Analysis of neutron yield produced by high-energy proton

Comparisons have been made between computational results obtained with the BNL code system and experimental data measured by Vasfl'kov et al. for 56 x 56 x 64 cm natural and depleted uranium blocks surrounded by lead walls and primary proton energies of 400 and 660 MeV. The energetic protons from a linear accelerator are used to produce an intensive neutron source inthe uraniumblocko The computercode system prepared at BNL to perform nuclear design analyses of linear accelerator reactors consists of six main programs: NMTC for spallation-evaporation processes above 15 MeV, HIST3D for the analysis of collision event records obtained by NMTC to get P₃ neutron source distribution, DLC-2 to compile 100 energy group cross sections, TAPEMAKER for format conversion, ANISN to collapse 100 group cross sections to fewer group P₃ cross section sets, and the principal code TWOTRAN-II which performs neutron reaction and transport calculations in the energy range below 15 MeV. Our computational method gives conservative total neutron yields, i.e., underestimates of about 16.8–29.8% in comparison with measured values depending on proton energy. Radiative capture²³⁸U(n,) density distributions have been compared between the calculation and experiment. The calculated distribution has the higher peak in the central part of the target system and the steeper gradient both in the r and z directions.Brookhaven National Laboratory, Upton, New York 11973. Published in Atomnaya Énergiya, Vol. 47, No. 2, pp. 83–91, August, 1979.     

CO2 reduction using hydrothermal method for the selective formation of organic compounds

The reduction of CO₂ under hydrothermal conditions has been investigated. In typical experiment, Fe-powder, Ni-powder, solvent, and CO₂ have been reacted in a batch-type micro autoclave under hydrothermal conditions for several hours. Methane, formic acid, and hydrogen were generated after treatment in water. With the rise of Ni amount, the methane yield increased while hydrogen and formic acid decreased. It is supposed that Ni has acted as a hydrogenation catalyst. In basic solution, CO₂ was converted to formic acid selectively at 300°C involved with trace of methane. Considering the reduction characteristics of formic acid, the reaction pathway has been discussed. In experiments with the mixture of Fe and Fe₃O₄, trace of methanol was detected at the experiments with less amount of metallic Fe. It is inferred that the control on the effect of reductant is indispensable for oxygenated organic compound formation. Experiment on the effect of water has been conducted using hydrogen. Ethane yield increased with the amount of water, while there was no drastic change in the yield of methane. From these results, it is supposed that the steam reforming reaction of methane was involved in the reduction of CO₂, and effected on the C–C bond formation.     

Viscosity of Gaseous Mixtures of HFC-125 + Propane from 298.15 to 423.15 K at Pressures to 6.7 MPa

This paper reports experimental results for the viscosity of gaseous mixtures of HFC-125 (pentafluoroethane) + propane. The measurements were carried out with an oscillating-disk viscometer of the Maxwell type at temperatures from 298.15 to 423.15 K. The viscosity was measured for two mixtures containing 50.11 and 75.03 mol% HFC-125 in propane. The viscosity at normal pressure was analyzed with the extended law of corresponding states developed by Kestin et al., and the scaling parameters were obtained for unlike-pair interactions between HFC-125 and propane. The modified Enskog theory developed by Vesovic and Wakeham was applied to predict the viscosity for the binary gaseous mixtures under pressure. From comparisons between experimental results and calculated values of the HFC-125 + propane system, it should be concluded that the Vesovic-Wakeham method gives reliable predictions for the viscosity of a gaseous mixture containing both polar and nonpolar compounds.     

Magnetic Correlation in BETS2(Cl2TCNQ)

We carried out⁷⁷Se NMR measurements on BETS₂(Cl₂TCNQ) under pressure in order to investigate the magnetic properties of the insulating state which appears above 0.6 GPa. The relaxation rate 1/T₁ at 0.7 GPa shows small peak-like anomaly at 20 K, indicating a spin density wave transition as observed in BETS₂(Br₂TCNQ).     

Are lebed’s magic angles truly magic?

We report high-resolution angle-dependent measurements of the Periodic Orbit Resonance (POR) effect in (TMTSF)₂ClO₄. We observe additional harmonic resonances that were not observed in previous studies. By measuring over a broad range of frequency, field, and field orientation, we find that all of the POR evolve from the Lebed magic angles observed in dc (ω=0) AMRO measurements. However, we find that the resonance angles vary with frequency in a manner that can easily be explained using a semiclassical model. This indicates that these angles are not ‘magic’ at frequencies on the order of the cyclotron frequency.     

