Steady-state Source Research Articles

Neutron diffraction residual stress analysis of steel engineering components: a study of the elastic and plastic anisotropy

Abstract The effect of the elastic and plastic anisotropy has been investigated in a welded pipe for nuclear applications (AISI 347) and in a welded plate for conventional power plants (Uni-Fe510D). The analysis has been performed exploiting neutron conventional and reverse time-of-flight spectra and comparing the single peak fit of some set of lattice planes with the Rietveld average. The results show that only some crystallographic directions (namely the 〈311〉 and the 〈111〉 for γ-Fe and 〈211〉 and the 〈110〉 for α-Fe) are in agreement with the average inherent in the Rietveld refinement. Those peaks are therefore recommended for residual stress analysis at steady state sources. The other peaks yield more scattered data (with higher statistical error), but allow spotting the influence of plastic anisotropy. The latter has a greater influence on all single peak data if the macroscopic stress exceeds the bulk yield strength.

Development of a 100eV, high-flux ion beam acceleration system

A new system of electrodes has been developed for a high-flux, steady-state ion source with a large irradiation area to study plasma-wall interaction in fusion reactors at energies in the 100eV range. These electrodes are multiaperture triode electrodes—the sizes of which are smaller as compared with those used in similar applications for previous systems. In particular, these electrodes have a thickness of 0.5mm and an aperture size of 0.9mm in diameter with 0.5mm gaps between them. The influence of the plasma sheath on the beam energy has to be estimated since the plasma sheath potential is comparable to the acceleration voltage in such a low energy region. Source plasma is produced by a hydrogen arc discharge, following which hydrogen ions are extracted by using the new electrode system. Ion fluxes of 1.5×1020–5.3×1020H∕m2s with energies ranging from 28to102eV∕H were obtained. These values are comparable to those of conventional high-flux ion sources with higher energies. This low energy ion beam can be used to investigate the plasma-wall interaction in fusion reactors.

Ion sources for the varying needs of ion implantation

A joint research and development effort whose ultimate goal is to develop steady-state intense ion sources to meet the needs of the two energy extremes of ion implanters (mega-electron-volt and of hundreds of electron-volt) has been in progress for the past two years. Present day high-energy ion implanters utilize low charge state (usually single charge) ion sources in combination with rf accelerators. Usually, a MeV linear accelerator is used for acceleration of a few milliamperes. It is desirable to have instead an intense, high charge state ion source on a relatively low-energy platform (dc acceleration) to generate high-energy ion beams for implantation. This endeavor has already resulted in very high steady-state output currents of higher charge states antimony and phosphorous ions. Low-energy ion implantation is performed presently by decelerating high-energy extracted ions. Consequently, output currents are low due to space charge problems. Contamination is also a problem due to gases and plasmas employed to mitigate the space charge issues. Our efforts involve molecular ions and a plasmaless/gasless deceleration method. A program overview is presented in this article. Although source specifics are described in accompanying papers, only this article contains our most recent results.

ITEP Bernas ion source with additional electron beam

A joint research and development program is underway to develop steady-state intense ion sources for the two energy extremes of MeV and hundreds of eV. For the MeV range the investigations were focused on charge-state enhancement for ions generated by the modified Bernas ion sources. Based on the previously successful ITEP experience with the e-metal vapor vacuum arc ion source [e.g., Batalin et al., Rev. Sci. Instrum. 75, 1900 (2004)], the injection of a high-energy electron beam into the Bernas ion source discharge region is expected to enhance the production of high charge states. Presented here are construction details and studies of electron-beam influence on the enhancement of ion-beam charge states generated by the modified Bernas ion source.

Transport line for beam generated by ITEP Bernas ion source

A joint research and development program is underway to investigate beam transport systems for intense steady-state ion sources for ion implanters. Two energy extremes of MeV and hundreds of eV are investigated using a modified Bernas ion source with an indirectly heated cathode. Results are presented for simulations of electrostatic systems performed to investigate the transportation of ion beams over a wide mass range: boron to decaborane.

