before1950,the equilibrium concentration above mentioned was226mBq/g C in the atmos-

phere.However,artificial 14C wasproduced and provided into the environment through the nuclear

weapons testing since1945.Therefore the concentration of 14C in the environment increased

abruptly after1950.In1963,the year ofPartialTest Ban Treaty,the atmospheric concentration of
14C reached the peak-of 450mBq/g C.After1963the concentrationlevelhasbeen gradually de-creased due to nuclearweapon test ban and mixing ofthe excess 14C through the carbon exchange-

cycle.Nevertheless,the present concentration sti1lremains in260mBq/g C in the atmosphere.The

phenomenon above mentioned is called Bomb Effect .
〇n the other hand,the buming of large quantities of fossilfuelsuchascoa1,oiland naturalgas

started in the19th century.The fossi1 fue11aid down so1ong ago that its 14C has tota11y decayed

away,resulting in Dead Carbon that contains no 14C.Accordingly carbon dioxide released
through the buming of fossi1 fueldilutes the atmospheric 14C relative to 13C and l 2C.This phe-

nomenon is ca11ed Suess Effect .It is sure that Suess Effect affects the atmospheric 14C since theIndustrialRevolution.
While it becomes rather comprehensive to evaluate the atmospheric 14C concentration due toBomb and Suess Effects,the radiocarbon dating is based on the principle that the equilibrium con-

centration of 14C is attained in the environment through the earth's history.However,when a plantor an animaldies,it ceases to participate in carbon exchange with the biosphere and atmosphere,
and no1onger take up 14C.Therefore,ifa tree would be cut off,the initia1 l 4C concentration o f A o-would be decreased according to the half life(T 1/2 ).The 14C concentration ofthe tree aftertime t,A,
could be related withAo by the following equation.

t =1/λ・ln(Ao/A)

(1)

λ =

l n 2 / T112

(2)-

The best estimate of T1/2 is5730y.For the historicalreason,however,the Libby half 1ife(5568y)is--conventionally used as T1/2 Using the Libby half life,the equation(1)could be rewrittenasfo1
10 W S .
t =- 8033・1n(A/Ao)(3)

This t is the radiocarbon age.The reference material,oxalic acid produced in1950,is used to de-term ine Ao,so that the radiocarbonage is presented in the form ofyears BP,meaning how many

years old than1950.In recent years,the calibration curves suchasINTCAL98,are developed toconvert the radiocarbonage to the calendar age.
As is understandablefrom the principle,the datable materialsare organic.That is,the materials,

which once formed partofthe biosphere,are datable.
2.2Measurement Method of 14C

There aretwo methods of measurement of l 4C.ThLe conventionalmethod detects the activityof
sample,that is, β一ray emitted by the decay of l 4C . I n the early stage ofradiocarbon dating, gas

counting method waswe1lused to measureβ一ray from 14C . I n this method,carbon ofthe sample isfina11y converted to gases suchascarbon dioxide,acetylene and methane.These gases are intro-

duced into a proportionalcounterascounting gases.Recentlyliquid scinti11ation counting method

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Synthesis of l i t h i m c a r b i d e

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(LSC)is welI used to measure β一ray from 14C in stead of gas counting method.In LSC,carbon of
the sample is fina11y converted to benzene or methano1.These are added with sma11amounts ofscinti1lator and subjected to LSC.Gascounting method is relatively complicate rather than LSC.
Furthermore,benzene couId contain relatively much more carbon as a component compared toother organic materials,so that LSC could attain the high sensitivity of measurement of l 4C . S o

now LSC is commonly used to measureβ一ray from 14C in the radiocarbon dating. A s comparedwith the conventional m e t h o d , accelerator mass

spectroscopy(AMS)is a very much more recent
technique and directly detects the number of 14CT
S amp le∞2

atoms in the samples relative to 13C and 12C atoms.
A M S hasthe higher sensitivity than LSC and re-quires only severalmg of sample to measure theconcentration of 14C . I n Japan,however,there are

only a few institutes that conduct A M S , a n d these
are not commercia11y available.

M u s t i o n or acid drのping

l

2C

十

with L S C . T h e schematic diagram for dating isshown in Fig.2.Samples subjected to the test are
deterged with alkaIine and acid solutions.First car-bon dioxide is produced through combustion of or

ganic samples or dropping phosphoric acid to car-bonatious samples.Next carbon dioxide reacts withlithium metalat the temperature of 700°C,produc-

inglithium carbide.Ifelementalcarbon remains,it

2Li

Li2C2

l
l

Li2C2

-

Synthesis of acetylene
← H20
Li2C2

C2H2

KEEA started the radiocarbon dating in 1993--

← 一 L i (at700°C)
2C02 十10Li
L i 2 C 2 十 4Li20

十

-

2H20

Synthesis of benzene

2LiOH

→

'

十

C2H2

・.

← C a t a l y s t ( c h r oln i L n ( III ) - a l l 1lina pellet)
3C2H2

C6H6

C6H6

Prりaration of LSC sle← S c i n t i l l a t i o n cocktail(PP0.POPOP in non radioactive b 8nzene)-

LSC sa n1l)lel 'Rad ioacr iv ity n easur eln ent

Fig . 2Schematic diagram of LSC for
the radiocarbon dating

reacts also withlithium metalto producelithium carbide.After cooling down the reaction vessel,water is added tolithium carbide to produce acetylene.Finall y acetylene is trimerized to obtain-benzene using the chromium(I[I) alumina pe11et as a catalyst.Approximately5m1of benzene is
obtained by processing severa110g of sample materia1.The above chemicalprocedure is done us

ing the apparatus,TASK Benzene Synthesizer,deve1oped by J.E.Noakes (3).After adding the scin -tillatorto the benzene sample at a constant ratio,the β一activity of 14C is measured using theliquid-

scintillation counter,Packard TRI CARB1050/LL.The radiocarbon age is calculated according to
the equation(3).
In recent years,AMS has been adopted in KEEA.1n this case,the gas of carbon dioxide corre-

sponding to5mg ofcarbon is produced from a sample and sealed into a glass ampoule. T h e glass
ampoule containing carbon dioxide is send to Center for Applied Isotope Studies,University ofGeorgia(CAIS).In CAIS,carbon dioxide is converted to graphite and subjected to AMS.
2.3Examples of Dating in KEEA

2.3.1Dating of Charcoa1
The remains of Shobaru is1ocated in Fukuoka prefecture,northem partof Kyushu Island.In

