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We cross-match and compare characteristics of galaxy clusters identified in observations from two sky surveys using two completely different techniques. One sample is optically selected from the analysis of three years of Dark Energy Survey observations using the redMaPPer cluster detection algorithm. The second is X-ray selected from XMM observations analysed by the XMM Cluster Survey. The samples comprise a total area of 57.4 deg$^2$, bounded by the area of 4 contiguous XMM survey regions that overlap the DES footprint. We find that the X-ray selected sample is fully matched with entries in the redMaPPer catalogue, above $\lambda>$20 and within 0.1$< z, Comment: Accepted for publication to MNRAS

In this paper we present the X-ray analysis of SDSS DR8 redMaPPer (SDSSRM) clusters using data products from the $XMM$ Cluster Survey (XCS). In total, 1189 SDSSRM clusters fall within the $XMM$-Newton footprint. This has yielded 456 confirmed detections accompanied by X-ray luminosity ($L_{X}$) measurements. Of the detected clusters, 382 have an associated X-ray temperature measurement ($T_{X}$). This represents one of the largest samples of coherently derived cluster $T_{X}$ values to date. Our analysis of the X-ray observable to richness ($\lambda$) scaling relations has demonstrated that scatter in the $T_{X}-\lambda$ relation is roughly a third of that in the $L_{X}-\lambda$ relation, and that the $L_{X}-\lambda$ scatter is intrinsic, i.e. will not be significantly reduced with larger sample sizes. Our analysis of the scaling relation between $L_{X}$ and $T_{X}$ has shown that the fits are sensitive to the selection method of the sample, i.e. whether the sample is made up of clusters detected "serendipitously" compared to those deliberately targeted by $XMM$. These differences are also seen in the $L_{X}-\lambda$ relation and, to a lesser extent, in the $T_{X}-\lambda$ relation. Exclusion of the emission from the cluster core does not make a significant impact to the findings. A combination of selection biases is a likely, but as yet unproven, reason for these differences. Finally, we have also used our data to probe recent claims of anisotropy in the $L_{X}-T_{X}$ relation across the sky. We find no evidence of anistropy, but stress that this may be masked in our analysis by the incomplete declination coverage of the SDSS DR8 sample., Comment: 23 pages, 20 figures, Accepted for publication to MNRAS

A large lead target with a U blanket was irradiated by 1.5 GeV protons at the Dubna Nuclotron accelerator. Spatial distributions of neutron fluxes were determined by Solid State Nuclear Track Detectors in the new experimental transmutation assembly. Slow and fast neutron components were studied inside sections of the setup and on the U blanket surface. Neutron distributions after Cd and polyethylene shielding were also investigated. The results show that the new arrangement is efficient mainly to transmutation experiments by fission and (η,χη) reactions as well as by (η,γ) reactions.

The neutron flux trap effect was experimentally studied in the subcritical assembly of the Atomic and Nuclear Physics Laboratory of the Aristotle University of Thessaloniki, using delayed gamma neutron activation analysis. Measurements were taken within the natural uranium fuel grid, in vertical levels symmetrical to the Am–Be neutron source, before and after the removal of fuel elements, permitting likewise a basic study of the vertical flux profile. Three identical flux traps of diamond shape were created by removing four fuel rods for each one. Two (n, γ) reactions and one (n, p) threshold reaction were selected for thermal, epithermal and fast flux study. Results of thermal and epithermal flux obtained through the 197Au (n, γ) 198Au and 186W (n, γ) 187W reactions, with and without Cd covers, to differentiate between the two flux regions. The 58Ni (n, p) 58Co reaction was used for the fast flux determination. An interpolation technique based on local procedures was applied to fit the cross sect...

The operation of a medical linear accelerator was simulated using the Geant4 code regarding to study the characteristics of an 18 MeV photon beam. Simulations showed that (a) the photon spectrum at the isocenter is not influenced by changes of the primary electron beam's energy distribution and spatial spread (b) 98% of the photon energy fluence scored at the isocenter is primary photons that have only interacted with the target (c) the number of contaminant electrons is not negligible since it fluctuated around 5×10−5 per primary electron or 2.40×10−3 per photon at the isocenter (d) the number of neutrons that are created by (γ, n) reactions is 3.13×10−6 per primary electron or 1.50×10−3 per photon at the isocenter (e) a flattening filter free beam needs less primary electrons in order to deliver the same photon fluence at the isocenter than a normal flattening filter operation (f) there is no significant increase of the surface dose due to the contaminant electrons by removing the flattening filter (g) comparing the neutron fluences per incident electron for the flattened and unflattened beam, the neutron fluencies is 7% higher for the unflattened beams. To validate the simulations results, the total neutron and photon fluence at the isocenter field were measured using nickel, indium, and natural uranium activation foils. The percentage difference between simulations and measurements was 1.26% in case of uranium and 2.45% in case of the indium foil regarding photon fluencies while for neutrons the discrepancy is higher up to 8.0%. The photon and neutron fluencies of the simulated experiments fall within a range of ±1 and ±2 sigma error, respectively, compared to the ones obtained experimentally.

