Abstract: The term “nano” in connection with crystalline or amorphous structures represents important materials from a scientific as well as from a technical point of view. In addition, it seems that, so far, Mossbauer spectroscopy is the most successful technique for obtaining information on these structures. A brief overview of the perspective which Mossbauer spectroscopy affords in the study of the structure of such materials is presented.

Abstract: Positronium formation (Ps) cross sections for positrons impinging on atomic hydrogen were measured in the impact energy range from 13 to 255 eV at the High Intensity Positron (HIP) beam at Brookhaven National Laboratory (BNL). The Ps-formation cross section was found to rise rapidly from the threshold at 6.8 eV to a maximum value of (2.98±0.18) ×10−16 cm2 for ∼15 eV positrons. By 75 eV it drops below the detection limit of 0.17×10−16 cm2 which is the present level of statistical uncertainty. A more elaborate data analysis was performed leading to somewhat smaller cross sections than originally published [1]. During the course of this experiment further relative data on impact-ionization cross sections were accumulated.

Abstract: Coupled-state calculations including positronium channels are reported for positron scattering by atomic hydrogen, lithium and sodium. Integrated cross sections and total cross sections are presented for all three atoms. For lithium differential cross sections are also given. Throughout, comparison is made between results calculated with and without inclusion of the positronium channels. S-wave cross sections for positron scattering by atomic hydrogen in the Ps(1s, 2s, 2p)+H(1s, 2s, 2p) approximation show the high energy resonance first observed by Higgins and Burke in the coupled-static approximation. This resonance has now moved up to 51.05 eV and narrowed in width to 2.92 eV. Other pronounced structure is seen in the S-wave cross sections between 10 and 20 eV; it is tentatively suggested that this structure may be due to the formation of a temporary pseudo-molecular collision complex. Results calculated in the Ps(1s, 2s, $$\overline {3s} ,\overline {4s} $$ , 2p, $$\overline {3p} ,\overline {4p} ,\overline {3d} ,\overline {4d} $$ ,+H(1s, 2s, $$\overline {3s} ,\overline {4s} $$ , 2p, $$\overline {3p} ,\overline {4p} ,\overline {3d} ,\overline {4d} $$ approximation show convergence towards accurate values in the energy region below and in the Ore gap. Contrary to previous work on lithium using only an atomic basis, it is found that coupling to the 3d state of lithium is not so important when positronium channels are included; this is because a mixed basis of atom and positronium states gives a more rapidly convergent approximation than an expansion based on atom states alone. The threshold behaviour of the elastic cross section and the Ps(1s) formation cross section for lithium is investigated. Results in the Ps(1s, 2s, 2p)+Na(3s, 3p) approximation for sodium show good agreement with the total cross section measurements of Kwan et al.

Abstract: Recent applications of high pressure Mossbauer spectroscopy using a diamond anvil cell are presented. High pressure Mossbauer studies of two perovskite-related iron oxides SrFeO2.97 and CaFeO3, magnetite Fe3O4, and wustite Fe1−δO have been carried out at 300 K at pressures of up to 74 GPa. A preliminary result by the resonant forward scattering of synchrotron radiation for high pressure Mossbauer spectroscopy using a diamond anvil cell is also presented.

Abstract: Magnetotactic bacteria contain magnetic particles that constitute a permanent magnetic dipole and cause each cell to orient and migrate along geomagnetic field lines. Recent results relevant to the biomineralization process and to the function of magnetotaxis are discussed.

Abstract: The principal and engineering aspects of a dedicated synchrotron radiation beamline under construction at the Advanced Photon Source for nuclear resonant scattering purposes are explained The expected performance in terms of isotopes to be studied, flux, and timing properties is discussed

Abstract: Zero field positive muon spin rotation method (μ +SR) is applied on La2−x Sr x CuO4 around forx=0.12 at which the high-T c superconductivity (SC) is suppressed. The magnetically ordered state of Cu-moments, which is not a spin glass state but an antiferromagnetic like state, appears below 15 K for 0.105≤x≤0.120. The magnetic phase boundary is very similar to the one of the La2−x Ba x CuO4 in which the structural transition from the low temperature orthorhombic (LTO) phase to the low temperature tetragonal (LTT) phase is observed aroundx=0.12. The present study suggests that there is no big difference of the electronic state of the CuO2 plane between the La-Ba system and the La-Sr system and that the magnetic ordering of Cu-moments plays an important role for the suppression of the high-T c SC aroundx=0.12 in both of the systems, although the LTO-LTT structural transition has not been observed yet in the La-Sr system.