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those remains,the place,where an old fumace for melting a meta1once stood,was discovered in
1995.The charcoalexcavatedfrom this place was sorted out byfloatation and subjected to the ra-diocarbon dating in KEEA.The radiocarbon age wasestimated by LSC to be2220±170years BP,
the early stage of Ylayoi age.Ylayoi age(400 BC - 300 A D ) i s the age after the rope sentence age(Jomon age)and prior to the ancient tomb age.However,there is a suggestion that the iron artifacts-

were produced in Shobaru remains. I f s o , t h i s result is very epoch making,because so far it has

been accepted in Japan that the iron manufacture was started in thelater stage ofYayoi age.
2.3.2Dating of Unearthed Fa]]en Tree-

The remains of Isouda D islocated near the Fukuoka City.Here the fa11en trees were unearthedf r o m 5 m be1ow ground.These trees had the marks of stoneax cutting and were dated to be

4800years BP.From these results,it wasrevealed that a1ogging field for pit dwe11ings was situatedhere in Jomon age.
2.3.3Dating of Carbonized Tree

The tephra is the generalterm ofthe pyroclastic materia1,which was emitted from the crater on

the occasion of an eruption and deposited on surface of the earth.In Japan many tephralayers are
distributed.The Aira tephralayer was formed by the eruption ofAira volcano,which was1ocated in

the southem part o f K yushu Island,and distributed a11over Japan,especia11y in Kyushu Island.The

carbonized tree was unearthed from the Aira tephralayer at Kagoshima prefecture,the southem
partof Ky ushu Island,and dated to be23500±700years BP.This result we11agrees with that in-

troduced from the geo1ogicalstudy.

2.3.4Dating of Wooden Block
Kourokan was the guesthouse for greeting the guest from a foreign countryfor about400years
from7th centuryto11th century.It wassituated at the center of Fukuoka City.From these remains

many kinds of relic such as wooden b1ocks,pieces ofcharcoa1,potteries and others were excavated
These wooden blocks and pieces of charcoalwere dated by LSC,and the calendar ages of 480 680 A D were obtained.These results seem to be contradictory to the fact of history.Taking thewood problem into account,however,there is no contradiction.That is,genera11y a wooden relicshows an earlier age than that in which it was used.
2.3.5 Dating of Underwater Remains

Imari Bay is1ocated in the northem part ofKyushu.In1281AD,the Mongolian army attacked

Imari Bay. A t that time many Mongolian's naval fleets were sunk to the seabed of the bay.The

main part of the anchor of a nava1 fleet was made of wood,and the big stones were fastened to itwith the bamboo.Recently some anchors were pulled up firom the seabed,and wooden and bamboo

parts were subjected to the radiocarbon dating.In this case,the results o f L S C were compared withthose ofAMS,resuIting in good agreement with each other(Fig.3).These results were also in good

agreement with the fact of history. S o it can be concluded that not only A M S but also LSC are ap

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plicable for dating the medievalrelics. I n Fi.3,the data without dendrochronologicalcalibration are
shown.In recent years the data calibrated by the calibration curve such as the IN TCAL98 (4) arerequested genera1ly. I n this case,the calendarage accompanied with certain probability is given.
1281AD︐

ao
P 0 qe

KEEA-23
KEEA-24
KEEA-25--

NUTA 5668
NUTA 5534
NUTA-5537
0

500

1000

1500

2000

Cal . Age (AD)-Fig. 3Comparison between LSC and AMS in radio
carbon dating
Sample:Anchor materials pulled up fromthe seabedof lmari Bay
KEEA :Results of LSC caried on at KEEA
NUTA :Results of AMS carried on at Nagoya Univ .
*Eaeh column of KEEA and NUTA shows the results forthe same sample as each other .

3.Source Estimation of Lead Using Lead Isotope Ratios

3.1Principle
In nature,there are4stable isotopes of lead, 2o4Pb, 2o6Pb, 2o7Pb and 2o8Pb.Among these,threeisotopes except 2o4pb are the finalproducts of naturalradioactive decay chains of 235U, 238U and
232 Th.So,ifuranium and thorium coexist withlead in a materia1,three isotopes of lead increase inquantitywith time,resulting in the change of lead isotope ratios suchas 2o6Pb/2o4Pb, 2o7Pb/2o6Pb,
2o8Pb/2o6Pb.Thelead isotope ratios are changing with time in a materialcontaininglead,uranium

and thorium at once.That is,lead isotope ratios of a certainlead ore are diff el rentfrom those ofothers depending on the geologicaland geochemicalhistories of individualmaterials. T h i s can besaid not only on ore samples,but also on other archaeo1ogicaland environmentalmaterials. C u m-ming and Richard studied thelead isotope ratios of earth materials,and proposed the theoryof-

growth curve of isotope ratios (5).〇n the basis of their theory,geo chrono1ogicalinformation ofrock samples can be obtained by measuringlead isotope ratios.According to the theoryof Cum-

ming and Richard,materials having relativelylow isotope ratios of 2o7Pb/2o6Pb and 2o8Pb/2o6Pb are
defined as more radiogenic ,whereasmaterials with relatively highisotope ratiosare definedas
1ess radiogenic .

So far,lead isotope ratios have been used for dating ofore and rock samples.However,lead that-

we encounter in our environment haspeculiar isotope ratios,and we can obtain some environ
mentalor archaeo1ogicalinformation by measuringlead isotope ratios.Mukai et a1.characterized

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the sources of lead in the urban air of Asia usinglead isotope ratios,and revealed that the exhaust

gasof automobile affects the urban airs of Bangkok and Jakartaseriously (6).They also revealed
that the airs ofKorean and Chinese cities have been aff el ctedfrom coalcombustion power plants,

and the air of Japanese cityhasbeen affiectedfrom refuse incineration factories.Sturges and-Harrison investigated the cross border air po1lution between USA and Canada usinglead isotope

ratios (7).They measured thelead isotope ratios of gasoline in Canada and USA,and of materials
emitted from smelters in Canada.
2 20
As to archaeo1ogy, i n Japan the measure

-

.

q

ment of lead isotope ratios hasbeen applied

2. 15
7

O

2 10
.

qd

e

807

-

/

bronze mirror contains copper,tin andleadeasthe maljor component.So it becomes pos

gd-

to estimate the producing center of an an
cient bronze mirror. That i s , a n ancient

2 05.

sible to estimate the producing center of2

mirror through measuring thelead isotope

0. 8

ratios.Mabuchi and Tominaga reviewed the

0. 84
207

methodology and scientific base (8). T h e

0.86

0. 88

0.9

pb/ 206 pb

Fig. 4Lead isotope ratio range of theancient bronze mirror excavatedin Japanbronze mirrors excavated from Japaneseruins were produced mainly in China of

A : G a l e n e produced in Japan
B:Mirror produced in Ghine of Eastern Han dynasty
C:Mirror produced in China of Western Han dynasty

West Han dynasty,China of East Han dy-

nastyand Japan.Plotting the dataon the
1ead isotope ratio diagram,it would be esti

0. 82

-

mated where the samples were produced(Fig.4).

