SPECTROSCOPY OF SHORT ELECTRON-BEAM PULSES BY SUPERCONDUCTING NB ALOX/NB TUNNEL-JUNCTIONS/

We have used superconducting Nb/AlO(x)/Nb tunnel junctions (STJs)for t he spectroscopy of short electron beam pulses, which contain only a fe w electrons with energy ranging between 6 and 35 ke V. The spectroscop y was performed by Low Temperature Scanning Electron Microscopy (LTSEM ) at T = 2.6 K. The spectra show that the number of beam electrons wit hin each single pulse follows the Poisson statistics and agree well wi th the theoretically expected spectra, Increasing the average number o f beam electrons per pulse shows that the STJ-detector response is lin ear up to a deposited energy of more than 500 keV. For a large average number of beam electrons the achievable energy resolution of the dete ctor is limited by the statistics of the beam electrons and the influe nce of the backscattered electrons.