Room-temperature, high-resolution, X-ray spectroscopy with silicon drift chambers

The development of detectors for high resolution room temperature X-ray spectroscopy represents a relevant progress in many fields of application, mainly in out-of-laboratory environments. A new type of silicon detector, the semiconductor drift chamber (SDC), allows one to obtain at room temperature, or with a moderate cooling, a resolution comparable to that obtained at liquid nitrogen temperature with traditional detectors of the same active area. The key feature of the SDC's is the very low output capacitance (about 100 fF) independent of the active area of the device. This feature, together with a good capacitive matching between the detector and the first stage of amplification, leads to high values of the resolution at short shaping times. We tested a simple 6-mm2 cylindrical SDC at room temperature and at -20°C (easily obtainable with electrical cooling), by using a specifically designed, low capacitance, JFET as the input transistor of the preamplifier. With a 55Fe source, we measured an equivalent noise charge (ENC) of 34 e- RMS and 27 e- RMS at room temperature and at -20°C respectively. To our knowledge these are presently the best values obtained for the same active area near room temperature.