3.2Measurement Method of Lead Isotope Ratios
As the archaeologicalsample material,a few10mg of rust was takenfrom an ancient bronze
mirror.As the sample for the environmentalresearch, fifty mg of coal,100mg of bottomash,-

100mg of soil,300mg of dried agriculturalproduct and a filter accompanied with SPM were sub

jected to analysis,respectively.Each sample wastaken into a Tef1on vesselspecially designed for

microwave decomposition (9),fo11owed by addition ofappropriate amount ofdeionized water and3
to4mlofnitric acid.In addition,a few mlofhydrofluoric acid,perch1oric acid or hydrogen perox-

ide wasadded depending on the compositionalsituation of sample.The important point is to makea blank sample,to which same kinds and same amounts of reagents are added as wellas a true
sample.After addition ofreagentsthe tightly sealed Tef1on vesselwasplaced in a microwave ovenfor kitchen use and the sample materialwasheated intermittently(5minX3times)at the power

corresponding to almost50W/sample.After microwave decomposition,the sample was filteredwith the filter paper(ADVANTEC5C).The filtrate wastaken into a volumetricflask and was
adjusted t o 2 5 o r 5 0 m l w i t h deionized water.This solution wasintroduced into ICP/MS formeasurement of lead isotope ratios. I n ICP/MS measurementtrue and blanksamples were-

measured simultaneously, a n d the net ion counts of individualisotopes were calculated bysubtracting the counts ofblanksample firom those oftrue sample.From the net countsof individual
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samplefrom those oftrue sample. F r o m the net counts of individualisotopes, 2o7P b / 2o6Pb and- -2o 8Pb/2o6Pb ratios were calculated,and these data were normalized to S R M PB 981by measuring

the reference materialsimultaneously.

3.3Application to the Archaeo1ogicaland EnvironmentalStudies in KEE A
3.3.1Producing Center Estimation ofAncient Bronze Mirrors--

6 5 432 10 08
9 0
1 1 111 11
2 2 222 22 2 2

In Japan there are many old tombs built in the an

kuoka City.In this citythere are many ancient tombs

0. 83

cient tombage,and sometimes the ancient bronze
mirrors are excavated flrom these tombs. T h e archae

q

-

d
q

a

The Maebaru City is1ocated in the west ofthe Fu・-logicalconsidering where the mirrors were produced.

o
dg

8

-

/

of these,because it is much important for archaeo-

o1ogists have the great interest in the producing center

0. 84

0. 85

0. 8 6

0. 87

0.88

207 Pb/ 206 Pb
Fig . 5Lead isotope ratios of the an G ientbronze mirrors excavated fromthe
Maebaru Gity . Fukuoka Prefecture

built in the ancient tomb age.Two ancient bronze

mirrors excavated from this citywere subjected to the-analysis of lead isotope ratios(Fig.5).From the ana
lyticalresults,the raw materials oftwo ancient mirrors
were considered to have originated either in China ofEastem Han dynasty,or the Korean peninsula.

An error bar shows the2σregion .
〇:mirror from Higashi -Makata No . 1mound tcmb●:mirror from Tateishi No. 1mound tom b

3.3.2Source Estimation of EnvironmentalPoliution

Coalcombustion power plants release pollutants,suchassulfur oxide(S〇x),nitrogen oxide(N〇x),suspended particulate matter(SPM)and gaseous materials,into the environment.Therefore,

it is necessaryto monitor these po11utants in the surrounding environment ofplant.In Japan,many

monitoring stations are arranged around a power plant to monitor SOx,NOx and SPM continuously,
and furthermore metalelements in air,soiland plants are measured periodicall y.However,many
artificialand naturalsources ofpo1lution,suchasincineration factories and volcanoes,exist in thesurrounding environment of power
plant.In this situation,it is very diffi

-

/

2.20

cult to estimate the in?uence of power

plant exactly using-

and fortunately hasfour stable isotopes.
Therefore,it enables us to do the envi-

ronmentalevaIuation using isotope ra

-

-

口

d
a

-

ing of coalcombustion power plant,◆-

inform ation only on concentrations of
po1lutants.
Lead is the usefuland important in
dicator for the environmentalmonitor

l的 s r d 里 e n i c

-

-

.

〇 tM l - - - IBonomash

eo e,

-

ロS P M
△
Sil◆Agriculturallllroduct/◆

more r a liogenic

2.00

0.80

0.82

0.86

0.84
207 p

f

0 6p b

0.8 8

0.9 0

0.92

Fig.6 L e a d isotoperatios ofcoal,bottom ash ,soil, S P M and agricultu ralprodu ・ts

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tios.So this technique was applied to evaluate the environmental impact of Reihoku coalcombus

tion power station,1ocated in the middle part ofKyushu Island.That is,the samples ofcoal,bottom

ash,soi1,suspended particulate matter(SPM)andagriculturalproduct were co1lected in the sur-rounding area o f station,and were subjected to the analysis of lead isotope ratios (1 o ).From the results shown in Fig.6,it wasrevealed that there is no environmentalinfluence ofthe power station
asfar aslead po11ution is concemed.
4.Conclusions
At the present,many techniques and equipments,relevant to radiation and isotope,are essentia]

for the humanlife.These have contributed to the deve1opments of industry,agriculture,medicine
and others since the end of 19th century.Especia11y the nuclear power became the main energy

source in thelater h a l f o f 20th century, a n d is thought to be essentialfor the sustainable deve1op-

ment ofthe mankind in future.In addition,the nuclear power generation is needed to sone extent

to prevent the increase ofcarbon dioxide in the atmosphere.

Considering the fact above mentioned, people should have the co1Tect knowledge about radiation,

radioactivity,isotope and nuclear.So it would become more importantto educate people,especia11y

young people,in these fields.In the archaeologicaland environmentalscience,many techniques,
which are relevant to radiation,radioactivity and nuclear,have been used.From the viewpoint o fradiation education,it would be very effective to teach about these theories,methodo1ogies andresults.

