HIGH-RESOLUTION DETECTION OF X-RAYS WITH A NB-BASED STJ DETECTOR

A high energy-resolution of 88 eV has been achieved for 5.9-keV x-rays with a large area (178 x 178 mum2) Nb/Al-AlOx/Al/Nb superconducting t unnel junction (STJ) detector, which is stable at room temperature and robust to thermal cycles. The energy resolution is higher than those of semiconductor detectors. The resolution and the short shaping-time- constant, 2 mus, of the main amplifier used to obtain the energy resol ution indicate that STJ detectors can be developed as nuclear radiatio n detectors with high energy resolution even for high rate radiations. Besides, a theoretical limit of energy resolution due to the statisti cal fluctuation of signal charges is discussed.