Srboljub Stankovic

Radioactive reliability of gas filled surge arresters

The goal of this paper is to determine use of gas filled surge arresters (GFSA) with a built-in radioactive sources in radiative environment. Furthermore, a pseudoempiric method has been developed to determine the GFSA pulse shape characteristics. These results are considered relevant for the use of this component in both military applications and space technology.

Investigation of the optimal method for improvement of the protective characteristics of gas-filled surge arresters-with/without the built-in radioactive sources

This paper presents an alternative approach aimed toward improvement of protective characteristics of gas-filled surge arresters (GFSA). Although so far GFSA with built-in radioactive sources proved to have superior protective characteristics, environmental concerns often challenge functional benefits. Experimental results show that a hollow cathode used in GFSA (no radioactive sources), offers significant improvement of protective characteristics as compared to classical designs. A number of theoretical predictions and conclusions are confirmed experimentally.

Influence of Gamma and X Radiation on Gas-Filled Surge Arrester Characteristics

This paper aims to find the possibility of stabilizing the gas-filled surge arresters (GFSA) static working point in gamma- and X-radiation fields by an appropriate choice of constructive parameters. The observed effects on some commercial components have been compared to the originally developed GFSA model with the aim of improving the characteristics of the commercial components. The type of noble gas, the pressure in the gas chamber, the inter-electrode gap value, the electrode material, and the manner of electrode surface processing are used as variable parameters. The obtained results are significant for a better understanding of the prebreakdown effects in gases at low pressures, but also have practical importance for the manufacturer of GFSAs

Temperature stability of components for overvoltage protection of low-voltage systems

In this paper, we present temperature stability investigations of different overvoltage protection components employed in low-voltage applications. The following components have been examined: transient suppresser diodes, metal-oxide varistors (MOVs), gas-filled surge arresters (GFSAs), and polycarbonate capacitors. The aim of the research presented here is to identify the effectiveness of the overvoltage protection as a function of temperature. Experimental results show that GFSAs have rather stabile operational characteristics in a wide temperature range (from -90/spl deg/C to +210/spl deg/C). As for MOVs, they exhibit certain improvement of their protective characteristics at higher temperatures. Experimental results are backed up by theoretical explanations.

Computer Simulation of Gamma Irradiation Energy Deposition in MOSFET Dosimeters

The application of MOSFETs as detectors or device components in pulse power technique requires an investigation of their characteristics in radiation fields. Computing possibilities of the renowned programs FOTELP and PENELOPE for determining the energy deposited in MOSFET structure and dose distribution within microscopic dimensions of the dosimeter sensitive volume were presented in this paper. Based on the obtained results, qualitative conclusions were drawn about the values of energy deposited in different material zones having various dimensions. The difference between the two codes used for calculations in materials physics and semiconductor technics, basically originates from the different physical models for numerical simulation of photon, positron, and electron transport through various materials

Aging of the over-voltage protection elements caused by over-voltages

The aim of this work is examining the influence of the number of the activation––over-voltage pulses to the aging of over-voltage protection elements. Both non-linear (gas-filled surge arresters (GFSA), varistors, over-voltage diodes) and linear (capacitors––constituents of filters) over-voltage protection elements were tested. The instruments employed allow reliable measurements, 1000 consecutive activation were tested. The double-exponential current pulse (amplitude I1max=13 A, I2max=16 A, rise time T1=8 μs, fall time T2=20 μs) for non-linear elements and a double-exponential over-voltage pulse (rise time T1=1.2 μs, fall time T2=50 μs) of the amplitude U1max=320 V, U2max=480 V and U3max=640 V for capacitors were used. The experimental results show that the over-voltage diodes are the most reliable elements in view of characteristic modifications that are consequence of aging. However, it was observed that varistors, GFSA and capacitors undergo noticeable changes in characteristics.

