Rayleigh scattering by hexagonal ice crystals and the interpretation of dual-polarisation radar measurements

Dual-polarisation radar measurements provide valuable information about the shapes and orientations of atmospheric ice particles. For quantitative interpretation of these data in the Rayleigh regime, common practice is to approximate the true ice crystal shape with that of a spheroid. Calculations using the discrete dipole approximation for a wide range of crystal aspect ratios demonstrate that approximating hexagonal plates as spheroids leads to significant errors in the predicted differential reflectivity, by as much as 1.5 dB. An empirical modification of the shape factors in Gans's spheroid theory was made using the numerical data. The resulting simple expressions, like Gans's theory, can be applied to crystals in any desired orientation, illuminated by an arbitrarily polarised wave, but are much more accurate for hexagonal particles. Calculations of the scattering from more complex branched and dendritic crystals indicate that these may be accurately modelled using the new expression, but with a reduced permittivity dependent on the volume of ice relative to an enclosing hexagonal prism.

A powder neutron diffraction study of the metallic ferromagnet Co3Sn2S2

Variable-temperature powder neutron diffraction data reveal that Co3Sn2S2 crystallizes in the shandite structure (space group R (3) over barm, a = 5.36855(3)angstrom, c = 13.1903(1) angstrom at 300 K). The structural relationship between Co3Sn2S2 and the intermetallic compound CoSn, both of which contain Kagome nets of cobalt atoms, is discussed. Resistivity and Seebeck coefficient measurements for Co3Sn2S2 are consistent with metallic behaviour. Magnetic susceptibility measurements indicate that Co3Sn2S2 orders ferromagnetically at 180(10) K, with a saturation moment of 0.29 mu(B) per cobalt atom at 5 K. The onset of magnetic ordering is accompanied by marked anomalies in the electrical transport properties. (c) 2008 Elsevier Masson SAS. All rights reserve

Complementarity of neutron reflectometry and ellipsometry for the study of atmospheric reactions at the air–water interface

The combined application of neutron reflectometry (NR) and ellipsometry to determine the oxidation kinetics of organic monolayers at the air–water interface is described for the first time. This advance was possible thanks to a new miniaturised reaction chamber that is compatible with the two techniques and has controlled gas delivery. The rate coefficient for the oxidation of methyl oleate monolayers by gas-phase O3 determined using NR is (5.4 ± 0.6) × 10−10 cm2 per molecule per s, which is consistent with the value reported in the literature but is now better constrained. This highlights the potential for the investigation of faster atmospheric reactions in future studies. The rate coefficient determined using ellipsometry is (5.0 ± 0.9) × 10−10 cm2 per molecule per s, which indicates the potential of this more economical, laboratory-based technique to be employed in parallel with NR. In this case, temporal fluctuations in the optical signal are attributed to the mobility of islands of reaction products. We outline how such information may provide critical missing information in the identification of transient reaction products in a range of atmospheric surface reactions in the future.

On the mass distribution of neutron stars

The distribution of masses for neutron stars is analysed using the Bayesian statistical inference, evaluating the likelihood of the proposed Gaussian peaks by using 54 measured points obtained in a variety of systems. The results strongly suggest the existence of a bimodal distribution of the masses, with the first peak around 1.37 M(circle dot) and a much wider second peak at 1.73 M(circle dot). The results support earlier views related to the different evolutionary histories of the members for the first two peaks, which produces a natural separation (even if no attempt to `label` the systems has been made here). They also accommodate the recent findings of similar to M(circle dot) masses quite naturally. Finally, we explore the existence of a subgroup around 1.25 M(circle dot), finding weak, if any, evidence for it. This recently claimed low-mass subgroup, possibly related to the O-Mg-Ne core collapse events, has a monotonically decreasing likelihood and does not stand out clearly from the rest of the sample.

