radiation resistivity of pure silica core image guides for...

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TitleRadiation Resistivity of Pure Silica Core Image Guides for Industrial Fib

erscopes

Author(s)Okamoto, Shinichi; Onishi, Tokuhiro; Kanazawa, Tamotsu; Tsuji, Yukio

; Hayami, Hiroyuki; Ishitani, Tadayoshi; Akutsu, Takeji; Suzuki, Koichi

Editor(s)

CitationBulletin of University of Osaka Prefecture. Series A, Engineering and nat

ural sciences. 1991, 40(1), p.183-202

Issue Date 1991-10-30

URL http://hdl.handle.net/10466/8540

Rights

183

Radiation Resistivity of Pure Silica Core

Image Guides for Industrial fiberscopes

Shinichi OKAMoTo', Tokuhiro OHNisHi', Tamotsu KANAzAwA', YUkio

Hiroyuki HAyAMI"", Tadayoshi IsHITANI"", Takeji AKuTsu"

and Koichi SuzuKI'"

TsuJII*

(Receiced June 15, 1991)

Industrial fiberscopes incorporating pure silica core image guides have been

extensively used for remote visual inspection in radiation fields includingnuclear power plants, bwing to their superior radiation resistivity. Theauthors have been intensively conducting R&D on improving radiation resis-tivity of pure silica core image guides. This paper reports the results of･experiments to compare the effects of core materials on radiation resistivityand to investigate the dependence of radiation resistivity on total dose, does

rate, and support pipe material. The results confirmed the superior radiationresistivity of the core material containing fluorine at any irradiation condition

and indicated the existence of a critical dose rate at which radiation-induceddeterioration was stabilized. No difference in radiation resistivity attributable

to support layer material was observed.

1. Introduction

Industrial fiberscopes incorporating a pure silica core image guide, which is a

coherent multiple optical glass fiber bundle with high purity silica glass core, have

been widely used for remote visual inspection in various fields. Above all, superior

radiation resistivity and color fidelity of high purity silica glass have extended the

use of fiberscopes as "the eyes seeing the invisible" in nuclear environments, where

the inspection using the conventional image guides made of multi-component glass

is impossible. With the extensive use for remote monitoring of nuclear instal!ations,

the demands for the image guides for use in severer nuclear environments have been

increasing.

As a result of our R&D on the improvement in radiation resistivity of image

guides'}, we have already revealed that the image guides with three-layer structure

of core, cladding and support layer, and OH-free, CI-free and F-containing silica core

have the best radiation resistivity.2}'3} In this paper, we report the effects of core

material and the dependence on total dose, dose rate, and support layer material of

image guides under gamma-ray irradiation.

*

**

Research Center of Radiation, Research Institute for Advanced Science and Technology.

Mitsubishi Cable Industries, Ltd.

184Shinich OKAMOTO', Tokuhiro OHNISHI', Tamotsu KANAZAWA', Yukio TSUJII', Hiroyuki HAYAMI", Tadayoshi ISHITANI",

Takeji AKUTSU" and Koichi SUZUKI"

2. Experiments

2. 1 Comparisen of core materials

Irradiation using 60Co as the irradiation source was carried out continuously.

Table 1 lists the image guide core copmositions subjected to the irradiation tests.

The image guides were composesd of multiple fibers in which each pixel with high

purity silica glass core is coherently aligned and fused. Our previous work has

already found that F is superior to OH in suppressing gamma-ray-induced degrada-

tion in high purity silica in visible wavelength region.2-`) In this experiment, we

compared radiation resistivity of various core materials in detail, under different

total doses and dose rates based on the previous experimental results. We also

investigated the effects of compositions of support layer on radiation resistivity.

