Formation of defects in vitreous Si02 under influence gamma-neutron (reactor) radiations

FORMATION OF DEFECTS IN VITREOUS S i0 2 UNDER INFLUENCE

GAMMA-NEUTRON (REACTOR) RADIATIONS

E.K. Mamedov

Azerbaijan National Academy of Science, Institute of Radiation Problems, AZ 1143

ABSTRACT

The vitreous dioxide of silicon (v-Si02) is one of irreplaceable materials of constructional optics and constantly is in the center of attention of researchers. Its unique properties - high temperature of fusion, chemical stability, low dielectric losses, etc., have led to to wide use in various industries. Special interest is represented its optical and paramagnetic properties, change of these properties at operation V-Sİ02 in fields of radiation, the nature and a structure of point defects.

1.INTRODUCTION

There are various types V-Sİ02 which are subdivided according to classification into 4 groups [1]. Glasses concerning to the 1 group contain of metal impurity in quantity, weight %; lxlCT2, OH<5 xlO 4 , to 2 group - lxlO "2,OH-1,5-4xl0"2, to 3 group <0.2xl(T2, OH-0,1; Cl - lxlO "2, to 4 group - <0.2x10" 4, OH<0,4 xlO"4, Cl ~2xl0~2 The basic sources of impurity - initial raw material and conditions at which synthesis of a glass is carried out. Initial raw material for synthesis V-Sİ02 can be a quartz powder, synthetic Sİ02, the gaseous product SİC14, etc. The technology of preparation of a glass includes; a) a source of heat - an electric furnace, a gas-flame way of heating, a hydrogen-oxygen torch, high-frequency heating, super high-frequency fusion, etc. b) an atmosphere of the furnace, c) the vessel in which is carried out synthesis of a glass, d) cleanliness of brought communications, etc. Choosing this or that way of synthesis receive V-Sİ02 with the various contents of impurity (table 1).

Table 1. The contents of impurity in various marks of V-Sİ02 (ppm) Number of group and mark of glass

Chemical element 1 2 3 4 Vitreosil I.R. Infrasil Vitreosil O.G. Spectrosil Coming 7940 Suprasil W A1 50-60 10-15 10 <0.02 2 0.1 Na 4 1 0.06 0.04 <5 0.04 Fe 0.74 0.8 0.51 <0.1 2 0.2 Ca 0.4 0.8-3 0.35 <0.1 1 0.1 B <0.5 0-0.1 <0.5 <0.01 <0.5 0-0.01 Sb 0.23 0.15 0.07 <0.0001 - 0.002 Mn 0.026 0.01 0.0017 <0.001 0.5 0-0.01 Cu 0.01 0.07 <0.0003 <0.0002 - 0.004 P 0.01 0.1 0.005 <0.0001 - 0.01-0,1 Total quantity of metal impurity 40-150 40-150 1-5 1-5

OH-cr

From the table follows that though total concentration of impurity in each separately taken group is approximately identical, the various quantity contents of impurity on each element takes place.

Despite of a wide choice of a V-Sİ02 their application in conditions of influence of radiation is limited. So for example, applying a glass optical fiber waveguides for the control of a radiating zone of a nuclear reactor they is exposed to an y,n-irradiation. In an waveguides with a core from v-Si02 (such as Coming) there are losses of probing light reaching up to -60 db/km and the can be applied at doses of an irradiation only up to

~103 rad. These restrictions on losses are connected to parameters of used devices of a source of probing light and the receiver of radiation [2]. All other types of V-Sİ02 also have the limited application on a dose of their irradiation in the radiating environment.

Losses of an information signal in waveguides it is caused by fundamental mechanisms of absorption and scattering (UV-absorption, Rayleigh scattering, IR-absorption in near range), and also losses on defects own and impurity the nature. At use of optical glass in the radiating environment of loss sharply grow because of formation in a matrix of a glass of the centers of selective absorption and play a dominating role in the common balance of losses. Essential influence on reducing of a signal are connected with impurity Fe,Cu, Cr, Mn, V, Ti and etc. Other metallic impurity Al, Ge, alkaline ions,... are usually shown only on radiation- spectral properties of glasses.

At manufacturing a V-Sİ02 impurity color centers can be considerably reduced at use of superpure raw materials. These materials receive under strict controllable technological conditions with application of superpure reactants. It is possible to receive, for example, with the contents of impurity of transitive metals less than 20x10 9 and on separate impurity less 1><10 9 [3], In v-Si02 contents more impurity than in raw materials used for its manufacturing. Hence the basic source of pollution is technological process of manufacturing. In process of development and perfection of technology of synthesis of a glass impurity the contents in it will be reduced. In V-Sİ02 with the low contents of impurity than in earlier glasses is received [4].

What high degree of cleanliness would not be achieved at synthesis of a V-Sİ02 at its irradiation there will be color centers and paramagnetism on own defects of a glass. Own defects arise at heating and cooling of a glass, during an extract of an optical fiber waveguides, during his irradiation. Under influence of radiation on own defects stable microinfringements are formed and they are kept long time. Own defects are defects arising on the line Si-O-Si, it is E-defect and defect on nonbridging atom of oxygen.

As it is established [5 and the given work] at all kinds of radiations (UV, X-ray, y, proton and reactor) in v- Sİ02 are induced the E'r center(fig.l).

Fig.l. Spectra ESR of a v-Si02 irradiated with various kinds of radiations; UV- ultraviolet, gamma (60 Co)-106-108 Gr, proton -1013-1016/sm2, reactor- 1019 neutron/sm2, H-magnetic field. The arrow specifies position of the standard, DPPH-diphenil-picril-hydrazine, g=2.0036.