Abstract: Heavy fermion systems have received a great deal of study by a wide variety of techniques, includingμSR. In a number of systems, coexisting superconducting and magnetic states have been reported, leading to speculation of an intimate connection between magnetism and superconductivity in these compounds. We observe a spontaneous magnetic field in the superconducting phase of UPt3. In addition, the broadening of the transverse field muon precession signal only onsets approximately 60 mK below the superconductingT c. Our results provide evidence that the “lower superconducting phase” in theH-T phase diagram of UPt3 is characterised by broken time-reversal symmetry. Measurements of URu2Si2 and CeCu2.2Si2 indicate that the magnetically ordered volume fraction is temperature dependent in both systems.

Abstract: 151Eu-Mossbauer spectroscopy is used to study the ternary intermetallics EuM2Ge2 (M=Ni, Pd, Pt), in which Eu is divalent, and EuNi2Si2 as a trivalent reference system in the pressure range 0–31 GPa. In EuNi2Ge2 and EuPd2Ge2, one observes a valence transition from Eu2+ to Eu3+ around 5 and 25 GPa, accompanied by a change in isomer shift of 9.3 and 10.1 mm/s, respectively. These are the largest pressure-driven changes in isomer shift for151Eu-spectroscopy observed up to now.

Abstract: By utilizing the intense pulsed proton beam available at the ISIS facility of RAL, the new muon facility project of an advanced superconducting muon channel funded by the RIKEN is now under construction. The new facility, by adopting the superconducting solenoid system, will produce the strongest backward decay pulsedμ + orμ −in the momentum range from 20 MeV/c to 120 MeV/c. Also, by adopting the pulsed magnetic kicker, each one of two muon pulses will be supplied to two extraction channels simultaneously. Various important muon science experiments including advanced pulsedμ −SR andmu +SR experiments will be realized.

Abstract: Zero field μSR has been used to probe spin dynamics in the concentrated spin glass Y(Mn0.9Al0.1)2. The spectra follow a stretched exponential form, Gz(t)=exp(−(λt)β), with β reaching 1/3 as the freezing temperature, Tg=60K, is approached. The evolution of Gz(t) with temperature is suggestive of the behaviour of the spin correlation function found by Ogielski in Monte Carlo simulations of the dynamics of the Ising spin glass model. The μSR results are correlated with results previously obtained by inelastic neutron scattering.

Abstract: The muon spin rotation (μ +SR) and NMR measurements provides clear evidences of the antiferromagnetic order of Cu-moment below 35 K for La2−x Ba x CuO4 and below 15 K for La2−x Sr x CuO4 in the narrow range ofx where the high-T c superconductivity (SC) is suppressed remarkably. The results suggest that the freezing of spin fluctuations of Cu-moment is relevant to the local suppression of SC under an change of the electronic state coupled with the lattice instability.

Abstract: Olivine tholeiites are mantle-derived magmas that are formed by partial melting of their deep sources and which have equilibrated with mineral assemblages at slightly different subcrustal pressure-temperature conditions prior to eruption. The minimum depth of the pre-eruptive reservoirs of these magmas is in the order of 10–15 km and their liquidus temperatures fall within the range of 1180–1240 ‡C. Three types of primitive olivine tholeiites are exposed along the rift zones in Iceland. In the present study, the ferric/ferrous ratios of natural glasses (pillow crusts) of the three types of olivine tholeiites were obtained by Mossbauer spectrometry. This technique is particularly well suited for the analysis of high-Mg glasses since it resolves microcrystallites of olivine which contribute to ferrous iron in chemical analysis. All results fall within 10–15% Fe(III). At the liquidus temperature of these glasses, this ferric/ferrous ratio corresponds to fugacity close to the fayalite-magnetite-quartz-oxygen (FMQ) buffer with an uncertainty of less than one log unit in fO2. This result confirms that there is no significant difference in the oxidation state of the three magma types.

Abstract: Mossbauer spectroscopy and XRD were employed to characterize the microstructural properties of iron-zinc binary alloys between 0–31 at.% Fe. Samples were prepared with accuracies of ±0.5 at.% Fe, and the Mossbauer and lattice parameters were monitored as a function of iron concentration across each phase. Two iron sites were observed in the Γ phase (18–31 at.% Fe), whose occupancies and isomer shifts varied continuously with iron content. However, the quadrupole splitting of each site remained constant. Within the Γ1 phase (19–24 at.% Fe), three iron sites were observed whose isomer shifts and quadrupole splittings remained constant, while their occupancies varied with iron concentration. For the first time, a third iron site was observed in the δ phase (8–13 at.% Fe), whose occupancy increases with iron content. Also, the site occupancies of the two other δ sites appear to remain constant, while other Mossbauer parameters vary continuously with iron content. Analysis of the ζ phase (6–7 at.% Fe) showed the presence of one iron site, whose parameters were not observed to change due to the small variance in iron concentration. XRD studies indicate the lattice parameters across the Γ and δ phases vary continuously with iron concentration. Moreover, a better understanding of these phases, as formed in galvanneal steel coatings, was obtained.

