calculations with his iron-carbon program. He found(15) that the carbon-vacancy complex does have a slight strain asymmetry; viz. 1 .O-1.5 % that of inte~titial carbon. In addition, the reorientation energy of the carbon-vacancy complex was calculated to be 0.78 eV. In Johnson's opinion these calculated values support our interpretation of peak V.'15)
Of the several new peaks observed in the damping spectra of irradiated Fe-C specimens, we have attempted to identify the peak at 400Β°K (30 c/s). From consideration of the annealing behavior, relaxation strength and activation energy of this peak, we conclude that the peak is the stress relaxation of abundant (^4 x lo-" at. 'A) carbon-vainly eomplexes formed during the long aging at -50Β°C after irradiation.
Further experiments are needed to determine the internal friction spectrum of irradiated Fe-C alloys before even room temperature aging. It would be in~resting, for example, to see if an internal friction peak can be observed for the defect responsible for the -30Β°C annealing step observed by Fujita and Damask.c2)
The authors are indebted to Brookhaven National Laboratory for making the specimens available for this study and to Dr. R. A. Johnson of Brookhaven National Laboratory for extending his calculations and permitting us to quote his results.