- POINT DEFECT SURVIVAL AND CLUSTERING FRACTIONS OBTAINED FROM MOLECULAR DYNAMICS SIMULATIONS OF HIGH ENERGY CASCADES ROGER E. STOLLER Metals and Ceramics Division Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge, TN 3783 1-6376 USA ABSTRACT The evolution of high-energy displacementcascades in iron has been investigated for times up to 200 ps using the method of molecular dynamics simulation. The simulations were carried out using the MOLDY code and a modified version of the many-body interatomic potential developed by Finnis and Sinclair. Previously reported results have been supplementedby a series of 10 keV simulations at 900 K and 20 keV simulations at 100 K. The results indicate that the fraction of the Frenkel pairs escaping in-cascade recombination is somewhat higher and the fraction of the surviving point defects that cluster is lower in iron than in materials such as copper. In particular, vacancy clustering appears to be inhibited in iron. Many of the larger interstitial clusters were observed to exhibit a complex, three-dimensional morphology. The apparent mobility of the <111> crowdion and clusters of 411> crowdions was very high. INTRODUCTION The method of molecular dynamics (MD) has seen broad application to the problem of simulating displacementcascades in irradiated materials [ 1-71, and the recent evolution of computer technology permits the simulationof higher energy events and higher temperatures with their requirementfor larger blocks of atoms. These same computing resources have permitted cascade simulations to be completed in sufficient numbers to allow for statistically meaningful trends to be determined as a function of simulationenergy and irradiation temperature, and for comparisonsto be made between different materials [5]. For example, the comparison of iron and copper contained in Ref. 5 is based on a database of over 600 cascades. Cascade energies from 60. eV to 10 keV were used at irradiationtemperatures of 100,600; and 900 K. The results presented herein supplementa collaborative study discussed in Ref. 5. The additional work includes the analysis of seven 10 keV cascades at 900 K and ten 20 keV cascades at 100 K. In order to investigatecascade evolution, one of the 10 keV cascades was run for 100ps and one of the 20 keV cascades for 200 ps. In addition, one of the 10 keV, 100 K cascades from ref. 5 was extended to 100 ps. The higher energy provides the opportunity to examine how the trends established at lower energies extrapolate into the domain of significant subcascade 1 Of7