It is estimated that until 1978 about 200000 lightning conductor rods with -a emitting sources attached to their end were installed worldwide. The sources were supposed to increase the lighting collection efficiency of these rods through the ionization of the surrounding air. Nevertheless, this improvement has never been established conclusively. Such devices are, in most cases, not accessible by the pub- lic; therefore, the dose to the population is considered insignificant. However, the possibility of radioactive material leakage, due to the source attachment failure, and the subsequent contamination of the surroundings that could lead to possible health risk of the public cannot be excluded. In this work, the case of 241Am contamination due to a lightning rod conductor failure is investigated. This contamination was accidentally detected on the surface soil around a laboratory building in the National Technical University of Athens Campus, during a routine in-situ gamma-ray measurement campaign that took place in 2003. A detailed survey revealed that this 241Am contamination was due to the leakage from two lightning rods on the building roof. Consequently the rods were removed from the building and the contamination pattern on the roof and on the surface soil around the building was examined in detail. From the results obtained so far it may be concluded that there exists well localized contamination on the roof and also around the building. It was established that the pathway through which contamination reached the ground was the rainwater drainage system of the building. The gamma ray dose rate due to 241Am contamination found on the roof and on the surface soil is low compared to that due to its natural radioactivity and does not seem to pose any health risk to the people working in the building or to the public.

It is estimated that until 1978 about 200000 lightning conductor rods with -a emitting sources attached to their end were installed worldwide. The sources were supposed to increase the lighting collection efficiency of these rods through the ionization of the surrounding air. Nevertheless, this improvement has never been established conclusively. Such devices are, in most cases, not accessible by the public; therefore, the dose to the population is considered insignificant. However, the possibility of radioactive material leakage, due to the source attachment failure, and the subsequent contamination of the surroundings that could lead to possible health risk of the public cannot be excluded. In this work, the case of 2 4 1 Am contamination due to a lightning rod conductor failure is investigated. This contamination was accidentally detected on the surface soil around a laboratory building in the National Technical University of Athens Campus, during a routine in-situ gammaray measurement campaign that took place in 2003. A detailed survey revealed that this Am contamination was due to the leakage from two lightning rods on the building roof. Consequently the rods were removed from the building and the contamination pattern on the roof and on the surface soil around the building was examined in detail. Prom the results obtained so far it may be concluded that there exists well localized contamination on the roof and also around the building. It was established that the pathway through which contamination reached the ground was the rainwater drainage system of the building. The gamma ray dose rate due to 241 Am contamination found on the roof and on the surface soil is low compared to that due to its natural radioactivity and does not seem to pose any health risk to the people working in the building or to the public.

Within the presented study, soil samples were collected in year 2007 at 20 different locations of the Greek terrain, both from the surface and also from depths down to 26 cm. Sampling locations were selected primarily from areas where high levels of 137Cs deposition after the Chernobyl accident had already been identified by the Nuclear Engineering Laboratory of the National Technical University of Athens during and after the year of 1986. At one location of relatively higher deposition, soil core samples were collected following a 60 m by 60 m Cartesian grid with a 20 m node-to-node distance. Single or pair core samples were also collected from the remaining 19 locations. Sample measurements and analysis were used to estimate 137Cs inventory and the corresponding depth migration, twenty years after the deposition on Greek terrain. Based on these data, the uncertainty components of the whole sampling-to-results procedure were investigated. A cause-and-effect assessment process was used to apply the law of error propagation and demonstrate that the dominating significant component of the combined uncertainty is that due to the spatial variability of the contemporary (2007) 137Cs inventory. A secondary, yet also significant component was identified to be the activity measurement process itself. Other less-significant uncertainty parameters were sampling methods, the variation in the soil field density with depth and the preparation of samples for measurement. The sampling grid experiment allowed for the quantitative evaluation of the uncertainty due to spatial variability, also by the assistance of the semivariance analysis. Denser, optimized grid could return more accurate values for this component but with a significantly elevated laboratory cost, in terms of both, human and material resources. Using the hereby collected data and for the case of a single core soil sampling using a well-defined sampling methodology quality assurance, the uncertainty component due to spatial variability was evaluated to about 19% for the 137Cs inventory and up to 34% for the 137Cs penetration depth. Based on the presented results and also on related literature, it is argued that such high uncertainties should be anticipated for single core samplings conducted using similar methodology and employed as 137Cs inventory and penetration depth estimators.

The purpose of this work was to investigate the effect of particle size on radionuclides in soil, particularly in relation to depth. A set of soil samples at the 0–10cm and 10–20cm depth layers were collected, separated into size fractions using a sieving machine and analyzed by gamma spectrometry to determine 238U, 226Ra, 210Pb, and 137Cs. Significant variations between different size fractions and depth layers were observed. A 0–20cm depth profile was also investigated.

