MOLECULAR-DYNAMICS SIMULATION OF IRRADIATION DAMAGE CASCADES IN COPPER USING A MANY-BODY POTENTIAL

The evolution of irradiation damage cascades in copper has been simula ted by molecular dynamics, using a many-body potential. Nearly 200 cas cades have been produced with random knock-on directions and primary k nock-on atom (PKA) energies in the range from 60 eV to 10 keV. The sta rting temperature for these simulations was 100 K and 600 K, this repo rt will confine itself to the data obtained at 100 K. The cascade evol ution has been followed for times typically up to approximately 10 pse c and in some cases up to approximately 30 psec. The cascades are char acterised by the sudden emission of replacement collision sequences an d with shape variations due to local channelling events. At the higher energies the core has been shown to be liquid-like structure with cav itation. The annealing phase leaves loosely clustered vacancies at the cascade centre but collapse to a vacancy loop is not generally observ ed. A feature of the more energetic cascades is the production by a ba llistic mechanism of interstitial atom clusters at the periphery of th e cascades. The large number of simulations have enabled an analysis o f the efficiency of point defect production to be followed as a functi on of PKA energy. The value obtained falls sharply from the classical value of 0.8 to 0.37 at 250 eV, followed by a steady decline to 0.28 a t 2 keV and 0.15 at 10 keV. Thus the creation of point defects in meta ls during irradiation is likely to be markedly less than the standard value of 0.8, used in many irradiation dose assessments. The effect of pre-existing features on the cascade evolution has also been investig ated. Here we insert into the block of atoms a range of features such as vacancy and interstitial loops and small voids. These structures ar e in equilibrium at 100 K prior to initiation of a 1 keV cascade. In a ll of these simulations a significant reduction in final defect produc tion is observed.