From antiferromagnetic insulator to correlated metal in pressurized and doped LaMnPO.

Widespread adoption of superconducting technologies awaits the discovery of new materials with enhanced properties, especially higher superconducting transition temperatures T(c). The unexpected discovery of high T(c) superconductivity in cuprates suggests that the highest T(c)s occur when pressure or doping transform the localized and moment-bearing electrons in antiferromagnetic insulators into itinerant carriers in a metal, where magnetism is preserved in the form of strong correlations. The absence of this transition in Fe-based superconductors may limit their T(c)s, but even larger T(c)s may be possible in their isostructural Mn analogs, which are antiferromagnetic insulators like the cuprates. It is generally believed that prohibitively large pressures would be required to suppress the effects of the strong Hund's rule coupling in these Mn-based compounds, collapsing the insulating gap and enabling superconductivity. Indeed, no Mn-based compounds are known to be superconductors. The electronic structure calculations and X-ray diffraction measurements presented here challenge these long held beliefs, finding that only modest pressures are required to transform LaMnPO, isostructural to superconducting host LaFeAsO, from an antiferromagnetic insulator to a metallic antiferromagnet, where the Mn moment vanishes in a second pressure-driven transition. Proximity to these charge and moment delocalization transitions in LaMnPO results in a highly correlated metallic state, the familiar breeding ground of superconductivity.

[Polonium-210 acute and chronic pathomorphology and pathogenesis].

In the present review, the data on the pathology of acute and chronic polonium injuries available from the an open-access domestic and foreign literature are primarily systemized and analyzed. The historical background of the research is presented in brief. On the basis of clinical and experimental generalizations, the current concept regarding the pathogenesis of polonium intoxication has been developed.

[The death of Yasser Arafat: molecular-genetic authentication of the remains as an indispensable condition for the evaluation of the medical hypotheses of the cause of his death].

The objective of the present study was the molecular-genetic authentication of the remains as an indispensable condition for the evaluation of the medical hypotheses of the cause of death in 2004 of Yasser Arafat, the former Palestinian leader and the first president of the Palestinian National Administration, the Nobel Peace Prize laureate. We carried out molecular-genetic investigations aimed at establishing the circumstances and cause of the death of Yasser Arafat including the analysis of the relevant medical documentation, the examination of the burial place at Ramallah, remains, and personal belongings stored in his Al Muqata'ah residence at Ramallah. The objective of the present molecular- genetic investigations was to confirm the authenticity of the fragments of Yasser Arafat's remains available for radio-toxicological, chemical toxicological, and other laboratory studies. The reference objects were the contact traces left on the personal belongings by their owner. The aggregate probabilistic estimate of the coincidence of genotype traits of autosomal DNA, Y-chromosomal DNA, and mtDNA was at least 99,(9)29 4% which gives evidence of the genetic identity of the objects of study. It is this value (99.999999 <...> 9999999(29) 4%) that characterizes the probability that the bone fragments provided for the laboratory studies are actually authentic remains of Yasser Arafat.

Influence of radioactivity on surface charging and aggregation kinetics of particles in the atmosphere.

Radioactivity can influence surface interactions, but its effects on particle aggregation kinetics have not been included in transport modeling of radioactive particles. In this research, experimental and theoretical studies have been performed to investigate the influence of radioactivity on surface charging and aggregation kinetics of radioactive particles in the atmosphere. Radioactivity-induced charging mechanisms have been investigated at the microscopic level, and heterogeneous surface potential caused by radioactivity is reported. The radioactivity-induced surface charging is highly influenced by several parameters, such as rate and type of radioactive decay. A population balance model, including interparticle forces, has been employed to study the effects of radioactivity on particle aggregation kinetics in air. It has been found that radioactivity can hinder aggregation of particles because of similar surface charging caused by the decay process. Experimental and theoretical studies provide useful insights into the understanding of transport characteristics of radioactive particles emitted from severe nuclear events, such as the recent accident of Fukushima or deliberate explosions of radiological devices.