An improved neutron activation technique is analyzed that can be used for the characterization of the neutron field in low neutron flux environments, such as medical Linacs. Due to the much lower neutron fluence rates, thick materials instead of thin have been used. The study is focused on the calculations of basic components of the neutron activation analysis that are required for accurate results, such as the efficiency of the gamma detector used for γ-spectrometry as well as crucial correction factors that are required when dealing with thick samples in different geometries and forms. A Monte Carlo detector model, implemented by Geant4 MC Code was adjusted in accordance to results from various measurements performed. Moreover, regarding to estimate the self-shielding correction factors a new approach using both Monte Carlo and analytical approach was presented. This improvement gives more accurate results, which are important for both activation and shielding studies that take place in many facilities. A quite good agreement between the neutron fluxes is achieved; according to the data obtained a mean value of (2.13±0.34)×105 ncm−2 s−1 is representative for the isocenter of the specific Linac that corresponds to fluence of (5.53±0.94)×106 ncm−2 Gy−1. Comparable fluencies reported in the literature for similar Linacs operating with photon beams at 15 MeV.

Two helium filled proportional counters (He-3, He-4) were irradiated with neu- trons in the energy range 0.025 eV - 10.7 MeV, in the Tandem accelerator, NCSR Demokritos, Athens. The full energy peak in He-3 proportional counter as well as the recoil peaks in He-3 and He-4 counters show linear dependence with neutron energy. A study of gamma ray contribution to the neutron spectra of He-4 counter was performed as a function of the pulse shaping time.

Monte Carlo calculations with Geant4 were performed to calculate the response of He-3 proportional counters for neutrons of the energy region of 230 keV – 7 MeV. The results are compared with experimental data obtained by irradiation of the detectors with monoenergetic neutron beams produced by 7Li(p,n)7Be and 2H(d,n)3He reactions in the Tandem accelerator, NSCR Demokritos Athens.

The inelastic cross section of relativistic protons in Lead was determined indirectly by measuring the neutron distribution along a Lead spallation neutron source. The spallation neutron source was irradiated by 1, 1.5 and 2 GeV protons. The experimental results were taken using passive methods. A fitting procedure has been applied to the experimental data and the results have been compared with analytical calculation of the produced hadrons’ spatial distribution based on High Energy Physics concepts. Using the beam attenuation coefficient the inelastic cross section of protons in Pb was estimated.

The background radiation level of (137)Cs at the urban atmosphere of Thessaloniki has been increased during the recent decade only due to the Fukushima accident fallout. Since then, no other signal of (137)Cs was observed until the winter period of 2013, when slightly elevated (137)Cs concentrations were measured. The (137)Cs signals observed were up to 12 μBq m(-3), mainly during holidays and weekends followed by lower or even non-detectable activities in the next working days. Those episodes are attributed to the increase of biomass products combustion for residential heating as this year the tax of oil for heating was drastically raised as a consequence of the financial crisis. A preliminary survey of various wood products as well as of bottom ashes from different domestic burning devices is presented. (137)Cs concentrations up to 11 Bq kg(-1) were measured in wood products and up to 500 Bq kg(-1) in ash samples.

The neutron flux trap effect was experimentally studied in the sub-critical assembly of the Atomic and Nuclear Physics Laboratory of the Aristotle University of Thessaloniki, using delayed gamma neutron activation analysis (DGNAA). Measurements were taken within the fuel grid, in vertical levels symmetrical to the Am-Be neutron source, before and after the removal of fuel elements, also permitting a basic study of the vertical flux profile. Three identical flux traps of diamond shape and an area of 96 cm 2 were created by removing four fuel rods for each one. Two (n, γ ) reactions and one (n,p) threshold reaction were selected for thermal, epithermal and fast flux study. For the thermal and epithermal flux, results obtained through the 197 Au(n, γ ) 198 Au, and 186 W(n, γ ) 187 W reactions were used, with and without Cd covers, to differentiate between the two flux regions. For the fast flux, the 58 Ni(n,p) 58 Co reaction was used. All measurements were taken in a HPGe detector of 42% relative efficiency, with a resolution of 1.8 keV at 1332 keV and analyzed in the SPECTRW software package, developed at NCSR Demokritos. An interpolation technique based on local procedures is used to fit the cross sections and the flux spectra. End results show a thermal flux increase of 105% at the source level, and 90% across all levels, pointing to a high potential to increase the available thermal flux for future experiments. Furthermore, the vertical flux profile was found to be slightly asymmetric, with higher flux values at the top part of the assembly.