References(1)E.C.Anderson and W.F.Libby:Phys.Rev. V,o.81,64(1951)(2)R.A.Mu1ler:Science,Vo1.196,489(1977)(3) J.E.Noaks et a1.:Proceedings ofthe6th IntemationalConference on Tritium and Radiocarbon

Dating,68(1965)(4)M.Stuiver et al.:Radiocarbon,Vol.40,1041(1998)(5)G.L.Cumming and J.R.Richard:EarthPlanet Science Letters,Vol.28,155(1975)(6)HMukai,N.Furuta,T.Fujii,Y.Ambe,K.Sakamoto and Y.Hashimoto:Environ.Sci.Techno1.
Vo1.27,1347(1993)(7) W.Sturges and RM.Harrison:Atmospheric Environment,Vo1.20,577(1986)( 8 ) H M a b u c h i and K.Tominaga: Ten Chapters for the archeo1ogy ,(1981),(The Univ.ofTokyo

Publication Assoc.,Tokyo)(9)H.Kawamura,H.Tagomori,N.Matsuoka,Y.Takashima,S.Tawaki and NMomoshima: J . R a
dioana1.Nuc1.Chem.,Vo1.242,717(1999)、(10)H.Tagomari,H.Kawamura,NMatsuoka and S.Tawaki:Environment and Measurement Tech

no1ogy, 1lol.26,20(1999)

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Charms ofRadiation Research
Mitio Inokut

Argonne NationalLaboratory,Argonne , Iiiinois60439,U. S. A.

-e mai1:Inokuti (a1 anl gov
Abstract

Most ofmyprofessionalefforts over nearly five decades have been devoted to radiation
research,that is,studies ofthe physica1,chemical,and bio1ogicalactions ofhigh-energy-

radiation on matter. (By the term high energyradiation I mean here x rays,γrays,
neutrons,and charged particles ofhigh enough energies to produce ionization in matter. I
exclude visiblelight,infrared waves,rmcrowaves,and sound waves.)Charms ofradiation

research lie in its interdisciplinarycharacter;although my training was in basic physics,thescope ofmy interest has gradually increased to cover many other areas,to my deep-

satisfaction. High energy radiation is an important component ofthe universe,and ofour
environ ment. It often provides an effective avenue for characterizing matter andunderstanding its behavior. Near Earth's surface this radiation is norma11ypresent inexceptiona11y1ow quantity,and yet it plays a significant role in some atmosphericphenomena such as auroras,and also in the evolution oflife. The recent advent ofvarious-

devices for producing high energy radiation has opened up the possibility ofmany

applications,including medicaland industrialuses.I have worked on some aspects of

those uses. At everyopportunityto address a broad audience I try to conveya sense o f
inte11ectualfun,together with some ofthe elements ofthe basic science involved . A goa1
ofradiation educationmight be to make the word radiation as common and familiar aswords such as fire and electricity''through increased usage.

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Work supported by the U. S. Department of Energy, 0ffice o f Nuclear Ph ysics- - - -

under Contract No . W 31 109 Eng 38 .

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1 . Pro1ogue

In August1945,when World War I I ended with the defieat ofJapan,I was a sixth

grader o f a Tokyo elementaryschoolbut wasliving safely in Nikko,a mountain resort120
kmnorth,owing to the student evacuation as a precaution against air raids.A few days

earlier the atomic bombs had been dropped at Hiroshimaand Nagasaki,and shortly

thereafter a science teacher told us students about the science and techno1ogy related tothe atomic bomb. Thelecture,shorter than an hour,made a profoundimpression and gavemelasting stimulation;I wanted toleam much more about the topic. I am sti11 studying apart ofthis topic.
The first technicalbook I ever read through in English,in1948,was the Smyth Report[1].It was the first o fficialdocument published about the atomic bombs,and thus wastranslated into manylanguages,and indeed was exce11entlywritten. In this book Ifirst saw
the name ofArgonne Laboratory,without a hunch thatlater I would work in the

successorlaboratoryfor1onger than forty years,unti1 today.

My specific interest in radiation and its interactions with matter was aroused by the
Fukuryumaru(Lucky Dragon)incident,which occurred afier the test o f a thermonuclear

device(named Bravo)in1954at the Bikini Ato11. The crew o f a Japanesefishing boat was

exposed to considerable radiation,and a member died shortly after retuming to Japan. At
the same time I began toleam about the beneficialuse o f x rays in medicaldiagnosisandtherapy and was even more intrigued by this. Since then I have maintained a desire tolearn
about radiation interactions with matter and to contribute something to the increase of

bowledge about them.

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The charmsofradiation science lie in its variety and diversity.High energy radiationand its actions on matter are related to studies ofelementaryparticles,nuclei,atoms,,

molecules,plasmas,and condensed matter,as we11 as accelerators,other radiation sources,-

and related instrumentation,within the discipline ofphysics.Some aspects ofhigh energy
radiation be1ong to various branches ofchemistry:physicaしorganic,inorganic,synthetic,

and analyticalchemistry.〇ther aspects fit into bio1ogy,medicine,environ mentalsciences,and some branches ofengineering. Therefore,radiation scienceisa good area ofstudy forsomeone,1ike me,whose range ofinterestisbroad. Radiation science is a potpourriof

dif fierent fields,and yet it represents an inte11ectualsynthesisofencyc1opedic knowledge.

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Some areas of science originated in phy1sics and eventualiy settled as a branch ofengineering,as exemplified bymechanicalengineering and electricalengineering. The-

twenty first century may see radiation engineering as a similarly established discipline.
Let me discuss some topics selected to i11ustrate various aspects ofradiation science.
2. Effects ofradiation on synthetic polymers

As a graduate student at the University ofTokyo I studied the topic in title. The

practicalimportance ofthis field does not seem to be as widely appreciated,as it should bein my view . Let me discuss an example that shows the importance.

A commonly available sample ofpolyethylene consists oflarge molecules(technica11y
ca11ed polymers),each ofwhich is alinear string and consists ofmany units(technica11y- --ca11ed monomers)ofchemicalstructure CH2 . Irradiation ofpolyethylene with highenergy radiation such as x rays orγrays produces a new chemicalbond between-

neighboring molecules.A chemicalbond thus produced is technica11y ca11ed a cross 1ink,

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and the process ofits formation cross 1inking. The cross 1inking process accounts for a
substantialfraction ofthe totalenergy absorbed fro m radiation,and in this sense itisa

main result ofradiation action.

