RESPONSE OF LARGE NB-BASED TUNNEL JUNCTION TO X-RAYS

摘要

High quality Nb-based tunnel junctions with surface areas of 100 x 100 mu m(2) and 200 x 200 mu m(2) were tested by irradiating X-rays. According to the decrease in the disappearance of quasiparticles before tunneling, the 200 x 200 mu m(2) junction exhibited better X-ray response than that of 100 x 100 mu m(2) one. In the operation of the 200 x 200 mu m(2) junction, two kinds of stable operation modes with different pulse heights were found by applying a magnetic field with different ramping speeds. The higher pulse height mode was observed with a ramping-speed faster than about 200 G/s. After tuning of the bias current in the higher mode operation, the energy required for single electron collection was obtained to be 6.5 meV and the junction detected 5.9 keV X-rays of Mn-55 with an energy resolution (FWHM) of 93 eV. The 200 x 200 mu m(2) junction has the largest dimension among tunnel junctions exceeding silicon-semiconductor detectors in energy resolution. [References: 9]