131I, 137Cs and 134Cs were observed in environmental samples in Milano (40°N), Italy and Thessaloniki (45°N), Greece, soon after the nuclear accident in Fukushima, Japan. The radionuclide concentrations were determined and studied as a function of time. In Thessaloniki the 131I in air was observed for the first time on March 24, 2011. In Milano, the first evidence of Fukushima fallout has been confirmed with 131I and 137Cs measured in wet precipitation collected 2 days later. The maximum 131I activity concentration in air of 467 ± 25 μBq m−3, observed in Milano on April 3–4, 2011, was almost similar to the highest value of 497 ± 53 μBq m−3 observed in Thessaloniki. The 134Cs/137Cs activity ratio values in air were around 1 in both regions. Soil, grass and milk samples were contaminated with 131I and 137Cs at a low level. Finally, a dose assessment for these two areas showed clearly that the detected activities in all environmental samples were far below levels of concern.

Analyses of 131I, 137Cs and 134Cs in airborne aerosols were carried out in daily samples at two different sites of investigation: Thessaloniki, Greece (40° N) and Milan, Italy (45° N) after the Fukushima accident during the period of March–April, 2011. The radionuclide concentrations were determined and studied as a function of time. The 131I concentration in air over Milan and Thessaloniki peaked on April 3–4, 2011, with observed activities 467 μBq m−3 and 497 μBq m−3, respectively. The 134Cs/137Cs activity ratio values in air were around 1 in both regions, related to the burn-up history of the damaged nuclear fuel of the destroyed nuclear reactor. The high 131I/137Cs ratio, observed during the first days after the accident, followed by lower values during the following days, reflects not only the initial release ratio but also the different volatility, attachment and removal of the two isotopes during transportation due to their different physico-chemical properties. No artificial radionuclides could be detected in air after April 28, 2011 in both regions of investigation. The different maxima of airborne 131I and 134,137Cs in these two regions were related to long-range air mass transport from Japan, across the Pacific and to Central Europe. Analysis of backward trajectories was used to confirm the arrival of artificial radionuclides following atmospheric transport and processing. HYSPLIT backward trajectories were applied for the interpretation of activity variations of measured radionuclides.

Fallout from the Fukushima Nuclear Accident has been monitored for about 1 month in Thessaloniki, Northern Greece. Three different radionuclides, one short-lived, one relatively long-lived and one long-lived fission product were identified in air, precipitation, soil, grass and milk samples. The 131I, 137Cs and 134Cs activity concentrations in air reached 497, 145 and 126 μBq m−3, respectively on 4 April, 2011. The external exposure dose rate to humans of the order of 14.4 pSv per day due to 137Cs deposited on the ground was very small compared to the normal background level. The accumulated dose equivalent to the adult thyroid from inhaled 131I varied from 0.4 to 3.5 nSv per day was insignificant and there was not any problem for the Greek population and no preventive measures were needed to be provided against the nuclear accident according to the Greek Atomic Energy Commission, the official agent of the Greek Government. Some special radioecological aspects in the air-grass-cow-milk-man pathway for 131I were particularly studied.

The inelastic cross section of relativistic protons in Pb was determined indirectly by measuring the neutron distribution along a Lead spallation neutron source. The spallation neutron source was irradiated by 1, 1.5 and 2 GeV protons. The experimental results were obtained using passive methods. By the use of the beam attenuation coefficient, deduced by a fitting procedure of experimental data, the inelastic cross section of protons in Pb was determined.

Regarding neutron spectrometry, energy calibration of a He-3 counter was performed for neutron energies up to about 7 MeV, for various operating voltages in the proportionality region. Full-energy peak position is linearly correlated with neutron energy, while the position of the 3He recoil peak deviates from a linear response, especially in the lower energy region. By means of the linear full-energy peak calibration, recoil peak energies are found to be significantly lower than those resulting from the kinematics of the reaction. The pulse-height loss is attributed to initial recombination. Using the Bragg curve of the recoiling nucleus in the counter gas mixture, it is determined that the pulse-height loss corresponds to a constant portion, 33.5±1.3 %, of the fraction of energy deposited by a 3He nucleus traversing the gas mixture with a stopping power higher than 450 eV/μm. The energy calibration equation for the recoil peaks is derived using the following: (i) the range-energy relation and the stopping power function for a 3He nucleus in the gas mixture where the coefficients of both functions were determined via Monte Carlo calculations, and (ii) the experimentally determined recombination coefficient.

Spallation sources are able to produce intense neutron fluxes using massive targets when irradiated by relativistic proton beams. Such sub-critical Accelerator Driven Systems (ADSystem) can be used for transmutation or incineration of long-lived radioactive waste by neutron captures or neutron induced fission. In the present study a spallation source consisted of a combined Pb/U target was irradiated by relativistic proton beams from 0.7 up to 2 GeV. Neutron fluences were measured using passive detectors. A benchmark analysis was applied on the experimental results taken under consideration Monte Carlo simulation data of neutron multiplicity. In order to evaluate the tolerance of the structural materials in source design, the neutron and proton distributions escaping the source surface were measured. The spallation source performance in terms of neutron and proton production as well as the effectiveness of a polyethylene shielding surrounding the spallation source is also discussed.