Flow of gravitationally falling thin liquid films over the outer cylindrical surfaces with or without concurrent steam flow has always been a fundamental problem of major importance at applied thermal hydraulics, especially, on thermal hydraulic phenomena that occur after a large or small break LOCA such as the rewetting of the overheated fuel elements by a top spraying ECCS and CCFL during reflux condensation. In this study an experimental apparatus has been set up, so as to thoroughly collect liquid films data at low Reynolds numbers by means of needle contact probes. Although this technique is not widely adopted, it is reliable and accurate as other probing techniques and it has the major advantage that it can provide direct measurements of the film characteristics as no calibration is needed. The probes' axial movement is controlled by the use of two step motors capable of 2.5 μm resolution. Step motors are directly connected with a computer that undertakes all the acquisition tasks and thus provides a fully automated measurement procedure. Measurements are performed within the liquid inception region where no surface wave formation is expected and at a proper longitudinal distance from the liquid entrance where the two-wave system would be well developed. Water in ambient pressure is fed to the test section through a slit type distributor with a slit width of 0.25 mm, and then flows freely along the outer surface of a 1.5 m stainless steel cylindrical test section at the temperature of approximately 300 K and volumetric flows between 1 and 3 L·min-1. Statistical processing of the collected data, for which probability density distribution of the film thickness, correlation and spectral analysis were used, provides experimental results for the film structure and the film flow characteristics as well. Experimental results for the film thickness distribution, the mean film thickness, the film wave frequency and celerity are presented and further compared to other theoretical and experimental results in the existing literature.

The radionuclides released during the accident at the Fukushima Daichii nuclear power plant following the Tōhoku earthquake and tsunami on 11 March 2011 were dispersed in the whole north hemisphere. Traces of (131)I, (134)Cs and (137)Cs reached Greece and were detected in air, grass, sheep milk, ground deposition, rainwater and drainage water. Members of Six Greek laboratories of the national network for environmental radioactivity monitoring have collaborated with the Greek Atomic Energy Commission (GAEC) and carried out measurements during the time period between 11 March 2011 and 10 May 2011 and reported their results to GAEC. These laboratories are sited in three Greek cities, Athens, Thessaloniki and Ioannina, covering a large part of the Greek territory. The concentrations of the radionuclides were studied as a function of time. The first indication for the arrival of the radionuclides in Greece originating from Fukushima accident took place on 24 March 2011. After 28 April 2011', concentrations of all the radionuclides were below the minimum detectable activities (<10 μBq m(-3) for (131)I). The range of concentration values in aerosol particles was 10-520 μBq m(-3) for (131)I, 10-200 μBq m(-3) for (134)Cs and 10-200 μBq m(-3) for (137)Cs and was 10-2200 μBq m(-3) for (131)I in gaseous phase. The ratios of (131)I/(137)Cs and (134)Cs/(137)Cs concentrations are also presented. For (131)I, the maximum concentration detected in grass was 2.2 Bq kg(-1). In the case of sheep milk, the maximum concentration detected for (131)I was 2 Bq l(-1). Furthermore, more than 200 samples of imported foodstuff have been measured in Greece, following the EC directives on the inspection of food and feeding stuffs.

This paper presents the Compton Suppression System, recently installed at the Nuclear Engineering Department of NTUA. The system consists of an XtRa Ge detector coupled with a NaI(Tl) guard detector. The electronic set-up allows for the simultaneous collection of both the suppressed and the unsuppressed spectra. System performance is investigated using certified point and volume sources. Parameters such as Peak Suppression Factors, peak-to-Compton ratios and minimum detectable activity for specific radionuclides are determined.

Phosphorimetry is an analytical technique for the determination of elemental uranium concentration in aqueous environmental or biological samples. Uranium phosphorescence from aqueous samples at room temperature is practically undetectable without the addition of a uranium complexant, i.e., a solution whose molecules bind to the uranyl ions present in the sample under measurement and protect them from non-luminescent de-excitation. Procurement of commercially available and proprietary in nature complexant solutions can prove cost in-effective. On the other hand, phosphoric acid is known for its phosphorescence protecting capabilities. This study investigates the optimisation of phosphoric acid use as uranium complexant, and assesses it in terms of accuracy, precision and longevity, with rather encouraging results.

The micron-precision RF structures are mounted and aligned on specially developed supporting girders, which provide stability and re-positioning. The supporting girders have stiffness and damping specifications imposed by stringent beam physics and RF requirements. In addition, several constraints, such as allocated space and weight limitation have to be taken into consideration. This paper describes different support concepts following various fabrication techniques and materials. Extensive qualification measurements have been performed on the first prototype units, and the main results are also reported.