Pion mass effects on axion emission from neutron stars through NN bremsstrahlung processes

The rates of axion emission by nucleon-nucleon bremsstrahlung are calculated with the inclusion of the full momentum contribution from a nuclear one pion exchange (OPE) potential. The contributions of the neutron-neutron (nn), proton-proton (pp) and neutron-proton (np) processes in both the non-degenerate and degenerate limits are explicitly given. We find that the finite-momentum corrections to the emissivities are quantitatively significant for the non-degenerate regime and temperature-dependent, and should affect the existing axion mass hounds. The trend of these nuclear effects is to diminish the emissivities. (C) 2009 Elsevier B.V. All rights reserved.

Investigation of whole blood of SJL/J mice using neutron activation analysis

The Br (0.0022 +/- A 0.0006 gL(-1)), Ca (0.113 +/- A 0.012 gL(-1)), Cl (3.07 +/- A 0.36 gL(-1)), K (2.63 +/- A 0.14 gL(-1)), Mg (0.045 +/- A 0.002 gL(-1)) and Na (2.09 +/- A 0.10 gL(-1)) concentrations were determined in whole blood of SJL/J mice using the Neutron Activation Analysis (NAA) technique. Eleven whole blood samples were analyzed in the IEA-R1 nuclear reactor at IPEN (So Paulo, Brazil). These data contribute for applications in veterinary medicine related to biochemistry analyses using whole blood. Moreover, the correlation with human blood estimation allows to checking the similarities for studying muscular dystrophy using this model animal.

Synchrotron X-ray imaging via ultra-small-angle scattering: principles of quantitative analysis and application in studying bone integration to synthetic grafting materials

Optimized experimental conditions for extracting accurate information at subpixel length scales from analyzer-based X-ray imaging were obtained and applied to investigate bone regeneration by means of synthetic beta-TCP grafting materials in a rat calvaria model. The results showed a 30% growth in the particulate size due to bone ongrowth/ingrowth within the critical size defect over a 1-month healing period.

Measurement of thermal neutron cross section and resonance integral for the (165)Ho(n, gamma)(166g)Ho reaction

The ground state thermal neutron cross section and the resonance integral for the (165)Ho(n, gamma)(166)Ho reaction in thermal and 1/E regions, respectively, of a thermal reactor neutron spectrum have been measured experimentally by activation technique. The reaction product, (166)Ho in the ground state, is gaining considerable importance as a therapeutic radionuclide and precisely measured data of the reaction are of significance from the fundamental point of view as well as for application. In this work, the spectrographically pure holmium oxide (Ho(2)O(3)) powder samples were irradiated with and without cadmium covers at the IEA-RI reactor (IPEN, Sao Paulo), Brazil. The deviation of the neutron spectrum shape from 1/E law was measured by co-irradiating Co, Zn, Zr and Au activation detectors with thermal and epithermal neutrons followed by regression and iterative procedures. The magnitudes of the discrepancies that can occur in measurements made with the ideal 1/E law considerations in the epithermal range were studied. The measured thermal neutron cross section at the Maxwellian averaged thermal energy of 0.0253 eV is 59.0 +/- 2.1 b and for the resonance integral 657 +/- 36b. The results are measured with good precision and indicated a consistency trend to resolve the discrepant status of the literature data. The results are compared with the values in main libraries such as ENDF/B-VII, JEF-2.2 and JENDL-3.2, and with other measurements in the literature.

Thermal wave scattering by two overlapping and parallel cylinders

In this paper an analytical solution of the temperature of an opaque material containing two overlapping and parallel subsurface cylinders, illuminated by a modulated light beam, is presented. The method is based on the expansion of plane and cylindrical thermal waves in series of Bessel and Hankel functions. This model is addressed to the study of heat propagation in composite materials with interconnection between inclusions, as is the case of inverse opals and fiber reinforced composites. Measurements on calibrated samples using lock-in infrared thermography confirm the validity of the model.