Table 1. Image guide samples,for irradiation tests

Preforn matevial Preform Nutberof

Corematerial Supportpipematerial structure pictur'e

Symbols Clcontent OHcantent Fcontent Spt)ols Clcontent oncontent elenents(ppm) .Cppm) (ppm) (ppm) Cppm)

A FT,ee Fme 3.500 x 4,OOO Free

Y 190 540

B Fpee Free 4,500 x 4,OOO Free lhree

3,OOO

c Free 750 Free x 4,OOO Free -la)rer

Y 190 540

D 1,700 30 Free x 4.000 Free

E Free 1･OO 1.seo x 4.000 Fr'ee

3. Results

3. 1 Comparison of core materials Figures 1 to 4 plot the spectral loss characteristics of image guides with differbnt

core materials under gamma-ray irradiation at 2×10`, 2× 105, 5×105, and 1×106 R/h (irradiation time was 50, 50, 20,and 25 hours, respectively). Core materials A and

B show superior resistivity particularly in visible wavelengths. Core material E,

which has lower resistivity than core materials A and B, shows the behavior peculiar

to both F and OH. As its OH content is as low as 100 ppm, its characteristics are

rather similar to those of core materials A and B than those of core material C,

which contains OH only. The difference in resistivity between core materials C and

D shows a turning point at around 57e nm; below this point, core material C has

better resistivity, and above this point alternatively, core material D is better. This

turning point shifts to longer region gradually as the dose rate becomes higher.

While core material D shows far higher radiation-induced loss in the region from 400

185

Radiation Resistivily of Reere Silica Core Image Guides for Industn'al rvberscqPes

to 500 nm, core material C is better than core material D in whole visible region. The

influence of OH in the core materials is clearly observed in the loss characteristics

at around 480 and 600 nm. Core material C, containing 750 ppm of OH, shows two

absorption peaks there. Core material E containing 100 ppm of OH, has a peak at 480

nm,but its'peak at 600 nm is obscure. Though it has been already reported that the

absorption at 600 nm depends on OH content,5) the absoption peak at 480 nm has not

been reported yet, even in our test results of OH containing single optical fibers. We

assume therefor that this peak is peculiar to image guides and is caused by the

combination of the presence of OH and the manufacturing process of image guides.

1.0

Ediyco-co

.88g o.s

-

o

tt:" /

:':･,Y'/

:':,:]Ns

: : : : x lt li tl . ,

A

l l

tI

t/ t/t

/

t/ t/t

×-/

,,ss..

B

...

/x

. ---..

E

..

'1kliA

"

"

"

v"! t, x

! st N

lk l tll

! SN

! N,

'･A tl s "As

,,× -1 , . .

N

.

N

Core･materlal @@@@@Supportplpematerial @

Doserate 2xio`Rth

Totaldose(lrradiatedtime)

1xtoeR

(50h)

lrradiatedlength 10m

/ y

-- N N

s

.

× - ----p- -

D

......

c

..-----

l- -'N

/N N N N N x N N

-- X,. NN

/ XXgx, Nx

..... xX, × """･. N Nx """"'X.

.

N

s.

Wavelength (nm)Fig. 1 Core material dependence of in-situ radiation-induced losses

(at 2×10` Rlh and 50-hour irradiations).

700

186

Ern･-･-

yco

mo-voo=vc-

4.0

3.0

2.0

1.0

o

Shinich OKAMOTO', Tokuhiro OHNISHI', Tamotsu KANAZAWA', Yukio TSUJII', Hiroyuki HAYAMI", Tadayoshi ISHITANI",

Takeji AKUTSU" and Koichi SUZUKI'･

t,

! / t t t t l t t t 1 t l t ' ' '

Nl Nl N/1 --

,: / wh / vt ,.,.,,, "" -i ts , , . . . -- ------

A

- XN 1

tAs

B

. --.

SsNXNA:N" l,N

li X

lt

N 1

.

N,

,l

t `

, t

t

t

,

s

l

.x'･･,N

-sss:

E

s

s

N

N

..

N

N

N

Corematerial @@@@@Supportplpematerial (*)

Doserate52xlORIh

Totaldose

(lrradiatedtlme)

7lxlOR(50h)

lrradiatedlength 5m

N

N- N /- NN /iNc

.

