High quality Nb-based tunnel junctions with surface areas of 100 x 100 μm2 and 200 x 200 μm2 were tested by irradiating X-rays. According to the decrease in the disappearance of quasiparticles before tunneling, the 200 x 200 μm2 junction exhibited better X-ray response than that of 100 x 100 μm2 one. In the operation of the 200 x 200 μm2 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 6.5meV and the junction detected 5.9keV X-rays of 55Mn with an energy resolution (FWHM) of 93eV. The 200 x 200 μm2 junction has the largest dimension among tunnel junctions exceeding silicon-semiconductor detectors in energy resolution.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Nuclear Energy and Engineering