Radon loss across the water‐air interface (Gulf of Thailand) estimated experimentally from 222Rn‐224Ra

We used 222Rn and 224Ra measured in the Upper Gulf of Thailand to estimate 222Rn atmospheric evasion across the water‐air interface. The Chao Phraya estuary represents a steady‐state source of these tracers and we looked at their horizontal distribution on a transect leading away from the estuary into the Gulf. The isotopes 222Rn and 224Ra have very similar half‐lives and are affected in the same manner by mixing processes but only radon will emanate to the atmosphere. We thus are able to estimate the radon air‐water exchange rate from the difference in the slopes of the 222Rn and 224Ra horizontal distributions. Estimated gas exchange velocities (k) based on our results were 1.1 cm hr−1 in the dry season (January 2004) and 2.1 cm hr−1 during the wet season (July 2004). These rates agreed reasonably well with some theoretical models developed for lakes, estuaries and coastal systems.

Decaborane beam from ITEP Bernas ion source

A joint research and development program is under way to develop steady-state intense ion sources for the two energy extremes of MeV and hundreds of eV. The difficulties of extraction and transportation of low-energy boron beams are investigated using a decaborane compound [I. Yamada, W. L. Brown, J. A. Northby, and M. Sosnowski, Nucl. Instrum. Methods Phys. Res. B 79, 223 (1993)]. Presented here are the results from ITEP experiments using the Bernas ion source with an indirectly heated LaB6 cathode.

Measurement and modelling of residual stresses in straightened commercial eutectoid steel rods

Neutron strain scanning measurements on a eutectoid steel rod that has been subjected to standard industrial coiling and straightening operations are presented. Strains were determined non-destructively using two different diffractometers, one at a steady-state neutron source and the other at a pulsed spallation neutron source, with measurements made in both the ferrite and cementite components of the pearlitic microstructure. The residual stress state is explained in terms of a simplified analytical model for a two-phase material, which takes into account the successive loading operations contributing to residual stress. The results show that residual stresses generated by bending–straightening operations are significant and are likely to play an important role in the mechanical properties of the final wires.

Microwave measurement of decaying plasma in liquid helium

Decaying plasma in a microwave cavity filled with liquid helium (LHe, hereafter) is studied. An X-band TE/sub 113/ mode cylindrical cavity is filled with LHe, and a high-voltage pulse with duration 7 /spl mu/s, voltage V/spl les/20 kV, and current I/spl les/360 A is applied between a tungsten needle electrode and a thin stainless-steel mesh which separates an adjacent small discharge space from the cavity. The transmission signals through the cavity show the presence of decaying plasma in LHe with decay time on the order of 200 ms for a temperature range from 4.2 to 2.3 K at saturating vapor pressure. The response signals are suppressed in the pressurized LHe, as well as in superfluid LHe below 2.17 K. Our estimated mass of the charged carriers just after the pulsed discharge, assuming a diffusion loss mechanism, is much less than the value known as an effective mass of heavy ions which were produced by a steady-state ion source in LHe measured by Poitrenaud and Williams (1972). Our experimental observation suggests that the heavy effective mass of ions in LHe might take time to develop to its full extent.

Elastodynamic Green's functions for a laminated piezoelectric cylinder

Elastodynamic Green's functions for a piezoelectric structure represent the electro-mechanical response due to a steady-state point source as either a unit force or a unit charge. Herein, Green's functions for a laminated circular piezoelectric cylinder are constructed by means of the superposition of modal data from the spectral decomposition of the operator of the equations governing its dynamic behavior. These governing equations are based on a semi-analytical finite element formulation where the discretization occurs through the cylinder's thickness. Examples of a homogeneous PZT-4 cylinder and a two-layer cylinder composed of a PZT-4 material at crystal orientations of ±30° with the longitudinal axis are presented. Numerical implementation details for these two circular cylinders show the convergence and accuracy of these Green's functions.

The performance of a multiplexing three-axis spectrometer

A novel multiplexing three-axis spectrometer for thermal neutrons has been tested for single-crystal spectroscopy. Measuring the entire 2D dispersion manifold in the bc plane of the spin-Peierls compound CuGeO3, we demonstrate that the spectrometer fascilitates investigations of large volumes in (Q,ω)-space from small single crystals. The performance of this multi-analyser spectrometer at a steady-state source compares well to an existing time-of-flight spectrometer at a pulsed source.

