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Galaxy clusters are widely used to constrain cosmological parameters through their properties, such as masses, luminosity, and temperature distributions. One should take into account all kind of biases that could affect these analyses in order to obtain reliable constraints. In this work, we study the difference in the properties of clusters residing in different large-scale environments, defined by their position within or outside of voids, and the density of their surrounding space. We use both observational and simulation cluster and void catalogues, i.e. XMM Cluster Survey (XCS) and redMaPPer clusters, Baryon Oscillation Spectroscopic Survey (BOSS) voids, and Magneticum simulations. We devise two different environmental proxies for the clusters and study their redshift, richness, mass, X-ray luminosity, and temperature distributions, as well as some properties of their galaxy populations. We use the Kolmogorov–Smirnov two-sample test to discover that richer and more massive clusters are more prevalent in overdense regions and outside of voids. We also find that clusters of matched richness and mass in overdense regions and outside voids tend to have higher X-ray luminosities and temperatures. These differences could have important implications for precision cosmology with clusters of galaxies, since cluster mass calibrations can vary with environment. [ABSTRACT FROM AUTHOR]

We study the possible rotation of cluster galaxies, developing, testing, and applying a novel algorithm which identifies rotation, if such does exist, as well as its rotational centre, its axis orientation, rotational velocity amplitude, and, finally, the clockwise or counterclockwise direction of rotation on the plane of the sky. To validate our algorithms we construct realistic Monte Carlo mock rotating clusters and confirm that our method provides robust indications of rotation. We then apply our methodology on a sample of Abell clusters with z ≲ 0.1 with member galaxies selected from the Sloan Digital Sky Survey DR10 spectroscopic data base. After excluding a number of substructured clusters, which could provide erroneous indications of rotation, and taking into account the expected fraction of misidentified coherent substructure velocities for rotation, provided by our Monte Carlo simulation analysis, we find that ~23 per cent of our clusters are rotating under a set of strict criteria. Loosening the strictness of the criteria, on the expense of introducing spurious rotation indications, we find this fraction increasing to ~28 per cent. We correlate our rotation indicators with the cluster dynamical state, provided either by their Bautz-Morgan type or by their X-ray isophotal shape and find for those clusters showing rotation within 1.5 h70-1 Mpc that the significance of their rotation is related to the dynamically younger phases of cluster formation but after the initial anisotropic accretion and merging has been completed. Finally, finding rotational modes in galaxy clusters could lead to the necessity of correcting the dynamical cluster mass calculations. [ABSTRACT FROM AUTHOR]

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 I, Cs and Cs activity concentrations in air reached 497, 145 and 126 μBq m, respectively on 4 April, 2011. The external exposure dose rate to humans of the order of 14.4 pSv per day due to Cs deposited on the ground was very small compared to the normal background level. The accumulated dose equivalent to the adult thyroid from inhaled I 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 I were particularly studied. [ABSTRACT FROM AUTHOR]

Abstract: Regarding neutron spectrometry, energy calibration of a He-3 counter was performed for neutron energies up to about 7MeV, 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 450eV/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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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 natCd is proved to be a useful activation detector for determining both thermal–epithermal neutron as well as secondary proton fluences. The fluences measured with natCd 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. 10cm) and of secondary protons towards the end of the target is observed. [Copyright &y& Elsevier]

Abstract: 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 230keV–22MeV, 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. [Copyright &y& Elsevier]

Abstract: High-energy protons in the range of 0.5–7.4GeV 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 1GeV. For higher proton beam energies it remains constant with a tendency to decline. [Copyright &y& Elsevier]

Abstract: Atmospheric concentrations of 7Be and 210Pb were measured for 15 years (1987–2001) in ground-level air at Thessaloniki, Northern Greece (40°38′N, 22°58′E). Mean activity concentrations of 7Be and 210Pb were 5.02mBqm−3 and 664μBqm−3, respectively, characteristic of the latitude of 40°N. Monthly atmospheric concentrations of 7Be 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 7Be concentrations and a number of meteorological parameters revealed that the sunspot number and temperature are the most significant parameters affecting the concentrations of 7Be in surface air. The observed strong positive correlation between the mean monthly concentrations of 7Be 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 7Be. Highest values of the mean monthly atmospheric concentrations of 210Pb were observed in the autumn and lowest in the spring period. The positive correlation that was observed between 210Pb and 7Be concentrations during the summer months suggests that these two radionuclides could be used together as tracers of environmental processes. [Copyright &y& Elsevier]

