Goniopolarimetry: Space-borne radio astronomy with imaging capabilities

The principles of space-based low-frequency radio astronomy (below 50 MHz) are briefly introduced. As the wavelength range considered does not allow the use of focusing systems, goniopolarimetric (or direction-finding) techniques have been developed. These inversion techniques provide the direction of the wave vector, the polarization state and the flux of the observed electromagnetic wave. In case of spatially extended sources, we can also infer an order of magnitude of the apparent source size. These techniques are presented, and their limitations are discussed. An example from a recent study illustrates the techniques and capabilities.     

Effect of epitaxial crystallization on packet-like space charge characteristics in low-density polyethylene under multi-field coupling conditions

In order to study the effect of epitaxial crystallization on charge transport in low-density polyethylene (LDPE) under multi-field coupling conditions, three typical epitaxial crystallizations, namely disorder (glass substrate), crossover (isotactic polypropylene substrate), and parallel (polytetrafluoroethylene substrate), were prepared and denoted as LD-G, LD-iPP, and LD-PT, respectively. Packet-like space charge through samples was analyzed by the pulsed electro-acoustic (PEA) method. It is shown that different microscopic surface morphologies appeared in the LDPE samples with different epitaxial crystallizations, which, however, do not change the crystalline structure of the bulk. Packet-like space charge phenomena were observed and the distortion field increased with the temperature which could be attributed to the larger amount of charge injection in a shorter period. The differences of the amount and injection rate of the space charge were explained and verified considering the typical chain alignment of epitaxial crystallization, which, in our opinions, contributes to the pass over of positive charge in LD-iPP samples.     

Extreme fluxes in solar energetic particle events: Methodological and physical limitations

In this study, all available data on the largest solar proton events (SPEs), or extreme solar energetic particle (SEP) events, for the period from 1561 up to now are analyzed. Under consideration are the observational, methodological and physical problems of energy-spectrum presentation for SEP fluxes (fluences) near the Earth's orbit. Special attention is paid to the study of the distribution function for extreme fluences of SEPs by their sizes. The authors present advances in at least three aspects: 1) a form of the distribution function that was previously obtained from the data for three cycles of solar activity has been completely confirmed by the data for 41 solar cycles; 2) early estimates of extremely large fluences in the past have been critically revised, and their values were found to be overestimated; and 3) extremely large SEP fluxes are shown to obey a probabilistic distribution, so the concept of an “upper limit flux” does not carry any strict physical sense although it serves as an important empirical restriction. SEP fluxes may only be characterized by the relative probabilities of their appearance, and there is a sharp break in the spectrum in the range of large fluences (or low probabilities). It is emphasized that modern observational data and methods of investigation do not allow, for the present, the precise resolution of the problem of the spectrum break or the estimation of the maximum potentialities of solar accelerator(s). This limitation considerably restricts the extrapolation of the obtained results to the past and future for application to the epochs with different levels of solar activity.     

Luminescence characterisation of alumina substrates using cathodoluminescence microscopy and spectroscopy

Polycrystalline alumina (Al₂O₃) substrates, found in many electronic devices and proposed as dosemeters in emergency situations, were invstigated using a scanning electron microscope (SEM) equipped with cathodoluminescence (CL) and elemental analysis probes. The characteristics of the CL spectra, surface morphology, and impurity content of the Al₂O₃ substrates were examined and compared with those of single crystal dosimetry-grade Al₂O₃:C. Whereas the CL spectrum, measured from 250 to 800 nm, for the Al₂O₃:C, contained resolved bands located at ∼340 nm and at ∼410 nm, the spectrum measured with the Al₂O₃ substrate was significantly broader, extending from ∼250 to ∼450 nm, and also included a narrow band at 695 nm. While it is likely that the accepted model of recombination at F⁺ (∼340 nm) and F (∼410 nm) in Al₂O₃:C also applies to the substrate, it is suggested that the presence of impurities within the alumina give rise to additional recombination centres. The 695 nm emission has been assigned to a Cr³⁺ ion impurity in previous work on alumina and a band indicated at ∼300 nm may be associated with Mg²⁺ or Ca²⁺_, the presence of which was confirmed by elemental mapping. Comparison of the spatial distribution of CL with the surface morphology and elemental composition of the samples indicates that the components of the emission spectrum can be qualitatively correlated with impurity content and morphological features of the samples.     

Comparative analysis of CR-39 sensitivity for different sets of measurable track parameters

In the present paper the sensitivity V of plastic nuclear track detectors CR-39 to the space radiation, accelerated heavy ions in wide LET range and α-particles is studied. Different approaches for V evaluation are considered and compared. Main attention is given to the method that is appropriate for the measurement of short range heavy secondaries of space radiation. Finally, the experimental verification of the designed V function is carried out via simulation of the secondaries with low energy α-particles in the vicinity of the Bragg peak.     