Signatures of the Z = 82 shell closure in α-decay process.

In recent experiments at the velocity filter Separator for Heavy Ion reaction Products (SHIP) (GSI, Darmstadt), an extended and improved set of α-decay data for more than 20 of the most neutron-deficient isotopes in the region from lead to thorium was obtained. The combined analysis of this newly available α-decay data, of which the (186)Po decay is reported here, allowed us for the first time to clearly show that crossing the Z = 82 shell to higher proton numbers strongly accelerates the α decay. From the experimental data, the α-particle formation probabilities are deduced following the Universal Decay Law approach. The formation probabilities are discussed in the framework of the pairing force acting among the protons and the neutrons forming the α particle. A striking resemblance between the phenomenological pairing gap deduced from experimental binding energies and the formation probabilities is noted. These findings support the conjecture that both the N = 126 and Z = 82 shell closures strongly influence the α-formation probability.

Review of chemical and radiotoxicological properties of polonium for internal contamination purposes.

The discovery of polonium (Po) was first published in July, 1898 by P. Curie and M. Curie. It was the first element to be discovered by the radiochemical method. Polonium can be considered as a famous but neglected element: only a few studies of polonium chemistry have been published, mostly between 1950 and 1990. The recent (2006) event in which (210)Po evidently was used as a poison to kill A. Litvinenko has raised new interest in polonium. 2011 being the 100th anniversary of the Marie Curie Nobel Prize in Chemistry, the aim of this review is to look at the several aspects of polonium linked to its chemical properties and its radiotoxicity, including (i) its radiochemistry and interaction with matter; (ii) its main sources and uses; (iii) its physicochemical properties; (iv) its main analytical methods; (v) its background exposure risk in water, food, and other environmental media; (vi) its biokinetics and distribution following inhalation, ingestion, and wound contamination; (vii) its dosimetry; and (viii) treatments available (decorporation) in case of internal contamination.

Ra-Po-Pb isotope systematics in waters of Sambhar Salt Lake, Rajasthan (India): geochemical characterization and particulate reactivity.

The Sambhar Salt Lake hydrological system, including river waters, groundwaters, evaporating pans and sub-surface brines, has been analyzed for the salt content (TDS) and naturally occurring radionuclides (210Po, 210Pb and 226,228Ra). The abundance of these radionuclides and their activity ratios show a wide variation in different hydrological regimes, which helps to geochemically characterize the lake system. A significantly lower Ra to total dissolved solids (TDS) ratio in the brines (by two to three orders of magnitude), when compared to the groundwaters and river waters, suggests removal of dissolved Ra by co-precipitation with Ca-Mg minerals at an early stage of the brine evolution. The concentration of Ra in evaporating lake/pan waters saturates at a value of about 10 mBq L (-1) [corrected] over the salinity range of 100-370gL(-1); attributable to its equilibration with the clay minerals. The two distinct regimes, saline lake system (lake water, evaporating pans and sub-surface brines) and groundwaters have been identified based on their differences in the distribution of 226,228Ra isotopes. This observation points to the conclusion that the groundwaters and the lake brines are not intimately coupled in terms of their origin and evolution. The abundances of 210Po and 210Pb along with their activity ratios (210Po/210Pb) are markedly different among the surface lake waters/evaporating pans, sub-surface lake brines and groundwaters. These differences are explained in terms of different geochemical behaviour of these nuclides in presence of algae and organic matter present in these water regimes.

On the role of 210Bi in the apparent disequilibrium of 210Pb-210Po at sea.