Nxx×

't"-.--'x-- --- . ------------

--- .

s

.

D c

N

N N N N N N N N N

XNx. ×X Xs"----- - × -- s . -- .

x

"Ng

400 500 600 700

Wavelength (nm)

Fig. 2 Core material dependence of in-situ radiation-induced losses

(at 2×105 Rlh and 50-hour irradiations).

Ern････--

vvcoco

o-v¢o sv=-

RadlatiOn Resistivity of Pbere Silica Cbre imcrge Guidds fo r indtastn'al FVberscopes

187

4.0

3.0

2.0

i.o

o

,/

l/

ll

lf

I

il

/

/

×/

･IN -/,.i sX" /

"Is"

""ss

Itsss

s---

A

"

N

N

N

N

, .l

1 s 1 ! l t t 1 1

/.-Ns

--------

B

--s

N

N

x

x

x

,

xN

lt

xX iS!x ! NN

! Ns

-" "s Xs

"sss s

----

E

N

N

N

N

×.-

Corematerial @@@@@Supportptpematerial (g)

Doserate 5xlOSRIh

Totaldose

(lrradlatedtlme}

lxlo7R

(20h)

lrradiatedlength 5m

D

N

N

.K" ny'

c

×--/-. --- ----- ------

. ----

N Nx

xX X Ns

sxXNN

...s>t5>'"

'･.. N -'."s

400

Fig. 3

500 600 Wavelength (nm)

Core material dependence of in-situ radiation-induced losse$

(at 5×le5 Rlh and 20-hour irradiations).

700

188

E.N

y8-o

voro=vc-

4.0

3.0

2.0

1.0

o

Shinich OKAMOTO', Tokuhiro OHNISHI', Tamotsu KANAZAWA', Yukio TSUJII', Hiroyuki HAYAMI"', Tadayoshi ISHITANI",


N

'N sx

,

'vt

,,....

A

'

--

/'

/

s

i

t

l

1

1

l , 1 l i t , s t 1 s t l

,!.X

--------

B

'N xx

N

'N

.

. s"sls"

E

...

,

t

N

1

s

t

N

×

..,

.

N

s

.

N

N

N

N.t

N

N

-

N

z

Corematerial @@@@@Supportpipematerial oo

Doserate6lxtORIh

totaldose

{lrradiatedtime)

2.sxlo7R

(25h}

lrradiatedlength 5m

N

/

N

!/

N tN/4x N

N

N

x

-As---Z ×

-- -- --- --- --- ------- -- . .

D

N

X NN

NNs

NX

.

s

.

c

NSs

Xsx"K

. ...

sxNX ×

"ts

N.... k. . '.. N -- ----

Wavelength (nm)

Fig. 4 Core material dependence of in-situ radiation-induced losses

(at 1×10` Rlh and 25-hour irradiations).

189

Radiation Resistivily of Pbere Silica Core image Gttides for industrial IVberscopes

3. 2 Dependence on total dose

Figures 5 to 9 show the spectral loss characteristics of image guides under

different total doses of gamma-ray irradiation. The dose rate was 2×10` Rlh.Irradiation time was 5, 20, 25, and 50 hours respectively. While the losses of F-free

core materials C and D increase in proportion to total dose, F-containing core

materials show lower losses in 20-, 25-, and 50-hour irradiation tests than in 5-hour

irradiation. Especially, the loss increase curves are flattened at the wavelengths

ionger than 500 nm. This behaviour is more obvious in QH-free core material A than

OH-containing core material E.

'i:i'

`Nr,,ecaco

o-voo=vc-

1.0

O.5

o

lI

N1

N ,N

,s

lN

1SN l

,,X N

:A N tNx.,N X.

"･,N × ssls- × ×

･× .... N-, ----- ----

s

× s

:.--`

-- -- .

