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