Nuclear track radiography of “Hot” aerosol particles

Nuclear track radiography was applied to identify aerosol “hot” particles which contain elements of nuclear fuel and fallout after Chernobyl NPP accident. For the determination of the content of transuranium elements in radioactive aerosols the measurement of the -activity of “hot” particles by SSNTD was used in this work, as well as radiography of fission fragments formed as a result of the reactions (n,f) and (γ,f) in the irradiation of aerosol filters by thermal neutrons and high energy gamma quanta. The technique allowed the sizes and alpha-activity of “hot” particles to be determined without extracting them from the filter, as well as the determination of the uranium content and its enrichment by ²³⁵U, ²³⁹Pu and ²⁴¹Pu isotopes. Sensitivity of determination of alpha activity by fission method is 5×10⁻⁶ Bq per particle. The software for the system of image analysis was created. It ensured the identification of track clusters on an optical image of the SSNTD surface obtained through a video camera and the determination of size and activity of “hot” particles.     

Gamma ray radiation induced visible light absorption in P-doped silica fibers at low dose levels

A CCD Fiber Optic Spectrometer has been used to monitor the gamma ray radiation induced loss in P-doped fibers at different dopant concentrations (1, 5 and 10 mol%) with a light source (an incandescent bulb with a temperature of 2800–3000 K). The range of dose rates is limited to that used in medical applications (cancer treatments), that is 0.1 to 1.0 Gray per minute (Gy/min). At low integral dose level (<2.0 Gy) four absorption peaks were observed (470, 502, 540 and 600 nm) within the visible region. It has been observed that the radiation induced loss at 470 and 600 nm depends strongly on dose rate. At dose rates of 0.2 and 0.5 Gy/min the induced loss shows nonlinear relation to the total dose. However, at high dose rate (1.0 Gy/min) and low dose rate (0.1 Gy/min) it seems to have a linear dependence with total dose. The conversion from NBOHCs to GeX centers was observed during gamma radiation at low dose rates (0.1–0.5 Gy/min). At the wavelength of 502 and 540 nm, the radiation induced losses show excellent linear relations with total dose (<2.0 Gy) with little dose rate dependence. Experimental results show that the sensitivity (induced loss (dB) per meter fiber per Gy) of 5 mol% P-doped silica fiber is more than 30 times greater than that of a standard multi-mode (MM) communication fiber. The results suggest that P-doped silica fiber is a good candidate as a sensing component in fiber optic dosimetry, especially for radiation therapy applications.     

Positive and negative linear magnetoresistance of graphite

The magnetoresistance (MR) of bulk graphite with different particle sizes is investigated. The MR of the graphite decreases with the particle size decreases. The graphite with micro-sized particles has a positive MR and exhibits positive linear field dependence of MR at about 50 K, whereas the graphite with particle size of 30.2 nm has a negative MR and exhibits negative linear field dependence of MR at about 25 K. The possible mechanism for the MR of graphite can be partially understood using ordinary MR theory, weak localization theory and diffuse scattering theory.     

Radioluminescence (RL) behaviour of Al2O3:C-potential for dosimetric applications

The radioluminescence (RL) of carbon doped aluminium oxide (Al₂O₃:C) TL dosimeter material (TLD-500) was investigated using a ¹³⁷Cs conversion electron source (which also emits β and γ) for simultaneous irradiation and luminescence excitation. Furthermore, RL dosimetry characteristics of this material were studied. The main RL emission occurs at 420 nm. That matches the known main TL and OSL emissions for this material as well as an emission that was investigated in earlier RL studies, excited at higher energies (4 MeV electrons) and very high pulse delivered doses (≈800 kGy·s⁻¹). Furthermore, the saturation dose for the main peak is reached at the dose level of ≈80 Gy as known from TL and earlier RL investigations. Other peaks at 700 and 790 nm and broad emission bands at photon energies higher than 3.00 eV and others between 2.00 and 2.50 eV were observed. The 700 nm emission shows growth also at higher dose levels, and saturates at an estimated dose of ≈800 Gy. The 790 nm emission reaches its maximum intensity at ≈10 Gy absorbed dose. The reported results give an outlook to the usability and the potential of Al₂O₃:C combined with RL measurements for radiation dosimetry as well as for beta source calibration, using radioluminescence.     