Abstract: Grass ecosystem was monitored for 137Cs, a relatively long-lived radionuclide, for about 16 years since the Chernobyl reactor accident occurred on April 26, 1986. Cesium-137 in grass gramineae or poaceae the species, ranged from 122.9Bqkg−1 (September 4, 1986) to 5.8mBqkg−1 (October 16, 2001) that is a range of five orders of magnitude. It was observed that there was a trend of decreasing 137Cs with time reflecting a removal half-time of 40 months (3 1/3 years), which is the ecological half-life, T ec of 137Cs in grassland. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

In controlling the natural radiation exposure for the residents of dwellings, it is necessary to determine the levels of natural radioactivity (external exposure) and radon exhalation rate (internal exposure) from building materials. Using a high-resolution gamma ray spectrometry system, the activity concentration of natural radionuclides was measured. The radon exhalation rate was measured by hermetically closing the sample in a container and following the radon activity growth as a function of time. Three different methods were applied in order to find the most appropriate, i.e. that with the less uncertainty for the less exposure time. Typical building materials were analyzed in order to examine the external and internal exposures. In addition, the total annual effective dose was evaluated for the residents of a typical Greek dwelling. [Copyright &y& Elsevier]

Accuracy in the measurements of 226Ra concentrations by gamma spectroscopy depends on an appropriate determination of the concentrations of 222Rn decay products (214Pb and 214Bi) 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 226Ra concentrations were used for the tests: soil with 5Bqkg−1 effective 226Ra (total 226Ra concentration 20Bqkg−1 and emanation factor 25%) and phosphate fertilizer with 22Bqkg−1 effective 226Ra (total 226Ra concentration 306Bqkg−1 and emanation factor 7%). From gamma-spectroscopy measurements it was found out that the increase in 226Ra concentration, when charcoal was added to the samples, was about 35% of the effective 226Ra of the sample. This could lead to an underestimate of about 10% of the 226Ra concentrations in voluminous samples with high emanation factor (25%). [Copyright &y& Elsevier]

Abstract: 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 131I, 137Cs and 134Cs activity concentrations in air reached 497, 145 and 126μBqm−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 131I were determined, as they are related to radiological impact of the Fukushima derived radionuclides on the public and environment. [Copyright &y& Elsevier]

Abstract: Thick Pb targets of different lengths were irradiated by 1GeV protons at the Nuclotron accelerator of the High Energy Laboratory, JINR, Dubna. To favor transmutation via reactions a paraffin moderator is used. Solid-state nuclear track detectors (SSNTDs) measured neutron distribution. A comparison of experimental results with calculation on the moderator surface is given. [Copyright &y& Elsevier]

Abstract: Radioiodine (131I) in air and rainwater as high as 497 μBq m−3 and 0.7 Bq L−1, respectively, as well as 137Cs and 134Cs in air as high as 145 μBq m−3 and 126 μBq m−3, respectively were recorded in Thessaloniki, Northern Greece (40°38′N, 22°58′E) from March 24, 2011 through April 09, 2011, after a nuclear accident occurred at Fukushima, Japan (37°45′N, 140°28′E) on March 11, 2011. [Copyright &y& Elsevier]

Cesium-137 in air as high as 88.1 µBq . m-3 was recorded in Thessaloniki, Northern Greece (40°38’N, 22°58’E) on June 3, 1998 very late after the Chernobyl reactor accident following a radiological incident occurred in a steel factory at Acerinox, Spain. [ABSTRACT FROM AUTHOR]

