  The Portevin-Le Chatelier (PLC) effect is a kind of plastic instability
observed in many dilute alloys when deformed at certain ranges of strain rate
and temperature. In this letter we establish that the dynamical process
responsible for the PLC effect is Poisson in nature by applying statistical
analysis to the observed experimental data obtained during the PLC effect in a
substitutional alloy, Al-2.5%Mg and in an interstitial alloy, low carbon steel
subjected to uniaxial tensile test at constant imposed strain rate.
