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Application of the reactor radiation at the definition of ecological conditions of environment

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Proceedings o f the Third Eurasian Conference “Nuclear Science and its Application”, October 5 - 8 , 2004.

APPLICATION OF THE REACTOR RADIATION AT THE DEFINITION

OF ECOLOGICAL CONDITIONS OF ENVIRONMENT

Abdukadirova I.Kh.

Institute o f Nuclear Physics, Tashkent, Uzbekistan

The work aims at investigation of spectroscopic characteristics of the reactor and source Co60 irradiated industrial silica glasses. The purpose of this investigation is the determination of the growth kinetics of radiation defects, their stability, dependence on radiation mode, irradiation conditions and the possible use of glass as the detector of gamma and neutron fluence in compound fields of reactors and for definition of ecological conditions of environment.

The optical registering capabilities (the absorption, luminescence, infrared and Raman spectra were measured before and after irradiation) of some types of silica glasses were studied have been chosen.

There are a lot of reports [1-4] about solid state based ionizing radiation detectors. For instance in [1,2] Al, Si, Be oxides based thermoluminescence detectors, photoluminescence [3] - made from glasses for gamma-rays registration, in [4] - activation and track detectors for neutron registration etc are discussed. However, majority of them has defects, namely, radiation sensitivity, ability to detect only up to 10 Gy, difficulty in information receiving etc.

The work is aimed at investigation of spectroscopic characteristics of the on the reactor and the gamma- source irradiated solid states oxides. The purpose of this investigation is the determination of the radiation damage growth kinetics, stability, dependence on radiation dose, irradiation conditions, for studied ecological investigations of environment.

As the investigation objects the silica glasses of I-IV types were selected. Some spectroscopic methods were used as the investigation methods. The photoluminescence and the absorption spectra of the samples were measured in appropriate spectrophotometers. The samples were irradiated at different doses in the WWR-SM reactor and by Co60 source.

The photoluminescence spectra in UV region are shown in Fig.l to illustrate the effect of gamma-radiation on the silica glasses of type II. The operating diapason of Co60 radiation (Dy = 10° - 105 Gy) was found where a linear slope of the wavelength 396 nm photoluminescence intensity was observed in the silica glasses of types I and II.

The influence of dose gamma-radiation power (Ai), irradiation temperature (A2), time of storage (A3) on the intensity change of 396 nm peak in type II glass is represented in Table 1.

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Proceedings o f the Third Eurasian Conference “Nuclear Science and its Application”, October 5 - 8 , 2004.

Table 1. The influence of external factors (A;) on band 396 nm intensity in type II glasses

A! [G y/s] J i [ a . u . ] A2[ °C] J2 [ a . u . ] A3[ h ] J3 [ a . u . ]

0,2 70 31 68 0,5 68

0,4 62 70 68 2,0 68

6,5 68 90 69 5,5 68

17,0 69 140 70 25,5 71

Absorption spectra of various glasses are measured in the region of ?i=200-600 nm. The intensity change of the bands caused by n-y in compound fields of reactors and gamma-radiation from 1 Gy to 10 MGy was studied. The amount of the optical absorption change for band 540 nm (band A) in the irradiated samples caused by gamma-rays is traced. In the range of Dy=102-106 Gy for type I glass and Dy=102-5xl06 Gy for type II glass the proportional growth of the bands intensity are noted.

band o f glass (1)

For example data of the dose dependence of optical density for the samples of types I at band 540 nm (the samples were irradiated at different doses in the WWR-SM reactor and by Co60 source) is given in Fig.l. The growth process of indicated visible colour center in the samples is characterized by the definite speed. The I and II type glasses have the most intensive colouring. Such parameters as the influence of time storage (Table2) for A-band, irradiation temperature (to 180°C) and exposure (to 500°C), dose power (to 17 Gy/s), effects of the thickness (to d=3,5 mm) of the samples on the measured parameters and possibility of the repeated use were estimated. The error of measurement shown Table 2 on measured is equal to 2,5-7,2%

Section III. Radiation ecology

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Proceedings o f the Third Eurasian Conference “Nuclear Science and its Application”, October 5 - 8 , 2004.