Abstract: Radon measurements were carried out, using solid-state nuclear track-etch detectors (SSNTDs) with type CA 80-15 cellulose nitrate films, in a Pleistocenic cave at Petralona, in Halkidiki, northern Greece, 55 km distant from the city of Thessaloniki. Radon levels as high as 88 kBq m−3 (2.38 nCi l−1) recorded inside the cave is equivalent to 11.90 WL in terms of occupational exposure to radon and its decay products. Absorbed dose rates were measured 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. [Copyright &y& Elsevier]

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 3 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 deg2, bounded by the area of four 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 λ > 20 and within 0.1 < |$z$| <0.9. Conversely, only 38 per cent of the redMaPPer catalogue is matched to an X-ray extended source. Next, using 120 optically clusters and 184 X-ray-selected clusters, we investigate the form of the X-ray luminosity–temperature (LX – TX), luminosity–richness (LX –λ), and temperature–richness (TX –λ) scaling relations. We find that the fitted forms of the LX – TX relations are consistent between the two selection methods and also with other studies in the literature. However, we find tentative evidence for a steepening of the slope of the relation for low richness systems in the X-ray-selected sample. When considering the scaling of richness with X-ray properties, we again find consistency in the relations (i.e. LX –λ and TX –λ) between the optical and X-ray-selected samples. This is contrary to previous similar works that find a significant increase in the scatter of the luminosity scaling relation for X-ray-selected samples compared to optically selected samples. [ABSTRACT FROM AUTHOR]

Abstract: A spallation neutron source consisted of a cylindrical Pb target and surrounded by uranium blanket was irradiated by deuteron beam 1.25GeV/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. [Copyright &y& Elsevier]

In this paper, we present the X-ray analysis of Sloan Digital Sky Survey 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 (LX) measurements. Of these clusters, 381 have an associated X-ray temperature measurement (TX). This represents one of the largest samples of coherently derived cluster TX values to date. Our analysis of the X-ray observable to richness scaling relations has demonstrated that scatter in the TX –λ relation is roughly a third of that in the LX –λ relation, and that the LX –λ scatter is intrinsic, i.e. will not be significantly reduced with larger sample sizes. Analysis of the scaling relation between LX and TX 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 LX –λ relation and, to a lesser extent, in the TX –λ relation. Exclusion of the emission from the cluster core does not make a significant impact on the findings. A combination of selection biases is a likely, but yet unproven, reason for these differences. Finally, we have also used our data to probe recent claims of anisotropy in the LX – TX relation across the sky. We find no evidence of anistropy, but stress this may be masked in our analysis by the incomplete declination coverage of the SDSS. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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)×10 5 ncm −2 s −1 is representative for the isocenter of the specific Linac that corresponds to fluence of (5.53±0.94)×10 6 ncm −2 Gy −1 . Comparable fluencies reported in the literature for similar Linacs operating with photon beams at 15 MeV. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Radiation exposure of the population can be increased appreciably by the use of building materials containing above-normal levels of naturally occurring radionuclides of terrestrial origin, as high as 1600 Bq. kg-1for 40K in granites, 700 Bq. kg-1for 226Ra in phosphogypsum and 360 Bq. kg-1for 232Th in granites. In a 25-year survey including more than two hundreds of different materials were investigated. Of the materials normally used in the building industry, i.e., red clay bricks, cement of Portland Types I and II, concretes, gravels and sand, contain regular levels of the primordial radionuclides. The adsorbed dose rate in indoor air, in general, does not exceed the dose criterion of 80 nGy. h-1or 0.3 mSv. y-1for the effective dose. Granites and phosphogypsum are the highly radioactive materials for which the absorbed dose rate in indoor air becomes up to five times higher than the dose criterion. It is recommended to avoid the use of those materials without radioactivity control. [ABSTRACT FROM AUTHOR]

In the general case of neutron measurement by passive detectors, the conversion of direct experimental data to neutron flux results by using (1) a cross-section of the reaction on which the detector is responding or (2) an appropriate calibration of the detector versus neutron energy. For a better estimation of the neutron flux, especially in real neutron fields, the calculation of the effective cross-section in the first case and the calculation of an effective conversion factor from Tracks to Neutrons (TN) in the second case, both corresponding to the neutron energy spectrum, is required. This work is an application on the determination and comparison of neutron fluxes in the experimental transmutation assemblies in Dubna using several types of passive detectors. For the calculation of the effective cross-sections as well as of the effective conversion factor TN for each experimental assembly the neutron energy spectral shape was estimated theoretically by using the high-energy transport code DCM-DEM. [Copyright &y& Elsevier]