Structure of liquid lithium

Neutron diffraction experiments, made at a steady-state reactor source, were used to study the structure of liquid7Li at temperaturesof 197, 452 and 595 °C. A careful data analysis procedure was undertaken in which specific issues taken intoaccount include (i) the influence of Brillouin modes on the measured diffractionpattern at small scattering vectors, (ii) inelasticity corrections that are significantfor light atom systems, such as lithium, and (iii) the effects caused by thediffractometer resolution function. Data sets taken for the same liquid temperatureusing different incident neutron energies yield ion–ion partial structure factors,SII(k), that are in agreement within the statistical errors. TheSII(k) are compared with previous experimental results and with the results obtainedfrom liquid state theory and molecular dynamics methods made using severaldifferent local pseudopotentials. Finally, the valence electron form factor,ρ(k), is estimatedby combining SII(k) with x-ray diffraction data and the ion–valence electron partial structure factor,SIe(k), is calculatedby combining SII(k) with the ρ(k) obtained from both experiment and theory. The results show that the extraction ofρ(k) and SIe(k) by a combination of neutron and x-ray diffraction methods is feasible in practice, butdemonstrates a need for new x-ray diffraction experiments on liquid lithium.

Astrophysics challenges of MeV-astronomy instrumentation

Meeting the new challenges of gamma-ray astronomy will be difficult. The variety of sources and the nature of their emissions over a wide range of energy and intensities will undoubtedly require an integrated observatory, or its equivalent, in the fashion of Compton. However, for the study of sources in the MeV range, a new Compton telescope will be necessary. It must possess an effective area much greater than COMPTEL, but also reject background more efficiently than COMPTEL. With these properties, one could easily attain an order of magnitude improvement in sensitivity over COMPTEL, opening up numerous investigations while providing a rich catalog of sources for subsequent study. Future goals not only include conducting observations over the wide energy range from 0.3 to 20 MeV, but also performing the best possible measurements of narrow and broad lines, point sources and extended objects, and steady state and transient sources with a large dynamic range. We review the demands on and the challenges in developing a medium energy Compton gamma-ray telescope that can make significant strides in our understanding of the Universe.

Prospects for the Use of the Pulsed Fields in Neutron Research of Condensed Matter

AbstractFor Abstract see ChemInform Abstract in Full Text.

Design of a low-energy multi-chopper spectrometer for a second target station at ISIS

We present a design for a low-energy-transfer, 1–20 meV, multi-chopper (MC) spectrometer, intended for the new second target station (TSII) at ISIS. At present, low-energy MC spectrometers exist only on steady-state sources, but our results show they are better suited to a pulsed spallation source.

Thermomorphic fluorous imine and thioether palladacycles as precursors for highly active Heck and Suzuki catalysts; evidence for palladium nanoparticle pathways

p-Iodobenzaldehyde is elaborated to the fluorous alcohol p-Rf8(CH2)3C6H4CH(OH)(CH2)2Rf8 (three steps/80%; Rf8 = n-C8F17), which is converted to imine p-Rf8(CH2)3C6H4C(N(CH2)3Rf8)(CH2)2Rf8 (6, two steps/93%) and thioether p-Rf8(CH2)3C6H4CH(S(CH2)3Rf8)(CH2)2Rf8 (12, 64%). Reactions with Pd(OAc)2 (AcOH, 95 °C) give palladacycles with [RC6H3CR′N(R)Pd(μ-OAc)]2 (7, 87%) and [RC6H3CHR′S(R)Pd(μ-OAc)]2 (13, 84%) cores. The former reacts with LiCl and LiI to give the corresponding bridging halide complexes (8, 9); LiCl/PPh3 affords monomeric RC6H3CR′N(R)Pd(Cl)(PPh3) (10). Palladacycles 7–9 and 13 are poorly soluble or insoluble in many solvents at 20–24 °C, but much more soluble at higher temperatures. The CF3C6F11/toluene partition coefficients of 6, 7, 12, and 13 are >91∶<9 (24 °C). Both 7 and 13 are excellent catalyst precursors for Heck reactions of aryl halides. Turnover numbers exceed 106 with phenyl iodide under homogeneous conditions in DMF at 140 °C. The palladacycles precipitate as bridging halides upon cooling, and can in theory be recovered by liquid/solid phase separations. However, since the quantities are small, the solvent C8F17Br is added for recycling. Induction periods in both the first and second cycles, and progressively lower activities, are noted. Transmission electron microscopy indicates the formation of soluble palladium nanoparticles. Together with other data, it is proposed that the nanoparticles are the active catalysts, for which the recyclable palladacycles constitute a steady state source, until exhausted. Complex 7 similarly catalyzes the Suzuki reaction (K3PO4, toluene, 130 °C).

