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ORIGINAL ARTICLE
Year : 2015  |  Volume : 38  |  Issue : 4  |  Page : 135-138  

High sensitivity gamma radiation dosimetry using (In2O3)0.1 (TeO2)0.9thin films


1 Department of Physics, Indian Institute of Technology, Kharagpur, West Bengal, India
2 Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, CTCRS, Anushaktinagar, Mumbai, India

Date of Web Publication11-Feb-2016

Correspondence Address:
Shivcharan Lal Sharma
Department of Physics, Indian Institute of Technology, Kharagpur - 721 302, West Bengal
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0464.176156

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  Abstract 

The effects of gamma irradiation of various levels on the current-voltage characteristics for the (In2O3)0.1 (TeO2)0.9 thin films, prepared by thermal evaporation in vacuum, have been studied in detail. The current increases linearly with the gamma radiation dose up to certain dose and decreases thereafter. The sensitivity of these thin films, at different applied voltages in the range 0–4.8 V, has been found to be in the range 35–190 mA/cm 2/Gy. Correspondingly, the minimum measurable dose has been found to be in the range 0.05–0.26 mGy. The values of the sensitivity are reasonably high in comparison to the commercially available gamma radiation dosimeters, revealing high scope for further developments.

Keywords: Current, gamma dosimetry, indium oxide, tellurium dioxide


How to cite this article:
Maity T K, Sudha A, Sharma SL, Sharma S D, Chourasiya G. High sensitivity gamma radiation dosimetry using (In2O3)0.1 (TeO2)0.9thin films. Radiat Prot Environ 2015;38:135-8

How to cite this URL:
Maity T K, Sudha A, Sharma SL, Sharma S D, Chourasiya G. High sensitivity gamma radiation dosimetry using (In2O3)0.1 (TeO2)0.9thin films. Radiat Prot Environ [serial online] 2015 [cited 2019 Sep 16];38:135-8. Available from: http://www.rpe.org.in/text.asp?2015/38/4/135/176156


  Introduction Top


The expanding applications of the ionizing radiations demand the development of radiation dosimeters of different variety and types including the miniaturized radiation dosimeters involving thin film technology. The exposure of solid thin films to ionizing radiation of any kind changes the structural properties, which in turn affect the optical and electrical properties of the films.[1],[2],[3],[4],[5] For the thin films of metal oxides, the ionizing radiation induced changes depend upon the type of radiation, the radiation dose and the parameters associated with the films.[6] Attempts have been made in the past to understand the radiation-induced changes in the structural, optical, and electrical properties of the thin films of several metal oxides due to the gamma irradiation of various levels in order to determine the suitability of these thin films in the real-time and postexposure gamma radiation dosimetry.[6],[7],[8],[9] The gamma radiation induced changes in the structural, optical, and electrical properties of the thin films of In2O3 and TeO2 mixture have also been the subject of some investigations in the recent past.[7],[9] However, lot more is to be done in order to fully realize the potential of the thin films of the said mixture. Present work aims to study the effect of gamma irradiation of various levels on the current-voltage (I-V) characteristics of the (In2O3)0.1 (TeO2)0.9 thin films of the thickness 600 nm in order to determine the sensitivity of these thin films representing the change in the current for unit change in the gamma radiation dose as well as the minimum measurable dose (MMD) (the minimum dose detection limit) representing the gamma radiation dose producing unit change in the current at several voltages in the range 0–4.8 V. The X-ray diffraction (XRD) patterns and field emission scanning electron microscope (FESEM) images have also been studied for the thin films, exposed to various levels of the gamma radiation dose, in order to understand the dose dependence of the current in terms of the changes in the structural properties.


  Experimental Details Top


Samples of the (In2O3)0.1 (TeO2)0.9 thin films of thickness 600 nm, having a coplanar structure as described earlier,[10] were prepared on the cleaned glass substrates by thermal evaporation in vacuum (10-5 mbar). Two rectangular layers of aluminum, each of the thickness of about 150 nm and having inner edge-to-edge separation of 3 mm, were deposited on each of the several cleaned glass substrates to act as electrical contacts. For the evaporation of aluminum, a coil-shaped tungsten filament was used. Using a tungsten boat, subsequently, a thin film of (In2O3)0.1 (TeO2)0.9 of thickness 600 nm was deposited on the top of each pair of the aluminum contacts. These thin film structures were subsequently exposed to various levels of the gamma radiation dose using a 60 co source at room temperature. The I-V characteristics of these thin film structures exposed to various levels of the gamma radiation dose were then recorded using Keithley Electrometer (Model: 6517B Electrometer/High Resistance Meter). At each value of the gamma radiation dose, the I-V plots were thus obtained for three good quality samples and these plots were found to have fluctuations of 5–8% about the corresponding mean I-V plot. We treated the mean I-V plot at a particular value of the dose as the typical I-V plot for that value of the dose. From the typical I-V plots at different gamma radiation doses, the current versus dose plots were thus obtained for various voltages applied to the coplanar structure. For the current versus dose plot at each voltage applied to the structure in the range 0–4.8 V thus obtained, the sensitivity defined as the change in the current per unit change in the gamma radiation dose was estimated. The MMD at each applied voltage was also estimated, representing the value of the gamma radiation dose required to produce a change in the current of 1 µA (the sensitivity of a typical current meter generally used) in these thin films.

