Investigation of primary chemical reactions of electrons by emission Mössbauer and positron spectroscopies

A set of early chemical reactions induced in frozen medium around decayed ⁵⁷Co or ^119mSn nuclei by emitted Auger electrons is suggested. The mechanism predicts a correlation between formation probabilities of final products, namely Fe²⁺-Fe³⁺ or Sn²⁺-Sn⁴⁺ ions, positronium atom and molecular hydrogen formed in similar medium after its irradiation by fast positrons and electrons. This correlation indicates a similarity of chemical processes occurring in nanovolumes around Mössbauer ⁵⁷Fe- and ¹¹⁹Sn-nuclei after radioactive decay as well as in tracks produced by fast positrons and electrons. The important role of quasi-free electrons is revealed.     

To the application of the emission Mössbauer and positron annihilation spectroscopies for detection of carcinogens

Being the main cause of cancer, almost all chemical carcinogens are strong electrophiles, that is, they have a high affinity for the electron. We have shown that positron annihilation lifetime spectroscopy (PALS) is able to detect chemical carcinogens by their inhibition of positronium (Ps) formation in liquid media. Electrophilic carcinogens intercept thermalized track electrons, which are precursors of Ps, and as a result, when they are present Ps atom does not practically form. Available biophysical data seemingly indicate that frozen solutions model better an intracellular medium than the liquid ones. So it is reasonable to use emission Mössbauer spectroscopy (EMS) to detect chemical carcinogens, measuring the yield of ⁵⁷Fe²⁺ions formed in reactions of Auger electrons and other secondary electrons they produced with ⁵⁷Fe³⁺. These reactions are similar to the Ps formation process in the terminal part the positron track: e⁺+ e^? =>Ps. So EMS and PALS are complementary methods for detection of carcinogenic compounds.     

Magnetic properties of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> surface

The magnetic properties of the magnetite Fe₃O₄(110) surface have been studied by spin resolved Auger electron spectroscopy (SRAES). Experimental spin resolved Auger spectra are presented. The results of calculation of Auger lines polarization carried out on the basis of electronic state density are presented. Problems related to magnetic moments of bivalent (Fe²⁺) and trivalent (Fe³⁺) ions on the Fe₃O₄(110) surface are discussed. It is established that the deposition of a thin bismuth film on the surface results in significant growth of polarization of iron Auger peaks, which is due to additional spin-orbit scattering of electrons by bismuth atoms.     

Electric field gradients in pyrochlore compounds

The lattice contribution to the electric field gradient was calculated for pyrochlore compounds as a function of the distortion parameter x(48f). It is shown that this simple model accounts well for the experimental Mössbauer quadrupole splitting of various compounds containing Fe³⁺, Fe²⁺, Sn⁴⁺, Sn²⁺, Sb⁵⁺ or Gd³⁺ ions. The use of Mössbauer data to determine the structural parameter x(48f) is outlined.     

Intensification of chemical reactions in aqueous solutions upon irradiation with an accelerated electron beam

The results from investigating the effect of radiation exposure on the rate of chemical reactions in acid aqueous solutions of Fe²⁺, which are widely used in hydrometallurgy of nonferrous metals to extract the target components into solution from ores, are presented. The potential of the applied method is demonstrated.     

Auger electron/X-ray photoelectron and cathodoluminescent spectroscopic studies of pulsed laser ablated SrAl2O4:Eu,Dy thin films

Auger electron/X-ray photoelectron and cathodoluminescent (CL) spectroscopic studies were conducted on pulsed laser deposited SrAl₂O₄:Eu²⁺,Dy³⁺ thin films and the correlation between the surface chemical reactions and the decrease in the CL intensity was determined. The Auger electron and the CL data were collected simultaneously in a vacuum chamber either maintained at base pressure or backfilled with oxygen gas. The data were collected when the films were irradiated for 14 h with 2 keV electrons. The CL emission peak attributed to the 4f⁶5d¹ → 4f⁷ transitions was observed at ∼521 nm and the CL intensity of the peaks degraded at different rates in different vacuum conditions. X-ray photoelectron spectroscopy (XPS) data collected from degraded films suggest that strontium oxide (SrO) and aliminium oxide (Al₂O₃) were formed on the surface of the film as a result of electron stimulated surface chemical reaction (ESSCR).     

