An overview of Fukushima radionuclides measured in the northern hemisphere

The Great East Japan Earthquake and tsunami on March 11, 2011 resulted in the tragic accident at the Fukushima Nuclear Power Plant (NPP) and subsequently uncontrolled release of radioactive contaminants into the atmosphere. This review article attempts to compile and interpret data collected by various national and international monitoring networks in response to the Fukushima releases across the northern hemisphere. The majority of the releases occurred during the period March 12-22 with a maximum release phase from March 14-17, 2011. The radioactivity released was dominated by volatile fission products including isotopes of the noble gases (xenon and krypton), iodine, cesium, and tellurium. The radioactive gases and particles released in the accident were dispersed over the middle latitudes of the entire northern hemisphere and for the first time also measured in the southern Hemisphere. Isotopes of iodine and cesium were detected in air, water, milk and food samples collected across the entire northern hemisphere. Elevated levels of fission products were detected from March to May 2011 at many locations over the northern hemisphere. This article focuses on the most prevalent cesium and iodine isotopes, but other secondary isotopes are also discussed. Spatial and temporal patterns and differences are contrasted. The activity ratios of (131)I/(137)Cs and (134)Cs/(137)Cs measured at several locations are evaluated to gain an insight into the fuel burn-up, the inventory of radionuclides in the reactor and the isotopic signature of the accident. It is important to note that all of the radiation levels detected outside of Japan have been very low and are well below any level of public and environmental hazard.

Adatoms and clusters of 3d transition metals on graphene: electronic and magnetic configurations

We investigate the electronic and magnetic properties of single Fe, Co, and Ni atoms and clusters on monolayer graphene (MLG) on SiC(0001) by means of scanning tunneling microscopy (STM), x-ray absorption spectroscopy, x-ray magnetic circular dichroism (XMCD), and ab initio calculations. STM reveals different adsorption sites for Ni and Co adatoms. XMCD proves Fe and Co adatoms to be paramagnetic and to exhibit an out-of-plane easy axis in agreement with theory. In contrast, we experimentally find a nonmagnetic ground state for Ni monomers while an increasing cluster size leads to sizeable magnetic moments. These observations are well reproduced by our calculations and reveal the importance of hybridization effects and intra-atomic charge transfer for the properties of adatoms and clusters on MLG.

Anti-inflammatory properties rather than anti-oxidant capability is the major mechanism of neuroprotection by sodium salicylate in a chronic rotenone model of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder manifesting in motor, cognitive and behavioral anomalies. Loss of dopaminergic neurons in the substantia nigra region of the brain is the hallmark feature of PD, which is attributed to oxidative and inflammatory stress besides other diverse factors and hence drugs targeting these pathways hold promise as neuro-therapeutics. The anti-oxidative as well as anti-inflammatory properties of sodium salicylate (SS), suggest its neuroprotective potentials in PD. Since PD is a progressive neurodegenerative disorder, the mechanistic basis for utilizing SS as a neuroprotectant in PD could be better understood in the chronic models. The present study utilizes a rotenone-based model of PD to evaluate the neuro-modulatory efficacy of SS. Subcutaneous injection of rotenone (2mg/kg body weight) was given to male SD rats every day, for a period of 5 weeks, which developed all the essential features of PD in these animals. Simultaneously, another group was injected SS intraperitoneally at the dose of 100mg/kg body weight, in addition to the rotenone. In the animals receiving rotenone+SS, significant improvement was observed in the various characteristic hallmarks of PD such as dopamine and tyrosine hydroxylase levels as well as the motor dysfunction symptoms. It attenuated the reactive oxygen species levels significantly but failed to reduce the levels of protein carbonylation and lipid peroxidation. However, SS effectively abridged the levels of inflammatory mediators like cyclooxygenase-2 (COX-2), nuclear factor kappa B and inducible nitric oxide synthase. Correspondingly, a significant decrease in the levels of pro-inflammatory cytokines interleukin-6, interleukin-1β and tumor necrosis factor-α was also observed following SS co-treatment. Thus, neuroprotective efficacy of SS in this chronic model of PD can be largely attributed to its anti-inflammatory effects rather than its free radical-scavenging properties.

