界面极化注极聚丙烯薄膜驻极体的电荷存储特性研究

本文报道一种基于双层介质界面极化机理的新型驻极体注极技术: 借助辅助层对PP薄膜进行注极. 采用表面电位测试方法考察了注极温度、注极电压对所获PP薄膜驻极体电荷存储性能的影响, 并利用热刺激放电技术研究了其高温电荷存储性能, 同时测试了PP薄膜驻极体在X和Y方向的静电场分布. 结果表明: 界面极化注极是一种比电晕注极更为优异的驻极体形成方法. 在一定温度下, 驻极体表面电位随注极电压的增加而增加, 而且两者呈线性关系, 这一结果与注极过程的电荷积聚方程的分析完全一致. 注极温度的影响研究表明, 在保持注极电压不变(注极电压范围为0.5–3.0 kV)的情况下, 温度低于75 ℃时, 温度的变化对于注极效果的影响不明显; 当注极温度大于75 ℃ 时, PP薄膜驻极体的表面电位随注极温度的增加而增加. 表面电位随时间的变化研究表明, PP薄膜驻极体具有良好的电荷存储稳定性. 对其表面电位分布的测试表明, 界面极化注极所形成的PP薄膜驻极体呈现均匀的静电场分布.     

Electrical properties of polylactides

A PLA film with low crystalline-phase content was investigated in a DC field within the temperature range of 25–70 °C. The polymer exhibits low electrical conduction with increasing activation energy within the area of the glass transition temperature. Electrets were made from the PLA film precursor using an isothermal polarization method. The charge on the electrets was assessed by measuring the field intensity. The surface charge of an electret has the character of a hetero-charge. After 4 months from termining the isothermal charging and cooling, the PLA film polarized at E_p > 16.7 MV/m was affirmed the applicable electret properties.     

Influence of the presence of humidity,ambient aerosols and thoron on the detection responses of electret radon monitors

This paper describes how the presence of humidity, ambient aerosols and thoron influences the detection responses of an electret passive environmental radon monitor (commercially E-PERM^®) using radon and thoron chambers of National Institute of Radiological Sciences (NIRS). From the initial experiments, the linear correlation between the conversion factor for radon and the midpoint voltage for the short-term and long-term electrets was determined. As a result, it was observed that the conversion factors were approximately 10% lower for the short-term electrets and 3% higher for the long-term electrets than those reported by the manufacturer. The evaluation of different magnitudes of radon concentration showed that the presence of humidity and ambient aerosols had little influence on the detection response for radon, with less than 10% relative standard deviation. In the case of thoron detection response, net voltage drop values increased linearly with time-integrated concentrations for both short-term and long-term electrets, as was the case with radon. The thoron responses to radon were less than 5% for both the electrets from the results of experiments and calculations.     

Gamma versus alpha sensors for Rn-222 long-term monitoring in geological environments

The behavior of alpha silicon diodes, gamma crystal scintillators and ionization chamber detectors employed for long-term radon monitoring in geological media was studied and a comparison of the efficiency and sensitivity, the capability to resolve signal to noise, background, stability, and reliability of their long-term measurements is presented. An understanding of the qualities of monitoring techniques is necessary for determining suitability to the characteristics of the individual monitoring site and what exactly they will measure: radon in an air cavity, in porous media or in water.The experimental layout was located inside the Amram Mountain research tunnel near Elat (Gulf of Aqaba), within a closed room in the tunnel core. This enabled monitoring natural temporal radon variations under fairly stable internal conditions, at a high-resolution sampling rate of once every several minutes. In an interval of several days, all the sensors responded simultaneously to the same eventual radon variations.An ionization chamber device, the AlphaGUARD designed with a long-time stable calibration factor and an inherent QA-System, was used as reference calibration of the different radon detectors.The results indicate that the higher sensitivity of 2–4 orders of magnitude exhibited by gamma sensors even with narrow dimensions (1" × 3" BGO detector) are preferred for long-term radon monitoring in comparison to the solid-state alpha detectors and ionization chambers.     

Collection and behaviour of radon progenies on thin Mylar foils

Thin Mylar foils are often used to protect detectors from contamination. However, these foils can be electrostatically charged, possibly leading to their contamination with airborne radon progenies. In the present work, the collection and behaviour of radon progenies on Mylar foils was investigated in detail using alpha spectrometry. The radon progenies collection rate of a small Mylar foil (3 cm²) is equivalent to an air sampler with a flow rate of approximately 0.1 m³/h. It was demonstrated that such contamination may jeopardise the validity of the entire analysis if not interpreted correctly.     