Monitoring synchrotron X‐ray‐induced radiolysis effects on metal (Fe,W) ions in high‐temperature aqueous fluids

Radiolysis‐induced effects on aqueous tungsten ions are observed to form a precipitate within seconds upon exposure to a synchrotron X‐ray micro‐beam in a WO₃ + H₂O system at 873 K and 200 MPa. In situ Fe K‐edge energy‐dispersive X‐ray absorption spectroscopy (ED‐XAS) measurements were made on Fe(II)Cl₂ aqueous solutions to 773 K in order to study the kinetics of high‐temperature reactions of Fe²⁺ and Fe³⁺ ions with transient radiolysis species. The radiolytic reactions in a fluid sample within a hydrothermal diamond anvil cell result in oxidation of the Fe²⁺ ion at 573 K and reduction of Fe³⁺ at temperatures between 673 and 773 K and of the Fe²⁺ ion at 773 K. The edge‐energy drift evident in the ED‐XAS data directly reflects the kinetics of reactions resulting in oxidation and/or reduction of the Fe²⁺ and Fe³⁺ ions in the aqueous solutions at high temperatures. The oxidation and reduction trends are found to be highly consistent, making reliable determinations of reaction kinetics possible.     

The synthesis and afterglow luminescence properties of a novel red afterglow phosphor: ZrO2:Sm3+,Sn4+

A novel ZrO₂:Sm³⁺,Sn⁴⁺ phosphor is synthesized by solid state reaction. The ZrO₂:Sm³⁺ does not show afterglow. But, after doping Sn⁴⁺, intense red afterglow luminescence is firstly observed in ZrO₂:Sm³⁺,Sn⁴⁺ and it can last more than 1000 s at maximum. The afterglow decay curves of ZrO₂:Sm³⁺,Sn⁴⁺ are fitted by three exponential components and the decay process consists of initial fast, intermediate and slow decay. The thermoluminescence indicates that the Sn⁴⁺ ions induce suitable traps with the depth of 0.436 eV and result in efficient afterglow luminescence of ZrO₂:Sm³⁺,Sn⁴⁺. The thermoluminescence filling and fading experiments further confirm the important role of the proper shallow traps induced by doping Sn⁴⁺ on the afterglow of ZrO₂:Sm³⁺,Sn⁴⁺.     

Measurement of the proton NMR field shift in aqueous solutions containing Cu2+, Cr3+, Fe3+ and Mn2+ ions

There are presented measurements of the NMR field shifts for aqueous protons in aqueous solutions containing paramagnetic inorganic compounds of Cu²⁺, Cr³⁺, Fe³⁺ and Mn²⁺ ions. The measurements have been performed on samples in the form of transversally magnetized long cylinders using both the internal and external NMR standards. The experimentally determined shifts are related to the NMR field position of protons in pure water. The results for demagnetizing shifts are compared with the data which were computed from the magnetic susceptibility values (measured by magnetostatic method), the chemical shifts are compared with the results of other authors. Results of measurements indicate a small chemical shift of internal standards in some solutions.     

Bulk magnetic properties of tetravalent ion substituted Cu-ferrite

The lattice parameter,a, increases with the increase of Ti⁴⁺ substitution while it decreases with the increase of Ge⁴⁺ substitution in Cu_1+x A _x Fe_2–2x O₄ compounds [A=Ti⁴⁺, Ge⁴⁺Sn⁴⁺]. On substitution of Sn⁴⁺,a does not vary. CuFe₂O₄ exhibits single domain (SD) behaviour that changes to multi domain (MD) type on Ti⁴⁺ substitution. On Ge⁴⁺ substitution initially all the compositions exhibit SD behaviour while forx>0.2 they show MD behaviour. All Sn⁴⁺ substituted compositions exhibit SD behaviour. The Curie temperature decreases on addition of Ti⁴⁺, Sn⁴⁺ and Ge⁴⁺. The magnetic momentn _B (77 K) initially increases and then decreases with the substitution of Ti⁴⁺, Ge⁴⁺, and Sn⁴⁺. This is explained by cation distribution and reduction of Fe³⁺ ions.The authors wish to thank Prof. R. N. Patil for encouragment and useful discussion. One of the authors (B.L.P.) is grateful to UGC (New Delhi) for granting Teacher Fellowship for Ph.D. course.     