Power system analysis using space-vector transformation

In this paper, the space-vector transformation used in machine vector control is applied to power system analysis. The proposed method is used to model electric machines, power electronic converters, transformers, and transmission lines and to analyze power sources and loads with different connections (delta and wye). This method can also be applied to analyze steady-state (or transient phenomena) and unbalanced sources, including harmonics. Models obtained with this method are as simple as those of the per-phase approach. With the space-vector transformation, instantaneous active and reactive power concepts can be generalized, and new power system control strategies can be developed when power electronic converters are used. Steady-state, transient behavior, and harmonic analyses examples and applications are presented to illustrate the performance and advantages of the proposed method. This method can be extended to unbalanced systems (e.g., unsymmetric faults) using instantaneous symmetrical components in polyphase balanced circuits.

Prospects for the use of the pulsed fields in neutron research of condensed matter

The peculiarities of the pulsed magnetic field usage in the research of magnetic properties of crystal substances with different pulsed and steady-state sources of neutrons are considered. The comparative characteristics of existing and some projected spectrometers intended for neutron researches are evaluated. The comparison of the efficiency of experiments on the most intensive neutron sources is discussed.

Optical characteristics of the steady-state plasma of a longitudinal discharge in a He/CFC-12 mixture

The emission from the plasma of a contracted longitudinal dc discharge in a He/CF2Cl2 mixture in the wavelength range 130–300 nm is investigated. It is shown that the discharge plasma emits within the range 150–260 nm. The emission consists mainly of the broad bands of Cl2 molecules and single-charged chlorine ions. The pressure and composition of the working mixtures, the discharge current, and the time during which the emitter can operate on a single gas fill are optimized to attain the best characteristics of UV and VUV radiation. The results obtained are of interest for developing a steady-state source of VUV and UV radiation to be applied in microelectronics, photochemistry, and medicine.

Neutron diffraction applied to geological texture and stress analysis

Texture is defined as preferred crystallographic orientation in a polycrystalline aggregate. The main mechanisms of geological texture formation are crystallization, sedimentation, plastic deformation, recrystallization and metamorphism. Textures of geomaterials are fingerprints of the earth's history. The complexity of geological texture analysis results mainly from the overprinting of different textures on several mineral components during different orogenic periods. Quantitative texture analysis, i.e., the calculation of a three-dimensional orientation distribution function of crystallites, is based on experimental pole figures which represent the orientation distributions of certain crystallographic directions and which can be obtained from X-ray or neutron-diffraction techniques. Due to the high penetration capability of neutrons, large specimens can be investigated resulting in global volume textures rather than local surface textures from X-rays. Neutron-diffraction pole figures are characterized by high grain statistics even on coarse-grained material. Individual pole figures can also be obtained from reflection-rich diffraction patterns of multiphase rocks and low-symmetry mineral constituents by using position-sensitive detectors and by pattern decomposition by means of profile-fitting methods. Neufron texture diffractometers are operated in the constant-wavelength mode at steady-state sources and using time-of-flight techniques at pulsed sources. Different experimental set-ups are discussed. Results of neutron-diffraction texture analyses on monomineralic and polymineralic rocks are presented, e.g., on calcite, quartzite, plagioclase, pyrrhotite ores, granite, and orthopyroxene-sillimanite-granulite. The wide application spectrum of neufron texture analysis includes objects of the outer solar system as in the low-temperature texture study on ice and the non-destructive investigations on rare pieces of meteorites. The application of neutron diffraction on strain measurements and residual stress analysis of geological material is discussed. Natural effects on rocks are orders of magnitude smaller than in technological material and drilling gives rise to stress relaxation. Experimental deformations can be observed during in situ measurements at various pressures and temperatures. Neutron strain diffractometers are described. Examples of recent results on the full strain/stress tensor in sandstone and on strain partitioning in polymineralic rocks are given. Future prospects of new high-intensity neutron sources are promising in performing combined structure, texture and stress analysis. New instruments are under construction and software packages on the basis of full-pattern Rietveld refinements are available.