N s

Corematerlat @Supportpipematerial oo

Doserate 2xlo4Rth

Totaldose

(lrradiatedtime}

lxlOSR(5h)

4xldSR(20h)

sxlo5R(25h>

1×10SR(50h),

Irradiatedlength 1Om

N,SN<.

txatfR 5 h

4xlcS5R 2o h

sxl d5R 25 h

lxl dSR so h

.'･..........t.-!A"x

".-. ･･･････--･･-:---ti:------

---- ----400

Fig. 5

500 600 Wavelength (nm)Total dose dependence of in-situ radiation-induced losses

(for core material A).

700

190

1,O

Ediyen-m-.

8g2 o.s

-

o



x

xxxxx

" 'N

X)t 'N

",,,N Sx

'x,,N

,.,.">

"s --

Corematerial @Supportpipematerial oo

Doserate 2xlo`Rth

Totalqose

{lrradiatedtime)

lxlOSR(5h)

4xio5R(2oh}

sxtcS5R(25h)

lxlOSR(50h)

lrradiatedtength 1Om

s

× s

s

lxl o5R s h

4xi o5R (2o h

sxl o5R (2s h

1×1 o6R(so h )

"" "t/:>'･x'

N,

...£ss Ns

× ss . k.N ････× ----

.

-- ----- ---------× ----

Ng- x s""'--b

N--------- x.･::-:･

---400 500 600 700

Fig. 6

Wavelength (nm)

L,Total dose dependence of in-situ radiation-induced losses

(for core rnaterial B).

191

Radintion Resistivity of Pbere Silica Cbre imtrge Guidbs for indtcstrial jFVberscopes

1.0

ecx,,,gco-co

-.

8g2 o.s

-

o

lt

lt

N tx

N

N

:N

:Itt-sl

sll

; /

!

//

//

! /":'

s/ /l/!yi'

v ls` /:':

/:i

:N,. / i'

: : tl ,-s--tt

/

･l--

'

l

!

N!

･"x:, i!

:"!

:･:"

i:"

:･:"

,wt

'i"

tl 'i"

-t :It

tl-t

IIII

: :i,X

tls"--

Corematerial @Supportpipemateriat

([2ii)

Doserate 2xi'o`Rm

Totaldose

(lrradiatedtime)

ixleSR{5h}

4xlO'R(20h}

5xlOSR(25h)

lxsoeR(soh)

Irradiatedlength 1Om

1.teR 5h

-/

'

/'

7'

4xldSR 20 h

sxlcti5R 2sh

1×1(SSR 50h

7-

/

/ ---- / -t--v ....-----t

-N

---- .

"Ns

Ns N,

xx"sN "'･Nx

'･･･NN

As

-l -1

lss

)(NiNs '･N

. . .g400

Fig. 7


Total dose dependence of in-situ radiation-induced losses

(for core material C).

700

192

E.x

ycoco

o-vmo=v=-

1.0

O.5

o



,N

:･,N:･,N

:i:N

tle"l

,t

N1

N t

N:･,Nx,:, :

Nl

N 1N

tNx,N

"

Nt

N sN s N

Corematerial @Supportpipematerial (g)'

Doserate 2×lo4Rth,

Totaldose

(lrradiatedtime)

lxlOSR{5h)

4xlo5R(2oh)

5xlOSR(25h)

lxlO"R(50h}

lrradiatedtength. 1Om

lxlo5R s h)

4xl d5R 2o h

"" ts t"

tts x,>< N

-s '" x ls '･･N N

ss '･･5

'･･5

...l)>

sxl o5R (2s h}

1xl (SSR (50 h )

X, Ns

×"5 Sx. ,." X Ss . ･× '..,,g S ･"...･ ---

-vt.t400 500 600

Wavelength (nm)

700

Fig. 8 Total dose dependence of in-situ radiation-induced losses

(for core material D).

etNt,,vv

coth

o-voo=vc-

Radiation Resistivity of Pbere Silica Core imcrge Gteides for indttstrial FVberscopes

193

1.0

O.5

o

x

iN,Nx

"s,x

:･,x

ltil,Nltllltlls

'

,/'N / 'N

/i×.1 i t thX 1

/ Ni 1,× 71,...L.." l

e" ts-t '----d

.