A new spallation source, efficient for transmutation experiments, was designed and constructed at the Dubna High Energy Laboratory (LHE). The spallation source has a cylindrical shape Pb target surrounded by nat U rods. Experiments with protons of 0.7–2 GeV were performed and neutron spatial distribution on the surface of U blanket was studied. Total neutron fluences and estimates of their energy distributions were determined using solid state nuclear track detectors. Slow and fast neutron components were studied as a function of the proton beam energy. The experimental results were fitted and compared with calculations derived from empirical relations based on physics near high-energy accelerators. The results show that neutron spatial distribution along the U blanket surface (parallel to the beam direction) has the same shape independent of the proton beam energy. The neutron fluence spatial distribution is characterized by an increase at the beginning of the target and after reaching a maximum drops as a function of the target thickness. The maximum is reached at about one mean free path of protons in the Pb target. The total number of neutrons produced, as was measured on U blanket surface, is an increasing function of the proton beam energy. © 2008 Elsevier Ltd. All rights reserved.

In the frame of international concern about long-lived nuclear waste, the construction of an effective accelerator driven system for the transmutation or incineration of fission products and actinides is a promising task. A spallation source consisting of a Pb target surrounded by paraffin moderator was studied by irradiation with relativistic proton beams. The spatial distribution of secondary proton and slow neutron were determined using the natCd activation technique and their multiplicity was calculated in order to verify the transmutation efficiency of the specific spallation source and to estimate the tolerance limit of source construction materials.

Two helium filled proportional counters (3He and 4He) were studied to establish the optimum operating conditions when these counters are used for fast neutron measurements, as well as to examine the linearity of the pulse height with neutron energy. The detectors were irradiated with mono-energetic neutrons in the energy range of 230 keV–22 MeV, produced via 7Li(n,p)7Be, 2H(d,n)3He and 3H(d,n)4He reactions in a Tandem Van de Graff accelerator. The gamma ray contribution to the obtained pulse height distribution and the resolution of the counters as a function of shaping time constant and applied high voltage were studied.

Transmutation, the procedure of transforming long-lived radioactive isotopes into stable or short-lived, was proposed for reducing the amount of radioactive waste resulting from technological applications of nuclear fission. The Accelerator Driven Systems (ADS) provide the possibility to generate intense neutron spectrum yielding in an effective transmutation of unwanted isotopes. Such experiments are being carried out for the last 10 years in Synchrophasotron / Nuclotron accelerators at the Veksler-Baldin Laboratory of High Energies of the Joint Institute for Nuclear Research in Dubna, Russia. Thick Pb and Pb-U targets, surrounded by moderators, have been irradiated by protons in the energy range of 0.5−7.4 GeV. Neutron fluence measurements have been performed by different techniques of passive detectors (neutron activation detectors, solid state nuclear track detectors). Transmutation of 129I, 237Np, 239Pu was studied. The results of these experiments are presented and discussed.

Radium-226 in phosphogypsum produced in a phosphate industry, SICNG operating at Thessaloniki, Northern Greece since May 1966, varied from 261 to 688 Bq kg(-1) (mean value 508 Bq kg(-1)). This radionuclide in soil tilled with phosphogypsum used for agricultural purposes varied from 50 to 479 Bq kg(-1) (average 205 Bq kg(-1)), while in the regular soil of cultivated fields it varied from 37 to 54 Bq kg(-1) (average 48 Bq kg(-1)). Radium-226 in rice originated from cultivated fields tilled with phosphogypsum or not varied from 0.36 to 1.98 Bq kg(-1) (average 1.53 Bq kg(-1)) with the higher values observed in samples originated from cultivated fields tilled with phosphogypsum. Radium-226 transfer factors, TF, from soil tilled with phosphogypsum to plants for the case of rice varied from 6.5 x 10(-3) to 2.0 x 10(-2) (geometric mean: 1.1 x 10(-2)). A mean (226)Ra content in rice 1.53 Bq kg(-1) results in a daily intake of (226)Ra by humans in Greece 0.0084 Bq day(-1) leading to an annual effective dose for adults 0.86 microSv y(-1) which is much less in contributing to the average exposure to natural radiation sources (2.4 mSv y(-1)) and particularly to the part due to ingestion (0.29 mSv y(-1)). It is necessary to continuously control (monitoring) (226)Ra in phosphogypsum before any use for agricultural purposes.

