Soft X-Ray Spectrometer Using 100-Pixel STJ Detectors for Synchrotron Radiation

Fluorescent X-ray absorption fine structure (XAFS) is an important tool for material analysis, especially for the measurement of chemical states or local structures of elements. Semiconductor detectors are usually used for separating the fluorescent of elements in question from background fluorescence. However, the semiconductor detectors cannot always discriminate K-lines of light elements and L-lines of various elements as different X-ray peaks at an energy range below about 3 keV. Superconducting tunnel junction (STJ) detectors are promising device for the soft Xray at synchrotron radiation beam lines because of excellent energy resolution, high detection efficiency, and high counting rate. We are constructing a fluorescent X-ray spectrometer having 100-pixel array of STJs with 200 mu m square. The array detector is mounted on a liquid cryogen-free He-3 cryostat. The sensitive area is the largest among the superconducting X-ray spectrometers operating at synchrotron beam lines. Each pixel is connected to a room temperature readout circuit that consists of a charge sensitive amplifier and a pulse height analyzer. The spectrometer will achieve a total solid angle of similar to 0.01 sr and a maximum counting rate of more than 1M count per second. The present status of developments of our fluorescent X-ray spectrometer was reported.