C. Papachristodoulou

Use of HPGe γ-ray spectrometry to assess the isotopic compositiion of uranium in soils

Gamma-ray spectrometry was used to determine uranium activity and investigate the presence of depleted uranium in soil samples collected from camping sites of the Greek expeditionary force in Kosovo. Assessment of 238 U concentrations was based on measurements of the 63.3 keV and 92.38 keV emissions of its first daughter nuclide, 234 Th. To determine the isotopic ratio of 238 U/ 235 U, secular equilibrium along the two radioactive series was first ensured and thereby the contribution of 235 U under the 186 keV peak was deduced. The uranium activity in the samples varied from 48 to 112 Bq kg 1 , whereas the activity ratio of 238 U/ 235 U aver

Measurements of natural radioactivity in phosphate fertilizers

Abstract The natural radioactivity, mainly due to radium ( 226 Ra), in phosphate fertilizers used in north-western Greece has been measured by γ-spectroscopy. Also radioactivity measurements were performed in soil samples and were compared to samples from undisturbed soils. 226 Ra belongs to the 238 U chain and is the precursor of radon gas ( 222 Rn). The radon concentrations in warehouses, where large quantities of fertilizers are kept, were measured with CR-39 SSNTDs. The radium concentrations in the fertilizers ranged from 0 to 4584 Bq kg −1 and the radon concentrations in warchouses were measured 540–3320 Bq m −3 . The results are discussed from the radiation protection point of view.

Radon Activity Levels And Effective Doses In The Perama Cave, Greece

Abstract— An investigation of atmospheric radon levels in the Perama Cave, North-western Greece, has been carried out using CR-39 detectors. The detectors were placed at various locations along the guided cave pathway and exposed during different sampling periods. Mean concentrations amounting to 925 ± 418 and 1,311 ± 352 Bq m−3 were recorded in the summer and winter months, respectively. As the Perama Cave is one of the most popular in Greece, attracting more than 85,000 tourists per year, the quantification of effective doses to staff and visitors was an issue of importance. Doses less than 5.1 μSv per visit were calculated for tourists and around 1.8 mSv y−1 for seasonal guides, employed for periods of high visiting frequency. The annual exposure of permanent guides was estimated to fall between 3 and 10 mSv, which is the range of action levels recommended by the ICRP.

A survey of 222Rn concentrations in dwellings of the town of Metsovo in North-Western Greece

A radon survey has been carried out of indoor radon concentrations in dwellings located in the town of Metsovo, in north-western Greece. To measure indoor radon concentrations, CR-39 detectors were installed in randomly selected houses and were exposed for about 3 mo, during summer and winter. Gamma spectroscopy measurements of the soil’s radium content also were performed. The indoor radon concentration levels varied from 17.6 to 750.4 Bq m−3, while the radium concentration of soil varied from 4.9 to 97.1 Bq m−3. Seasonal variation of the radon levels and the influence of house features and soil are discussed.

Neutron cross-section measurements in the Th–U cycle by the activation method

The 232 Th(n,2n) 231 Th reaction cross-section was measured relative to the 56 Fe(n,p) 56 Mn and 27 Al(n,a) 24 Na reaction cross-sections with the activation method for neutron energies up to 11 MeV. Neutrons were produced by the 2 H(d,n) reaction in the 5.5 MV Tandem accelerator of the NCSR ‘‘Demokritos’’. The characteristic g lines of the product nuclei 231 Th (25.646 keV) and 56 Mn (846.771 keV) or 24 Na (1368 keV) were measured with an 80 mm 2 Si(Li) and a 20% reverseelectrode coaxial germanium detector, respectively. The results indicate that our values are in agreement with the JEF2 and BROND2 database values up to 9 MeV and slightly higher than those from all the libraries for higher energies. r 2003 Elsevier Science B.V. All rights reserved.

Effect of soil amendments on radiocesium transfer to alfalfa.

