Superfluid Contributions to General Turbulence Theory

We analyse a numerical solution of a mathematical model of thermal superfluid turbulence. We elaborate on key points of the statistical phenomenology and point out their impact on fundamental issues of general turbulence theory.     

Mean interface magnon dispersion curves obtained by means of the matching procedure

A theoretical approach based on the matching procedure in the random-phase approximation has been developed to investigate the spin fluctuations dynamics on an interface of the Heisenberg biferromagnetic layers. The two ferromagnetic layers are considered directly coupled by magnetic exchange interactions. No electronic effects are considered. The analytical approach solves for the three-dimensional crystal spin field in the bulk and the interface domain, that arises owing to the reduced of magnetic translation symmetry for the system. The calculations presented here are an application of a theoretical method based on Green functions formalism discussed in previous work. Analytic expressions are obtained for the dispersion relations and spectral intensities of the localized spin-waves and the quantized bulk spin waves near an interface. The effects of varying the bulk-interface coupling exchange near the interface are studied. Also, the condition for the appearance of the acoustic and optical interface modes is discussed. Numerical examples of the modes are given and provide some indication of how the magnon spectrum is affected by interface parameters. These factors influence the energies of localized modes, as well as their frequency, intensity and attenuation.     

Effects of energetic heavy ion irradiation on the structure and magnetic properties of FeRh thin films

Fe-54at.%Rh thin films were irradiated with 10 MeV iodine ions at room temperature. Before and after the irradiations, the changes in magnetic properties and the lattice structure of the samples were studied by means of a SQUID magnetometer and X-ray diffraction. For the low fluence irradiation, the SQUID measurement at 20 K shows that the anti-ferromagnetic region of the thin film is changed into ferromagnetic region by the irradiation. As the film thickness is much smaller than the ion range, we can discuss the relationship between the density of energy deposited by ions and the change in magnetization quantitatively. For the high fluence irradiation, the magnetization of the film is strongly decreased by the irradiation, which can be explained as due to the change in lattice structure from B2 into A1 structure by the irradiation.     

Scintillation light produced by low-energy beams of highly-charged ions

Measurements have been performed of scintillation light intensities emitted from various inorganic scintillators irradiated with low-energy beams of highly-charged ions from an electron beam ion source (EBIS) and an electron cyclotron resonance ion source (ECRIS). Beams of xenon ions Xe^q+ with various charge states between q = 2 and q = 18 have been used at energies between 5 and 17.5 keV per charge generated by the ECRIS. The intensity of the beam was typically varied between 1 and 100 nA. Beams of highly charged residual gas ions have been produced by the EBIS at 4.5 keV per charge and with low intensities down to 100 pA. The scintillator materials used are flat screens of P46 YAG and P43 phosphor. In all cases, scintillation light emitted from the screen surface was detected by a CCD camera. The scintillation light intensity has been found to depend linearly on the kinetic ion energy per time deposited into the scintillator, while up to q = 18 no significant contribution from the ions’ potential energy was found. We discuss the results on the background of a possible use as beam diagnostics, e.g. for the new HITRAP facility at GSI, Germany.     

Mutation of rice (Oryza sativa L.) LOX-1/2 near-isogenic lines with ion beam implantation and study of their storability

In this paper, Wanjian 2090 without LOX-1 and LOX-2, a rice variety, was irradiated by ion beam to screen LOX-1/2 near-isogenic lines, which had the similar genetic background while the enzyme activities of either LOX-1 or LOX-2 were different. When these rice seeds were stored under both the accelerated ageing conditions for 12 days and the natural ageing conditions for 18 months, our results showed that the germination percentages of lines lacking both LOX-1 and LOX-2 were always higher than those either with LOX-1 or with LOX-2. In addition, rice lines with the presence of both LOX-1 and LOX-2 have the lowest germination percentages. The germination percentages of all genotype near-isogenic lines under two ageing conditions were correlated positively and significantly.     

A low-cost, accurate and non-intercepting continuous method for beam current measurements in a high-current ion implanter

The development of a low-cost, accurate, non-intercepting continuous method for measuring the beam current in a high-current ion implanter is described. The method, named a differential current monitor, is based on the electric charge conservation principle, applied to the currents that flow in the implanter electrical system, due to the acceleration voltage applied to the ion beam and the leakage currents to ground. This method allows for continuous measurement of the ion beam current without intercepting it. Since its installation, it is possible to accurate measure ion beam currents from tens of μA to mA, which is the normal range for this type of system.     

Monte Carlo simulation of the Greek Research Reactor neutron irradiation facilities

A Monte Carlo simulation of the Greek Research Reactor was carried out using MCNP-4C2 code and continuous energy cross-section data from ENDF/B-VI library. A detailed model of the reactor core was employed including standard and control fuel assemblies, reflectors and irradiation devices. The model predicted neutron flux distributions within the core in good agreement with calculations performed using the deterministic code CITATION and measurements using activation foils. The model is used for the prediction of the neutron field characteristics at the reactor irradiation devices and enables the design and evaluation of experiments involving material irradiations.     

Silver surface enrichment controlled by simultaneous RBS for reliable PIXE analysis of ancient coins

Evidence of silver surface enrichment of ancient silver-copper coins has been pointed out in the past years. Surface enrichment can be fortuitous or intentional. In this paper, we have investigated the cleaning procedures usually performed after excavation or in museums. We have shown that chemicals or commercial products routinely used dissolve preferentially the copper phase and consequently contribute to the silver surface enrichment. As a result, surface analyses such as PIXE or XRF can be strongly affected by this effect. By using simultaneously RBS and PIXE, it is possible to check through the silver surface enrichment and then select the reliable measurements, characteristic of the bulk composition. Results on coins recently discovered and mechanically or chemically cleaned are presented.     

Semiconductor characterization by scanning ion beam induced charge (IBIC) microscopy

The acronym IBIC (ion beam induced charge) was coined in the early 1990s to indicate a scanning microscopy technique which uses MeV ion beams as probes to image the basic electronic properties of semiconductor materials and devices. Since then, IBIC has become a widespread analytical technique to characterize materials for electronics or for radiation detection, as testified by more than 200 papers published so far in peer-reviewed journals. Its success stems from the valuable information IBIC can provide on charge transport phenomena occurring in finished devices, not easily obtainable by other analytical techniques. However, IBIC analysis requires a robust theoretical background to correctly interpret experimental data. In order to illustrate the importance of using a rigorous mathematical formalism, we present in this paper a benchmark IBIC experiment aimed to test the validity of the interpretative model based on the Gunn’s theorem and to provide an example of the analytical capability of IBIC to characterize semiconductor devices.     

Diffuse conditions for efficient solution of multislab radiation transport problems

In this article, we make use of recently developed spectral nodal methods for anisotropically scattering media and we derive mathematical conditions for the diffuse reflection and transmission of radiation in the discrete ordinates formulation of particle transport theory for plane-parallel applications. The conditions arise from a suitable reformulation of spatially discretized equations defined on the boundary layers of a multislab domain. As a result, the boundary layers can be removed from the radiation transport calculations and replaced with exact and numerically stable equivalent conditions. In order to illustrate the applicability and computational merit of our discrete ordinates conditions for diffuse reflection and transmission in radiation transport calculations, we perform numerical experiments with atmospheric radiative transfer and nuclear reactor core models.