Acoustic detection of high-energy electrons in a superconducting niobium resonant bar

We have performed all experiment. based on a suspended cylindrical bar, hit by an electron beam, for investigating the results on cosmic rays detected by the gravitational wave antenna Nautilus. The experiment is aimed at measuring the amplitude of the fundamental longitudinal mode of oscillation of a, niobium bar, excited by the pressure impulse due to the local interactions of high-energy electrons. We report. oil the amplitude measurements in a wide temperature range. For niobium in normal state the amplitude agrees within few percents with the predictions of the underlying theory. The amplitude shows a discontinuity at the temperature of transition to superconducting state and, in this state, we measure a, reduced amplitude with respect to the normal state. Data in the superconducting state are compared with two models.