Abstract— Greenhouse experiments were carried out to evaluate the effect of different soil-based countermeasures on radiocesium transfer to Medicago sativa (alfalfa) grown on artificially contaminated loamy-clayey soil. Various rates of potassium, ammonium, and Prussian Blue supplements were applied, and the uptake of radiocesium by control and treated alfalfa plants was monitored during four growth periods. Transfer factors ranging between 0.06 and 0.02 were determined for control plants. Application of potassium at rates higher than 0.1 meq per 100 g soil was found to suppress radiocesium uptake, the effect being more pronounced at increasing fertilization rates. On the contrary, soil treatment with ammonium enhanced the bio-accumulation of radiocesium, indicating that Cs+ ions, previously unavailable to plant roots, were released from soil particles. Prussian Blue supplements had practically no effect on soil-to-alfalfa transfer of the radionuclide.

Measurements of222Rn migration in soil

The concentration of radon (222Rn) was measured in the soil near the ground surface, using CR/39 solid state nuclear track detectors. The measurements were carried out in PVC tubes at 0.25 m intervals up to 1.25 m. The detectors were etched in 7N NaOH solutions at 80°C. The α-tracks from radons decay were counted using a microscope. A microscope-camera-computer system developed for automatic counting was also used. The results provide evidence for the non-diffusive transport of radon in soils. A transport length of (46.9±3.2) cm was estimated for radon transport near ground surface. Also the variation of soils radon concentration was correlate to humidity and atmospheric pressure.

A two-dimensional magnetic hybrid material based on intercalation of a cationic Prussian blue analog in montmorillonite nanoclay

A highly ordered two-dimensional hybrid magnetic nanocomposite has been prepared by synthesizing and intercalating a new cationic aluminum-hydroxy ferric ferrocyanide compound into a cation-adsorbing nanoclay (montmorillonite). Chemical and structural properties were investigated by X-ray diffraction, transmission electron microscopy, thermogravimetric and differential thermal analyses, Fourier transform infrared, X-ray photoemission, and Mössbauer spectroscopies. Elemental analysis was based on proton-induced gamma ray emission and X-ray fluorescence spectroscopy data, N/C elemental ratios, and cation-exchange capacity measurements. Magnetic properties were studied by SQUID magnetometry. The results suggest: (i) that the cationic Prussian blue analog comprises Al-hydroxy cations embedded into a monolayer thick two-dimensional ferric ferrocyanide array; and (ii) that the clay-Prussian blue nanohybrid consists of such arrays stacked between the clay layers. The latter material orders ferromagnetically at approximately 5K showing a hundred times higher remanence than that of the starting material, soluble Prussian blue (ammonium ferric ferrocyanide).

A new approach for enhancing Sr2+ retention by an Al-PILC in acidic solutions

Abstract Strontium uptake by an aluminum pillared montmorillonite has been studied in aqueous solutions of pH values ranging from 3 to 8. Desorption of Sr 2+ has been observed when the concentration of H 3 O + in the solution raises. In order to limit this effect, the material has been modified by inserting organic molecules in the interlayer. Results with glycerol and oxalic acid as modifying agents demonstrate that it is feasible to shield the metal cations against hydronium attack and thus reduce strontium desorption in acidic environments. These results are of a particular interest from a view point of the potential application of PILCs as antidotes against strontium radiocontamination of ruminants.

Reaction channels of 6,7Li+28Si at near-barrier energies

The production of α-particles in the reactions 6,7 Li+ 28 Si was studied as a means to disentangle the various reaction channels at near-barrier energies. The competition between compound and direct reactions was determined by using the shape of angular distributions and statistical model calculations. DWBA calculations were also performed to probe the various direct channels. It was found that, approaching barrier, transfer channels are the most dominant for both reactions. For 7 Li+ 28 Si d-transfer is one of the contributing channels without excluding t-transfer, while for 6 Li+ 28 Si, n-transfer and p-transfer have substantial contribution but without excluding d-transfer.