The combinational effect of PP electret and monoolein on transdermal delivery of cyclosporine A in vitro

In this study, single and combined enhancing effect of polypropylene (PP) electret and 10% monoolein (Mono) on cyclosporine A (CsA) transdermal delivery were studied using improved Franz diffusion cell and high performance liquid chromatography (HPLC) technique. Single use of each PP electret or 10% Mono could enhance the transdermal delivery of CsA. +500 V or ?500 V corona charged electret in combination with 10% Mono had the most significant enhancing effect. The PP electrets with the same corona voltage in absolute value had the similar enhancing effect on transdermal delivery of CsA when they were used in combination with Mono.     

Indoor radon measurements in a Greek city located in the vicinity of lignite-fired power plants

This work presents indoor radon measurements in 42 dwellings in the city of Megalopolis, Southern Greece, located in the vicinity of 2 lignite-fired power plants and examines the effect of season, floor level and age of the dwellings on indoor radon concentration. The radon measurements have been carried out using the LR-115, type II and CR-39 alpha track detectors in “closed-can” geometry. The average annual indoor radon concentration (GM) was found to be 52 Bq m^?3, which is well below the recommended action level of the European Union. This value corresponds to an annual effective dose to the population of 1.3 ± 0.4 mSv. Season and age of the examined dwellings represent factors that affected significantly the indoor radon in Megalopolis, while the effect of floor level appeared to be not significant. Radium activity concentration values, measured by γ-ray spectrometry in 20 sub-samples of six soil cores (60–135 cm depth), collected from the surrounding area of the city, were found to be consistent with the Greek and world average values. Based on the results of this study, it is concluded that the effect of the lignite-fired power plants on indoor radon concentration in Megalopolis’ dwellings was not significant.     

Variation of radon flux along active fault zones in association with earthquake occurrence

Radon flux measurements were carried out at three radon stations along an active fault zone in the Langadas basin, Northern Greece by various techniques for earthquake prediction studies. Specially made devices with alpha track-etch detectors (ATDs) were installed by using LR-115, type II, non-strippable cellulose nitrate films (integrating method of measurements). Continuous monitoring of radon gas exhaling from the ground was also performed by using silicon diode detectors, Barasol and Clipperton type, in association with various probes and sensors including simultaneously registration of the meteorological parameters, such as precipitation height (rainfall events), temperature and barometric pressure. The obtained radon data were studied in parallel with the data of seismic events, such as the magnitude, M_L of earthquakes, the epicentral distance, the hypocentral distance and the energy released during the earthquake event occurred at the fault zone during the period of measurements to find out any association between the rad on flux and the meteorological and seismological parameters. Seismic events with magnitude M_L ≥ 4.0 appeared to be preceded by large precursory signals produced a well-defined “anomaly” (peak) of radon flux prior to the event. In the results, the radon peaks in the obtained spectra appeared to be sharp and narrow. The rise time of a radon peak, that is the time period from the onset of a radon peak until the time of radon flux maximum is about a week, while the after time, that is the time interval between the time of radon flux maximum and the time of a seismic event ranges from about 3 weeks or more.     

恒流电晕充电对聚四氟乙烯多孔薄膜驻极体驻极态的影响

利用常温下恒流和恒压电晕充电、充电后的等温表面电位衰减、热刺激放电和扫描电镜等实 验手段研究了恒流和恒压电晕充电技术对聚四氟乙烯多孔薄膜驻极体驻极态的影响.与恒压电晕充电相比较，恒流电晕充电时由于流过薄膜的电流恒定，增加了注入电荷在多孔结构厚度方向界面处的俘获概率，使沉积电荷密度上升，改善了驻极体的储电能力.然而，这些位于不同层深多孔界面处的俘获电荷在这类功能膜储存或使用过程中，经外激发从脱阱位置 以跳动（hopping）模式输运至背电极的路径相对缩短将导致脱阱电荷衰减较快. 关键词： 恒流电晕充电 聚四氟乙烯多孔膜 驻极体 电荷稳定性     

About ageing and fading of Cr-39 PADC track detectors used as air radon concentration measurement devices

