It is important to detect low energy gamma rays precisely for the purpose of diagnosis in nuclear medicine, gravitational wave research and detection of underground nuclear test. Since a silicon sensor has an advantage of fast response, good intrinsic energy resolution and providing high signal yield in a small active volume, it can be used to detect low energy gamma rays without the help of a scintillator. We developed silicon PIN diodes and photodiodes on high resistivity, n+ doped, and 6-in. double-side polished silicon wafers. We present measurements of responses, such as signal pulse heights, signal-to-noise ratios and energy resolutions, of these detectors to low energy gamma rays from 241Am, 133Ba and 57Co radioactive sources which provide gamma rays between 14.4 keV and 136.5 keV of energy. We also compare the measurement results depending on the diode thickness.
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