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After sufficient exposure to radiation,enough cross 1inks are formed to connect-

polyethylene molecules into a three dimensionalnetwork(technica11y ca11ed a ge1). Then,,the sample becomes extremely strong and resistant both mechanica11y and chemica11y.This

phenomenonled to many industrialapplications. 0 n e application has to do with thecooling ofthe engine o f a n automobile with water. Ti11thelate1960s I often witnessed the
1oss ofcooling water,1eading to overheating ofthe engine and eventua11y to disabling of

the automobile. This occurred as a result ofdegradation ofrubber tubes and pipes because
ofoxidation,which is inevitable a fter repeated changes oftemperature and in constantcontact with oxygen in air. Young people probably do notknow this kind ofautomobile-

failure,because it has been completely eliminated by the use o f irradiated,cross 1inked-

polyethylene in the water cooling system.
Interestingly this eminentlypracticalapplication began in Japan,years afier its scientificbasishad been discovered byArthur Charlesby[2,3]in the U. K. and by MalcolmDole[4]in the U. S.,independently ofeach other. Thishistory is similar to that ofthe transistor

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and its application to radios and other common devices,and it iiiustrates different kinds ofstrengths of diff ei rent countries.

Eff el cts ofradiation on polymers in generaldepend on the molecular species,theirconfiguration,and other characteristics,and therefore these eff el cts offer a rich field of
research sti11 to be pursued[5,6] . Wishing toleam more about the topic,I became an

associate ofDole at Northwestem University in1962,and thus began mylife in the U. S .

Gradua11y my scientific interest went deeper and deeper .
3 . Electronic excitation and ionization of molecules

Gases such as air, 1iquids such as water or gasoline,and solids such as synthetic

polymers or bio1ogicalce1ls are made ofmolecules and therefore are technically ca11ed
molecular substances. Most ofthem are electricalinsulators. The action ofhigh-energy
radiation on these substances begins with disturbances ofthe motion ofelectrons,which

are the main agents ofchemicalbinding between atoms and hence are crucialto molecular
structure. Most ofthe energy ofradiation is expended in changing the motion ofelectrons,

because they are the lightest constituents ofmatter,indeed much lighter than ato rnic nuclei
As a consequence,electrons maybe raised to an orbit ofhigher energybut sti11 be boundin an atom or molecule;technica11y we ca11 this event electronic excitation. Altematively,
electrons may be pushed out o f a n atom or molecule and thusliberated to movefar away;
technica11y w e ca11this event ionization,because what remains behind wi11be a positive ion
Anion is a charged atom or molecule. The radiation that causes ions to form is ca11ed
fomzlng radiafion .

As a novice in science I wanted to understandfu11y a11themicroscopic processes
sketched above,but I had no appreciation ofthe vastness and depth ofthe subject area. It

encompasses electronic structures ofatoms,molecules,and their assembly intoliquids andsolids,as well as collision phenomena. Afier nearly five decades I continue my study withno prospect o f a n end .

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4. Two teachers I had in Chicago

I was fortune to become associated with two masters ofphysics and chemistryrelated
to radiation,U . Fano and R. L . Platzman.〇ne ofthe benefits ofstudying any field of

science is to be acquainted with persons ofhigh inte11ectualability and devotion.
Fano camefi・om Italy and was trained in Rome by Enrico Fermi,one ofthe greatest

physicists ofthe twentieth century. Fano contributed much to various areas oftheoretica1
physics[7,8] . Ilearned fromhimthe basics ofradiation's interactions with matter, firstfrom his papers during my student days in Tokyo andlaterfromnumerous conversationsin Chicago . He taught me many things. However,I remain most impressed with hisstatement to the fol1owing effect: When we do something in an applied fieldlike radiation

science,we must sti11 maintain intellectualstandards high enough to command respect by abasic scientist. T h e truth ofthisidea has been becoming clearer and clearer to me,as I

see more and more ofmediocre work in applied sciences.
Platzman was anAmerican,trained first at Chicago by James Franck,one ofthegreatest chemists ofthe twentieth century,andlater in Copenhagen byNiels Bohr,andgrew to be a pioneer in theoreticalradiation chemistry[9] . Platzman invented severa1-

notions seminaltolater deve1opments. In1963hehired me as co worker atArgonne.He

taught me much,including severalways to study electronic excitation ofmolecules,,

including the use ofsynchrotron radiation,which is now realized in numerous institutions

throughout the world.

The bestknown ofPlatzman's accomplishments is the1952prediction ofthe hydrated
electron. Inliquid water underirradiation,ionization occurs abundantly;in other words,,

manyelectrons areliberated and move into the water medium,1eaving positive ions behind
To discuss what happens to these electrons,we need to reca11a property ofthe watermolecule:the outermost electrons in the molecule tend to be c1oser to the oxy1gen atom
than to either ofthe two hydrogen atoms. Therefore,when seenfi・o m far out,themolecule1ookslike a dipole,namely,aline segment with one end positively charged andthe other end negatively charged . We express the strength ofthe dipole by the electric

dipole moment,defiined as the product ofthelinelength and the magnitude ofthe charge

at either end. Thus,we say that the water molecule has an electric dipole moment.Indeed,
many characteristics ofwater are attributable to thelarge dipole moment. Molecules in

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water at room temperature are moving around,are vibrating intemaliy,and mostimportantly,are rotating or changing the orientation oftheir dipoles,a11as a consequence
ofthermalmotion . Ifseveralneighboring dipoles happen to be directed to a centralregion,
then,to an approaching electron,this region appearslike a fixed positive charge. Thus,theelectron is drawn andmight be attached to this region ifit1oses some ofits excess energy.

Once the electron stays in the region for a while,then the arrangements ofmolecularorientations and hence dip1oes become more favorable for trapping the electron. Platzman

ca11ed an electron thus trapped in water the hydrated e11ectron and reasoned that it ought
to survive1ong enough to permit spectroscopic detection and also to act as a readily

identifiable species in chemicalreactions.
In1962,Hart and Boag[10,11]observed the absorption spectrum ofthe hydrated

electron. Shortly therea fier I witnessed a conversation among Platzman,Boag,and Hart,,

sharing the jubilation ofthe great discovery.Indeed,this discovery is perhaps the mostimportant contribution ofradiation chemistryto chemistryin genera1.Similar states ofelectrons occurring in many dielectricliquids,such as ammonia and alcohols,are ca11ed

sollv ate d electrons. They act as a reducing species.
5 . Effects of radiation on water

Chemicalreactions initiated ionizing radiation are important subjects ofstudy in two

respects. First,manynuclear reactors use water as coolant.Second,water is the major
constituent of the bio1ogicalcel1.
Pioneers in nuclear engineering such as Eugene Wigner were justifiably concemedabout the efliects ofradiation on materials they considered using in reactors. Water iscertainly one ofsuch materials,because it is available at1ow cost,and it contains hydrogenatoms,which are most efficient as a neutron moderator. 0 n e maynaively ima gine thathydrogen molecules(H2 )and oxygen molecules(02 )would be producedf ro m water(H20)underirradiation,1eading to the production ofhydrogen and oxygen gases. Ifthis
occurred,then gas bubbles would emergefrom the water coolant in a running reactor andgive rise tohigh gas pressure in the reactor containment,posing a nasty engineering
problem,as wellas a potentialfor exp1osion.

