Search

A theory for calculating nuclide composition changes is presented. (By summing isotopes, the composition changes in terms of elements can also be calculated.) The core of the theory consists of differential equations of composition change that can be solved by numerical techniques or by approximate analytic methods, depending on the accuracy desired. The superposition principle for multicomponent materials and graphical techniques for the display of composition are presented. One of the graphical methods is the mixture diagram which can provide composition information for many irradiated mixtures within a mixture system.

A systematic study of the effects of cold work and precipitation on the critical current density of an Nb-27at.%Zr alloy is reported. Heavy cold working, leading to a reduction of more than 99% in the area by swaging and wire drawing increases Jc in a transverse magnetic field of 4 T by a factor of about 13 relative to Jc for the recrystallized alloy. Precipitation of β-Zr, in combination with cold work, further enhances Jc. The highest level of Jc results when the precipitation heat treatment is given at an intermediate stage of working. Such a process in this study gives a value of Jc at H = 4 T, that is more than five times higher than Jc in the most heavily cold-worked specimen. Optical metallographic examination reveals that deformation twinning takes place in this alloy and that precipitation of β-Zr occurs preferentially at deformation twin boundaries.

The influence of deformation on the microstructural stability of a directionally solidified PbSn lamellar eutectic was studied. Direct observations of coarsening and microstructural changes of as-grown and deformed specimens, annealed at 93% of the absolute eutectic temperature, were made and the results quantitatively compared with values predicted by a two-dimensional fault migration coarsening model. The structural faults responsible for coarsening include as-grown faults as well as terminations resulting from recovery processes as proposed by Nakagawa and Weatherly. The number of such terminations increases generally with increasing prior deformation. For specimens with prior deformation less than 50% reduction-in-area by rolling, good agreement between the experimental and predicted coarsening rates was observed. The coarsening of heavily deformed specimens (60% and 70% R.A. by rolling) is not described by the simple model utilized in this work because the actual microstructure is not emulated by the modeled one. However, the basic concepts describing the initial rate of coarsening in heavily deformed materials are probably similar to those in lightly deformed ones. The fault migration velocity obtained from coarsening data in this study compares well with theoretical and previously observed values of this velocity.

Composition changes that occur during neutron bombardment have been calculated for the first wall of a hypothetical fusion reactor. The first wall materials studied are pure niobium, zirconium, molybdenum, and vanadium, and some of their binary alloys. Two integrated neutron flux intensities, 3.8 x 10$sup 14$ n/(cm$sup 2$ sec) and 3.8 x 10$sup 15$ n/(cm$sup 2$ sec) up to a fluence of 3.6 x 10$sup 23$ n/cm$sup 2$, have been used in the calculations of the first three materials. In addition, the composition as a function of fluence (maximum fluence = 4.0 x 10$sup 23$ n/cm$sup 2$) has been calculated for a vanadium wall. Graphs for each material have been plotted to show the variation of composition as a function of time and/or fluence. Rates of production of hydrogen and helium have been calculated for all four materials; comparisons for niobium and vanadium walls with literature values show agreement that it is not poor. Furthermore, mixture diagrams have been constructed for two binary alloy systems, niobium- zirconium and niobium-vanadium, to relate composition at constant irradiation time to the initial composition.

A high magnetic‐field magnetization technique has been devised which allows rapid measurement of superconducting to normal transition fields (Hc2*) for bulk high‐field superconductors in pulsed magnetic fields up to 200 kG. Values of Hc2* so obtained are in good agreement with those obtained by resistive techniques. A complete magnetization curve is obtained in the same time that one point could be determined for a resistive critical current density vs field curve. The significance of such a dynamic magnetization curve is discussed.

Simple electronic structures of transition metal alloys are considered through a comparison of superconducting critical temperatures. It is found that hydrogen, nitrogen and oxygen act as electron donors in group V transition metals. With the exception of hydrogen, the interstitial elements only donate p -electrons. Interstitial elements apparently act as electron acceptors in group VII transition metals. Comparisons of materials with different crystal structures are necessary for an understanding of electronic structures.

Superconducting properties of the ternary system Ti–Nb–Ta were measured. Critical temperatures were found to decrease with increasing amount of Ta in the alloys from those of Ti–Nb binary alloys. However, a broad plateau of high critical fields (above 120 kG) was observed in the region around the composition 63 at.% Ti‐31 at.% Nb‐6 at.% Ta. This plateau is discussed in relationship with the corrected Abrikosov upper critical field and with the Maki upper critical field which includes the effects of Pauli paramagnetism and spin‐orbit scattering. Critical current density data are also reported for one alloy.

An investigation has been made of the superconductive properties of the niobiumcarbon-nitrogen ternary system. These compounds always have a range of composition, and previous investigators have often neglected the effect of stoichiometry. Both critical temperature (Tc) and upper critical field (Hc2) are dependent on composition, although not in the same way. The trend of Hc2 at 4.2°K with decreasing nitrogen content is always down. The maximum Tc (17.8°K) occurs for nearly stoichiometric compounds having a C/Nb ratio of about 0.3. The critical temperature of substoichiometric NbN, which contains a small amount of carbon rather than the more common impurity oxygen, is 17.2–17.3°K.