Parameters Electron Spin Resonance (ESR) of the E'r center; g(||) = 2.0018, g( _|_ ) =2.0006, AH~2,4 G (width of a line). The optical absorption at -215 nm. Registration of spectra ESR was carried out on radiospectrometer RE-1306 at frequency ~9.4 GHz. Here spectra v-Si02 subjected by rather high doses of radiations -gamma, proton, in a reactor submitted. At these kinds of radiations in some types of v-Si02

high doses y,n(reactor) irradiations the form of a line from the E'i-center changes and gets a kind (fig. 1). These changes are connected to infringement of local structure of the center or occurence of the additional center. At UV influence of radiation on glass (special conditions of an irradiation) the signal with g= 1.999 is shown also; in the given work the nature and structure of this center is not discussed

Various models of a structure of the E'ı -center have been earlier submitted in survey work [6], In spectrum ESR of a glass irradiated in a reactor alongside with a signal in the area of g~2.00 (E'ı-center) is present the wide anisotropy resonance line with three axes of the g-factor; gi =2.0016, g2 =2.0067, g3 =2.070 (fig.2).

Fig. 2. Spectra ESR v-Si02 (“KV”) of the irradiated in reactor.

The center of hole type, the hole is located on nonbridging atom of oxygen.

These two types of the centers -E'ı and the center on nonbridging atom of oxygen have strongly distinguished parameters ESR. Therefore the E'ı -center registered at a level of capacity several pw and amplitude of modulation 0.1-0.2 Gs to avoid distortion of the form and saturation of a line. The line with gi =2.0016, g2 =2.0067, g3 =2.070 can be written at a level of microwave capasity -200 mw and amplitude of modulation of several Gs [7], To take record of these lines it is simultaneously impossible therefore registration of signals are carried out separately, that is, at different operating conditions of a radiospectrometer. Record of two spectral lines by us was carried out under conditions corresponding to parameters of registration of a line from the E'ı-center. In this case alongside with a line from the E'!-center observed only a part of a spectral line from the hole center about g2 =2.0067 (fig.3 on the left and a).

Fig. 3. Influence of temperature on a kind of spectrum ESR of a glass “KV” irradiated in a reactor 2 x 1020 neutron/sm2 , time of heat treatment - 30 minutes, temperature of registration -77 K, on the left and a - before heat treatment.

We shall look after relative changes intensity lines from the E'-center and a line with g2 at heat treatment of glass. At temperature 600 °C alongside with line g2 it is shown a component of a line with gi belonging to the hole center (fig.3,b,c). Sensitivity of the device has allowed to register a signal and at temperature treatment of glass 700 °C (fig.3,e,g). As it is established [8] that the radiation-induced centers in Sİ02 completely disappear at 950 °C. This temperature is lower than the temperature started softening fused silica - 1200­ 1300 °C. Heat treatment at 950°C results in structural reorganization in defective places of glass. Glass subjected to thermal processing at the maximal temperature can be reused in the radiating environment.

3 .C O N S L U S I O N

Interesting features in behavior of the centers are observed at heat treatment of a glass at low temperatures. It is known that as a rule at thermal processing a glass, subjected to influence of radiation, induced the color centers and paramagnetism are reduced. However here we see simultaneous growth of intensity of signals from E and from hole center with g2 (fig.4).

Fig. 4. Influence of temperature on intensity of lines from E'-center (electron center) and with g2 belonging to the hole center, a - before heat treatment, b-200 °C, c - 250 °C. The similar behavior of signals with g~2.01(hole center) and g -1.96 (electron center) in glasses system Na20-Si02 subjected to an irradiation in a reactor is revealed us (fig.5).

Fig.5. Dependence of intensity of lines with g-2.01 and g-1.96 in the irradiated alkali-silicate glass from temperature short-term treatment 10 minutes.

Apparently these features of behaviour of the centers at heat treatment glasses are caused by their intense condition after an irradiation high doses of radiation.

4. REFERENCES

1. Mazurin O.V.,Strelzina M.V.,Shvayko-Shvaykovskaya T.P. Svoustva stekol i stekloobrazuyushikh rasplavov. -Spravochnik, Ch.,1, Izd. Nauka, 1973, 443s.

2. Friebele E.J. Optical fiber waveguides in radiation environments. “Optical Engineering”, 1979,v. 18,N6,p.552-561.

3. K.Dj.Beyls, K.R.Dey, E.G.Dann, S.Partington. Volokna iz mnogokomponentnikh stekol dly sistem opticheskoy sviyzi.-TIIER, T.68,N. 10,1980,s.27-30.

4. Yamagata Shigeri. Silica glass product for an optical element and method for its production. Patent N 00125181.8 . 30.05.2001.

5. Brekhovskikh S.M.,Tuylnin V.A., Mamedov E.K. Vozdeystviye visokodoznikh gamma i reaktomogo izlucheniya na silikatniye stekla i narusheniye pervoy koordinazionnoy sfery iona-stekloobrazovateliy. Fizika i himiya stekla, 1978,T.4,N4,s.443-449.

6. Mamedov E.K., Tuylnin V.A. Evoluyziya predstavleniy o sobstvennikh tochechniy defektakh stekloobraznogo kremnezema. Dep. Ruk. D 06278, Moskva. Referat opubl. v “TTE”, seriya “T”, vip.25, za 1984 g.

7. GriscomD.L. Defects in amorphous insulators. J.Non-Cryst.Sol.,1978,V.31,N 1,2, p.241-266.

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