Spallation product distributions and neutron multiplicities for accelerator-driven system using the CRISP code

Neutron multiplicities for several targets and spallation products of proton-induced reactions in thin targets of interest to an accelerator-driven system obtained with the CRISP code have been reported. This code is a Monte Carlo calculation that simulates the intranuclear cascade and evaporationl fission competition processes. Results are compared with experimental data, and agreement between each other can be considered quite satisfactory in a very broad energy range of incitant particles and different targets.

An experimental and theoretical investigation into positron and electron scattering from formaldehyde

We report on measurements of total cross sections (TCSs) for positron scattering from the fundamental organic molecule formaldehyde (CH(2)O). The energy range of these measurements was 0.26-50.3 eV, whereas the energy resolution was similar to 260 meV. To assist us in interpreting these data, Schwinger multichannel level calculations for positron elastic scattering from CH(2)O were also undertaken (0.5-50 eV). These calculations, incorporating an accurate model for the target polarization, are found to be in good qualitative agreement with our measured data. In addition, in order to compare the behaviour of positron and electron scattering from this species, independent atom model-screened additivity rule theoretical electron TCSs, now for energies in the range 1-10 000 eV, are also reported.

Dipole polarizability and Rayleigh light scattering by the hydrated electron

Assuming the existence of a confined state of the electron in bulk water the polarizability of the hydrated electron is analyzed. Statistically uncorrelated supermolecular structures composed of seven water molecules (first solvation shell) with an extra electron were extracted from classical Monte Carlo simulation and used in quantum mechanical second-order Moller-Plesset calculations. It is found that the bound excess electron contributes with 274 a.u. to the total dipole polarizability of 345 a.u. for (H(2)O)(7)(-). From the calculated polarizabilities the Rayleigh elastic light scattering properties are inferred and found to considerably enhance activity and light depolarization. (C) 2009 Elsevier B.V. All rights reserved.

Resonant neutrino scattering: An impossible experiment?

The experimental feasibility was investigated for the resonant scattering of monoenergetic neutrinos emitted in the two-body beta decay. A simple general formula shows that the resonance cross section can be as large as of the order of 10(-17) cm(2). The Mossbauer setup using a solid crystal was examined with a focus on the electronic structure of the emitter and the absorber. Based on realistic calculations, we show that interactions of valence electrons in the solid lead to a level broadening of the atomic ground state, which considerably suppresses the resonant scattering of neutrinos. (C) 2010 Elsevier B.V. All rights reserved.

Sub-barrier fusion of two-neutron halo nuclei

The tunneling of composite systems, where breakup may occur during the barrier penetration process, is considered in connection with the fusion of halo-like radioactive, neutron- and proton-rich nuclei, on heavy targets. The large amount of recent and new data clearly indicates that breakup hinders the fusion at energies near and below the Coulomb barrier. However, clear evidence for enhancement due to halo properties seems to over ride the breakup hindrance at lower energies, owing, to a large extent, to the extended matter density distribution. In particular we report here that at sub-barrier energies the fusion cross section of the Borromean two-neutron halo nucleus (6)He with the actinide nucleus (238)U is significantly enhanced as compared to the fusion of a similar projectile with no halo. This conclusion differs from that of the original work, where it was claimed that no such enhancement ensues. This sub-barrier fusion enhancement is also observed in the (6)He + (209)Bi system. (C) 2010 Elsevier B.V. All rights reserved.

Microwave induced magnetoresistance oscillations and inelastic scattering time in double quantum wells

The interference of microwave-induced resistance oscillations and magneto-intersubband oscillations in double quantum wells exposed to a continuous microwave irradiation is under study. By comparing experimental and theoretical magnetoresistance traces at different temperatures, we confirm that the inelastic mechanism of photoresistance explains our observations up to T similar or equal to 4 K. For higher temperatures, our results suggest a deviation of the inelastic scattering time tau(in) from the predicted T(-2) dependence. (C) 2009 Elsevier B.V. All rights reserved.