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Natura11y,studies on chemicalchanges of water and other materials caused by radiation

began early in the Manhattan Project.These studies were soon established as a field of
research ca11ed rad iation c he mistry,and continue today. It was quickly found that only

smallamounts ofgas come out ofwater under irradiation. More strikingly,irradiatedwater rebuilds itselfalmost completely after a period that is short but1ong enough topermit numerous co11isions between molecules. During this period,diverse chemica1
reactions occur among hydrated electrons,hydroxylradicals(0H),and other intermediate

species produced byirradiation. Fu11 explanation ofa11this[12]is highly technical,but it isnoteworthy that common molecular substances are usua11y incapable ofref ol rming
themselves afterirradiation. For example,irradiation ofoi1or gasolineleads to very

appreciableproduction ofhydrogen,methane,and other gases. As an exception,carbon
dioxide C〇2 in gas or liquid is effective in reforming itselfafterirradiation,and is-radiation resistant .
As for radiation effects on the bio1ogicalce1いt is i mportant to appreciate that water
dominates in the absorption ofenergyfrom radiation. Moreover,the atomic composition(more importantly,the electron density)ofproteins and other constituent molecules in a

ce11difliers only slightlyf rom that ofwater;therefore,itisnot a bad approxmation toconsider pure water in place o f a ce11,asfar as energy absorption is concerned. Thus,apartofradiation effects on a ce11 must stemfrom energy absorption by water;in other-words,hy,droxylradicals and other chemicalspecies are producedfi o m water and reactwith biomolecules,1eading to some radiation effects. These are called indirect effects.

Altematively, some ofradiation efliects are attributable to energy absorption byproteins,,( cts. Most of
histones,DNA,and other molecules in a ce11. These are called d i recte◆1lfe

experts in radiation bio1ogybelieve that no consideration based on either indirect or direct

effects a1one can be complete;in other words,these two pathways are comparable inimportance.We wi11retum to radiation bio1ogy in Section8.

6 . Radiation efllei cts on metals〇ne ofthe charms ofradiation research lies in the great dif fierences in radiation efliects

on diflierent kinds ofmatter . Metals behave radica11y d ifferentlyfi・o m molecular substancessuch as water and polymers,for example,for reasons to be sketched be1ow .

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Most of the electrons in a piece of metalare tightly bound to an atomic nucleus. Theseelectrons move around in theimmediate vicinity ofthe nucleus(technica11y ca11edinnershe11s)and playlittle role in determining atomic structure and materialproperties. 0nly a-modest number ofelectrons moving farfi o m any atomic nuclei are decisive for atomic
structure and materialproperties related to electricity,magnetism,and optics. These are

ca11ed conduction electrons because they cause electric conduction. Ionizing radiation

gives some energy to a11ofthe electrons in matter,and roughly speaking similarly to eachofthem. Most ofthe energy given to the electrons degrades rapidly into alarge number ofquanta ofatomic vibration(technica11y ca11ed phonons )and then to thermalenergy,
without causing irreversible displacements ofatomsfio m their no r malpositions in the

crysta11ine structure;thus,radiation heats the metalto some extent but causeslittlechanges in materialproperties.
To observe efliects ofradiation on meta1,one must do something specia1. 0 n e way is tocause a huge amount o f x rays orγrays to be absorbed . Another way is to use protons,ot
particles,or heavier ions of1ow speeds,comparable to the speeds ofconduction electrons

or1ower;such s1ow particles hardly excite electrons,but they give energy to atoms to set
them in motion,1eading to an appreciable probability of irreversible displacements ofatoms and hence to appreciable changes in materialproperties. Fina11y,neutrons cause

atomic displacements directly,or indirectly through the generation ofmoving ions.

Consequently,considerations ofradiation effiects on reactor materials usua11y focus on

neutrons,heavy ions,and particles resultingfi om reco i1 ofthem[13].
'In a personalconversation near the end ofhis life,I asked Charlesby,one ofthe-

discoverers ofthe cross 1inking ofpolyethylene I mentioned in Section2,how he made thediscovery. Hisreplywas in ef fiect the fo11owing . In1949,when he was new at Atomic

Energy Research Establishment at Harwe11,his assignment was to study eff el cts ofradiation on major materials used in nuclear reactors,especia11y,structura11yimportant
metals.Earlier studies had shown that metals are not highly sensitive to radiation,but his

task was to determine the extent ofradiation effects. quantitatively. For months he tried tomeasure changes in properties such as electricalconductivity,heat conductivity,andelastic modulus,but in vain.The changes resultingfrom a moderate period ofirradiation in

a Harwe11 reactor were sominute that measuring devices conventionalat that time gave no

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reliable results;thus,hefelt that the task was both boring andfrustrating.Then,on a walkin the city ofOxford,near Harwe11, a n idea struckhim;he saw cheap wristwatches on sale

at a store and bought many ofthem. The wristwatches then,unlike electronic ones today,
ran with the unwinding ofsteelsprings. He wound a 11 ofthe watchesfu11y,set them at thecorrect time,and put them in the Harwe11reactor. He took them out successively after?区ed periods oftime,and read the time; he found changes ofthe time readings,

appreciable enough to be observed at good precision and also closelyproportionalto theperiod ofirradiation.He was able to convertthe observed results to changes in elastic
modulus and other mechanicalproperties ofsteel, and he managed to write a report . This

anecdote shows his masteryofexpermentalphysics in perceiving a huge enhancement of
the sensitivity ofmeasurements by the use ofwristwatches.

This experience drove Charlesby to1ook for a materialthat would show ef liects ofradiation more easily. Havingirradiated manykinds ofmaterials at hand,he was fortunate
to hit upon polyethylene,that is,a novelmaterialat that time.
7 . Measurement of radiation
In te11ing the story ofwristwatchirradiation by Charlesby(Section6),I mentioned anefliect(changes ofthe time reading)occurring in proportion to the time ofirradiation.Let
us consider this point at some depth.For simplicity,1et us assume that the power o f areactor stays the same . This means that the energyproduced per unit time intervalis-

constant,as is the number ofnuclear fission processes per unit time intervaland also thenumber of secondary charged particles produced per unit time interva1.We are tempted to

say that a wristwatch in the reactor receives a constant amount ofradiation per unit tme
interva1. What does the amount ofradiation mean?The wristwatch in the reactor isbombarded byparticles ofdifferent kinds and diff 1erent kinetic energies.We may choose toobserve some quantity as an indicator ofradiation action on matter. Which quantity is themost suitable?Pioneers ofradiation science a century ago stumbled over thisproblem.