Saturation and BFKL dynamics in the HERA data at small-x

We show that the HERA data for the inclusive structure function F₂(x,Q²) for x10⁻² and 0.045Q²45 GeV² can be well described within the color dipole picture, with a simple analytic expression for the dipole–proton scattering amplitude, which is an approximate solution to the non-linear evolution equations in QCD. For dipole sizes less than the inverse saturation momentum 1/Q_s(x), the scattering amplitude is the solution to the BFKL equation in the vicinity of the saturation line. It exhibits geometric scaling and scaling violations by the diffusion term. For dipole sizes larger than 1/Q_s(x), the scattering amplitude saturates to one. The fit involves three parameters: the proton radius R, the value x₀ of x at which the saturation scale Q_s equals 1 GeV, and the logarithmic derivative of the saturation momentum λ. The value of λ extracted from the fit turns out to be consistent with a recent calculation using the next-to-leading order BFKL formalism.     

Exploring the need for localization in ensemble data assimilation using a hierarchical ensemble filter

Good performance with small ensemble filters applied to models with many state variables may require ‘localizing’ the impact of an observation to state variables that are ‘close’ to the observation. As a step in developing nearly generic ensemble filter assimilation systems, a method to estimate ‘localization’ functions is presented. Localization is viewed as a means to ameliorate sampling error when small ensembles are used to sample the statistical relation between an observation and a state variable. The impact of spurious sample correlations between an observation and model state variables is estimated using a ‘hierarchical ensemble filter’, where an ensemble of ensemble filters is used to detect sampling error. Hierarchical filters can adapt to a wide array of ensemble sizes and observational error characteristics with only limited heuristic tuning. Hierarchical filters can allow observations to efficiently impact state variables, even when the notion of ‘distance’ between the observation and the state variables cannot be easily defined. For instance, defining the distance between an observation of radar reflectivity from a particular radar and beam angle taken at 1133 GMT and a model temperature variable at 700 hPa 60 km north of the radar beam at 1200 GMT is challenging. The hierarchical filter estimates sampling error from a ‘group’ of ensembles and computes a factor between 0 and 1 to minimize sampling error. An a priori notion of distance is not required. Results are shown in both a low-order model and a simple atmospheric GCM. For low-order models, the hierarchical filter produces ‘localization’ functions that are very similar to those already described in the literature. When observations are more complex or taken at different times from the state specification (in ensemble smoothers for instance), the localization functions become increasingly distinct from those used previously. In the GCM, this complexity reaches a level that suggests that it would be difficult to define efficient localization functions a priori. There is a cost trade-off between running hierarchical filters or running a traditional filter with larger ensemble size. Hierarchical filters can be run for short training periods to develop localization statistics that can be used in a traditional ensemble filter to produce high quality assimilations at reasonable cost, even when the relation between observations and state variables is not well-known a priori. Additional research is needed to determine if it is ever cost-efficient to run hierarchical filters for large data assimilation problems instead of traditional filters with the corresponding total number of ensemble members.     

Growth of aligned carbon nanotube arrays on metallic substrate and its application to supercapacitors

Aligned carbon nanotube arrays (ACNTAs) with lengths up to 150 μm were fabricated on metallic alloy (Inconel 600) substrates by pyrolysis of iron (II) phthalocyanine (FePc) in the presence of ethylene (C₂H₄). The as-grown ACNTAs, formed by aligned multi-walled carbon nanotubes with high purity, were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and Raman spectroscopy techniques. The ACNTAs were used directly as electrode materials in supercapacitors with (Et)₄NBF₄ + propylene carbonate (PC) as electrolyte, and their electrochemical properties were investigated. A rectangular-shaped cyclic voltammetry (CV) curve was observed even at a sweep rate of 1000 mV s⁻¹. The specific capacitance measured at 1000 mV s⁻¹ was about 57 % (47 F g⁻¹) of that obtained at 1 mV s⁻¹ (83 F g⁻¹), and an equivalent series resistance (ESR) of 0.55 Ω was measured for the ACNTA and activated carbon pair electrodes embedded in a coin cell. The results indicated that the ACNTAs could be a promising candidate as electrode materials in supercapacitors.     

Identification of the Li ground state

The proton-stripping reaction from a ¹¹Be radioactive beam incident on a beryllium target demonstrates that only (7±3)% of the ⁹Li residues in the reaction are in coincidence with the 2.7 MeV γ-ray corresponding to the ⁹Li first excited state. This implies that the previously observed low-energy neutrons from the decay of the unbound nucleus ¹⁰Li represent a direct l=0 transition to the ⁹Li ground state. Consequently, neutron-unbound ¹⁰Li is proven to have the same parity inversion as occurs in the case of ¹¹Be with a  intruder state below the natural parity state.     

