Zr–1Nb samples were irradiated with 116 MeV O⁵⁺ ions at different doses ranging from 5 × 10¹⁷ to 8 × 10¹⁸ O⁵⁺/m². X-ray diffraction line profile analysis was performed to characterize the microstructural parameters of these samples. Average domain size, microstrain and dislocation density were estimated as a function of dose. An anomaly was observed in the values of these parameters at a dose of 2 × 10¹⁸ O⁵⁺/m². Positron annihilation spectroscopy was used to determine the existence and nature of vacancy clusters in the samples. Isochronal annealing was carried out for a sample to study the evolution of defect clusters.

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 paper we present a comprehensive statistical analysis of the observed experimental data obtained during PLC effect and establish that the occurrence probability of the stress drops in the dynamical process responsible for PLC effect is Poisson in nature.