Table 2. Stability of the A-band intensity (Y, a.u.) of glasses at different storage time (t, h)

and thickness (d, mm) type d t=l t=5 t=10 t=25 t=100 t=2000 W[%] I 0,7 0,30 0,28 0,29 0,28 0,30 0,29 2,5 I 1,0 0,45 0,44 0,40 0,45 0,40 0,47 6,9 I 3,5 1,9 1,94 1,93 1,94 2,00 1,74 2,7 II 1,3 0,64 0,59 0,61 0,66 0,60 0,57 5,0 II 0,5 0,34 0,34 0,36 0,30 0,32 0,29 7,2 II 3,5 1,87 1,81 1,89 1,77 1,82 1,77 2,9

Thermal and optical discolouring for revealing its nature, interrelation of the following colour centers were studied. The centers decay law and activation energies were examined. The bands of visual colour used in health monitoring of gamma doses in compound fields of reactors were obtained (Dy=102-105 Gy).

Influence of thermal neutrons and additive gamma-irradiation was evaluated for the case of cadmium envelope usage. The growth of observed centers within 103 - 106 Gy was concluded to be due to gamma-component of the complex radiation.

In order to expand the dose interval of solid state detectors to high radiation doses the red photoluminescence of spectra were examined in the reactor-irradiated samples. Generation of neutrons of the non-bridge oxygen atoms [5] (red bands of photo luminescence) was revealed in some glasses (I, IV types), with their concentration increasing smoothly in the interval doses of 106 - 3xl08 Gy and then saturating. Correlation was found between the dose dependences of spectroscopic and X-ray characteristics of the silica glasses. The role of radiation defects in the structure changes was observed at concentration used at measurements of high neutron radiation doses.

The study of the structural defect formation in glasses by infrared absorption method is of special interest. The influence of neutron radiation was reduced to the change of transmission in the region of 4000-3000 cm'1. The growth of the band intensity 3670 cm'1 in the interval of 1018- 1020 cm'2 for glasses is set up close to linear behaviour. Evidently, the notion of the valent oscillation activation of «free» OH-group is connected with the growth of displacement number and the fracture of the Si-0 connection, coefficient of the hydrogen diffusion and of local intensities. The possible use of this effect in the selective dosimetry of neutron radiation is suggested based on the dosimetry characteristics (influence of geometry, time storage, temperature of exposure) analysis.

IR spectra glasses dynamics at the frequency of v = 800-1400 cm'1 was studied. It was shown that spectral characteristics of main vibration of Si-O-Si bands change nonmonotonously with the growth of irradiation dose. Characteristics of antisymmetrical valent vibrations of bridge ties at the frequency of v = 1125 cm'1 up to F = 1018 cm'2 were found to be stable.

Then as a result of fast neutron fluence growth changes, connected with removal of a band position ( v ) and intensity ( R ), can be observed in the spectrum - fig. 2. It turned out that the area of largest softening of mode (Av= 15 cm' ) and decreasing of R within the F = 10 -10 cm' . Such a pronounced transformation of valent vibration is, probably, caused by structural transformation in glass.

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Proceedings o f the Third Eurasian Conference “Nuclear Science and its Application”, October 5 - 8 , 2004.

Fig. 2. IR spectra of samples at F=0, 5, 10, 60, 100, 1000-1018 cm'2 - curves 1-6

Thus, observed during the reactor irradiation the decrease of R and v valent vibrations band (a curves function R(F) and v(F)), caused by rupture in bridge ties and decreasing of valent angles, testifies for the fact that as a result of radiation influence a substantial change of silica glass structure takes place due to destruction and deformation of basis framework. This is a possible use for dosimeter of the neutron fluence in compound field of reactors.

Generation of band at 608 cm'1 in Raman spectra was revealed in some types of reactor- irradiated glasses, with concentration increasing smoothly in the interval doses of F = 5.108-5.1020 cm'2 and then saturating. This indicates irradiation at defect production on pure glass. Thermal and optical stability of the bands are studied.

Thus, the growth kinetics of radiation damage and defect formation in the silica glasses after irradiation in nuclear reactor was determined and their possible use in measurement of absorption dose of neutron emissions and gamma-quanta of source Co60 and at investigation of ecological conditions of environment was studied.

REFERENCES

1. M. S. Akselrod, V.C.Kortov , Phys. Stat. Sol. (a). 87 (1985) 629. 2. Y. D. Dzafarov, A.A. Garibov, Atom, energ. 65 (1988) 60. 3. T. Nakayima, Rad. Prot. Dosim. 22 (1988) 119.

4. K. V. Ettinger, J.Brondo, J. Holowaer, Rad. Prot. Dosim. 33 (1990) 163. 5. R. A. Devine, Phys. Rev. B. 35 (1987) 9783.

Section III. Radiation ecology

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