Boyaryntsev A. Processes of plastic deformation of large-size NaI(Tl) crystals for obtaining of scintillation detector plates

The thesis is devoted to the elaboration of the technological process for obtaining of uniform large area NaI(Tl) polycrystals and following production of high quality gamma imaging detectors for single photon emission computer tomography (SPECT). The technological process of large area scintillation detectors fabrication includes the following main stages: high-temperature forging; crystal cutting and finishing treatment providing the high uniformity of light yield distribution in the crystal sample. High temperature forging process has been improved to create material with uniform scintillation characteristics. Structural non-uniformity of the crystal has been identified and assigned to the peculiarities of the plastic flow and deflected mode. To provide physical integrity of large area material optimal conditions for using of the multiple relaxation method have been revealed. It has been found that changing in the surface treatment mode allows modifying the light spread function width within 30 mm range. The latter enables formation of the given light spread function over the whole detector space. Use of the materials with different reflection coefficients provides change in the light yield value along the detector perimeter from +12% to -6% in comparison with the average light output in the center of the detector.