Deformation Welding Of Scintillating Materials
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ABSTRACT Experiments on connecting scintillating crystals to form homogeneous pieces by means of plastical deformation are described. Optical transmission, radiation hardness, and scintillation spectra have been used for the evaluation of the quality of the bond. The results of experiments on fluorides of cerium, barium, and lead; and cesium iodide confirm that deformation welding can be used successfully for economic manufacturing of large homogeneous scintillators from several smaller parts. INTRODUCTION In the field of scintillating material applications there is a need for large size scintillators with high homogeneity of properties. It is well known that the expense of manufacturing large crystals or glasses increases much faster than the volume of the material. From this point of view it seems much more economical to assemble large scintillating elements from several smaller parts than to grow it as a whole. The homogeneity problems in this case can be easily solved by preliminary selection of the pieces with identical optical and scintillating parameters. But serious requirements for optical transparency, radiation hardness, and light output homogeneity of the scintillator of over its entire volume induce rigid limitations on the means of connections between adjacent parts. For example, gluing is problematic because it is difficult to find an adhesive with adequate radiation hardness, refractive index, and optical transparency. From this point of view, it is promising to connect crystalline or amorphous solids by means of direct pressing of their surfaces together in order to adjust them by plastical deformation up to nanometer distances where they are then connected by interatomic forces. A similar method called "diffusion welding" is widely used for connections between various metals or between metals and nonmetallic materials (ceramics, glasses and some crystals). 1 In this case, at least one participant of the connection has good plasticity, thus enabling satisfactory adjustment of the surfaces. But when both participants are non-metallic and rather brittle, as in the case of the most of scintillating materials (except polymers), the adjustment of the surfaces by means of plastical deformation meets serious difficulties because of the danger of cracking when the stresses exceed some critical value. One of the possible ways to achieve satisfactory adjustment of the surfaces to be joined and to avoid the cracking lies in preliminary high-quality polishing of the surfaces up to the optical contact (that is when the spacing between the connected surfaces at respectively weak pressing doesn't exceed several tens of nanometers). This method has been applied successfully for diffusive welding of some crystalline materials. 2 Since polishing for optical contact requires much effort, this method of welding can hardly be considered economical. On the other hand, we have shown experimentally that for a large number of brittle optical materials (alkali halides, fluorides, etc.) there is a range of temperatures and s
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