Measurement of the distance to gamma-ray burst surces

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Soft X-ray photons below 1 keV are required to observe the hydrogen column density to gamma-ray burst sources from which we can measure the distance to the source. A low leakage current of the X-ray detector is required to detect such a soft X-ray photon. Unlike silicon, high purity diamond exhibits a very high natural resistivity. Diamond also has a very large energy band gap of 5.5 eV compared with that of silicon of 1.1 eV.Thus, even with the application of a high electric field, only a feeble current flows through the detector.We produced the radiation sensor from several kinds of diamonds such as natural diamonds, chemical vapor deposited (CVD) diamonds, and high pressure synthesized diamonds. As a result, it was found that the sensor of a high pressure synthesized diamond has the excellent energy resolution of 25.4 keV (FWHM) for 5.486 MeV alpha particles from ^<241>Am, which ismuch better than the previously reported value of 82 keV (FWHM) of the natural diamond. The obtained energy resolution is almost the same as silicon sensor and a promising data for the future X-ray detector of gamma-ray bursts.