An improved analysis of sphere transmission experiments for average capture cross sections

Monte Carlo and Bethe methods for calculating neutron cross sections with effective scattering cross section

Transport analysis of measured neutron leakage spectra from spheres as tests of evaluated high energy cross sections

Integral tests of evaluated ENDF/B high-energy cross sections have been made by comparing measured and calculated neutron leakage flux spectra from spheres of various materials. An Am-Be (alpha,n) source was used to provide fast neutrons at the center of the test spheres of Be, CH2, Pb, Nb, Mo, Ta, and W. The absolute leakage flux spectra were measured in the energy range 0.5 to 12 MeV using a calibrated NE213 liquid scintillator neutron spectrometer. Absolute calculations of the spectra were made using version 3 ENDF/B cross sections and an S sub n discrete ordinates multigroup transport code. Generally excellent agreement was obtained for Be, CH2, Pb, and Mo, and good agreement was observed for Nb although discrepancies were observed for some energy ranges. Poor comparative results, obtained for Ta and W, are attributed to unsatisfactory nonelastic cross sections. The experimental sphere leakage flux spectra are tabulated and serve as possible benchmarks for these elements against which reevaluated cross sections may be tested

Precision Synthesis of Silicon Nanowires with Crystalline Core and Amorphous Shell

A synthetic route to crystalline silicon (Si) nanowires with an amorphous Si shell is reported. Trisilane (Si3H8) and Sn(HMDS)(2) are decomposed in supercritical toluene at 450 degrees C. Sn(HMDS)(2) creates Sn nanoparticles that seed Si nanowire growth by the supercritical fluid-liquid-solid (SFLS) mechanism. The Si : Sn ratio in the reaction determines the growth of amorphous Si shell. No amorphous shell forms at relatively low Si : Sn ratios of 20 : 1, whereas higher Si : Sn ratio of 40 : 1 leads to significant amorphous shell. We propose that hydrogen evolved from trisilane decomposition etches away the Sn seed particles as nanowires grow, which promotes the amorphous Si shell deposition when the higher Si : Sn ratios are used.Robert A. Welch Foundation F-1464U.S. Department of Energy Office of Science, Office of Basic Energy Sciences DE-SC0001091National Defense Science and Engineering Graduate FellowshipChemistr

Ages of D/d,n/He sup 3 and T/d,n/He sup 4 neutrons in water and tungsten-water mixtures

Ages for D-D and D-T neutrons in water and tungsten-water mixture

Teacher Evaluation and Classroom Practice: Teacher Perceptions in Northeast Tennessee

The purpose of this quantitative study was to investigate the perceptions of K-12 teachers as they relate to the implementation of the Tennessee Educator Acceleration (TEAM) evaluation framework. Survey links were sent to 1,115 K-12 teachers from 4 Northeast Tennessee school districts. The survey achieved a 24% return rate for a total of 270 participants. The research evaluated K-12 teachers’ overall perceptions of the TEAM evaluation framework, their perceptions of changes to their lesson planning processes, their perceptions of changes in the use of instructional strategies in their classrooms, and their perceptions of changes in the amount of time needed to prepare lessons for instruction since the implementation of the TEAM evaluation framework. Data sources analyzed consisted of an online survey design using a 5-point Likert-type scale. There were 4 research questions included in this research each with a corresponding null hypothesis. Each research question was analyzed with a series of single sample t-tests with mid-point of the scale (3.0) as the test value representing neutrality. All data were analyzed at the .05 level of significance. Findings from the data indicated a significant difference in perceptions of teachers in 3 of 4 areas. First the planning process for their lessons was reported to be more structured and focused on the evaluation rubric. Next, the instructional strategies used in their lessons were reported as more focused on higher order thinking skills. And finally the time required to plan instruction had increased since the implementation of the TEAM framework

Domain wall anisotropic magnetoresistance in planar nanowires

The anisotropic magnetoresistance AMR of individual magnetic domain walls in planar nanowires has been systematically investigated as a function of the micromagnetic wall structure, width, and thickness of the nanowire. Experimentally derived thickness dependence of both the thin film resistivity and the anisotropic magnetoresistance were incorporated into the calculations. We found that the AMR value can be used to identify the wall structure and that the wall resistance is sensitive to wire width for widths less than 300 nm. Furthermore, in comparison with the detailed analysis here, a previous simplified domain wall model significantly underestimates domain wall resistance in narrower wires