Biodosimetry versus physical dosimetry for emergency dose assessment following large-scale radiological exposures

Existing data on intercomparisons involving biodosimetry or physical dosimetry methods are analyzed and the results interpreted regarding their efficacy in triage in emergency dosimetry following mass casualty radiological events. The biodosimetry technique examined is dicentric chromosome aberrations (DCA). The physical dosimetry techniques include electron paramagnetic resonance (EPR) of biological material (teeth) and physical material (smartphone screen glass), and optically stimulated luminescence (OSL) of electronic components (surface mount resistors) from mobile phones. Issues relating to calibration and interpretation of the data are discussed. An important conclusion of the analysis is that more research is critically needed to interpret the efficacy of the various methods. Included in this needed research are intercomparisons of the various methods in controlled experiments and the need to harmonize protocols.     

Non-contact in-situ pulsed electro acoustic method for the analysis of charge transport in irradiated space-used polymers

The characterization of dielectric materials in space environment requires to understand and predict their electric behaviour, taking into account ionisation, and ageing effect (through electron or UV radiation, thermal cycling, …)For this purpose, new methods have been developed for the characterisation and qualification of space materials and satellite structure. These studies led initially to the development of dedicated facilities for the simulation of representative irradiation conditions. This work is focused on a new non-disturbing technique for the measurement of charge distribution within space irradiated polymers. This technique named PEA (Pulsed Electro-Acoustic) has been implemented in the irradiation facility for in-situ and real time measurement during irradiation and relaxation of polymer materials. Implementation and validation of this technique are presented and discussed in this paper.     

A regularised boundary element formulation for contactless SAR evaluations within homogeneous and inhomogeneous head phantoms

This work presents a Boundary Element Method (BEM) formulation for contactless electromagnetic field assessments. The new scheme is based on a regularised BEM approach that requires the use of electric measurements only. The regularisation is obtained by leveraging on an extension of Calderón techniques to rectangular systems leading to well-conditioned problems independent of the discretisation density. This enables the use of highly discretized Huygens surfaces that can be consequently placed very near to the radiating source. In addition, the new regularised scheme is hybridised with both surfacic homogeneous and volumetric inhomogeneous forward BEM solvers accelerated with fast matrix–vector multiplication schemes. This allows for rapid and effective dosimetric assessments and permits the use of inhomogeneous and realistic head phantoms. Numerical results corroborate the theory and confirms the practical effectiveness of all newly proposed formulations.     

Geometric and operational optimization of 20-kHz probe-type sonoreactor for enhancing sonochemical activity

The use of a 20-kHz probe-type sonicator irradiating downward in a 500 mL vessel was optimized for the enhancement of the sonochemical activity in terms of the geometric and operational factors. These factors included the probe immersion depth (the vertical position of the probe), input power, height of the liquid from the bottom, horizontal position of the probe, and thickness of bottom plate The sonochemical oxidation reactions were investigated both quantitatively and qualitatively using calorimetry, KI dosimetry, and luminol (Sonochemiluminescence, SCL) techniques. The sonochemical activity was very positively affected by the vertical boundaries. The highest sonochemical activity was obtained when the probe was placed close to the bottom of the vessel (immersion depth of 60 mm), with a high input power (input power of 75%), and optimal liquid height condition (liquid height of 70 mm). The SCL image analysis showed that the cavitational activity zone gradually expanded around the probe body and changed into a circular shape as the experimental conditions were optimized, and consequently the sonochemical activity increased. The formation of a large bright circular-shaped activity zone could be attributed to the strong reflections of the ultrasound firstly, at the vessel bottom and secondly, at the liquid surface. On the other hand, the cavitational activity zone and the sonochemical activity were negatively affected by the horizontal boundaries when the probe was placed close to the side wall of the vessel. In addition, it was found that the sonochemical activity was also significantly affected by the thickness of the support plate owing to the reflection and transmission of the ultrasound at the boundary between the liquid and the solid media.     

高效透明导电膜荧光屏的研究

介绍了一种新型荧光屏结构,采用透明导电膜代替传统荧光屏中的铝膜作电极.分别测试了新型荧光屏和传统荧光屏的加电特性.实验结果表明新型荧光屏具有较高的耐压性能,对提高X射线变像管的空间分辨率有重要作用,而且能延长变像管的寿命.采用透明导电膜制作荧光屏还具有工艺简单,成本低和成品率高的优点.