Abstract
A single crystal of Bi2Sr2CaCu2O8 (Tc similar 84 K) has been exposed to fast neutron irradiation up to a fluence of 6 · 1017 cm−2 (E > 0.1 MeV). D.c. magnetization measurements made prior to and following irradiation show significant enhancements of irreversibility in the magnetization loops and a shift of the "irreversibility" line to much higher fields and temperatures. This provides evidence for the absence of phase transitions in the flux line lattice and the predominance of depinning phenomena at high fields and temperatures.