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The activation energy, activation volume, snd frequency factor were evaluated for yielding (delay time for yielding, upper yield stress, lower yield stress, and Luders band propagation) and flow (friction stress, flow stress, and dislocation mobility) for various irons and steels from data in the literature. It was found that the values of these flow parameters and their stress dependence were the same, within experimental error, for both yielding and flow, and for all the materials considered. This suggests that either the same dislocation mechanism is controlling in every case, or that one or more mechanisms possees approximately the same values for these parameters. The dislocation mechanism for which there was closest agreement between theoretical calculations snd experimental data was overcoming the Peierls stress. On the basis of the available experimental data and the present analysis, it is suggested that the upper and lower yield stresses in iron and steel may represent the sudden generation of a large number of dislocations by the double cross-slip mechanism of Koehler and Orowan, rather than the breaking away from a Cottrell atmosphere. (auth)

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tems were cast and cured. Results of chemical tests on aa epoxy curlang exudate are included. Comparison of solvent effects on retention of radioelements by stainless steel was started and data are tabulated for Ac/sup 227/, Th/sup 227/, a nd Ra/sup 22//sub 3/. Work on protactinium was resumed after suspension of this project in 1960. Methods for preparation of small quantities of highly enriched U isotopes are being examined. Included in the survey are chemical exchange, electromagnetic separation, gaseous and liquid thermal diffusion, gas centrifugation, and photochemical techniques. Continued investigation of viscosities of La and Pr for use in Pu alcontinued along with studies of Pu bearing glass fibers. (J.R.D.)

Dense UN specimens for property tests were fabricated primarily by an isostatic hot-pressing technique in which consolidated powder sealed in a refractory metal container was subjected to a 10,000-psi external gas pressure at 1480 to 1540 deg C for 3 to 4 hr. The thermal conductivity of uranium mononitride increased from 0.04 cal/(cm)(sec)( deg C) at 200 deg C to 0.06 cal/ (sec)(cm/sup 2/)( deg C) at 1000 deg C, which by an integrated thermal- conductivity criterion, makes it some eight times more effective than UO/sub 2/ in transferring heat. Thermal-expansion coefficients of 9.0 x 10/sup -6/ per deg C and 9.9 x 10/sup -6/per deg C over the ranges 20 to 800 deg C and 20 to 1600 deg C, respectively, were measured. UN retained about 80% of its room- temperature hardness at 1100 deg C. Above this temperature, the hardness dropped rapidly with increasing temperature. The specific heat is cal per g mole can be conveniently described by the equition C = 13.32 + 1.19 x 10/sup -3/ T --2.10 x 10/sup 5/ T/sup -2/ over the range 273 to 142 3 deg K. Electrical conductivity dropped with increasing temperature a metallic characteristic. Anomalies were noted in attempts …

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