The disequilibrium of the grandparent-daughter pair 210Pb (t1/2=22.3 years)-210Po (t1/2=138 days) has been used to estimate the export fluxes of particulate organic carbon in the ocean using particulate-matter-associated 210Po. 210Po is produced from 210Bi, not from 210Pb. The half-life of 210Bi (t1/2=5.01 days) is sufficiently long compared to the rates of biological particle formation and decomposition or dissolution occurring at sea. The role of 210Bi has not yet been assessed quantitatively in the apparent disequilibrium between 210Pb and 210Po, partly due to the non-existence of 210Bi depth profile measurements at sea up to now. However, greater affinity of 210Bi over 210Po and 210Pb was found recently in coastal waters and phytoplankton 207Bi uptake experiments. Build upon these findings, we developed a primitive and simple analytical approach to elucidate the role of 210Bi in the 210Po-210Pb pair in the ocean using a simplified two-box irreversible steady-state ocean model. We assumed that the activity concentrations in the dissolved and particulate phases of 210Pb, 210Bi, and 210Po in a given water column are solely determined by the concentration of the particles, their input and output, the distribution coefficients between dissolved and particulate phases, and decay constants of these radionuclides in the steady-state ocean. The 210Bi contribution to the 210Pb-210Po activity difference in seawater is found to be significant, therefore, it needs to be considered in estimating particle fluxes using 210Pb-210Po secular equilibrium at sea.

137Cs and 210Po in Pacific walrus and bearded seal from St. Lawrence Island, Alaska.

The activity concentration of Cesium-137 ((137)Cs) and naturally-occurring Polonium-210 ((210)Po) were measured in the muscle tissue, kidney and liver of Pacific walrus (Odobenus rosmarus divergens) and bearded seal (Erignathus barbatus) collected by native hunters from the Bering Sea during May 1996. The mean (137)Cs concentrations in muscle, liver and kidney of Pacific walrus were 0.07, 0.09 and 0.07 Bq kg(-1) (n=5, wet weight), respectively, and 0.17, 0.10, and 0.17 Bq kg(-1) (n=2, wet weight), respectively, in bearded seal. In general, (137)Cs tissue concentrations are significantly lower than those previously reported for mammals from other regions. By comparison, (210)Po activity concentrations are more variable and appear to be higher level compared with mammal data from other regions. The mean (210)Po concentration in the muscle tissue, liver and kidney of Pacific walrus (n=5, wet weight) were 28.7, 189, and 174 Bq kg(-1), respectively. This compares with (210)Po concentration values (n=2, wet weight) of 27, 207 and 68 Bq kg(-1) measured in the muscle tissue, liver and kidney, of bearded seal, respectively. Estimated concentration factors--as defined by the radionuclide concentration ratio between the target tissue to that in sea water--were two to three orders of magnitude higher for (210)Po that those of (137)Cs. We conclude from radiological dose estimates that ingestion of (137)Cs in foods derived from walrus and seal will pose no threat to human health. This work has important implications for assessment of risks of Alaskan coastal communities concerned about the dumping of nuclear waste in the Russia Arctic.

210Po and 210Pb in forest mushrooms of genus Leccinum and topsoil from northern Poland and its contribution to the radiation dose.

Wild growing mushrooms are traditional food items for man and also an important source of nutrients for small and big wildlife. Nevertheless, they can be species - specifically vulnerable for contamination with heavy metals and radionuclides. We studied a less known phenomenon of accumulation of highly toxic, the alpha-radiation emitter such as 210Po and the beta emitter 210Pb by three Leccinum mushrooms: orange oak bolete L. aurantiacum (Bull.) Gray (previous name Leccinum aurantiacum var. quercinum Pilát), foxy bolete L. vulpinum Watling and slate bolete L. duriusculum (Schulzer ex Kalchbr.) Singer. Fungal and soil materials were collected from areas of a different geochemical composition in the northern regions of Poland. In parallel evaluated was the risk to human consumer due to possible intake of 210Po and 210Pb with a mushroom meal. Results showed a heterogeneous distribution of 210Po and 210Pb activity concentrations within caps and stipes of fruiting bodies. Overall activity concentration for whole dried fungi material ranged from 0.59 ±â€¯0.38 to 3.2 ±â€¯0.2 Bq 210Po kg-1 and from 0.45 ±â€¯0.04 to 3.1 ±â€¯0.2 Bq 210Pb kg-1. Evaluation showed that Leccinum mushrooms consumed by locals in typical quantity of 0.5 kg (dry biomass) can contribute into annual effective radiation dose at 0.90-3.81 µSv from 210Po decay and 0.31-2.14 µSv from 210Pb decay, which is a small portion of the annual effective radiation dose of 210Po and 210Pb for human inhabiting the northern regions of Poland.

