High-resolution superconducting X-ray spectrometers with an active area of 282 /spl mu/m/spl times/282 /spl mu/m

Superconducting tunnel junctions coupled to superconducting absorbers may be used as high-resolution, high-efficiency X-ray spectrometers. We have tested devices with niobium X-ray absorbing layers coupled to aluminum layers that serve as quasiparticle traps. In this work we measure the current pulses from a large-area tunnel junction using an amplifier based on an array of 100 SQUIDs. Using this amplifier and a 282 /spl mu/m/spl times/282 /spl mu/m junction, we have measured an energy resolution of 19 eV FWHM for 1.5 keV X-rays and 21 eV for 2.6 keV X-rays. The area of this junction is eight times the area of any junction previously measured to have such high energy resolution.