The concentration of trace elements and radionuclides in fly ash particles of different size can exhibit significant variation, due to the various processes taking place during combustion inside a coal-fired power plant. An investigation of this effect has been performed by analyzing samples of fly ash originating in two different coal-fired power plants, after separation into size fractions by sieving. The samples were analyzed by gamma-ray spectrometry, including low-energy techniques, radon exhalation measurement and instrumental neutron activation analysis for the determination of Al, As, Ga, K, La, Na, Mn, Mg, Sr, Sc, and V. Variations are observed in the results of various samples analyzed, while the activity balances calculated from the results of individual size fractions are consistent with those of the raw ash samples. Correlations among the radionuclides examined are also observed, while individual nuclide behavior varies between the two types of fly ash examined.

The paper deals with a specific aspect of a general survey, that is being carried out during last ten years in several regions of Serbia (former Yugoslavia, former Serbia and Montenegro) to assess population exposure to natural radioactivity based on geochemical and integrative pattern research approach. The originality regarding this work is related to the facts such as follows: the first identification and assessment of high areas of natural radiation in Serbia which provides insight into its regional characteristics, the interpretation of the results in terms of geological aspects, building types and human habits, the first introduction and field applicability of both (surface and volume trap) retro techniques in Serbia and assessment of doses and risks to the population in investigated high natural radiation rural communities.

In this paper, the leaching, toxicity behaviour and the radioactivity content of solid residues coming from the co-combustion of biomass with coal were studied. A variety of samples collected from semi-industrial scale tests were analysed for their leaching and toxicity properties. Natural radioactivity and radon exhalation rate were also measured in samples collected from tests performed in a pilot facility in Germany (IVD, University of Stuttgart) and large-scale power plants. The high toxicity levels detected in the ash samples of olive kernel could be attributed to the relatively increased concentrations of Zn, Ni, Mn, Co, Cd. The effect of biomass co-combustion on the radioactivity content of fly ash was dependent on the fuel mixture used as well as the ash sampling location along the flue gas pathway. Activity concentrations of most nuclides of interest, namely 238U, 226Ra, 210Pb and 232Th are comparable to those of fly ash produced when burning pure coal, while increased concentrations where observed for 40K. In some cases the artificial radionuclide 137Cs was also detected.

Lipases are triacyl glycerol acyl hydrolases, which catalyze hydrolysis of esters, esterification and transesterification reactions, among others. Some of these enzymes have a large hydrophobic pocket covered by an alpha-helical mobile surface loop (the lid). Protein–protein interactions can occur through adsorption of two open lids of individual lipases. We investigated the conformation and oligomeric state of Thermomyces lanuginosus lipase (TLL) in solution by spectroscopic and mass spectrometry techniques. Information about oligomerization of this important industrial enzyme is only available for TLL crystals; therefore, we have done a throughout investigation of the conformation of this lipase in solution. SDS-PAGE and mass spectrometry analysis of size-exclusion chromatography eluted fractions indicated the presence of both monomeric and dimeric populations of TLL. The stability of the enzyme upon thermal and guanidine hydrochloride treatment was examined by circular dichroism and fluorescence emission spectroscopy. Small angle x-ray scattering and ion mobility mass spectrometry analysis revealed that TLL is found as a mixture of monomers and dimers at the assayed concentrations. Although previous x-ray diffraction data showed TLL as a dimer in the crystal (PDB: 1DT3), to our knowledge our report is the first evidencing that TLL co-exists as stable dimeric and monomeric forms in solution.