Viscosity of Alternative Refrigerants R407C and R407E in the Vapor Phase from 298.15 to 423.15 K

This paper presents new measurements of the viscosity of gaseous R407C (23 mass% HFC-32, 25 mass% HFC-125, 52 mass% HFC-143a) and R407E (25 mass% HFC-32, 15 mass% HFC-125, 60 mass% HFC-143a). The measurements were carried out with an oscillating-disk viscometer of the Maxwell type at temperatures from 298.15 to 423.15 K. The densities of these two fluid mixtures were calculated with the equation-of-state model in REFPROP. The viscosity at normal pressures was analyzed with the extended law of corresponding states developed by Kestin et al., and the scaling parameters needed in the analysis were obtained from our previous studies for the viscosity of the binary mixtures consisting of HFC-32, HFC-125, and HFC-134a. The modified Enskog theory developed by Vesovic and Wakeham (V-W method) was applied to predict the viscosity for the ternary gaseous HFC mixtures under pressure. As for the calculation of pseudo-radial distribution functions in mixtures, a method based on the equation of state for hard-sphere fluid mixtures proposed by Carnahan-Starling was applied. It was found that the V-W method can predict the viscosity of R407C and R407E without any additional parameters for the ternary mixture.     

Dominant stress region for crack initiation at interface edge of microdot on a substrate

In order to examine the mechanics of crack initiation at the free interface edge of a microcomponent on a substrate, delamination tests are carried out for two specimen shapes of Cr microdots on a SiO₂ substrate. The microdots of the first specimen are shaped like the frustum of a round cone. The Cr microdots are successfully delaminated from the SiO₂ substrate in a brittle manner and the critical load is measured by atomic force microscopy (AFM) with a lateral loading apparatus. Stress analysis reveals that a singular stress field exists near the interface edge and the strength for the crack initiation is governed by the intensified normal stress field. The critical stress intensity parameter is evaluated as K_σC ≈ 0.24 MPa m^0.39. Similar delamination tests are conducted for microdots shaped like the frustum of an oval cone. The stress distributions at the crack initiation of this specimen shape show a higher normal stress than the first specimen shape in the region near the interface edge of about x < 40 nm, while it is lower in the region of about x > 50 nm (x: distance from the edge). This suggests a limitation of conventional fracture mechanics: namely, the crack initiation in these specimens is not uniquely governed by the intensity of the singular field. It is found that the delamination crack is initiated when the averaged stress σ_ya in the region of 90-130 nm reaches 190-270 MPa, regardless of the specimen shape. This indicates that the dominant stress region of crack initiation is roughly estimated as 90-130 nm and the criterion is given in terms of the averaged stress in the region.     

Thermoelectric properties of Bi and Cu co-doped Ca3Co2O6single crystals

Single crystals of Bi and Cu-doped Ca₃Co₂O₆were synthesized in a molten K₂CO₃flux. Using an obtained single crystal of (Ca_0.985(5)Bi_0.015(5))₃(Co_0.990(3)Cu_0.010(3))₂O₆elongated to the c-axis direction of the crystal structure, the electric resistivity (ρ) and Seebeck coefficient (S) were measured from room temperature to over 1000 K in air. The single crystal showed p-type semiconducting behavior with ρ values of 1.8 Ω cm at 303 K and 0.017 Ω cm at 1000 K. The S values were +254 μ VK^{− 1} at 325 K, +360 μ VK^{− 1} at 420 K, and +214 μ VK^{− 1} at 1000 K. The power factor (S ² ρ ^{− 1}) increased with an increase of temperature and attained 2.70 × 10^{− 4} Wm^{− 1}K^{− 2} at 1000 K.     

A 63-mW H.264/MPEG-4 audio/visual codec LSI with module-wise dynamic Voltage/frequency scaling

A single-chip H.264 and MPEG-4 audio-visual LSI for mobile applications including terrestrial digital broadcasting system (ISDB-T / DVB-H) with a module-wise, dynamic voltage/frequency scaling architecture is presented for the first time. This LSI can keep operating even during the voltage/frequency transition, so there is no performance overhead. It is realized through a dynamic deskewing system and an on-chip voltage regulator with slew rate control. By the combination with traditional low power techniques such as embedded DRAM and clock gating, it consumes only 63 mW in decoding QVGA H.264 video at 15 frames/sec and MPEG-4 AAC LC audio simultaneously.     

Elements and their transitions feasible for NEET

Electron and nuclear transitions in the nuclear excitation by electron transition (NEET) process have been investigated. The NEET transitions for nuclei are presented in a table in which the electron and nuclear transitions, their transition energies, transition multipoles, and nuclear spin angular momentum are given. The elements are listed for which the difference between the electron and nuclear transition energy is <5 keV, because the NEET probability will be appreciable if the electron transition energy is close to the nuclear transition one. As both the experimental and theoretical studies for NEET are at an early stage, only the elements and their parameters related to NEET are listed here. The present compilation, however, provides a useful direction for future studies of NEET and its applications to nuclear science.