Estimation of radon and thoron caused dose at exraction and processing sites of mineral sand mining area in Vietnam (HA TINH province)

Mineral sands are mined in several countries to supply to the titanium and zircon producing industries. Coastal black mineral sands usually contain, besides ilmenite (FeTiO₃) and rutile (TiO₂), radioactive minerals such as zircon (ZrSiO₄) and monazite (RePO₄). Radon and thoron activity concentration originated from natural radioactive contents of the black mineral sand was monitored at the extraction and processing for black minerals in the coastal areas of Ha Tinh Province, one of the around 40 coastal mineral sand deposits in Vietnam. The survey was carried out with the Raduet chambers made by Radosys Ltd—Hungary. The obtained results for 25 investigated points show that the measured values are not high in the residential houses and in case of the sand extraction site as well. At the titanium processing plant the measured values were higher than outside the facility (Radon: 18–55 Bq/m³ with average of 34 Bq/³ and Thoron 33–118 Bq/m³ with average of 58 Bq/m³) but still comparable to the average concentration of the world published by UNSCEAR. The typical outdoor levels of radon and thoron gas are each of the order of 10 Bq/m³. Although the radon concentrations were low in the zircon and titanium processing plants, the thoron concentrations in the houses for separating rutile and zircon were very high. At zircon processing factory, the thoron concentration could reach 2,931 Bq/m³ and the estimated annual effective dose would be 21.4 mSv/a. Intervention has to be taken in order to reduce the thoron level in this factory since the level of thoron and its progenies corresponding to an annual occupational effective dose is beyond the action level of 6 mSv/a.     

Mn site substitution of La0.67Ca0.33MnO3 with closed shell ions: Effect on magnetic transition temperature

Mn site is substituted with closed shell ions (Al, Ga, Ti, Zr and a certain combination of Zr and Al) and also with Fe and Ru ions carrying the magnetic moment (S=5/2 and 2 respectively) at a fixed concentration of 5 at %. Substitution did not change either the crystal symmetry or the oxygen stoichiometry. All substituents were found to suppress both the metal-insulator and ferromagnetic transition temperatures (T _p(ρ) and T _C, respectively) to varied extents. Two main contributions identified for the suppression are the lattice disorder arising due to difference in the ionic radii between the substituent (r _M) and the Mn³⁺ ion (r _Mn ³⁺) and in the case of the substituents carrying a magnetic moment, the type of magnetic coupling between the substituent and that of the neighboring Mn ion.     

A polar corundum oxide displaying weak ferromagnetism at room temperature

Combining long-range magnetic order with polarity in the same structure is a prerequisite for the design of (magnetoelectric) multiferroic materials. There are now several demonstrated strategies to achieve this goal, but retaining magnetic order above room temperature remains a difficult target. Iron oxides in the +3 oxidation state have high magnetic ordering temperatures due to the size of the coupled moments. Here we prepare and characterize ScFeO(3) (SFO), which under pressure and in strain-stabilized thin films adopts a polar variant of the corundum structure, one of the archetypal binary oxide structures. Polar corundum ScFeO(3) has a weak ferromagnetic ground state below 356 K-this is in contrast to the purely antiferromagnetic ground state adopted by the well-studied ferroelectric BiFeO(3).     

New flavonoid and stilbene derivatives from the fruits of Macaranga balansae

Abstract

Two new prenylated flavonoids, 4´-methyl-8-prenyltaxifolin (1) and 6,8-diprenyl-4´-methyl-naringenin (2) and a new geranylated stilbene, 4′-deprenyl-4-methoxymappain (3) together with eight known flavonoids (4–11) were isolated from the fruits of Macaranga balansae Gagnep. Their chemical structures were determined by means of spectroscopic methods including 1D, 2D NMR, and MS data. Compound 2 showed the highest cytotoxic activity against PanC1, A549, KB and LU-1 cell lines with IC₅₀ values range from 7.89 to 22.81?µM.     

Effect of thermal annealing on the ac impedance of Co/Al2O3/Co/Al2O3/Co double-barrier MTJs

Double-barrier magnetic tunnel junctions (DBMTJs) were prepared from Co(75 nm)/Al₂O₃(2.3 nm)/Co(5 nm)/Al₂O₃(2.3 nm)/Co(50 nm) sputtering pentalayer films. The ac electrical properties of as-deposited DBMTJs and those annealed in a vacuum at 100–350 °C for 30 min were then investigated using a complex impedance spectroscopic technique. The ac impedance responses as a function of annealing temperature were further analyzed based on Maxwell's layered dielectric barrier and Maxwell–Wagner capacitor models after considering the DBMTJs as having double-capacitor-type structures. The effect of thermal annealing on the ac transport behavior of the DBMTJs was interpreted by examining the equivalent electric circuits fitted to Nyquist plots of each different sample. The effects were found to be due to changes in the structural characteristics in both bulk and interface morphologies of Co and Al₂O₃ layers. The structural morphology determined the different ac transport modes that occurred in the DBMTJs.     

Effect of protonation exothermicity on the reaction of gaseous Brønsted acids with halobenzene derivatives

The protonation of haloaromatics by [N₂H]⁺ and [CO₂H]⁺ has been studied by chemical ionization mass spectrometry. In general, the fragmentation reactions following protonation by [CO₂H]⁺ are similar to those observed following protonation by [CH₅]⁺, while the fragmentation reactions induced by protonation by [N₂H]⁺ are intermediate between those observed on reaction with [CH₅]⁺ and with [H₃]⁺. These results are consistent with the conclusion that the fragmentation mode is determined by the protonation exothermicity since the proton affinity of CO₂ is the same as that of CH₄ while the proton affinity of N₂ is intermediate between that of CH₄ and H₂.     

Site of protonation in the reaction of gaseous Brønsted acids with halobenzene derivatives

The site of protonation in the reaction of gaseous Brønsted acids with chlorobenzene and fluorobenzene derivatives has been examined using deuterium labelling of chlorobenzene and deuterated reagent gases (D₂ and N₂/D₂). In the protonation of chlorobenzene by [H₃]⁺ ～30% of the [MH? HCl]⁺ fragment ions arise from a chlorine-protonated species while ～70% arise from a ring-protonated species in which complete hydrogen scrambling has occurred. In the reaction of [N₂H]⁺ with chlorobenzene ～75% of the fragment ions arise from the chlorine-protonated form with ～25% arising from the ring-protonated form of [MH]⁺. By contrast fluorobenzene fragments almost entirely from the fluorine-protonated form. Similar results are obtained for dihalobenzenes. The mechanistic implications are discussed.