The XRD patterns, as well as the FESEM images, were recorded, respectively, using grazing incident-XRD (Model: X'pert PRO PANalytical) and ZEISS Scanning Electron Microscope (Model: SUPRA-40) for the (In2O3)0.1(TeO2)0.9 thin films, exposed to various levels of the gamma radiation dose.


  Results and Discussion Top


[Figure 1] shows the typical I-V characteristics for the coplanar structure of the (In2O3)0.1 (TeO2)0.9 thin films of thickness 600 nm, exposed to various levels of the gamma radiation dose. All the I-V plots clearly show the semiconducting behavior of the film. The variation of the current with the gamma radiation dose was then obtained at each of the voltages applied to the thin film structure in the range of applied voltage 0–4.8 V. The current versus gamma radiation dose plots for the applied voltages of 3.0 V, 3.5 V, 4.0 V, and 4.5 V are shown in [Figure 2]. The regression analysis was carried out for each plot in [Figure 2], first for the data points up to the gamma radiation dose of 160 Gy and later for the entire data points. The R2 values in the first case have been found to be in the range 0.97–0.99 and those for the later case in the range 0.83–0.89. Clearly, the current increases linearly with the gamma radiation dose up to a dose of 160 Gy at each of the applied voltages. Beyond 160 Gy, however, the current is found to decrease at each applied voltage. Similar observations have also been reported by Arshak and Korostynska [7] for the thin films of In2O3 and TeO2 mixture. For the linear part of each of the current versus dose plots, the sensitivities were found to be in the range of 35–190 mA/cm 2/Gy and the MMDs in the range 0.05–0.26 mGy correspondingly. Clearly, the values of the sensitivity are reasonably high in comparison to the commercially available gamma radiation dosimeters.
Figure 1: The typical current versus voltage plots for the coplanar structure of the (In2O3)0.1 (TeO2)0.9thin films of thickness 600 nm, exposed to various levels of the gamma radiation dose

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Figure 2: The typical current versus dose (I-D) plot for the coplanar structure of the (In2O3)0.1 (TeO2)0.9thin films of thickness 600 nm for the voltage of (a) 3.0 V, (b) 3.5 V, (c) 4.0 V, and (d) 4.5 V

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[Figure 3] shows the XRD patterns of the as-deposited (i.e., unexposed) as well as exposed (In2O3)0.1 (TeO2)0.9 thin films. These XRD patterns show that the as-deposited (i.e., unexposed) thin films as well as the thin films exposed to various levels of the gamma radiation dose are amorphous in nature. The FESEM images of the (In2O3)0.1(TeO2)0.9 thin films of thickness 600 nm, exposed to gamma radiation doses of 0, 80, 160, and 200 Gy are shown in [Figure 4]. It is observed from the FESEM images that the as-deposited (i.e., unexposed) thin films are quite nonuniform, and the uniformity of the films grows with the gamma radiation dose up to a certain dose value and that the large-sized cluster formations with voids occur in the films exposed to higher doses. The variation of the I-V plot with the gamma radiation dose can be understood in terms of the structural changes occurring in the films due to the gamma irradiations. The as-deposited thin films contain lattice defects as well as the geometrical and physical imperfections, all distributed on the surface as well as throughout the volume leading to amorphous nature with high level of nonuniformity. The increase in the current with the gamma radiation dose may be attributed to the healing effect leading to better uniformity.[11] During the gamma irradiation, the defects are created as well as they are annihilated even under the normal room temperature conditions.[12] At low doses, the thin film has fine homogeneous grain structure without any big pores, and the number of defects (induced plus residual intrinsic defects) is smaller than the number of intrinsic defects due to the recombination of defects. The recombination of defects reduces the resistivity of the thin film, giving rise to an increase in the current. The creation and annihilation of defects coexist, and the number of defects created due to irradiation becomes much more than the number of defects annihilated at higher gamma radiation doses. In addition, the recombination of defects gives rise to the formation of the large clusters with voids reducing the conductivity of the films.
Figure 3: The typical X-ray diffraction patterns for the (In2O3)0.1(TeO2)0.9thin films of thickness 600 nm, exposed to various levels of the gamma radiation dose