Site occupancy of ferrous ions in iron garnets

Fe²⁺ site occupancy in iron garnets is investigated by means of optical absorption and magnetic circular dichroism. In particular measurements are carried out on bulk single crystals of yttrium iron garnet (YIG) doped with Si⁴⁺, Nb⁵⁺, Sn⁴⁺, Zr⁴⁺, Ti⁴⁺ and Th⁴⁺. The results are discussed in the light of the recent discovery of tetrahedral Fe²⁺ in Nb-doped YIG. We find that, in general, Fe²⁺ occupies both octahedral and tetrahedral sites, the actual distribution being related to site occupancy of the donor centers. This correlation may be relaxed by photoinduced charge transfer between iron sites, at low temperatures. Contrary to recent attributions, no dodecahedral component is found in the infrared spectra above 1 μm wavelength.     

Monte Carlo calculation of electron spectra produced in water phantoms by 20 keV-1 GeV photons

Abstract

A Monte Carlo calculation for the energy spectra of electrons and positrons produced in infinite and semiinfinite water phantoms by photons ranging in energies from 20 keV to 1 GeV are presented. The dominant processes considered are the photoelectric effect, Auger effect, Compton effect, pair, and triplet production. Bremsstrahlung produced by electrons and positrons with energies greater than 1 MeV is also included. The effect of multiple Compton scattering, not considered in the earlier calculation, for the infinite phantom for photon energies higher than 2 MeV has been incorporated. For a semi-infinite phantom, multiple Compton scattering and backscattering through the top are considered. The results are compared with the earlier calculations for the first-collision spectrum. It is found that the inclusion of multiple Compton scattering significantly increases the average number of electrons/cm³ per photon/cm² at all energies considered whereas bremsstrahlung reduces the number of high energy electrons and produces more low energy electrons in the spectrum.     

Molecular dynamics and local electronic states of Sn and Fe in metallocytochrome and metalloporphyrin

In Sn-porphyrin tin appears in the Sn⁴⁺ state while in Sn-cytochrome c Sn⁴⁺ and Sn²⁺ states are observed. In Fe-porphyrin iron exhibits temperature-dependent mixed Fe²⁺-Fe³⁺ valency. In Fe-cytochrome iron is in the Fe³⁺ state. The bounded diffusion is observed in Fe-porphyrins above 300 K. The temperature dependence of the metal mean square displacement in cytochrome c and in Sn-porphyrin shows a deviation from the Debye model, which may be explained either by a new vibrational degree of freedom occurring above 150 K or by anharmonicity of the usual vibrations.     

Arrangement of ferric and ferrous ions at low temperatures in FeCl3 intercalated graphite

Previous work has shown that electrons donated by the graphite to the FeCl₃ intercalant freeze onto some Fe³⁺ ions to change them into Fe²⁺ ions at low temperatures. We show that the created Fe²⁺ ions are not randomly situated. Indirect evidence suggesting the formation of a specific chemical superlattice of Fe³⁺ and Fe²⁺ ions is presented. A method for direct observation of this superlattice is suggested.     

A tin-119 Mössbaer spectroscopic study of tin-doped niobium titanium phosphate

¹¹⁹Sn Mössbauer spectroscopy shows that the reaction of metallic tin with niobium titanium phosphate, NbTiP₃O₁₂, results in the accommodation of Sn²⁺ in two types of sites within channels in the NbTiP₃O₁₂ structure. The Sn²⁺ absorptions are characterised by highly positive chemical isomer shifts which decrease as increasing concentrations of Sn²⁺ are incorporated within the NbTiP₃O₁₂ structure. At very high tin concentrations the Mössbauer spectra show the presence of some unreacted elemental tin. The¹¹⁹Sn Mössbauer data are endorsed by X-ray powder diffraction data and are discussed in terms of the incorporation of highly ionic Sn²⁺ species.     

Optical absorption of s2-configuration ions in alkali halide crystals—III: The A band in Sn2+-doped crystals

The line shape of the A band in KCl:Sn²⁺, KBr:Sn²⁺, KI:Sn²⁺, RbCl:Sn²⁺ and RbBr:Sn²⁺ has been measured as a function of temperature between about 15 K and room temperature. As the spectra for all these systems are similar detailed results are presented only for RbCl: Sn²⁺, RbBr:Sn²⁺ and KBr: Sn²⁺. The experimental data resemble those of a previous study on KBr:In⁺ and KG:In⁺ in that the A band consists of two broad, overlapping components designated A₁ (the low energy component) and A₂. The separation between A₁ and A₂ is more marked at low temperature for Sn²⁺ than for In⁺, and no inversion of the ratio of the peak heights of A₁ and A₂ occurs as the temperature is varied, as was so for In⁺. Detailed calculations of the line shape are presented for KBr:Sn²⁺. These calculations show that one cannot account for the line shape purely in terms of the dynamical Jahn-Teller effect and that there is in addition a static splitting of the A state caused by a lowering in the symmetry of the crystal field.     