Fallout from the Fukushima nuclear accident has been monitored for about 1 month in Thessaloniki, Northern Greece. Three different radionuclides, one short-lived, one relatively long-lived and one long-lived fission product were identified in air, grass and milk samples. The 131 I, 137 Cs and 134 Cs activity concentrations in air reached 497, 145 and 126 μBq m −3 , respectively on 4 April, 2011. These radionuclides are of particular concern regarding their transfer from the environment to population through the ingestion pathways for the assessment of the Fukushima accident consequences. Radioecological indexes (eco-indexes) of fallout measurements in the air–grass–cow-milk–man pathway for 131 I were determined, as they are related to radiological impact of the Fukushima derived radionuclides on the public and environment.

Two methods for radon emanation factor determination were performed and compared regarding their measuring accuracy: (a) by hermetically closing the sample in an airtight container and measuring the induced radon activity, and (b) by mixing charcoal and sealing the sample hermetically and after placing the sample in an open vessel with no charcoal addition, measuring each time the 226Ra content using gamma-spectrometry. Measurements of radon emanation factor of cement and pozzolanic additives, i.e. fly ash and phosphogypsum were also performed.

Radioactive emissions into the atmosphere from the damaged reactors of the Fukushima Dai-ichi nuclear power plant (NPP) started on March 12th, 2011. Among the various radionuclides released, iodine-131 ( 131I) and cesium isotopes ( 137Cs and 134Cs) were transported across the Pacific toward the North American continent and reached Europe despite dispersion and washout along the route of the contaminated air masses. In Europe, the first signs of the releases were detected 7 days later while the first peak of activity level was observed between March 28th and March 30th. Time variations over a 20-day period and spatial variations across more than 150 sampling locations in Europe made it possible to characterize the contaminated air masses. After the Chernobyl accident, only a few measurements of the gaseous 131I fraction were conducted compared to the number of measurements for the particulate fraction. Several studies had already pointed out the importance of the gaseous 131I and the large underestimation of the total 131I airborne activity level, and subsequent calculations of inhalation dose, if neglected. The measurements made across Europe following the releases from the Fukushima NPP reactors have provided a significant amount of new data on the ratio of the gaseous 131I fraction to total 131I, both on a spatial scale and its temporal variation. It can be pointed out that during the Fukushima event, the 134Cs to 137Cs ratio proved to be different from that observed after the Chernobyl accident. The data set provided in this paper is the most comprehensive survey of the main relevant airborne radionuclides from the Fukushima reactors, measured across Europe. A rough estimate of the total 131I inventory that has passed over Europe during this period was \textless1% of the released amount. According to the measurements, airborne activity levels remain of no concern for public health in Europe. © 2011 American Chemical Society.

Accuracy in the measurements of 226 Ra concentrations by gamma spectroscopy depends on an appropriate determination of the concentrations of 222 Rn decay products ( 214 Pb and 214 Bi) in the sample. As an inert gas, radon can leak from the sample vessel or accumulate in the void upper part of it. In the latter case, radon decay products can be attached on the inner surface of the sample container, and therefore the gamma rays have another geometry and self-absorption factor which differs from the one assumed (similar to the calibration sample). The influence of the above procedures on the accuracy of the measurements depends mainly on the emanation factor of radon in the sample, the geometry used in the measurement and the structure of the sample container. Results of the tests that have been performed with a new technique developed in order to eliminate radon diffusion through the sample are presented. Two materials with different effective 226 Ra concentrations were used for the tests: soil with 5 Bq kg −1 effective 226 Ra (total 226 Ra concentration 20 Bq kg −1 and emanation factor 25%) and phosphate fertilizer with 22 Bq kg −1 effective 226 Ra (total 226 Ra concentration 306 Bq kg −1 and emanation factor 7%). From gamma-spectroscopy measurements it was found out that the increase in 226 Ra concentration, when charcoal was added to the samples, was about 35% of the effective 226 Ra of the sample. This could lead to an underestimate of about 10% of the 226 Ra concentrations in voluminous samples with high emanation factor (25%).

High spallation neutron fluxes were produced by irradiating massive heavy targets with proton beams in the GeV range. The experiments were performed at the Dubna High Energy Laboratory using the nuclotron accelerator. Two different experimental set-ups were used to produce neutron spectra convenient for transmutation of radioactive waste by (n,x) reactions. By a theoretical analysis neutron spectra can be reproduced from activation measurements. Thermal-epithermal and fast-super-fast neutron fluxes were estimated using the 197Au, 238U (n,gamma) and (n,2n) reactions, respectively. Depleted uranium transmutation rates were also studied in both experiments.