Is Polonium-210 a Good Indicator for Anthropogenic Radioactivity?

Anthropogenic radioactivity generated by nuclear or chemical events results in the liberation of quadrillions of Becquerel and tons of materials to the environment. These events include nuclear accidents, nuclear weapon experiments, and high levels of generated radioactive and chemical waste. 210Po is a high-energy α emitter that presents in the environment at extremely low concentration. It is considered as one of the highly toxic elements and is estimated to contribute about 7% of the total effective dose equivalent to humans from ingested natural internal radiation. The assessment of 210Po activity/concentration in the environment could be used as an indicator of the level of anthropogenic radioactivity. The 210Po concentration present in the most frequently sold cigarette produced in Lebanon was assayed using α spectrometry after a radiochemical separation and spontaneous deposition of Po on a copper disk. Although the geographical nature of Lebanese land is an extension of Syrian territory, the polonium activity concentration obtained is 8.8 times higher and attributable to the excessive use of phosphate fertilizers in agriculture. The individual committed effective dose was estimated to be equal to 219 ± 17 µSv/year of cigarette smoking.

Determination of 210Pb and 210Po in soil or rock samples containing refractory matrices.

A new method has been developed for determination of (210)Pb and (210)Po in soil or rock samples containing refractory matrices. The samples were first fused with Na(2)CO(3) and Na(2)O(2) at 600 degrees C for pre-treatment and then (210)Pb and (210)Po were sequentially leached out at 200-250 degrees C with HNO(3)+HF, HClO(4) and HCl. About 10% of the leaching solution was used for (210)Po determination, carried out by spontaneous deposition of polonium on a silver disc from a weakly acidic solution that contained hydroxylamine hydrochloride, sodium citrate and (209)Po tracer, measurement being made by alpha-spectrometry. The remains of the leaching solution were used for determination of (210)Pb, conducted by precipitation as sulphate, purification with Na(2)S as PbS in 6M ammonium acetate, separation from alpha-emitters by an anion-exchange resin column, source preparation as PbSO(4), and measurement with a beta-counter. The procedure has been checked with two certified IAEA reference materials, showing good agreement with the recommended values. The lower limits of detection for 1g of analysed soil or rock samples were found to be 0.75 Bqkg(-1) for (210)Po and 2.2 Bqkg(-1) for (210)Pb. A variety of solid sample species analysed through use of the procedure gave average yields of 90.0+/-9.8% for (210)Po and 88.4+/-7.1% for (210)Pb.

Removal of 210Po from aqueous media and its thermodynamics and kinetics.

In this study, the composite adsorbent as granule was prepared by mixing of polyacrylonitrile (PAN) and a natural zeolite (clinoptilolite) in specific conditions. The prepared composite adsorbent was used for investigating the adsorption behaviour of 210Po. Adsorption of 210Po was studied in a column system. The effective parameters such as initial activity concentration of 210Po, pH of the aqueous solution, contact time and temperature of solution for adsorption behaviour of 210Po were studied. Adsorption yield of 210Po on composite adsorbent from aqueous solution in optimum conditions were determined as 75.00 ± 0.15%. The adsorption equilibrium data was examined using various well-known isotherm models such as Freundlich, Langmuir, Dubinin and Radushkevish and Tempkin, and it was observed that the experimental equilibrium data well fitted and found to be in good agreement with the Tempkin model. Adsorption thermodynamics and kinetics of the polonium were studied. It was found that the processes for 210Po were exothermic and spontaneous. The kinetic data conformed better to the pseudo-second order equation.

Comparison between an unipolar corona charger and a polonium-based bipolar neutralizer for the analysis of nanosized particles and biopolymers.