A high resolution search for the tensor glueball candidate ξ(2230)

We report results of a high resolution search for the tensor glueball candidate ξ(2230) in a formation experiment. π⁰π⁰ and ηη decay channels were measured in a scan of the mass region 2220 MeV to 2240 MeV. No evidence for the existence of ξ(2230) was found. 95% confidence upper limits for the possible existence of ξ are presented.     

Simultaneous measurements of the p+d→(A=3)+π reactions

A stack of annular detectors made of high-purity germanium was used to measure simultaneously pd → ³H π⁺ and pd → ³He π⁰ differential cross sections at beam momenta of 750 MeV/c, 800 MeV/c, and 850 MeV/c over a large angular range. The extracted total cross sections for the pd → ³He π⁰ reactions bridge a gap between near threshold data and those in the resonance region. The ratio of the cross sections for the two reaction channels taken at the same η=p^cm_π/m_π yields 2.11±0.08 indicating that a deviation from isospin symmetry is very small.     

Measurements of light scattering by a characterized random rough surface

Measurements are presented of the angular distribution of four wavelengths of light scattered by a one-dimensional random rough surface, whose probability density function is Gaussian with a standard deviation σ=1.22±0.02 μm and whose lateral correlation function is also Gaussian with 1/e width τ=3.17±0.07 μm. The wavelengths used are 0.63, 1.15, 3.39 and 10.6 μm. The surface is used in two forms: coated with gold and as an almost lossless dielectric. The results are compared to those predicted by a double scattering form of the Kirchhoff formulation. Agreement is good at small angles of incidence but less good at larger angles of incidence.     

Upper limit on the decay Σ(1385)→Σγ and cross section for γΣ→Λπ

Coherent Λπ⁻ production on Pb of 600 GeV Σ⁻ hyperons has been studied with the SELEX facility at Fermilab. Using the Primakoff formalism, we set a 90% CL upper limit on the radiative decay width Γ[Σ(1385)⁻→Σ⁻γ]<9.5 keV, and estimate the cross section for γΣ⁻→Λπ⁻ at  GeV to be 56±16 μb.     

Excess molar heat capacity of isobutyric acid–water binary liquid mixtures near and far away from the critical temperature

The heat capacity of the liquid–liquid mixture isobutyric acid–water has been measured for the first time near and far away from its critical point using an adiabatic calorimeter. The measurements were performed at atmospheric pressure, in the one phase region as a function of three temperatures: (1) T − T_C = 0.055 °C, (2) T − T_C = 3.055 °C, (3) T − T_C = 8.055 °C and of the composition X in acid (IA). The heat capacity C_p decreases rapidly when X increases at the used temperatures. Near the critical composition, C_p is not affected by the correlation of the concentration fluctuations.

The molar excess heat capacity of the system under investigation was analysed along the phase diagram and considered as a structural transformation effect.     

The CMSSM parameter space at large tanβ

We extend previous combinations of LEP and cosmological relic density constraints on the parameter space of the constrained MSSM, with universal input supersymmetry-breaking parameters, to large tanβ. We take account of the possibility that the lightest Higgs boson might weigh about 115 GeV, but also retain the possibility that it might be heavier. We include the most recent implementation of the b→sγ constraint at large tanβ. We refine previous relic density calculations at large tanβ by combining a careful treatment of the direct-channel Higgs poles in annihilation of pairs of neutralinos χ with a complete treatment of χ– coannihilation, and discuss carefully uncertainties associated with the mass of the b quark. We find that coannihilation and pole annihilations allow the CMSSM to yield an acceptable relic density at large tanβ, but it is consistent with all the constraints only if m_χ>140 (180) GeV for μ>0 (μ<0) for our default choices  GeV, m_t=175 GeV, and A₀=0.     

Frequency and amplitude alterations of sound modes in a space-dependent random mass density field

We investigate the effect of a space-dependent random mass density field on small amplitude acoustic modes that are settled in a semi-infinite medium of a temperature growing linearly with depth. Using a perturbation method, the dispersion relation is derived in the form of Hill's determinant. Numerical solutions of this equation lead to the following conclusions: (a) a weak random field (with σ_eff = 0.05) essentially affects long waves which experience attenuation and a frequency reduction; (b) for a stronger random field (with σ_eff = 0.1), high-order sound modes behave as sound waves as they are attenuated and their frequencies are increased; (c) for a sufficiently strong random field (with σ_eff = 0.2), mode coupling occurs, as a result of which the dispersive curves cross each other, the sound modes loose their identities, and some modes are amplified. Here σ_eff denotes the effective strength of a random field.     