Plutonium in the WIPP environment: its detection, distribution and behavior

The Waste Isolation Pilot Plant (WIPP) is the only operating deep underground geologic nuclear repository in the United States. It is located in southeastern New Mexico, approximately 655 m (2150 ft) below the surface of the Earth in a bedded Permian evaporite salt formation. This mined geologic repository is designed for the safe disposal of transuranic (TRU) wastes generated from the US defense program. Aerosol and soil samples have been collected near the WIPP site to investigate the sources of plutonium in the WIPP environment since the late 1990s, well before WIPP received its first shipment. Activities of (238)Pu, (239+240)Pu and (241)Am were determined by alpha spectrometry following a series of chemical separations. The concentrations of Al and U were determined in a separate set of samples by inductively coupled plasma mass spectrometry. The annual airborne concentrations of (239+240)Pu during the period from 1998 to 2010 show no systematic interannual variations. However, monthly (239+240)Pu particulate concentrations show a typical seasonal variation with a maximum in spring, the time when strong and gusty winds frequently give rise to blowing dust. Resuspension of soil particles containing weapons fallout is considered to be the predominant source of plutonium in the WIPP area. Further, this work characterizes the source, temporal variation and its distribution with depth in a soil profile to evaluate the importance of transport mechanisms affecting the fate of these radionuclides in the WIPP environment. The mean (137)Cs/(239+240)Pu, (241)Am/(239+240)Pu activity ratio and (240)Pu/(239)Pu atom ratio observed in the WIPP samples are consistent with the source being largely global fallout. There is no evidence of any release from the WIPP contributing to radionuclide concentrations in the environment.

BaVS3 probed by V L edge x-ray absorption spectroscopy

Polarization dependent vanadium L edge x-ray absorption spectra of BaVS(3) single crystals are measured in the four phases of the compound. The difference between signals with the polarizations E perpendicular to c and E is parallel to c (linear dichroism) changes with temperature. Besides increasing the intensity of one of the maxima, a new structure appears in the pre-edge region below the metal-insulator transition. More careful examination brings to light that the changes start already with pretransitional charge density wave fluctuations. Simple symmetry analysis suggests that the effect is related to rearrangements in the E(g) and A(1g) states, and is compatible with the formation of four inequivalent V-sites along the V-S chain.

Monitoring of gross alpha, gross beta and actinides activities in exhaust air released from the waste isolation pilot plant

The simultaneous measurements of gross alpha and beta activities is one of the simplest radioanalytical technique used as a method for screening samples of both high and low activities of alpha and beta emitting radionuclides in environmental and bioassay samples. Such measurements are of great interest from both a radiological, waste disposal viewpoint, and to establish a trend of radioactivity based on long term monitoring. At the WIPP (Waste Isolation Pilot Plant) site, unfiltered exhaust air from the underground repository is the most important effluent. As part of its monitoring program, the particulates from WIPP exhaust air are collected everyday at a location typically called the Fixed Air Sampler (FAS) site or Station A, this site is located at the release point for aerosol effluents from the underground to the environment. The measurements of gross alpha and beta activity on air filter samples were performed using an ultra low level counter, PIC-MPC 9604-α/β, from Protean Instrument Corporation. The high sensitivity of the gross alpha and beta instrument enables detection of low value activity from the air filters. In 2009, the values of gross alpha and beta activity concentrations ranged from <MDC (≈0.1 mBq/m(3)) to 1.03 mBq/m(3) and <MDC (≈0.2 mBq/m(3)) to 15.8 mBq/m(3); the density varied from <MDC (≈0.9 Bq/g) to 63.5 Bq/g and <MDC (≈1.7 Bq/g) to 114 Bq/g.