In this work we present results on the charging efficiency of nanoparticles by means of a corona based unipolar charging unit. This device was designed to replace a Po210 bipolar charger unit in a commercial electrospray aerosol generator (TSI Mod 3480). The charging efficiency has been investigated for negative and positive charged particles of various chemical composition in the size range between 5 and 18 nm. The corona current has been found to be the most influential operation parameter on the charging efficiency. With a positive electrospray droplet charge and a negatively-biased corona needle, a rapidly decreasing yield of singly positively charged aerosol particles with increasing corona current was found. An increasing yield of negatively charged particles was observed with increasing current of the corona process. Providing appropriate corona settings nanoparticles with charge levels similar to these obtained with a Po210 charger were found. At optimal corona settings the yield of singly charged particles was found to be two to four times higher for negative and positive particles compared to bipolar charging. This gain in the charging efficiency increases directly the sensitivity of analysis and enhances all measurement and manipulation processes of airborne nanoparticles for which electrical charging is required.

Assessing the 210At impurity in the production of 211At for radiotherapy by 210Po analysis via isotope dilution alpha spectrometry.

A method for assessing the impurity 210At in cyclotron-produced 211At via isotope dilution alpha spectrometry is presented. The activity of 210At is quantified by measuring the activity of daughter nuclide 210Po. Counting sources are prepared by spontaneous deposition of Po on a silver disc. Activity of 210At (at the time of 210Po maximum activity) is found to be 83.5+/-9.0 Bq, corresponding to an atom ratio (210At:211At at the time of distillation) of 0.010+/-0.007% (k=2). The method produces high-quality alpha spectra, with baseline alpha-peak resolution and chemical yields of greater than 85%.

Impact of northern and southern air mass transport on the temporal distribution of atmospheric (210)Po and (210)Pb in the east coast of Johor, Malaysia.

Concentration activities of (210)Pb and (210)Po in the PM10 were determined to discuss their distribution and chemical behavior in relation to meteorological parameters especially in air mass transport during monsoon events. Marine aerosol samples were collected between January 2009 and December 2010 at the coastal region of Mersing, which is located in the southern South China Sea and is about 160 km northeast of Johor Bahru, as part of the atmosphere-ocean interaction program in Malaysia. About 47 PM10 samples were collected using the Sierra-Andersen model 1200 PM10 sampler over a 2-year sampling campaign between January 2009 and December 2010. Samples were processed using acid digestion sequential extraction techniques to analyze various fractions such as Fe and Mn oxides, organic matter, and residual fractions. While, (210)Pb and (210)Po activities were measured with the Gross Alpha/Beta Counting System model XLB-5 Tennelec® Series 5 and the Alpha Spectrometry (model Alpha Analyst Spectroscopy system with a silicon-surface barrier detector), respectively. The distribution activities of (210)Pb and (210)Po in the PM10 samples were varied from 162 to 881 µBq/m(3) with mean value of 347 ± 170 µBq/m(3) and from 85 to 1009 µBq/m(3) with mean value of 318 ± 202 µBq/m(3), respectively. The analysis showed that (210)Po activity in our samples lies in a border and higher range than global distribution values due to contributions from external sources injected to the atmosphere. The speciation of (210)Pb and (210)Po in marine aerosol corresponds to transboundary haze; e.g., biomass burning especially forest fires and long-range air mass transport of terrestrial dust has enriched concentrations of particle mass in the local atmosphere. The monsoon seems to play an important role in transporting terrestrial dust from Indo-China and northern Asia especially during the northeast monsoon, as well as biogenic pollutants originating from Sumatra and the southern ASEAN region during southwest monsoon events.

Prompt detection of alpha particles from 210Po: another clue to the origin of rock varnish?

