Study of gamma-radiation-induced optical effects in Ge–Se–Cd for possible industrial dosimetric applications

doi:10.1016/j.radphyschem.2004.03.013

Radiation Physics and Chemistry

Volume 72, Issue 4, March 2005, Pages 419-422

https://doi.org/10.1016/j.radphyschem.2004.03.013 Get rights and content

Abstract

The effect of ⁶⁰Co γ-irradiation on the optical properties of the amorphous chalcogenide semiconductor, Ge₁₄Se₇₁Cd₁₅ is studied. γ-radiation-induced darkening is observed after irradiation of the thin film samples for doses up to 500 kGy. The changes in the optical absorption coefficient have been attributed to the amorphous network rearrangements and the degree of disorder caused by the γ-irradiation. The dosimetric characteristics of Ge₁₄Se₇₁Cd₁₅ for γ-irradiation measurements are proposed. The absorption coefficient was found to increase with the increase of dose in a nearly linear manner. The optical energy gap was found to decrease with the increasing dose. The values of the absorption coefficient in the absorption edge region are suitable control parameters of the proposed dosimeter material, which is characterized by the sensitivity and reproducibility of measurements. The proposed dosimeter material has a minimum detectable effect at a dose of 100 kGy. This makes the material a good candidate for dosimetry in high-dose industrial applications such as sterilization.

Introduction

Amorphous chalcogenide semiconductors are characterised by the sensitivity to the influence of external factors especially ionizing radiation with average energy more than 1 MeV (Shpotyuk (1994), Shpotyuk (1995); Shpotyuk et al., 1994). The influence of γ-radiation on the optical properties of amorphous chalcogenide semiconductors has been investigated in the ternary Ge₁₄Se₇₁Cd₁₅ composition. It is well known that the optical properties of amorphous chalcogenide semiconductors are determined by the coordination defect concentration (Shpotyuk and Matkovskii, 1994). Hence, we suppose that the level of radiation influence can be estimated as arising from radiation-induced defect changes. It has been previously proposed that these amorphous semiconductors can be used as radiation dosimeters for industrial purposes (Shpotyuk (1994), Shpotyuk (1995); Shpotyuk et al., 1994; Shpotyuk and Matkovskii, 1994). Optical dosimetric systems (ODS) based on amorphous chalcogenide semiconductors can be used for radiation measurements in a wide range of absorbed doses (from 10²–10⁷ Gy) of high-energy ionizing radiation (Shpotyuk et al., 1998). This type of ODS is characterised by a low barrier of information bleaching (440–470 K) in comparison with the widely used dosimeters based on coloured oxide glasses (Feltz, 1986). The physical principles of their functioning are the so-called radiation–polymerization transformations accompanied by concentration changes of coordination defects. The same effect can be found in crystalline semiconductors, however, they have a low level of registered doses and sensitivities.

Section snippets

Experimental

The Ge₁₄Se₇₁Cd₁₅ amorphous semiconductor composition was synthesized from high-purity (5N) elements by the standard melt quenching method. The required amounts of the constituent elements were introduced into a silica ampoule, which was then evacuated and sealed under vacuum of 10⁻⁵ Torr. The synthesis was carried out in a high-temperature furnace. A maximum temperature of 1200 K was achieved by step-wise heating and was maintained for 24 h. The ampoule was regularly rocked by hand during heating

Results and discussions

The absorption coefficient (α) was calculated using the following relations: the law of light absorption I=I₀e^−αt and accordingly $α=2.303 log (I_{0} /I)t=2.303(A/t)$ , where, I₀ and I are the incident and transmitted intensities, respectively, A is the absorbance and t is the film thickness. This relation assumes double reflection at the film–air and substrate–film interface and an exponential law for the absorption process. Fig. 1 depicts the variation of the absorption coefficient α with incident

Conclusions

The work presents results of the optical measurements on as-deposited and γ-irradiated Ge₁₄Se₇₁Cd₁₅ thin films with different doses. It is shown that ⁶⁰Co γ-irradiation leads to a long-wave shift of the fundamental absorption edge. This effect is supposed to be connected with bond rearrangements and atomic disorder in the investigated amorphous chalcogenide composition. The value of the absorption coefficient at a particular energy in the absorption edge region was found to increase with the

Acknowledgements

One of the authors would like to thank the International Atomic Energy Agency (IAEA) for awarding the fellowship (IAEA Fellow No. EGY/02034R) for visiting the University of Surrey. Also, thanks to Dr. J. Keddie for permitting the measurements to be carried out in his laboratory.

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Study of gamma-radiation-induced optical effects in Ge–Se–Cd for possible industrial dosimetric applications

Abstract

Introduction

Section snippets

Experimental

Results and discussions

Conclusions

Acknowledgements

J. Phys. Chem. Solids

Solid State Commun

Radiat. Phys. Chem

J. Non-cryst. Solids

Sensors and Actuators