tt :

:

::

Corematerial @Supportpipematerial

(Ei})

Doserate 2xlo`Rth

Totaldose

(lrradiatedtime)

1×lo5R(sh}

4xio5R(2oh)

sxtd5R(2sh)

lxleSR(50h)

trradiatedlength 1Om

1×lo5R s h

4×1 OSR 20 h

sxlo5R 25h

lxlOeR(50 h

:t,sN

:,,N '

N

A,xX×"'/

....× ti N- .--

-s

5---------e-------------

XN Xs>N X .s --s ...::Ns

-- s･:NXN.y

" >)r

400

Fig. 9


Total dose dependence of in-situ radiation-induced losses

(for core material E).

700

194Shinich OKAMOTO', Tokuhiro OHNISHI', Tamobsu KANAZAWA',

.Yukio TSUJII', Hiroyuki HAYAMI", Tadayoshi ISHITANI",

Takeji AKUTSU"'and Koichi SUZUKI"

3. 3 Dependence on dose rate

Figures 10 to 14 show the loss increase characteristics of the image guides

irradiated at 2×10`, 2×105, and 1×106 R/h, respectively. Only Fig. 10, where the

results of core material A are shown, uses the longitudinal scale which doubled the

scales of other graphs so that the loss characteristics are more clearly observed. It

is apparent in these figures that radiation-induced loss of the image guides core

materials C and D increases in proportion to the dose rate even under the same total

does of 1×106 R/h. In particular, image guide core material D, which contains 1700

ppm of Cl, exhibits this behavior more clearly. Image guides core materials A, B and

E, containing F, show smaller loss increase at 2× 10` R/h, but noticeable differenceis not observed at higher dose rates under the same total dose. '

: s

,

1.0

Edivv

co

8

8g2 o,s

-

o

lstsSl l! sN"

XXN s""

N".,,N

N",. N

N<..,,

N".

N

Corematertat @Suppertptpematerial oo

Doserate

(lrradlatedtime)

2xlo`Fvh(soh)2xlOSM(Sh)5xlofRth(2h)sxlo`Rth{ih)

Toleldose lxlofR

irrsdiatedtength 10m,5m

x ×---- ×Nk. N "'N"･;:ll:",,X

N"･N ' N".,×

"× N<･... X

N '.. .× N". N-:i---- N<

-t-e------t--

------

Dose rete

2x!ofRth

2xt OSM

5xlOSRth

txidRni

×'N"'..X

N<･･.N

N ･.. × ×,l'....r:,.:.. ....

N ---- N. × '-' -hN------.-. - -

400

Fig. Ie

soe ' 6oo Wavelength (nm)Dose rate dependence of in-situ radiation-induced losses


700

E.x

ecoco

o-voO=v=-

Radlatibn Resistivity of Pbere Silica Cbre imtrge Guidbs for industn'al jFVberscqPes

195

2.0

1.0

o

1-l

ves

Nlirtststs,

N;L':::r.

×.EEtr..

N"×.;s),

tpt

NX N "N.

N

Corematerial @Supportpipematerial o

oDoserate

(lrradiatedtime}

2xlo`Rlh(soh)2xlOSFUh(5h)5xlOSRM{2h)1×10SRth{1h)

Totaldose 1xlCfR

lrradiatedlength10m,5m

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

--- - --- e-- ---

sc>">.-･-.･

N- .d-

Dose rate

2xl ofRth

2xteM

5xteFVh

1xlofRlh

$s<<..

･esl.:""'

N -----

------

N" '.h".b,

400

Fig. rl

500 - 600 Wavelength (nm)

Dose rate dependence of in-situ radiation-induced losses

(for core material B).

700

.

.