A large Pb target with a U blanket was irradiated with 1.5 GeV protons at the Dubna Nuclotron accelerator. Solid-state nuclear track detectors measured neutron spatial distributions 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 for transmutation experiments by (n,f) and (n,xn) reactions as well as by (n,γ) reactions. [Copyright &y& Elsevier]

Abstract: 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 100mSv. The lower detectable dose appears to be depended on the dose rate. [Copyright &y& Elsevier]

There have been several reports of a detection of an unexplained excess of X-ray emission at |$\simeq$| 3.5 keV in astrophysical systems. One interpretation of this excess is the decay of sterile neutrino dark matter. The most influential study to date analysed 73 clusters observed by the XMM–Newton satellite. We explore evidence for a ≃3.5-keV excess in the XMM -PN spectra of 117 redMaPPer galaxy clusters (0.1 < z < 0.6). In our analysis of individual spectra, we identify three systems with an excess of flux at |$\simeq$| 3.5 keV. In one case (XCS J0003.3+0204), this excess may result from a discrete emission line. None of these systems are the most dark matter dominated in our sample. We group the remaining 114 clusters into four temperature (T X) bins to search for an increase in ≃3.5-keV flux excess with T X – a reliable tracer of halo mass. However, we do not find evidence of a significant excess in flux at ≃3.5 keV in any T X bins. To maximize sensitivity to a potentially weak dark matter decay feature at ≃3.5 keV, we jointly fit 114 clusters. Again, no significant excess is found at ≃3.5 keV. We estimate the upper limit of an undetected emission line at ≃3.5 keV to be 2.41 × 10−6 photons cm−2 s−1, corresponding to a mixing angle of sin 2(2θ) = 4.4 × 10−11, lower than previous estimates from cluster studies. We conclude that a flux excess at ≃3.5 keV is not a ubiquitous feature in clusters and therefore unlikely to originate from sterile neutrino dark matter decay. [ABSTRACT FROM AUTHOR]

Neutron spectrum of the sub-critical nuclear assembly-reactor of Aristotle University of Thessaloniki was measured at three radial distances from the reactor core. The neutron activation technique was applied irradiating 15 thick foils – disc of various elements at each position. The data of 38 (n,γ), (n,p) and (n,α) reactions were analyzed for specific activity determination. Discs instead of foils were used due to the relevant low neutron flux, so the gamma self-absorption as well as the neutron self-shielding factors has been calculated using GEANT simulations in order to determine the activity induced. The specific activities calculated for all isotopes studied were the input to the SANDII code, which was built specifically for the neutron spectrum de-convolution when the neutron activation technique is used. For the optimization of the results a technique was applied in order to minimize the influence of the initial-“guessed” spectrum shape SANDII uses. The neutron spectrum estimated presents a peak in the regions of (i) thermal neutrons ranged between 0.001 and 1 eV peaking at neutron energy ∼0.1 eV and (ii) fast neutrons ranged between 0.1 and 20 MeV peaking at neutron energy ∼1.2 MeV. The reduction of thermal neutrons is higher than the fast one as the distance from the reactor core increases since thermal neutrons capture by natural U-fuel has higher cross section than the fast neutrons. [ABSTRACT FROM PUBLISHER]

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 the197Au (n,γ)198Au and186W (n,γ)187W reactions, with and without Cd covers, to differentiate between the two flux regions. The58Ni (n,p)58Co reaction was used for the fast flux determination. An interpolation technique based on local procedures was applied to fit the cross sections data and the neutron flux spectrum. End results show a maximum thermal flux increase of 105% at the source level, pointing to a high potential to increase in the available thermal flux for future experiments. The increase in thermal flux is not accompanied by a comparable decrease in epithermal or fast flux, since thermal flux gain is higher than epithermal and fast neutron flux loss. So, the neutron reflection is mainly responsible for the thermal neutron increase, contributing to 89% at the central axial position. [ABSTRACT FROM PUBLISHER]