Damage Induced by Neutron Radiation on Output Characteristics of Solar Cells, Photodiodes, and Phototransistors

This study investigates the effects of neutron radiation on - characteristics (current dependance on voltage) of commercial optoelectronic devices (silicon photodiodes, phototransistors, and solar panels). Current-voltage characteristics of the samples were measured at room temperature before and after irradiation. The diodes were irradiated using Am-Be neutron source with neutron emission of n/s. The results showed a decrease in photocurrent for all samples which could be due to the existence of neutron-induced displacement defects introduced into the semiconductor lattice. The process of annealing has also been observed. A comparative analysis of measurement results has been performed in order to determine the reliability of optoelectronic devices in radiation environments.

Investigation the optimal method for improvement the protective characteristics of gas filled surge arresters-W/O the built in radioactive sources

This paper presents an alternative approach aimed to improve protective characteristics of gas filled surge arresters (GFSA) by an optimal way. Regardless of the fact that GFSA with built-in radioactive sources, have better protective characteristics, environmental concerns often challenge functional benefits. Experimental results show that hollow cathode used in GFSA (no radioactive sources), offer improvements of protective characteristics over classical design. Most theoretical explanations and conclusions are confirmed experimentally.

Radioactive Reliability of Programmable Memories

The aim of this paper is to examine the reliability of EPROM and EEPROM components under the influence of gamma radiation. This problem is significant for military industry and space technology. Total dose results are presented for the JL 27C512D EPROM and 28C64C EEPROM components. There is evidence that EPROM components have better radioactive reliability than EEPROM components. Also, the EPROMs changes are reversible and after erasing process and reprogramming EPROM components are functional. On the other hand EEPROMs changes are irreversible and under the influence of gamma radiation all EEPROM components became permanently nonfunctional. The obtained results are analyzed and explained via the interaction of gamma radiation with oxide layers.

HEAVY METAL AND BACTERIAL POLLUTION OF THE SAVA RIVER IN SERBIA

Heavy Metal and Bacterial Pollution of the Sava River in Serbia The aim of this study was to establish microbial and heavy metal pollution of the Sava River at three locations close to industry and urban areas (Šabac, Obrenovac, Beograd) in Serbia. Heavy metal analysis included Cu, Zn, Pb, and Cd in the river water and sediment samples. Using the microbiological analysis we tried to establish the effectiveness of total coliforms, faecal coliforms and Escherichia coli in detecting pollution of surface waters. We found that E. coli levels steadily increased downstream from Šabac (location 1; 2100 MPN per 100 mL) to Belgrade (location 3; 10000 MPN per 100 mL). To prevent bacterial contamination, it is necessary to reduce the discharge of wastewater with faecal matters near highly populated towns. Heavy metal levels in sediments correlated with those in the river water. Fluctuations attributed mainly to anthropogenic sources were not high. These results point to acceptable anthropogenic contribution to heavy metal content in the Sava River and to low environmental risk. Onečišćenje rijeke save u srbiji teškim metalima i bakterijama Ispitivani su mikrobiološki parametri i teški metali u rijeci Savi na tri lokacije u blizini industrijskih i urbanih centara (Šabac, Obrenovac, Beograd). Analiza je obuhvatila parametre kvalitete: teške metale - Cu, Zn, Pb i Cd u riječnoj vodi i sedimentu te bakterije i patogene bakterije u riječnoj vodi. Radi utvrđivanja bakterijske kontaminacije površinskih voda testirani su koliform Escherichia coli i fekalni koliformi. Brojnost E. coli povećava se od lokacije 1 prema ušću Save od 2100 do 10000 u 100 mL NVB (najvjerojatniji broj). Nađen je velik broj biološki aktivnih mikroorganizama i bakterija. Koncentracija teških metala u sedimentu u korelaciji je s njihovom koncentracijom u riječnoj vodi ako se izrazi s pomoću koeficijenta distribucije Kd (dm3 kg-1) između čvrste i tekuće faze. Predložen je postupak za procjenu toksičnosti teških metala.