196

gtN,,,vv

coco

o-v¢o=v=-

2.0

1.0

o

Shinich OKAMOTO', Tokuhiro OHNISHI', Tamobsu KANAZAWA', Yukio TSUJII', Hiroyuki HAYAMI", Tadayoshi ISHITANI",


:

:-l:"x,,, ,"･

:ttt

:lt

i/ itt

i: //

i lt/

i:"

""

/fv

/

""

"x

-. :,,,

N",

NNs:'`

Nl":

xx"i

"'i

" t'i'

l'ii

ii

:t---

l-t"

"NL "-ii" e

v･･････"

N,",./

Corematerial @Supportpipematerial (*)

Doserate

{lrradiatedtlme)

2xlo4Rm(soh)2xlOSRIh(5h)sxto'Rth(2h)lxlOeRM(1h)

Totaldose 1xlofR

lrradiatedlength 10m,5m

Dose rate

----e

Xv

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

------

-- i- - ttt-ett

2xl O`M

2xlOSRth

5xlOSRM

ixtohth

.

s--ss

"--"

･e"xN "'

x'･･,

N'･･,

N"･･.

K･･.

Nti;:..

. N.rN;:･･

×.

400 500 600 700

Wavelength (nm)

Fig. 12 Dose rate dependence of in-situ radiation-induced losses


Ediycoto

o-voo=v=-

Radiation Resistivity of Pbere Silica Co,e imtrge Guides for indt`stn'al FVberscopes

197

2.0

1.0

o

N:

x, NN :N 'x N Nt XN x,' N N xN x,, NN X

'x., X Xt

', N ･･, , N '. N ･, N N '., N 'v N N ', N ･., N N ', N N ', N '.. N ', N ', N ',, N '.. N .,, N iss tss

Ceremateriai @Supportpipematetial oo

Doserate

(lrradiatedtime}

2xlo`Rth(soh)2xlOSFVh(5h)sxlo5Rth(2h)lxlO"RIh(1h)

Totaldose lxlo6R


.s.

------------t

--- --- ---- -

X

N

ss

N

N

NN

N

IN l" "s

s-

x

ss

Dose rate

2xt(S`Rth

2xteRth

5xlrfFUh

1×leRth

xN

×

nN "s N .... N

ss

x

.N

--

× NN N. ---- -- --

400

Fig. 13


Dose rate dependence of in-situ radiation-induced losses

(for core material D).

700

198

2.0

Ec")""c}vvco-co

.8ge i.o

-

o

Shinich OKAMOTO', Tokuhiro OHNISHI', Tamotsu KANAZAWA',

Yukio TSUJII', Hiroyuki HAYAMI", Tadayoshi ISHITANI",

Takeji AKUTSU" and Koichi SUZUKI."

N

""ts ',N N.

'..N .f.

---

td----s ." c".:`- N

Corematerial @Supportpipematerial o

oDoserata

(lrradiatedtime)

2xlo`Rth(soh)2xlOSRth(5h)5xlOSRM(2h)lxleeR/h(1h)

Totaldose lxlo6R


-------------,

l"te - - - - - -" v,, MK

"b

'>xN' N

'"?.N ×z-N ･-N<･.･･..pf"".･>1s.sx

'･5

Dose rate

2xi o`Rm

2xlo5Rth

5xl OSRIh

lxlOeRIh

･5X '""s × "S N.. 'N - "e:.-- --

400 500

Wavelength

600

(nm)

700

Fig. 14 Dose rate dependence of in-situ radiation-induced losses

(for core material E>.

199

Radiation Resistivity of Rtre Silica Core Image Guides for industn'al jFliberscopes

3. 4 Dependence on support layer material

Figures 15 to 16 plot the loss increase characteristics of image guides to compare

the infuluence of OH content in support layer material. Core materials used for this

experiment were A and C. It is observed in Fig. 15 that the results on core material

A have little dependence on the support layer material. In Fig. 16, the results on core

material C have no substantial difference owing to support layer material, except

that the results on the support layer without OH are higher at the wavelengths

shorter than 500 nm.