We now use as an index the energy ofradiation absorbed by matter ofunit mass,ca11ed

absorbed d ose. The unit of thisquantity is the gray or joule/ki1ogram. With abbreviations,w e w r i t e l G y = 1 J/kg. We apply the idea ofabsorbed dose to anykind ofradiation andto any kind ofmatter. This notion certainly reflects some empiricalknowledge. According

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to measurements,cross 1inks in polyethylene,atomic displacements in a metal, charge

carriers in a semiconductor,and ions in a gas are a11 produced in numbers c1osely

proportionalto the absorbed dose,under certain conditions. It is not simple to describe theconditions completely,but they always include an upperlimit for the absorbed dose andhence for the number ofproduct species. Typica11y,the number ofproduct species departs
from the proportionalityto the absorbed dose when the latterisveryhigh.
Can w e derivefrom theorythe proportionality of the number ofproduct species to theabsorbed dose?I have tried to solve this question.However,my answer is not verysimple,
and it certainly is too technicalto explain here[14]. A11 I can say here is that the

proportionality is only approximate and is subject to severalrather restrictive assumptions
about microscopic processes involved. Consequently,we see that the use ofthe absorbed

dose is not unequivoca11y dictated by science but is in essence a stipulation adopted forconvenience.

Despite the above qualification,experimentaland theoreticalstudies on the absorption
ofradiation energy by matter form a branch ofradiation science called dosime lry,which isimportant in manypracticalcontexts in medicine,industry,andlaw,and thereforeis

pursued by manyworkers. Current studies in dosimetry concem ever more kinds o favailable radiation and also quantities far more detailed than the absorbed dose[14] .

The goa1ofthe InternationalCommission on Radiation Units and Measurements(ICRU)is to provide,starting with the absorbed dose,intemationalstandards conceming

quantities related to radiation,techniques for their measurement and calculation,datanecessary fio r suchtasks,reporting ofresults,and applications to medicine,industry,and
research in other fields. The ICRU was formed in1925to address needs ofmedica1
radio1ogists. I have been a member since1985.The mainjob ofthe ICRU is to selectfrom
the broad topicalarea ofradiation measurements a timely theme suitable for a report,to?ind standards ofknowledge and judgment reflecting an intemationalconsensus,and to

publish a report describing the standards. For this purpose,scientists best qualified toprepare a manuscript are appointed to fio rm a reportcommittee . Afier work for severa1
years,the report committee submits a manuscript to the Commission.Most often the

manuscript is revised after the Commission's deliberations and is eventua11y adopted for
issue as a report . So far71reports have been produced and made available to the public .

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Since2001 I have been serving as the Scientific Editor,and have worked on the fina1-stages for Report Nos. 65 71 . For afu11account ofthe ICRU activities,I recommend the
web site atwwwicru.org,which includes an electronic joumalentitled ICRU N ews .
8.Bio1ogicaleffects of radiation
Fol1owing up Secti o n 5 , I now brieflydiscuss bio1ogy. The ce11ofso ft tissue consists ofmany kinds ofmolecules and has ahierarchicalstructure ofmanylevels.According tomost experts,bio1ogicaleffects stem fro m changes in molecular bonds and structure inDNA(deoxyribonucleic acid)in the ce11 nucleus,1eading to perturbations ofnorma1
加ctions. Bio1ogicaleffects include the ce11death,mutation or transformation ofgenes,,

and malfunctions or diseases oforgans.Carcinogenesis,the most notable ofthe eff el cts,is
attributable to a 1lia ilure ofhealthy ce11replication and programmed ce11 death(technica11y

ca11ed apoptosis). However,the ce11 contains many components other than DNA such as
histones,other proteins,and molecules forming ce11 membranes. Radiation must cause agreat dea1ofphysicaland chemicalchangeinthose components;consequences ofthesechanges remain little studied,as far as I know .

-]ln contrast,radiation induced changes in DNA have been studied extensively.

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Molecules o f D N A in a ce11are present as the we11 known double helix structure,which isd ifferent fi・ommany synthetic polymers. Thus,scientists working on this topic distinguish--between single strandbreaks and double strand breaks and te11 us that thelatter kind ofbreaks shouldlead to more severe consequences than the former kind . It has been also

we11 established that a majority ofthe breaks or damages of DNA are detected by enzymes
andimmunityagents and are repaired;no similarprovision is present in inani mate matter.
如other remarkable aspect is that the amount o f a bio1ogicalefliect is usua11y notproportionalto the absorbed dose,even when the absorbed doseissma11. 〇ften theamount o f a n effect appears to consist o f t w o parts,one ofwhich is proportionalto theabsorbed dose and the other to the square ofthe absorbed dose. What does this mean?
First,one reason for the departure ofthe amount of some eff el ctfromproportionality is-

physicaland is related to the non uniformity ofenergy absorption over a scale(about amicrometer orless)that happens to be comparable to the scale ofmicroscopic structuresofconstituents ofthe ce11. Second,a bio1ogicalef flect w e observeisoften not a response

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o f a single molecule or even a single cell,but is a coordinated response of a system of ce11s,

as has recently been recognized increasingly clearly[15] .
Even the first(that is,physica1)reason a1one points to notable consequences.0ne isthat the amount o f a n effect for a given absorbed dose depends on kinds and kinetic

energies ofparticles ofradiation,because w e k n o w f i・o m physics that the spatia1
distribution ofenergy absorption in matter is different for diflierent kinds and kinetic

energies ofparticles. Another consequence is that the relation between the absorbed doseand its effect depends on how the intensity ofradiation varies with time .

To ki11halfofthe ce11s in a specific culturemight require an absorbed dose o f 2.0 Gywhen we use x rays,but only 0 . 8 G y when we use neutrons. It is customary to consider xrays as standard and to express the above fiinding by saying that the relatlve bio1ogica1?ectiveness for neutrons is2.0/0. 8 = 2. 5.
In medicine andlegalregulations,one uses operationalquantities ca11ed alose eq,ulva lentor equlva lent d ose,that is,the product ofthe absorbed dose and a modifying factor . The
value ofthis dimensionless modifying factor is determined through analysis ofdata startingwith the relative bio1ogicalef flectiveness and the kind andkinetic energy of everyparticle

making up the radiation under consideration. The unit for the operationalquantities can be
J/kg,but a specialname sievert(abbreviated as Sv)is recommended to emphasize thedistinctionfrom gray. Thelimit ofexposure o f a person ofthe generalpopulation i s l m S v/ y. Thelimit ofexposure o f a radiation worker is20 mSv/y,on the average,over five

years.
Examples of somelarger values are as fo11ows. A member o f a crew on an internationa1

space station norma 1lyreceives aboutlmSv/d,chie1aydue to energetic protons firom theSun and cosmic rays. Alarge exp1osion on the sur face ofthe Sun,ca1led a solarflare,,

increases the exposure by nearly a factor o f 10 . A standard goalfor ki11ing cancer ce11s intherapy is60 Sv.Exposure of 100 Sv over the whole body is fata1. (Note that therma1energy o f 100 .f/kg delivered to a human body wi11 raise the temperature by 0 .024°C
only. )
Itisimportant to set standards for exposures ofhumans and the environment.
Considerations necessary for thispurpose,ca11ed radiationprotect1o n,extend fa r beyond-

naturalscience and include elements ofeconomics,1aw,and decision making strategy.

