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We have demonstrated in this paper with Cs-137, a backscattered source with energy of ∼ 200 keV could be obtained effectively for radiation detector calibration applications. Vertical arrangements of source and 1-cm3 CdZnTe detector were tested. Lead block of 10 cm was used to stop the full energy peak of Cs-137. Then we have optimized our backscatter layout to minimize undesirable low energy photons, experimentally. Monte-Carlo simulation (EGS5 code) results reproduced the measurements results well with peaks appearing at correct values around the 200 keV. By considering the backscatter radiation field uniformity both experimentally and theoretically, the optimal backscatter arrangement was obtained for backscatter peak at 189 keV with FWHM of 4.6% (8.7 keV, 14.4ch). Under this condition, we obtained sufficient dose rate of 5.39 µSv/hr for calibration applications with a Cs-137 source intensity of 207.8 MBq.