High concentrations of natural radionuclides in the soil can result in high dose rates outdoors mainly due to external exposure. In dose calculations, the main radionuclides of interest are Ra-226 Th-232 and K-40. Research till recent years has focused mainly on the evaluation of Ra-226 concentration, due to radon exhalation from the ground, and due to its relatively simple determination through its gamma emitting decay products. Other radionuclides of the uranium series such as U-231 and Pb-210, emitting low energy photons, are not usually determined due to gamma-spectroscopic difficulties, and for dosimetric calculations an assumption of radioactive equilibrium among the nuclides of the uranium (U-238) series as well as the nuclides of the thorium (Th-232) series is usually adopted. Radioactive disequilibrium may exist among the nuclides of the uranium series, and this is the case for the relatively long-lived nuclides U-238 (T-1/2 = 4.47 x 10(9) y), Ra-226 (T-1/2 = 1600 y) and Pb-210 (T-1/2 = 22.2 y) for several reasons, such as leaching, rock weathering, radon exhalation from the ground, etc. Radioactive equilibrium may also be disturbed because of human activities, such as the operation of coal-fired power plants and the resulting fly-ash dispersion and fallout. An extensive research program has been undertaken by the Nuclear Engineering Section of the National Technical University of Athens (NES-NTUA) for the investigation of the natural and artificial radioactivity in Greek surface soils. This research has resulted in the mapping of Ra-226, Th-232 and K-40 in Greek surface soils, as well as the mapping of radionuclides of the Chernobyl fallout in Greece. The gamma spectroscopic determination of U-218 and Pb-210, which emit low energy photons at 63.29 and 46.5 keV, respectively, with very low yields, requires the use of detectors with high efficiency in the low region below 200 keV, such as LEGe or XtRa detectors, and special techniques for correction due to self-absorption inside the samples. Due to the time consuming and difficult determination of the low activities of U-238 and Pb-210 in environmental samples, such as soil, it is only recently that such results are reported in the literature. In the framework of this research soil samples from all over Greece are analyzed for U-238, Ra-226 and Pb-210. From the samples analyzed so far, the conclusion may be drawn that, when Ra-226 concentration is much lower than about 25 Bq kg(-1), which is incidentally the mean value for Ra-226 in Greek surface soils, radioactive equilibrium is significantly disturbed, and the Ra-226/U-238 ratio may be as low as 0.3. In the case where Ra-226 activity is much higher than 25 Bq kg(-1), radioactive equilibrium is again significantly disturbed with the Ra-226/U-238 ratio reaching values as high as 4. The above findings indicate that very high values of Ra-226 in surface soils may be the result of Ra-226 transport to that soil. Concerning the concentration of Pb-210 in surface soils, the analyses performed show that it is usually higher than that of Ra-226, probably due to radon exhalation from the ground. Analyses of soil samples from deeper soil layers are also performed, in order to investigate the vertical profile of the radionuclides under study. (c) 2005 Elsevier Ltd. All rights reserved.

The Megalopolis lignite field basin is located in the centre of the Peloponnesus peninsula in southern Greece. The lignite fired power plants in operation in this region have a total capacity of 850 MW and produce over 2 million metric tons of fly ash annually; this is primarily disposed of in deposits located mainly at exhausted lignite mines. The disposed fly ash has a Ra-226 content of about 1000 Bq kg(-1). An extensive research project for the determination of the natural radioactivity of lignite and ash from the Megalopolis power plants started in the Nuclear Engineering Section of the National Technical University of Athens (NES-NTUA) in 1983. The project has evolved to an integrated radioenvironmental survey of the Megalopolis lignite field basin area. The present work aims at the presentation of the radioenvironmental survey of the fly ash deposits in the vicinity of the power plants. Results regarding (a) gamma-dose rate, (b) radon concentration in the ambient air, (c) soil radon exhalation rate and (d) soil gas radon concentration are reported from systematic field measurements at three deposit sites. In addition, soil sampling of the surface and 0-80 cm layer has been conducted at the deposits to allow for the determination of the activity of natural radionuclides, namely Ra-226 Th-232, K-40, Th-234 and (210)pb. The radiological characterisation of the fly-ash deposits obtained through these results is compared to the natural radioactivity background in the wider Megalopolis area, using the additional results of a previous similar survey. It can be concluded that, from the radiological point of view, the Megalopolis fly ash deposits do not differ significantly from the rest of the Megalopolis lignite field basin, despite the fact that most of the underground soil layers consist of fly ash with high Ra-226 content.

This paper presents the Medical Physics Department-Radon Dosemeter (MPD-RD). A calibration technique is introduced and the results of the calibration of the MPD-RDs are reported. A method for stabilising the radon concentration was employed and checked. The results showed that the MPD-RDs respond exponentially with time and linearly to exposures.

A total of 1440 samples of soil, collected across Greece from the 1 cm surface layer, were analysed for natural radioactivity (226Ra, 232Th, and 40K). The samples were air-dried and then hermetically sealed in 0.282 L plastic boxes covered with a film of epoxy resin to ensure that no gases escaped from them. Secular equilibrium of 226Ra and 232Th with their decay products was obtained before the samples were analysed using high resolution Ge gamma-ray detectors. A Unix-based in-house built complex Data Base/Geographical Information System (DBGIS) was used to analyze the data and present them in map form. The analysis of a second 1 cm thick sample, collected at several sites at a depth of 10 cm, led to the statistically justified conclusion that the natural radioactivity content of the surface and of 10 cm deep soil layers do not significantly differ. According to these results, the natural radioactivity content of Greek surface soils is rather low and is for 226Ra: 25 ± 19 Bqkg−1, for 228Ra: 21 ± 16 Bqkg−1, and for 40K: 355 ± 220 Bqkg−1. They entail a gamma-ray dose rate outdoors of 40 nGyh−1. A statistical analysis showed that only 90 samples, collected at 67 locations, have 226Ra content exceeding their mean value by more than 1.65σ. The 226Ra232Th and 226Ra40K concentration ratios were 1.10 ± 0.48 and 0.06 ± 0.03, respectively.