Radon concentration measurements were carried out using solid-state nuclear track-etch detectors (SSNTDs) type CA 80-15 cellulose nitrate films, in a Pleistocenic cave at Petralona, in Halkidiki, Northern Greece, at 55 km from the city of Thessaloniki. Radon levels as high as 88 kBq.m-3 (2.38 nCi.l-1) have been recorded inside the cave equivalent to 11.90 WL in terms of occupational exposure to radon and its decay products. Absorbed dose rates were performed using TL dosimeters, type TLD-200 (CaF2-Dy) in a continuous monitoring program (integrated measurements). Dose rate levels as high as 110 nGy.h-1 were recorded inside the cave. In interpreting the high levels of radiation doses, radioactivity measurements regarding the naturally occurring 238U, 232Th and 40K radionuclides were carried out in various speleothems found at different sites in the cave.

A coloured rain event originating from the Sahara Desert occurred on April 9, 2000 at Thessaloniki, Northern Greece (40°38′N, 22°58′E). The radioactive nuclides that were determined in a coloured rain dust sample were 137 Cs of Chernobyl origin, 7 Be of cosmogenic origin and 40 K of terrestrial origin. Cesium-137 still remained 14 years after the Chernobyl accident, reaching 26.6 Bq kg −1 in the coloured rain dust.

Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) with a LiF powder placed on their surface were used as neutron dosemeter. The effect of thermal neutron irradiation on the threshold voltage of the transistor was studied in order to determine the sensitivity of these detectors. Irradiations were performed at the thermal column of the reactor in IPTA, Demokritos, Athens and at the subcritical reactor of Nuclear Physics Laboratory, Thessaloniki. The sensitivity of the MOSFETs as a function of thermal neutron dose was found to be practically linear up to 100 mSv. The lower detectable dose appears to be depended on the dose rate.

Measurements of fallout-derived 137Cs and of naturally occurring radionuclides, such as 40K and 7Be, in soils and grass were made in the Thessaloniki area of northern Greece, in the temperate zone (40°N), in order to determine their transfer factors from soil to plants. Long-term measurements over an 11-year period showed 137Cs concentrations ranging from 3.73 to 1307 Bq kg-1 (avge. 210.5 Bq kg-1) in soils and from 0.4 to 334.9 Bq kg-1 (avge. 14.5 Bq kg-1) in grass. Potassium-40 concentrations ranged from 141.4 to 580.2 Bq kg-1 (avge. 224.4 Bq kg-1) in soils and from 66.3 to 1480 Bq kg-1 (avge. 399.8 Bq kg-1) in grass. Beryllium-7 concentrations ranged from 0.53 to 39.6 Bq kg-1 (avge. 14.4 Bq kg-1) in soils and from 2.1 to 348.0 Bq kg-1 (avge. 54.4 Bq kg-1) in grass. Cesium-137 transfer coefficients, TF, from soil to plants (grass) ranged from 0.002 to 7.42 (avge. 0.20). Potassium-40 TF values from soil to plants (grass) ranged from 0.25 to 2.42 (avge. 0.73). Beryllium-7 TF values from soil to plants (grass) ranged from 0.027 to 2.37 (avge. 0.42). An ecological half-life, Tec, for 137Cs in grassland of 3 1 3 years could be derived, while TF values varied between 0.1 and 0.01 over an 11-year period since the contamination event (May 1986). An almost similar Tec value ( 3 2 3 years) was derived for 40K in grassland.

The background radiation measurements in the lower atmosphere at different altitudes above sea level up to 1100 m and over the land were made at a temperate latitude (40°) in the Thessaloniki region, North Greece, before and after the Chernobyl accident (26 April 1986), using a portable γ-ray scintillation detector and a Cutie-pie survey meter with an ionization chamber. The average value of the total background radiation at ground level was 87 nGy h-1 (10.0 μR h-1, 25 cps), i.e. 60% from terrestrial radiation, 55 nGy h-1 (6.3 μR h-1, 15 cps) and 40% from cosmic radiation, 32 nGy h-1 (3.7 μR h-1, 10 cps), before the Chernobyl accident, while, after it, the total background radiation was doubled, due to the long-lived radioactive fallout suspended in the atmosphere and or deposited onto the ground.

Hg(Br x I 1− x ) 2 crystals were grown by the Bridgman method for 0.2 x 241 Am and 55 Fe were used as radioactive sources. From the corresponding energy spectra, it is evident that crystals with x = 0.2 show enhanced resolution at low energies (below 200 keV), competing those fabricated from HgI 2 and CdTe. Crystals with higher x 's were of lower resolution.

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 (

Radon concentrations indoors were determined in 24 typical occupied apartments in the city of Thessaloniki, North Greece (40 degrees 38'N, 22 degrees 58'E), by means of 12 surveys, each 2 mo long, over a 2-y period starting October 1989. The ratio of the winter and summer averages for the first year of measurements was 1.8 +/- 0.78, and for the second year of measurements was 1.6 +/- 0.61. The indoor radon concentration in the summer (1990) period ranged between 8 and 81 Bq m-3, while in the winter (1989-1990) it ranged between 20 and 143 Bq m-3 for the first year of measurements or between 8 and 92 Bq m-3 in the summer (1991) period and between 12 and 119 Bq m-3 in the winter (1990-1991) for the second year of measurements. These results were obtained by type CN-85 alpha track detectors. Some parameters that influenced the concentrations, such as precipitation rates and use of fly ash in building materials, are discussed.