Abstract: Differential cross sections for elastic scattering and Ps(1s) formation are calculated in the truncated coupled-static (TCS) approximation. Comparison is made with the elastic scattering measurements of Dou et al. on Ar and Kr. There is no support from the TCS approximation for the view that structure seen in the experimental results for Ar in the energy range 55–60 eV may be due to a resonance associated with coupling to the positronium formation channel. Rather, we believe that Dou et al. are right in correlating this feature with the maximum in the ionization cross section. In the experiment on Kr structures are observed at 25 and 200 eV. It is tentatively suggested that the structure at 200 eV may be the resonance seen in the TCS calculation at 100 eV, but modified by polarization and absorption effects. It is also suggested that the feature at 25 eV could be associated with coupling to excited states of positronium. The TCS results for the Xe target predict some very pronounced behaviour which would be worth experimental investigation. TCS differential cross sections for Ps(1s) formation by capture of an electron from the outer p-shell of the atom are presented for impact energies up to 75 eV. A noticeable property of these cross sections is that they do not usually peak at the forward direction; this is consistent with an experimental observation by Laricchia et al. on He and Ar targets. The importance of also looking at electron capture from inner shells is emphasized and illustrated by the cross section for electron capture from the 3s shell of Ar.

Abstract: Clusters of metal atoms show a significant increase of the ionization energy beyond the bulk work function when the particle size is reduced. Analogously, the electron detachment energy, i.e. the electron removal energy for a negatively charged cluster decreases with decreasing size. Thus the work function of an initially macroscopic metal particle splits into two well-separated components. Experimental evidence of this behaviour will be reviewed and compared with theoretical models.

Abstract: Mossbauer spectroscopic and magnetic measurements have been made on a novel magnetic protein produced by the controlled reconstitution of ferritin. The data indicate that the predominant mineral form in the iron-containing cores is maghemite (γ-Fe2O3) rather than magnetite (Fe3O4).

Abstract: Mossbauer measurements have been performed on amorphous and nanocrystalline alloy ribbons of nominal composition Fe86Zr7Cu1B6. The nanocrystalline samples were obtained by annealing the as-quenched alloy at different temperatures in the range between 650 and 870 K. Mossbauer spectra of the as-quenched amorphous sample have been recorded at 77 K, room temperature and above the Curie temperature (≈330 K) at 360 K. We have also performed Mossbauer measurements at room temperature in the nanocrystalline alloys to characterize the phases that appear after the annealing and their relative concentration. The as-quenched sample spectra reveal the existence of two inequivalent sites for Fe. Such a feature is also observed in the remaining amorphous phase of the annealed samples. In the first steps of crystallization, α-Fe precipitates and its concentration increases with the annealing temperature. The experimental results suggest that the composition of the whole amorphous phase does not suffer large changes during crystallization.

Abstract: The Xinyang and Jilin meteorites were investigated using Mossbauer spectroscopy. In addition to troilites and silicates, the Jilin meteorite contains taenite and kamacite, while the Xinyang meteorite contains kamacite only. The Mossbauer data of these two meteorites confirm them as ordinary H chondrites. The Mossbauer parameters can be interpreted by a model based on the cooling history of these meteorites.

Abstract: Nuclear spin-lattice relaxation in paramagnetic systems is treated using the classic expression for transition probability between the coupled electron and nuclear spin states. The rate equations governing the incoherent occupancies of these states are solved analytically (where possible) and numerically (where not) to construct the relaxation function for the nuclear spin. The method is illustrated for muonium, and the muonium-substituted molecular radicals, for the case of perturbation due to fluctuation of the local field,i.e. modulation of the interaction with a third spin. A slight departure from single exponential behaviour is demonstrated for slow fluctuations.