PADC detectors are widely used as air radon concentration measurement devices and the typical procedure that a Radon Service Laboratory uses to manage the detectors provides a calibration phase followed by the field measurement. The calibration is performed in a reference radon concentration atmosphere, using high radon concentration values in order to achieve typical exposure values of few MBq h m^?3 with an exposure time of few days. On the other hand the field measurement is characterized by long term exposures lasting up to six months and by radon concentrations that are quite lower than the ones used in the calibration.The aim of this study is to check whether the calibration procedure is actually representative of a field measurement, or, in other words, whether and how much ageing or fading can affect the calibration factor.We found that the ageing and fading effect can produce a decrease in the detector sensitivity leading to an underestimation of the radon concentration up to 40% for exposure lasting few months. An important issue is that both ageing and fading can be ascribed to a decrease in the track etching velocity V_t.In the paper we also provide an algorithm to compensate for the sensitivity variation due to fading/ageing effect.     

充电栅压对聚四氟乙烯多孔膜驻极体储电能力的影响

利用室温下栅控恒压电晕充电、热脉冲技术、开路热刺激放电电流谱以及对在充电过程中通过样品电流的监测等方法，系统地研究了充电栅压对具有开放性孔洞结构的聚四氟乙烯（PTFE）多孔膜储电能力的影响，并讨论了导致这类影响的电荷动力学特性和材料的微结构根源 .结果显示，过高的充电栅压会导致沉积电荷密度下降和电荷衰减加剧，不利于这类新结构 功能材料压电活性的提高及其热稳定性的改善.合理的优化充电条件能使负极性充电PTFE多 孔膜驻极体在有机聚合物材料中显示优异的储电能力及电荷稳定性，并改善其作为双极性空 间电荷型压电传 关键词： 聚四氟乙烯 驻极体 储电能力 多孔膜     

Optimization of corona discharge process using Box–Behnken design of experiments

The corona discharge process was studied using Box–Behnken design of experiments in conjunction with response surface methodology of analysis. The single as well as interaction effects of process factors namely applied voltage, time of charging, and distance between electrodes on the surface potential of meltblown nonwoven electret media were examined. The response surface model predicting the surface potential of the electrets displayed a very good correspondence with the experimental results. The optimized corona discharge process run by keeping the predicted levels of process factors yielded surface potential of the electret media very close to that predicted from the model.     

毫米级栅型电场分布FEP薄膜驻极体的制备及其电荷存储性能研究

采用电晕注极和热注极技术, 在厚度为25 μm的氟化乙丙烯共聚物(FEP)表面制备了宽度为2 mm和3 mm的具有栅型电场分布的驻极体, 研究了注极温度和电极宽度对其电荷存储性能的影响. 样品注极后经150天的存储, 栅型电场分布变得清晰而有规律, 覆盖铝电极区电位已衰减至接近零, 未覆盖铝电极区仍保持高电位; 对电极宽度为2 mm和3 mm的样品, 覆盖铝电极区与未覆盖铝电极区的表面电位差分别为110 V和130 V(电场强度差分别为44 kV/cm和52 kV/cm). 表面电位跟踪测试结果表明: 电晕注极样品初始表面电位高于热注极样品; 在相同的注极方法下, 注极温度越高初始表面电位越高, 电极宽度越小初始表面电位越低. 依据电晕注极和热注极原理对实验结果的分析表明, FEP和金属铝在电荷存储性能上的差异是FEP表面蒸镀铝电极后能获得栅型电场分布的原因所在.     

Systematic grid-wise radon concentration measurements and first radon map in Cyprus

A systematic study of the indoor airborne radon concentration in the central part of the Nicosia district was conducted, using high-sensitivity active radon portable detectors of the type “RADIM3A”. From a total of 108 measurements in 54 grids of 1 km² area each, the overall mean value is 20.6 ± 13.2 Bq m^?3 (A.M. ± S.D.). That is almost twice less than the corresponding average worldwide value. The radon concentration levels in drinking water were also measured in 24 sites of the residential district, using the high-sensitivity radon detector of the type “RADIM3W”. The mean value obtained from these measurements is 243.8 ± 224.8 mBq l^?1, which is relatively low compared to the corresponding internationally accepted level. The associated annual effective dose rates to each measurement were also calculated and compared to the corresponding worldwide values. From the geographical coordinates of the measuring sites and the corresponding radon concentration values, the digital radon map of the central part of the Nicosia district was constructed for the first time, by means of the ArcMap software package.     

