Development of a prototype superconducting X-ray spectrometer using a Ta crystal as an absorber

Superconducting tunnel junctions can be used as high resolution X-ray and γ-ray spectrometers. Until recently, most results were from detectors that consisted of niobium and aluminium thin films deposited on insulating substrates. Typically Nb films with thicknesses of several hundred nanometers are used as absorbers. These thin-film devices inherently suffer from poor quantum efficiency. To increase this efficiency a foil or a single crystal can be used as the supercounducting absorber. We are working on using ultra-pure, high-Z, superconducting crystals as the X-ray and γ-ray absorbers. We are developing a prototype detector with a 10 μm-thick Ta crystal as an absorber, which will have a quantum efficiency of greater than 99% at 6 keV. In this paper we present several of the design and fabrication issues involved in assembling the prototype superconducting crystal X-ray spectrometer.