Abstract: A distinctive field dependence of longitudinal muon spin relaxation in acetone liquid and vapour suggests that modulation of the isotropic hyperfine coupling of the (CH3)2COMu radical is the dominant relaxation mechanism The temperature dependent correlation time extracted from the data then corresponds to the lifetime of the states of internal libration of the molecule The variation of relaxation rate may also be followed into the solid phase, peaking at the freezing transition

Abstract: Electric dipole transitions in the microwave range have been induced between the fine-structure levels of positronium in the excited staten=2. As an indication of the transitions, we used the increase in Lyman-α radiation when the metastable 23S1-level is depopulated. The results for the transitions 23S1→23P0,1,2 areΝ 0=18499.65±1.20±4.00 MHz,Ν 1=13012.42 ±0.65±1.54 MHz andΝ 2=8624.38±0.54±1.40 MHz. The first error is statistical and the second systematic. The precision of the present measurement has improved by a factor of 3, compared to previous data. Recent bound state QED-calculations have been extended to the orderR t8 α 4lnα −1. The not yet completely calculated orderR t8 α 4 is estimated to contribute less than 1 MHz. Our experimental results are in good agreement with theory. By applying a weak magnetic field, we were able to observe the transition 23S1→21P1 which is strictly forbidden byC-invariance in zero field. Our result, corrected for Zeeman- and motional Starkeffect, isΝ 3=11180.0±5.0±4.0 MHz. An upper limit for theC-violating matrix element of $$|\langle 2^1 P_1 |H_ ot\subset |2^3 P_1 \rangle |< 76$$ MHz could be deduced. Our experiment used moderated slow positrons from the bremsstrahlung and pair production of a pulsed electron linear accelerator (TEPOS facility at the university of Giessen).

Abstract: Mechanical alloying is a method of synthesis of advanced materials, often with non-equilibrium structures, and, remarkably, of crystalline materials with nanometersized grains. Grinding is also a way of inducing or activating chemical reactions. After having described some general characteristics and some applications of high-energy ball-milling, we sketch out some contributions which Mossbauer spectroscopy has made to gaining a deeper understanding of synthesis mechanisms and of mechanosynthesized materials.

Abstract: Mossbauer spectroscopy of basalt lava samples, exhibiting reversible thermal magnetization (Js-T) curves with Curie temperatures of about 840 K, has revealed considerable amounts of maghemite (γ-Fe2O3) in many samples. In view of the expected instability of maghemite at temperatures above 620 K, this reversibility came as a surprise. For further studies of the magnetization-temperature relationship of these minerals, we have constructed an elliptical radiation-heated furnace in which Mossbauer spectra can be acquired at temperatures between 300 and 900 K. Measurements at different temperatures have been obtained for two types of basalts, one in which the magnetic minerals are nearly pure magnetite and the other where the room temperature spectrum indicates a mixture of maghemite and magnetite. The two series show different features of the collapse of the internal magnetic hyperfine field, and the composition of minerals in the samples changes during the treatment, showing maghemite.

Abstract: We report on recent results obtained for longitudinal field (T 1) spin relaxation of the muonium-substituted (“muonated”) free radicals MuCO, MuC2F4, MuC2H3F, and MuC4H8 (t-butyl), comparing with results reported earlier for MuC2H4 (and MuC2D4). Some comparison with transverse field (T 2) data is also given. These data are fit to a phenomenological model based on NMR theory of spin relaxation in gases. The parameters of these fits are presented and discussed.

Abstract: A multichannel system for Mossbauer spectroscopy was developed and is presented. The system, constructed as an NIM module, is connected to the DMA port of an ATARI ST computer and can be used for six detectors simultaneously, thus allowing the operation of simultaneous triple radiation Mossbauer spectroscopy (STRMS). The multichannel system is explained and its capabilities are demonstrated.

Abstract: Investigation by Mossbauer spectroscopy of non-aggregated nanometric γ-Fe2O3 particles dispersed in polymer is reported. Magnetic interactions between the particles were controlled by varying the particle concentration in the polymer. The results show that over the investigated range, the interactions make the relaxation time shorter. Infield experiments show spin canting which increases with decreasing particle size.

Abstract: Mossbauer studies of Parkinsonian and control Substantia Nigra (SN) show that the overall amount of iron in SN is about the same in PD and control. At least 90% of this iron is ferritin-like and Fe2+ and/or neuromelanin iron, if present at all, can constitute only less than 10% of the overall iron. During storage in formalin, iron is slowly removed from ferritin and bound to a chelating agent.

Abstract: Mossbauer spectroscopy studies of precipitated Fischer-Tropsch (FT) iron catalysts, viz. 100 Fe/5 Cu/4.2 K/x SiO2, wherex=0,8, 16, 24, 25, 40, or 100, have shown that reduction of the oxide precursor in CO gives rise to χ-carbide Fe5C2 whose amount decreases with an increase of SiO2 content. The χ-carbide is converted into magnetite Fe3O4 while catalyzing the FT synthesis reaction. A correlation between FT activity and the content of χ-carbide in the catalysts was found, which indicated that χ-carbide is active for FT synthesis reaction.