The use of soil gas as radon source in radon chambers

A procedure is described in which soil gas is utilized as an alternative to the ²²⁶Ra source for the supply of the radon gas required to fill a radon chamber where radon-measuring devices are calibrated. The procedure offers opportunities to vary the radon concentration within the chamber around an average value of about 500 Bq/m³, which is considered to be sufficient for calibrating indoor radon detectors. The procedure is simple and the radon source does not require radiation protection certification (for import and/or use), unlike the commercially produced standard radioactive (²²⁶Ra) sources.     

Silicon based polytetrafluoroethylene electrets: Preparation and corona charging characteristics

In this paper, silicon based planar technology and high performance fluorocarbon polymer polytetrafluoroethylene (PTFE) are combined to achieve PTFE thin film electrets on wafer. The PTFE film is fabricated onto SiO₂ substrates and Pt substrates using spin coating and annealing processes, and its electret effect is demonstrated using negative corona charging method. PTFE electrets with different surface morphology exhibit different charge storage capability. Maximally, surface potential of ?396 V is achieved on Pt substrates and ?361 V is achieved on SiO₂ substrates. The average retain rate of surface potential over 240 h is 90.6% for Pt substrates and 76.3% for SiO₂ substrates. The proposed method presents the primary step toward integrated electrostatic devices.     

Radon concentrations in schools of the Neapolitan area

A radon survey was carried out in 30 schools located in the metropolitan area around Naples, Italy. Radon concentration was measured using the SSNTD (Solid State Nuclear Track Detectors) method with LR115 detectors. Time integrated measurements covered two consecutive 6-month periods at different locations inside the school buildings: classrooms, laboratories and offices. Data distribution is well fitted by a log-normal curve. The arithmetic mean annual radon concentration is 144 Bq m⁻³, the geometric mean is 86 Bq m⁻³; the standard deviations are respectively 7 Bq m⁻³ and 3. The fractions of rooms where radon concentrations exceed the reference levels of 200, 400 and 500 Bq m⁻³ are 21.3%, 7.6% and 4.5% respectively.The results show that radon concentration in scientific laboratories and in offices is higher than in classrooms.     

Efficacy of electrostatically charged glyphosate on ryegrass

Using a TX-VK3 spray tip attached to an electrostatic sprayer operated at 483 kPa pressure, ryegrass was sprayed with glyphosate at 0.0033 kg ae ha⁻¹. Charge-to-mass ratio (Q/M) for the spray solution was 1.686 mC kg⁻¹ at +10.0 kV charging voltage. Treatment efficacy was assessed using NDVI (Normalized Difference Vegetation Index) spectral reflectance values. Electrostatic charging of glyphosate significantly increased volume median diameter of spray droplets (D_v0.5 = 112.8 μm) compared to uncharged glyphosate (D_v0.5 = 106.5 μm). Ryegrass health declined 80% faster by charging the glyphosate spray solution compared to the uncharged spray.     

Morphology and electret behaviour of microcellular high glass temperature films

Here we report the processing of cellular, high-temperature polymers for electret applications based on polyetherimide (PEI) and polyetheretherketone (PEEK). The two approaches were utilized to improve the electret properties by insertion of cavities are the physical batch foaming process using carbon dioxide as the blowing agent and the stretching of polymeric plates containing suitable particles, which allows the manufacturing of porous films. The electret properties of foamed PEI and PEEK as well as stretched PEI containing NA11 particles are characterized by isothermal charge decay measurements at 90 °C after corona charging to surface potentials of about 400 V. Investigation of the cellular morphologies was achieved by scanning electron microscopy (SEM) and micro-computertomography (μCT). As result, the cellular films show a clear improved charge storage behaviour compared to the compact films. The best results were achieved with porous PEI films, prepared by stretching and after twofold charging. PACS 77.22.-d; 77.84.Jd; 73.61.Ph; 61.43.Gt; 52.80.Hc     

Electrostatic charging of a conducting sphere using another conducting sphere at constant voltage

This study uses results of classical electrostatics to predict the resulting voltage of a conducting sphere that is charged by a second sphere maintained at a constant voltage. The voltage of the charged sphere is calculated as a function of the charging voltage and the size ratio of the two spheres. Theoretical predictions are verified experimentally using conducting spheres of various sizes and a Faraday ice pail apparatus. The results may seem somewhat counterintuitive. For example, a charging sphere held at 100 V will charge another sphere of equal size only to 69.3 V by contact.