Helium filled proportional counters are widely used in the field of neutron detection and spectrometry. A review of some parameters and physical effects that influence the He-3 proportional counters response is presented through the experimental study of a commercially available counter. The impact of these effects is taken into account in the description of detector performance when the response is calculated with the Monte Carlo method. A method to determine neutron energy distribution with a bare He-3 counter in an unknown neutron field is presented. The neutron energy range extends up to about 7 MeV. The method does not require a hypothesis about neutron spectrum shape. It is based in the calculated counter response with Geant4, the validity of which is experimentally verified. A detailed description of the steps needed is presented.

Neutron and proton yields. spatial and energy distributions were determined on an electronuclear set-up irradiated with relativistic deuteron beams. The experimental results, acquired using both passive and active methods, are compared with the data obtained using MC simulation. The U-blanket performance in terms of fission production rate as well as plutonium accumulation is discussed. An evaluation between the data obtained using relativistic deuteron and proton beams is presented regarding to study the set-up efficiency to incinerate and/or transmute the actinides and fission products. (C) 2009 Elsevier Ltd. All rights reserved.

The behavior of naturally-occurring radionuclides 238U, 226Ra, 210Pb, 228Ra (232Th) and 40K in lignites and fly ashes is described. The concentrations of 238U, 226Ra and 210Pb in lignites were increased with decreasing concentrations of 40K, resulting in an inverse relationship, whereas the concentration of 228Ra (232Th) increased with an increasing concentration of 40K. In fly ashes, 238U and 210Pb were enriched on smaller particles, while 40K decreased. The content of the two isotopes of radium, 226Ra and 228Ra, also decreased in finer particles of fly ash but the rate of decrease for 226Ra was found to be weaker than on the corresponding one of 228Ra as well as of 40K. The above observations are discussed.

The 137 Cs concentrations in lichens and mosses were significantly high five years after the Chernobyl accident. In some species of foliose lichens and mosses, the uptake of 137 Cs during the long period of time was dominant in respect of its natural removal. In some species of fruticose lichens, decrease of the 137 Cs concentration was only observed with time passed, resulting in an effective half-life of 137 Cs, averaging 2.6 y at latitude 40°N. Uptake rates of 137 Cs in some species of foliose lichens were determined, varying from about 3 400 to 7 000 (average 4 800) Bq/kg·y.

1350-4487/$ – see front matter doi:10.1016/j.radmeas.2009.02.001 In Fig. 2a the reported values of neutron fluencemust be divided by a factor of 1.8. That correction has to be applied after the experience gained over the proton beam profile and fluence during short-term irradiation (1011 protons). The same treatment must be applied to the values referred to intermediate–fast neutron fluence, as those presented in Fig. 2b. In particular, the intermediate–fast neutron fluence must be divided by an additional factor of 1.4, after the correction that has been considered in order to take into account the contribution of the neutrons with energy from 3 up to 5 MeV, which is also detected but with lower response. All the above corrections should be applied also to the presented values of neutron multiplicity in Table 1.

Neutron dose measurements and calculations around spallation sources are of importance for an appropriate shielding study. Two spallation sources, consisted of Pb target, have been irradiated by high-energy proton beams, delivered by the Nuclotron accelerator (JINR), Dubna. Dose measurements of the neutrons produced by the two spallation sources were performed using Solid State Nuclear Track Detectors (SSNTDs). In addition, the neutron dose after polyethylene and concrete was calculated using phenomenological model based on empirical relations applied in high energy Physics. Analytical and experimental neutron benchmark analysis has been performed using the transmission factor. A comparison of experimental results with calculations is given.

A spallation neutron source consisted of a cylindrical Pb target and surrounded by uranium blanket was irradiated by deuteron beam 1.25 GeV/amu provided from the Nuclotron accelerator at High Energy Laboratory, JINR, Dubna. For radiation protection purpose a polyethylene shielding was placed around the spallation neutron source. Neutron distributions along the surface of the U-blanket were measured by using solid state nuclear track detectors (SSNTDs) as particle and fission detectors. The neutron distributions appear to be similar to those obtained by proton irradiations. Applying a fitting procedure to the experimental data the inelastic cross section of deuteron in Pb was estimated. The escaping neutron distribution from the polyethylene shielding and parallel to the target was also measured and presented to be two orders of magnitude less than that over the U-blanket surface. (C) 2008 Elsevier Ltd. All rights reserved. 23rd International Conference on Nuclear Tracks in Solids, Sep 11-15, 2006, Shanxi Normal Univ, Inst Modern Phys, Beijing, Peoples R China