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Figure 4: The field emission scanning electron microscope image for the (In2O3)0.1 (TeO2)0.9thin films of thickness 600 nm exposed to the gamma radiation dose of (a) 0 Gy, (b) 80 Gy, (c) 160 Gy, and (d) 200 Gy

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The linear increase of the current with the gamma radiation dose up to a dose of 160 Gy is the working region for the real-time as well as post exposure gamma radiation dosimetry employing the coplanar structure of the (In2O3)0.1 (TeO2)0.9 thin films of thickness 600 nm. Accordingly, gamma radiation dosimeters prepared from the (In2O3)0.1 (TeO2)0.9 thin films of thickness 600 nm and operated at a voltage of 4 V will possess a sensitivity of about 115 mA/cm 2/Gy. Correspondingly, the radiation dosimeters with a sensor element of the (In2O3)0.1 (TeO2)0.9 thin film of thickness 600 nm, width 1.8 cm (the width of each of the samples used in the present studies), and a current meter of sensitivity of 1 µA (the sensitivity of the electrometer employed in the present current measurements) will have the MMD for the gamma radiation doses in the range 0.05–0.26 mGy for the applied voltages 0–4.8 V. Clearly, the (In2O3)0.1 (TeO2)0.9 thin films have high scope for their use in the gamma radiation dosimetry in monitoring of the gamma radiation doses under a variety of practical situations involving a very low level of the gamma radiation doses such as those involved in the teaching and research laboratories.


  Conclusions Top


The (In2O3)0.1 (TeO2)0.9 thin films of thickness 600 nm having coplanar structure were prepared on the cleaned glass substrates by thermal evaporation in vacuum. The I-V characteristics of these films indicate that the current increases linearly with the gamma radiation dose up to a certain dose and decreases thereafter. The radiation dosimeters prepared from the (In2O3)0.1 (TeO2)0.9 thin films of thickness 600 nm, operated either in the real-time mode or in the post exposure mode, is expected to possess the sensitivities in the range of 35–190 mA/cm 2/Gy and MMDs in the range 0.05–0.26 mGy for the applied voltages of 0–4.8 V. The values of the sensitivity are reasonably high in comparison to the commercially available gamma radiation dosimeters. The (In2O3)0.1 (TeO2)0.9 thin films have high scope for their use in the gamma radiation dosimetry in monitoring of the gamma radiation doses under a variety of practical situations involving a very low level of the gamma radiation doses such as those involved in the teaching and research laboratories.

Acknowledgments

Authors acknowledge with thanks the financial assistance provided by the Board of Research in Nuclear Sciences, Department of Atomic Energy, Government of India, in the form of a research project with sanction number 2011/36/23-BRNS.

Financial support and sponsorship

The financial assistance provided by the Department of Atomic Energy, Govt. of India, in the form of a research project with sanction number 2011/36/23-BRNS.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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Atanassova E, Paskaleva A, Konakova R, Spassov D, Mitin VF. Influence of γ radiation on thin Ta2O5-Si structures. Microelectronics J 2001;32:553-62.  Back to cited text no. 4
    
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Colby E, Lum G, Plettner T, Spencer J. Gamma radiation studies on optical materials. IEEE Trans Nucl Sci 2002;49:2857-67.  Back to cited text no. 5
    
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Arshak K, Arshak A, Zleetni S, Korostynska O. Thin and thick films of metal oxides and metal phthalocyanines as gamma radiation dosimeters. IEEE Trans Nucl Sci 2004;51:2250-5.  Back to cited text no. 6
    
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Arshak K, Korostynska O. Thin films of (TeO2)1-x(In2O3)x as gamma radiation sensors. Sens Rev 2003;23:48-54.  Back to cited text no. 7
    
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Arshak K, Korostynska O. Response of metal oxide thin film structures to radiation. Mater Sci Eng 2006;B-133:1-7.  Back to cited text no. 8
    
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Sharma SL, Maity TK. Effect of gamma radiation on electrical and optical properties of (TeO2)0.9 (In2O3)0.1 thin films. Bull Mater Sci 2011;34:61-9.  Back to cited text no. 9
    
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Maity TK, Sharma SL, Chourasiya G. Real-time gamma radiation dosimetry with TeO2 thin films. Radiat Meas 2012;47:145-8.  Back to cited text no. 10
    
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Zaykin YA, Aliyev BA. Radiation effects in high-disperse metal media and their application in powder metallurgy. Radiat Phys Chem 2002;63:227-30.  Back to cited text no. 11
    
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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]



 

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