Nuclear Radiation Detection Scintillators based on ZnSe(Te) crystals
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Nuclear Radiation Detection Scintillators based on ZnSe(Te) crystals. Volodymyr D. Ryzhikov Institute for Scintillation Materials of STC “Institute for Single Crystals” NAS of Ukraine, 60 Lenin Ave., Kharkov, 61001, Ukraine
ABSTRACT We describe development of semiconductor scintillators (SCS) on the basis of AIIBVI compounds has bridged the gap in a series of “scintillator-photodiode” detectors used in modern multi-channel low-energy devices for visualization of hidden images (tomographs, introscopes). In accordance with the requirements of eventual applications, such SCS materials as ZnSe(Te) show the best matching of intrinsic radiation spectra to photosensitivity spectra of silicon photodiodes (PD) among the materials of similar kind. They are characterized by high radiation and thermal stability of their output parameters, as well as by high conversion efficiency. In this work, a thermodynamic model is described for interaction of isovalent dopants (IVD) with intrinsic point defects of AIIBVI semiconductor structures at different ratios of their charges, a decisive role of IVD is shown in formation of the luminescence centers, kinetics of solid-phase reactions and the role of a gas medium are considered under real preparation conditions of ZnSe(Te) scintillation crystals, and luminescence mechanisms in IVD-doped SCS are discussed. INTRODUCTION The use of ȺIIȼVI compounds, namely, CdS(Te), as highly efficient scintillators was first proposed by J.Thomas e.a. [1,2]. They also assumed that the scintillation mechanism could be determined by radiative recombination centers on isoelectronic traps. Otherwise, in [3] it was shown that luminescence related to isoelectronic traps (IET) is of exciton character, and the corresponding emission spectra, e.g., in ZnTe(O) and ȺIIIȼV compounds are narrow discrete lines, as distinct from broad diffuse bands characteristic for the centers involving intrinsic defects. The luminescence maximums and the character of the bands are similar to centers involving defects introduced by other means, such as radiation damage [4,5] and thermal treatment [6]. Thus, an isovalent dopant (IVD) atom, differing from the substituted atom by its ion radius and electronegativity, stimulates formation of defects in the neighboring sublattice. In particular, J.Watkins [7] showed by EPR methods that introduction of tellurium into zinc selenide leads to formation of vacancies Zn(VZn); the displaced Zn moves to the interstitial position, and the VZn Zni complex, stable up to 400 K, is formed in the vicinity of tellurium atom. Alongside CdS(Te), other scintillators with IVD are of great interest. We were the first to obtain scintillator ZnSe(Te) [8,9]. As distinct from CdS(Te), its luminescence efficiency is comparable to or higher than in traditional materials like CsI(Tl). At present, ZnSe(Te) scintillators are widely used in inspection equipment.
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In a series of studies ([10-12] and others] we have considered in detail thermodynamics of defect formation, preparation methods of ZnSe(Te) and its main
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