Fallout-derived 137Cs and naturally occurring radionuclides, such as 40K and 40Be in soils and grass were measured in Thessaloniki area, Northern Greece, at temperate zone (40°), in order to examine their behaviour in natural ecosystems. For long-term measurements over a 15-y period, 137Cs concentrations ranged from 3.73 to 1307 Bq kg−1 (avg. 210.5 Bq kg−1) in soils and from 0.4 to 334.9 Bq kg −1(avg. 14.5 Bq kg−1) for grass. Potassium-40 concentrations ranged from 141.4 to 580.2 Bq kg−1 (avg. 224.4 Bq kg−1) in soils and from 66.3 to 1480 Bq kg−1 (avg. 399.8 Bq kg−1) for grass. Beryllium-7 concentrations ranged from 0.53 to 39.6 Bq kg−1 (avg. 14.4 Bq kg−1) in the soils and from 2.1 to 348.0 Bq kg−1 (avg. 54.4 Bq kg−1) for grass. Cesium-137 transfer coefficients, TF from soil to plants (grass) ranged from 0.002 to 7.42 (avg. 0.20). Potassium-40 TF values from soil to plants (grass) ranged from 0.16 to 2.42 (avg. 0.73). Beryllium-7 TF values from soil to plants (grass) ranged from 0.027 to 2.37 (avg. 0.42) 137 An ecological half-life, Tec for 137Cs in grassland 3 1/3 y could be derived, when TF values varied between 0.1 and 0.01 in an 11-y elapsed time since contamination (May 1986). An almost similar Tec value (3 2/3 y) was derived for 40K in grassland.

High-energy protons in the range of 0.5–7.4 GeV have irradiated an extended Pb target covered with a paraffin moderator. The moderator was used in order to shift the hard Pb spallation neutron spectrum to lower energies and to increase the transmutation efficiency via (n,γ) reactions. Neutron distributions along and inside the paraffin moderator were measured. An analysis of the experimental results was performed based on particle production by high-energy interactions with heavy targets and neutron spectrum shifting by the paraffin. Conclusions about the spallation neutron production in the target and moderation through the paraffin are presented. The study of the total neutron fluence on the moderator surface as a function of the proton beam energy shows that neutron cost is improved up to 1 GeV. For higher proton beam energies it remains constant with a tendency to decline.

Various spallation sources have been used to transmute long-lived radioactive waste, mostly making use of the wide energy neutron fluence. In addition to neutrons, a large number of protons and gamma rays are also emitted from these sources. In this paper nat Cd is proved to be a useful activation detector for determining both thermal–epithermal neutron as well as secondary proton fluences. The fluences measured with nat Cd compared with other experimental data and calculations of DCM-DEM code were found to be in reasonable agreement. An accumulation of therma–epithermal neutrons around the center of the target (i.e. after approx. 10 cm) and of secondary protons towards the end of the target is observed.

The MDT chambers of the ATLAS Muon Spectrometer will operate in a heavy LHC background environment mainly from photons and neutrons. The ionization produced by neutron recoils is much higher than the one from photons or muons and can be simulated by the use of alpha particles. A systematic study of the behavior of the ATLAS Monitored Drift Tubes (MDTs) under controlled irradiation has been performed. The presence of alpha particles results in the reduction of the gas gain due to space charge effects. The gas gain reduction has been studied in a single tube set up using a well controlled radium (/sup 226/Ra) source in order to enrich the tube gas (Ar/CO/sub 2/) with the alpha emitter /sup 220/Rn and irradiate the tubes internally. The results are confronted with Garfield simulations.

Atmospheric concentrations of (7)Be and (210)Pb were measured for 15 years (1987--2001) in ground-level air at Thessaloniki, Northern Greece (40 degrees 38'N, 22 degrees 58'E). Mean activity concentrations of (7)Be and (210)Pb were 5.02 mBqm(-3) and 664 microBqm(-3), respectively, characteristic of the latitude of 40 degrees N. Monthly atmospheric concentrations of (7)Be showed a strong seasonal trend with the highest values being observed in the summer and the lowest in the winter period. Multiple regression analysis of the data of (7)Be concentrations and a number of meteorological parameters revealed that the sunspot number and temperature are the most significant parameters affecting the concentrations of (7)Be in surface air. The observed strong positive correlation between the mean monthly concentrations of (7)Be and the temperature confirms that the increased rate of vertical transport within the troposphere, especially during the warm months, has as a result to carry down to the surface layer air masses enriched in (7)Be. Highest values of the mean monthly atmospheric concentrations of (210)Pb were observed in the autumn and lowest in the spring period. The positive correlation that was observed between (210)Pb and (7)Be concentrations during the summer months suggests that these two radionuclides could be used together as tracers of environmental processes.