Iron-57, tin-119, and antimony-121 mössbauer spectroscopic investigations of metal atom incorporation into the oxide NbTiP3O12

Tin-119 and iron-57 Mössbauer spectroscopy show that the incorporation of tin and iron into the white oxide NbTiP₃O₁₂ to form black compounds of composition Sn_0.5NTiP₃O₁₂ and Fe_0.33NbTiP₃O₁₂ involves the accomodation of Sn²⁺ and Fe²⁺ in two types of sites in the NbTiP₃O₁₂ host lattice. The change in colour is associated which charge transfer arising from the transfer of electrons from the incorporated metal to the host lattice and the partial reduction of Nb⁵⁺ to a lower oxidation state.The compound SbTiP₃O₁₂ has been synthesised and shown by antimony-121 Mössbauer spectroscopy to contain Sb⁵⁺. The resistance of the SbTiP₃O₁₂ structure to the incorporation of tin and iron is associated with the reluctance of Sb³⁺ to adopt octahedral coordination.     

Observation of high-energy electrons from a metal target irradiated by protons with a mean energy of 25 keV

Electrons with abnormally high energies of up to 16 keV are detected from an iron target irradiated by ions (H⁺, Fe⁺, Fe²⁺, Fe³⁺) with energies ranging from 20 to 100 keV from the plasma of a high-power femtosecond laser pulse with an intensity of 10¹⁶ J/(s cm²). These electrons indicate that the energy of an incident ion is almost completely transferred to an electron knocked out of the target. In a range of 6–16 keV, the spectrum of electrons knocked out of the K shell of iron atoms by protons with an energy of 22 ± 2 keV is quasi-exponential with an exponent of 4 keV. For 8-keV electrons, the double differential cross section for ionization by such protons is estimated as 10^?7 b/(eV sr).     

Die Reichweite von Elektronen und Positronen kleiner Energie in Kupfer,Silber und Gold

In continuation of previous work the range of 40 to 160 keV monoenergetic electrons and positrons in copper, silver, and gold is determined and the corresponding range-energy-relations are stated. In copper the positrons have a shorter range than electrons of the same energy, but in silver and gold they have a longer range, in disagreement with the values calculated byNelms 2. For the three absorption materials all the ranges of electrons can be described by the formula E^?=14,3 · (Z^4/3/A) · R^{0, 61}, and all the ranges of positrons by E⁺=29,7 · (Z/A) · R^{0, 60} (E in keV, R in mg/cm²). The ratio of the range of positrons to that of electrons for copper agrees rather well with the calculated one, but for silver and gold it differs considerably. This might be due to the increasing influence of the elastic scattering of the particles on nuclei.     

Experiments on screening effect in deuteron fusion reactions at extremely low energies

The enhanced electron screening effect in nuclear reactions taking place in dense astrophysical plasmas is extremely important for determination of stellar reaction rates in terrestrial laboratories as well as in prediction of cross sections enhancement in interiors of stars such as White and Brown Dwarfs or Giant Planets. This effect resulting in reduction of the nuclear Coulomb potential by the atomic electrons has been confirmed in many laboratory experiments. Unfortunately, experimental screening energies are much higher than the theoretical predictions and the reason for that remains unknown. Here, we present absorbing results of the experiment studying d + d nuclear reactions in different deuterized metallic targets under ultra high vacuum conditions. The total cross sections and angular distributions of the ²H(d,p)³H and ²H(d,n)³He reactions have been measured using a deuteron beam of energies between 8 and 30 keV provided by the electron cyclotron ion source. The atomic cleanness of the target surface has been secured by combining Ar sputtering of the target and Auger electrons spectroscopy. Due to application of an on-line analysis method, the homogeneity of the implanted deuteron densities could be continuously monitored. We will discuss probable causes of the large discrepancy between theoretical and experimental data.