Alpha particles have been measured coming from the surfaces of rocks covered with dark red-brown rock varnish, as well as rocks that appear to have little, if any, varnish. A pronounced peak at 5.3 MeV indicates the presence of 210Po, a short-lived natural-radioactive element. Surface activities for 33 samples range from 0.008 Bq/cm2 to 0.065 Bq/cm2. It is estimated that this nuclide is concentrated 10(11) times in these paper-thin coatings above its concentration in ground-level air. Gamma rays from the decay of 137Cs, a product of testing nuclear weapons some 50 years ago, were also detected. Analysis of samples of varnish stripped from the rock revealed traces of 239,240Pu and 238Pu. The presence of all of these isotopes strongly supports the theory that varnish films derive their building blocks from the atmosphere and, with time, all rocks in arid environments will become coated.

Optimisation study of alpha-cyclotron production of At-211/Po-211g for high-LET metabolic radiotherapy purposes.

The production of no-carrier-added (NCA) alpha-emitter (211)At/(211g)Po radionuclides for high-LET targeted radiotherapy and immunoradiotherapy, through the (209)Bi(alpha,2n) reaction, together with the required wet radiochemistry and radioanalytical quality controls carried out at LASA is described, through dedicated irradiation experiments at the MC-40 cyclotron of JRC-Ispra. The amount of both the gamma-emitter (210)At and its long half-lived alpha-emitting daughter (210)Po is optimised and minimised by appropriate choice of energy and energy loss of alpha particle beam. The measured excitation functions for production of the main radioisotopic impurity (210)At-->(210)Po are compared with theoretical predictions from model calculations performed at ENEA.

Bimodal unattached 218Po Radon progeny and the influence of enhanced deposition effect at high-radon levels.

Unattached fraction (218)Po airborne particle size distributions from graded screen array diffusion batteries are analysed for bimodal constituents. The analysis is for the high (222)Rn concentration range from 10 to 50 kBq m(-3) where the recently reported enhanced deposition effect is in transition. We find that the single unattached fraction is distributed nominally at an arithmetic mean diameter (AMD) of 0.8-1.0 nm, and consists of two (218)Po molecular species with AMD congruent with 0.756 and 1.101 nm, respectively. In unfiltered room air the 0.756 nm species is the least stable, decreases monotonically in concentration magnitude beginning at 12 kBq m(-3) and disappears completely at approximately 32 kBq m(-3) (at a relative humidity of 54%). The AMD congruent with 1.101 nm mode does not become unstable until it reaches approximately 32 kBq m(-3) (222)Rn level and completely disappears at approximately 50 kBq m(-3). Similar behaviour is observed for filtered air but with some distinct differences. This work supports the bimodal findings for the (218)Po unattached fraction of Porstendorfer and co-workers and provides further details of the high-radon enhanced deposition effect.

Fraction of the positive 218Po and 214Pb clusters in indoor air.

The fraction of the positively charged unattached radon decay products, 218Po and 214Pb in indoor air was determined by model calculations. The results of the calculations were confirmed by measurements in a test chamber (volume: 8 m3). The fraction of both radionuclides depends on the attachment parameter (S(1)) and the neutralisation rate (nu) in room air. The total removal parameter S1 = lambda1 + v + q(f) + X = lambda1 C1f/C0 considers the attachment rate to aerosol particles (X), plate-out rate to room surfaces (q(f)) and the ventilation rate (nu) (lambda1: decay constant of 218Po). The S1-value of room can be determined by measurement of the concentration of the unattached 218Po clusters (C1f) and radon (C0). The neutralisation rate (nu) in environmental air depends mainly on the ion production rate. The influence of the relative humidity in the range 30-95% (temperature: 20 degrees C) is negligible. In addition, equal neutralisation rates for 218Po and 214Pb could be derived. In room air with ion production rates between 5 and 500 nC kg(-1) h(-1) mainly generated by the alpha emitters of radon, thoron and their short-lived decay products, the fractions for positive 218Po clusters vary between 55 and 17% and for 214Pb clusters between 53 and 14%. For a typical average concentration of radon (50 Bq m(-3)) and thoron (10 Bq m(-3)) in homes, 48% of 218Po clusters and 45% of 214Pb clusters are positively charged.