  We describe a result coming from an experiment based on an Al-Mg alloy (~ 5%
Mg) suspended bar hit by an electron beam and operated above and below the
termperature of transition from superconducting to normal state of the
material. The amplitude of the bar first longitudinal mode of oscillation,
excited by the beam interacting with the bulk, and the energy deposited by the
beam in the bar are the quantities measured by the experiment. These
quantities, inserted in the equations describing the mechanism of the mode
excitation and complemented by an independent measurement of the specific heat,
allow us to determine the linear expansion coefficient of the material.