Electronic and magnetic reconstructions in La0.7Sr0.3MnO3/SrTiO3 heterostructures: a case of enhanced interlayer coupling controlled by the interface

We report on the magnetic coupling of La0.7Sr0.3MnO3 layers through SrTiO3 spacers in La0.7Sr0.3MnO3/SrTiO3 epitaxial heterostructures. Combined aberration-corrected microscopy and electron-energy-loss spectroscopy evidence charge transfer to the empty conduction band of the titanate. Ti d electrons interact via superexchange with Mn, giving rise to a Ti magnetic moment as demonstrated by x-ray magnetic circular dichroism. This induced magnetic moment in the SrTiO3 controls the bulk magnetic and transport properties of the superlattices when the titanate layer thickness is below 1 nm.

Electronic structure studies of nanoferrite Cu(x)Co(1-x)Fe2O4 by X-ray absorption spectroscopy

Pure and mixed cobalt copper ferrites are of great interest due to their widespread application in electronics and medicine. We report on the electronic structure of a nanoferrite Cu(x)Co(1-x)Fe2O4 (0.0 < or = x < or = 1.0) system studied by X-ray absorption spectroscopy. These magnetic nanoferrites (average crystallite size approximately 31-43 nm) were synthesized by an auto combustion method and are characterized by high resolution X-ray diffraction and near edge X-ray absorption fine structure measurements at the O K and Co, Cu, and Fe L-edges. The O K-edge spectra suggest that there is a strong hybridization between O 2p and 3d electrons of Co, Cu and Fe cations and Fe L3,2-edge spectra indicate that Fe ions coexist in mixed valence states (Fe3+ and Fe2+) at tetrahedral and octahedral sites of the spinel structure. Copper and cobalt ions are distributed in the divalent state in octahedral sites of the spinel structure. The origin of high saturation magnetization and coercivity in cobalt-copper ferrites are explained in light of these results.

Bi-substitution-induced magnetic moment distribution in spinel Bi(x)Co(2-x)MnO(4) multiferroic

We report the near-edge x-ray absorption spectroscopy (NEXAFS) at the Co/Mn L(3,2) edge and oxygen K edge of the well-characterized Bi-substituted Co(2)MnO(4) multiferroic samples. The evolution of peak features in NEXAFS spectra of the Co/Mn L(3,2) edge and O K edge show the Bi-induced redistribution of magnetic cations (Co/Mn). The variation in valence states of Co and Mn in all the substituted compositions is consistent with the observed ferrimagnetic behaviour of the samples. Magnetization data show the decrease in molecular field complementing the ferrimagnetism. The role of Bi in the enhancement of magnetic interactions as well as the appearance of ferroelectricity in Bi(x)Co(2-x)MnO(4) (0≤x≤0.3) is discussed.

Mixed-ligand chelate extraction of thorium(IV) and uranium(VI) with thenoyltrifluroacetone and various imidazoles

The synergistic extraction of thorium(IV) and uranium(VI) has been studied using mixtures of thenoyltrifluoroacetone (Htta) and various imidazoles such as imidazole (Imz), 2-methylimidazole (2-Meimz), benzimidazole (Bimz) or 2-pyridylbenzimidazole (2-Pybimz). The extraction data have been analysed by both graphical and theoretical methods by taking into account chemical mass action principles. The results demonstrate that these metal ions are extracted into chloroform as Th(tta)4 and UO2(tta)2 with Htta alone and as Th(tta)4 · nS and UO2(tta)2 · nS in the presence of imidazoles (where n = 1 and 2 for thorium(IV) and n = 1 for uranium(VI); S represents imidazole). The equilibrium constants of the above extracted complexes have been deduced by non-linear regression analysis. The addition of an imidazole to the metal chelate system enhances the extraction efficiency of these metal ions. The complexation strength of these metal ions with various imidazoles follows the order: Imz > 2-Meimz > Bimz > 2-Pybimz.

Sorption of U(VI) species on hydroxyapatite

The sorption of uranyl (UO22+) cations to hydroxyapatite was studied as a function of the amount of sorbent, ionic strength, U(VI) concentration, pH and temperature. The rate of uranyl sorption on hydroxyapatite decreased with increased uranyl concentrations. The amount sorbed decreased with increased ionic strength and increased with pH to a maximum at 7–8. The sorption data for UO22+were fitted well by the Freundlich and Dubinin–Radushkevich (D–R) isotherms. The anions Cl−, NO3−, SO42-and CH3COO−decreased the sorption of uranium on hydroxyapatite while S2O32-slightly increased it. The sorbed uranium was desorbed by 0.10 M and 1.00 M solutions of HCl and HNO3.