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2005 -001〇ne issue often discussed in this co nnectioniswhether the risk of an adverse eff el ct

increases in proportion to the absorbed dose when it is verysmal1or whether it isnegligible up to some value(ca11ed a threshold)ofthe absorbed dose. Questions ofthis
kind are difficult to answer when consideredfrom the point ofview ofpure science;-indeed,they are not precise enough to permit a clear cut scientific answer. Ananswer to aquestion ofthis kind cannot be inconsiste1nt with the scientific knowledge withinits current
1imitations,but usua11y involves a decision or a policy related to the management in a

broad sense.
The IntemationalCommission on Radio1ogicalProtection(ICRP)isresponsible for

issuing recommendations related to radiationprotection.The ICRPand the ICRU

maintain cooperative relations;often the ICRPraises issues to be considered,and the
ICRU provides a scientific basis for considerations necessary to resolve the issues.
9 . Role of physics in radiation research and applications-

The greatest contribution to human wel1 being among applications ofradiation is-

medicaldiagnosis byx rays. Initiated by Rontgen over a century ago,x ray medica1
imaging has now deve1opedinto the computerized tomography(CT),which represents afeat inimaging techno1ogy. It is often said that the CT machine has saved more human
1ives than any other machine. Theimaging techno1ogy with ionizing radiation or with other-agents(such as ultrasonic or1ow frequency electromagnetic waves)has many applications

also in materials science,mechanicaland structuralengineering,geosciences,astronomy,,

and military technology.
In connection with diagnosis,Ilke to point out a wonderfuladvance I witnessed. The

largest contributor to the totalexposure ofthe generalpublic in the1960s was x rays used
for medicaldiagnosis. Now thelargest contributor is naturalradioactivity. Anappreciablereduction in human exposure was achieved byimprovements in machines and detectors
such as photographic films.
A reason for the success oftheimaging by radiation is that this technology is based on?mknowledge oflargely established physics. To clarifythe foregoing statement and toshow the role ofphysics,1et me present a genera1observation. I find it appropriate to-separate radiation physics problems into two classes.Problems ofClass I concem the fate-

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o f radiation after interaction with matter.Problems of Class I I concem thefate of matter

after interaction with radiation. A typicalproblem ofClass I is the degree ofattenuation of-high energyphotons(that is,x raysorγrays)penetrating matter and its dependence on
the particular kind ofmatter.Unless the photon energy is extremely1ow or high,andunless the atomic number ofthe matter is veryhigh,wehave reliable answers to thisproblem fro m theoryand experment,which serve as a basis for theimaging techno1ogy.
Problems ofClass I are easy to study expermenta11y,because one needs merelyto analyze
radiation after transmission through matter . Indeed,most ofthe problems ofClass I havebeen solved in principle,apartfrom exceptionalcases. (Anexample is when numerica1

results ofextremely high precision are requiredAnother is when matter is highly

momogeneous.)
知yproblem ofClass I I is difficult to study,because a complete solution would requirein principle analysisofa11 the major product species present inirradiated matter.

Techniques available to us now do not meet this requirement. In other words,any
hadiated matter represents a new materialin the sense that we do not know a11 thecomponent species,and a complete solution would meanfu]1 characterization of a11 these

species. In addition,anyirradiated matter is not in thermalequilibrium,and therefore its
properties should be varying with time.Consequently,no complete solution o f a Class I I
problem has been obtained,,-

I have persona11y devoted severalyears to a simple 1ooking problem:to characterizetheoretically a11the major pathwaysby which radiation energy is absorbed by pureh;ydrogen gas and to evaluate the probability o f eachpathway. The solution I obtained-with the help ofseveralco workers tumed out to be usefulf ol r some astronomers,because

pure hydrogen gas serves as a basis for some considerations about coolregions ofinterste11ar c1ouds and about the atmosphere ofJupiter.
知other Class I I problem is old,we11known,and much more complicated . This is to

ask in eff el ct what happens in a Geiger counter . It contains a gas and a pair ofelectrodes,,

and the passage o f a n ionizing particle causes aminute discharge that is amplified into a、current that is measurable extemally.According to empiricalwork,it is good to use a gas-

mainly made ofargon,with a sma11amount o f a n alcoho. ,an ether,or a ha1ogencontaining molecule. I cannot explain why and how this gas compositionisoptima1.

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Fina11y,I wish to add an observation about the role of physics in radiation research. It isclearfrom an analysis[14]that contributions ofphysics have been substantialand decisivein the deve1opment ofinstrumentation in a broad sense,including radiation sources,,

dosimetry,and methods for detecting and analyzing some particular kinds ofproductspecies. However,contributions ofphysics to the elucidation ofmechanisms ofradiation
action on matter rerriainlimited and tentative.This trend islikely to continue.
10. Epiiogue

I hope that the foregoing discussion conveys a sense ofthe research I have been

participating in. Limitations o f m y ability and a11otted space prevented me fir omtreating abroader range ofrelated topics.Some ofthem concem radiation and radioactivity as

ubiquitous components ofthe environment and ofthe universe,as exce11ently surveyed by

Draganic,Dragani0,and Ad1off [16].〇ther topics are related to nuclear power andnuclear weapons. A recent book by Garwin and Charpak[17]presents a masterly survey

ofthe topics.

Acknowledgments
I owe deep gratitude to manyfriends who taught me much over years in which I formed

ideas described in the present article. I thankPaulA.Benioff,Ilya A. Shkrob,andAndre

Wambersie in particular for valuable comments on an earlier manuscript.

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Cambridge,U. K.,1989.
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16. I. G. Draganic, Z. D. Draganic,and J . P . Ad1off Radiat1o n andRadioactivityonEartha n d Beyond, Seco n d Ediao n, C R C Press,Boca Raton,F1orida,1993.
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