;- : -:

E.x

gcoco

o-ny---

voo=vc-

2.0

1.0

o

:-si tl

l- lt

tl --

: II : It 11 11 -l l- Ie lt t- II ll･II lt l- -- "i tl lt II i-- -1- sl-

-I -l ls t s- d--- -i --- sl -l ll t- t- lt 1- -l tI tl lt lt sI sl . -t ----- l -- ･l -sl t- sl lt It ll : It II il

" t-

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400 500 , 600 Wavelength (nm)Fig. 15 Support layer dependence of in-s.itu radiation-induced losses


700

200

4.0

Ag 3.og'IK-m.8g2 2.ont

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o

Shinich OKAMOTO', Tokuhiro OHNISHI', Tamotsu KANAZAWA', Yukio TSUJII', Hiroyuki HAYAMI"', Tadayoshi ISHITANI",


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Fig. 16 Support layer dependence of in-situ radiation-induced losses


201

Radiation Resistivity of iFbure Silica Core Image Guides for Industn'al JFVberscqPes

4. Discussion

4. 1 Irradiatio,n time

The loss increases under 5 hours irradiation and more than twenty hours of

irradiation were compared. At a dose rate of 2× 10` R/h, the loss increase under 5

hours irradiation was higher than the results obtained in longer irradiation time in

wavelengths from 500 to 700 nm, as shown in Figs. 5, 6 and 9. At higher dose rates,

this behavior was not observed and the losses increased in proportion to the irradia-

tion time.

4.2 Dose rate Dependence on dose rate of loss increase the same total dose was considered. The

image guides containing F show the smallest loss increase at dose rate of 2× 10`R/h, as shown in Figs. 10, 11 and 14.

4.3 Discussion The results summarized in sections 4. 1 and,4. 2 suggest that the F-containing core

has a critical dose rate at which radiation-induced deterioration is stabilized when

the number of electrons produced by gamma-ray irradiation exceeds a certain value.

The results of these experiments indicate that the cr.itical dose rate exists in the

range from 2×10` to 2×105 R/h. We a'ssume that this is because the electronsliberated by gamma rays and the electrons re-attracted by F atoms in the core

material exist simultaneously and because, at a dose rate lower than said critical

value, the re-attracted electrons exist in such a relatively large number that they do

not promote radiation-induced deterioration.

5. Conclusion

We have investigated the effects of core material on radiation resisitivity of image

guides, by comparing four materials : F, OH, Cl+OH, and F+OH. The resultsrevealed that radiation resiStivity of these materials was in the order of, from the

best, F, F+OH, OH, and Cl+OH, at any irradiation condition. The superior resis-

tlvity of F-containing core image guides was reconfirmed. Influence of four levels of

dose rates on radiation-induced spectral loss increase was investigated under a total

dose of 1×106 R. As the result, loss increase in the image guide with F-containing

core was the smallest at the lowest dose of 2 × 10` R/h, and clear difference was not

found in the loss increase at the other three dose rates. This result indicates that a

critical dose rate at which radiation-induced deterioration in F-containing core is

stabilized exists in the range from 2×10` R/h to 2×105 R/h.

202

1)

2)

3)

4)

5)


Takaji AKUTSU'" and Koichi SUZUKI"

6. References

H. Hayami, T. Ishitani, O. Kishihara and K. Suzuki, Mitubishi Cable Industries Review, No. 76

(1988).

H. Hayami, T.Ishitani and K. Suzuki, Fall Meeting of the Atomic Energy Society of Japan, F

41, p. 287 (1989).

H. Hayami, M. Yamagishi, S. Ikebe and K. Suzuki, ENC'90 ENSIANS-Foratom Conference

Transactions, Volume llI 26121, 13, p. 1452 (1990).

T. Ohnishi, S. Okamoto, T. Kanazawa, Y. Tsujii, T. Ishitani, H. Hayami, T. Akutsu and K.

Suzuki, Bull. of Univ. Osaka Pref., 39, 245 (1990).

L N. Skuja, A. R. Silin and A. G. Boganov, J. Non-cryst. Solids, 63, p. 413 (1984).

radiation resistivity of pure silica core image guides for...

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