The role of alkali ions in the 190 K TSL peak in quartz

The role of alkali ions in the creation of the thermally stimulated luminescence (TSL) peak at 190 K in quartz has been investigated by wavelength resolved TSL and thermally stimulated current (TSC) measurements performed on synthetic crystals, both as grown and hydrogen swept, characterised by alkali content of about 1–3 and 0.1 ppm respectively. The 190 K peak has been efficiently produced in as-grown crystals by a double irradiation procedure consisting of a first x-ray irradiation at 90 K followed by heating in the 170–300 K temperature range and a second irradiation at 90 K; this effect has not been observed in the hydrogen swept crystal. Moreover, the study of the spectral composition of the emitted light has shown the existence of two emission bands, one peaking at 450 nm (T<150 K) and the second one evidenced for T>150 K and peaking at around 380 nm.

In as grown samples, TSC peaks at 205, 260 and at around 350 K (composite structure) have been detected: their intensities are much stronger in the as grown crystal and with the electric field oriented along the z-axis indicating that they have an ionic character. By taking into account the mechanism of formation of the [SiO₄/M⁺]⁰ (M⁺=Li⁺, Na⁺) traps (previously found to be responsible for the 190 K TSL peak), the 205 K TSC peak can be attributed to the radiation induced dissociation of alkalis from [AlO₄/M⁺]⁰ defect centres and subsequent migration near to Si sites; on the other hand, the 260 K TSC peak can be related to the subsequent disintegration of [SiO₄/M⁺]⁰ defects involving the migration of alkalis to different ionic traps.

PACS: 78.60.K–61.72.J–42.70.Ce     

Characterization of palmitic and lauric acid aerosols from rapid expansion of supercritical CO2 solutions

Palmitic acid aerosols and lauric acid aerosols were generated by rapid expansion of supercritical CO₂ solutions. The particle properties were analysed by rapid-scan infrared spectroscopy in situ, by X-ray powder diffraction, with a scanning mobility particle sizer, and by scanning electron microscopy. Particles with irregular elongated shapes were found. Most particles and agglomerates have sizes between 250 and 750 nm. Fewer agglomerates with sizes up to several microns are observed. Our investigation reveals that strong agglomeration takes place at the Mach disc. Palmitic and lauric acid particles are both crystalline and most particles crystallize in the C-form.     

Comparative studies of the reflectance and degree of linear polarization of particulate surfaces and independently scattering particles

We compare measurements of the phase-angle dependencies of the intensity and degree of linear polarization of particles in air and particulate surfaces. The samples were measured at two spectral bands centered near 0.63 and 0.45 μm. The surfaces were measured with the new photometer/polarimeter at the Astronomical Institute of Kharkov National University. The scattering measurements of the particles in air were carried out with the equipment currently located at the University of Amsterdam. We study a suite of samples of natural mineral particles of different sizes all in the micrometer range, i.e. comparable with the wavelengths. The samples are characterized by a variety of particle shapes and albedos. The samples have been studied in several works and in this paper we include new SEM microphotographs of particles and spectra of powders in a wide spectral range, 0.3–50 μm, using the RELAB equipment of Brown University. We made measurements of particulate surfaces in a phase-angle range, 2–60° that is significantly wider than that of our previous studies. We confirm our earlier results that the negative polarization of the surfaces may be a remnant of the negative polarization of the single scattering by the particles that constitute the surfaces. We also find differences in the spectral behavior of the polarization degree of particles in air and particulate surfaces at large phase angles.     

A 2D fixed-sectional approach to model the coagulation of (highly) charged aerosols

Many simulations of charged aerosols are limited to moderately charged aerosols. In order to simulate highly charged aerosols, a 2D extension of the fixed-sectional approach, capable of dealing with negative values, is derived which is more efficient than standard 2D sectional models. Assuming that the charge and the volume of the aerosol particles are independent of each other, this model preserves the 0th and 1st moment in both dimensions. The relaxed grid requirements allow to include higher charges in the simulation without increasing the computational effort or reducing accuracy of the obtained results.