The thermodynamic parameters for the sorption of UO22+were measured at temperatures of 298, 313, 323 and 333 K. The temperature dependence confirmed an endothermic heat of sorption. The activation energy for the sorption process was calculated to be +2.75±0.02 kJ/mol.

Np(V)O2 + sorption on hydroxyapatite-effect of calcium and phosphate anions

The sorption of NpO2 + from aqueous solution on hydroxyapatite was studied as a function of the amount of sorbent, initial NpO2 + concentration, ionic strength and pcH. The hydroxyapatite was characterized by SEM, EDS, XRD, FT-IR and ICP-MS measurements. At ionic strengths of 0.10 to 5.00 M NaClO4, the sorption increased with increased pcH to a maximum between pcH 8−8.5, then decreased as the pcH increased.

The kinetics of NpO2 + sorption on hydroxyapatite followed Lagergren first order kinetics. The temperature dependence of sorption was small in the range of 273−283 K, but increased more sharply at higher temperatures of 298−333 K. The heat of sorption of NpO2 + was endothermic and the free energy values were exothermic indicating large, positive entropy. The activation energy for the sorption process was calculated to be 29.52±1.2 kJ/mole. The effect of calcium and phosphate on NpO2 + sorption was studied as a function of concentration and pcH.

Structural, magnetic and electronic structure studies of NdFe(1-x)Ni(x)O(3) (0 ≤ x ≤ 0.3)

We present here the structural, electronic structure, magnetic and Mössbauer studies of NdFe(1-x)Ni(x)O(3) (0≤x≤0.3) samples. All the samples exhibit a single-phase orthorhombic structure with space group Pbnm. The near-edge x-ray absorption fine structure (NEXAFS) studies reveal that, with the Ni substitution at Fe sites, a new spectral feature about 1.5 eV lower than the pre-edge structure of NdFeO(3) in the O K edge is observed due to the 3d contraction effect and is growing monotonically with the increase of Ni concentration. The Fe L(3,2), Ni L(3,2) and Nd M(5,4) edges confirm the trivalent state of Fe, Ni and Nd ions. The Mössbauer spectra fitted with two Zeeman sextets confirm the different surroundings of Ni around Fe ions. With the increase in Ni concentration, the sextets are broadened. The increase of quadrupole splitting and the decrease of the hyperfine field suggest the change in the ordered regime of the system. The magnetic behaviour at low temperatures is explained in the context of competition among moments of rare earth (Nd) and transition metal ions (Fe/Ni). The strong paramagnetic contribution of the Nd magnetic sublattice and spin flip phenomenon is observed from the temperature dependence of zero-field-cooled and field-cooled magnetization where spin crossover is observed. The isothermal hysteresis loops show a decrease of magnetization and increase of coercivity with the increase in temperature and complements magnetization versus temperature. The results are explained on the basis of the spin reorientation phenomenon.

NEXAFS and XMCD studies of single-phase Co doped ZnO thin films

A study of the electronic structure and magnetic properties of Co doped ZnO thin films synthesized by ion implantation followed by swift heavy ion irradiation is presented using near-edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD) measurements. The spectral features of NEXAFS at the Co L(3,2)-edge show entirely different features than that of metallic Co clusters and other Co oxide phases. The atomic multiplet calculations are performed to determine the valence state, symmetry and the crystal field splitting, which show that in the present system Co is in the 2+ state and substituted at the Zn site in tetrahedral symmetry with 10Dq = -0.6 eV. The ferromagnetic character of these materials is confirmed through XMCD spectra. To rule out the possibilities of defect induced magnetism, the results are compared with Ar annealed and Ar-ion implanted pure ZnO thin films. The presented results confirm the substitution of Co at the Zn site in the ZnO matrix, which is responsible for room temperature ferromagnetism.