Abstract: The background radiation level of 137Cs 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 137Cs was observed until the winter period of 2013, when slightly elevated 137Cs concentrations were measured. The 137Cs 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. 137Cs concentrations up to 11 Bq kg−1 were measured in wood products and up to 500 Bq kg−1 in ash samples. [Copyright &y& Elsevier]

Abstract: 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 2GeV 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. [Copyright &y& Elsevier]

Abstract: 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 2GeV. 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. [Copyright &y& Elsevier]

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

Abstract: Long-lived isotopes can be transmuted into stable or short-lived elements either by neutron captures or neutron induced fission. The need of a large excess of neutrons has led to the use of accelerator driven sources (ADS). A series of experiments were carried out at the Synchrophasotron/Nuclotron of the Joint Institute for Nuclear Research (JINR) Dubna, using protons of 1.0GeV. Solid Lead and Uranium targets surrounded by paraffin moderator were irradiated. On the outer surface of the moderator a number of Solid State Track Detectors were placed to monitor neutron spatial distribution. The results showed that the maximum neutron production was reached within the range of one to two proton mean free paths in the target. Then decreasing neutron production follows the proton beam attenuation along the target. Moreover, the results showed both targets neutron production evolution along the target, to be the same. However, neutron flux per incident proton is depended on the target mass, which was found to be higher for the heavier target. [Copyright &y& Elsevier]

Abstract: The BIS Monitored Drift Tube (MDT) chambers form the innermost station of the ATLAS Muon Spectrometer and are constructed in Greece by three Universities. The performance of a BIS chamber (Module 0) with cosmic muons has been extensively studied at the University of Thessaloniki. In this work we report on the performance of the chamber, i.e., drift times, resolution, efficiencies as well as gain properties under different high-voltage operating conditions. The experimental results are also confronted with expectations from GARFIELD simulations. A systematic study of the behavior of the ATLAS Monitored Drift Tubes (MDTs) under controlled irradiation by alpha particles has also been performed. The aim of the study was to quantify the response of the drift tubes to alpha particles and consequently to heavily ionizing particles. [Copyright &y& Elsevier]

ATLAS (a toroidal LHC apparatus) is a general purpose experiment that will start its operation at the large hadron collider (LHC) at CERN in 2007. The ATLAS detector is designed to explore numerous physics processes by recording, measuring, and investigating the products emerging from proton-proton collisions at energies up to 14 TeV. High-precision muon momentum measurement (dp/p ∼ 10% at pT = 1 TeV/c) over large areas using monitored drift tube (MDT) chambers is crucial for the ATLAS experiment. More than 1200 MDT chambers, consisting of approximately 370 000 drift tubes, will provide a total coverage of 5500 m². Three Greek universities have taken the responsibility to construct 130 barrel inner small (BIS)-MDT chambers using 30 000 drift tubes of ∼ 1.7 m length that have been quality tested before assembly. The design of the muon drift tubes aims at high detection efficiency (> 95%) and a spatial single tube resolution of < 80 μm. This paper describes the cosmic ray test setup, which has been instrumented in order to verify that the BIS-MDT chamber Module-0 fulfills its design requirements. The analysis of its data shows that the chamber meets these requirements; it has low noise levels, uniform drift properties, good spatial resolution, and high particle detection efficiency. [ABSTRACT FROM AUTHOR]

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,γ) and (n,2n) reactions, respectively. Depleted uranium transmutation rates were also studied in both experiments. [Copyright &y& Elsevier]

Abstract: Hg(Br x I1−x )2 crystals were grown by the Bridgman method for 0.2&#60; x &#60;1.0. They were tested for potential implementation as X- and γ-ray detectors at room temperature. 241Am and 55Fe 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 200keV), competing those fabricated from HgI2 and CdTe. Crystals with higher x''s were of lower resolution. [Copyright &y& Elsevier]

Abstract: 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 natU rods. Experiments with protons of 0.7–2GeV 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. [Copyright &y& Elsevier]