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ISSN (Print) 1572-9540 - ISSN (Online) 0304-3843
• Mössbauer study of intermediate superparamagnetic relaxation of maghemite (γ-Fe 2 O 3 ) nanoparticles
• Abstract: Abstract In the present work, we have synthesized and characterized magnetic nanoparticles of maghemite γ-Fe2O3 to study their structural and magnetic properties. For the preparation, magnetite precursor, were oxidized by adjusting the pH = 3.5 at about 80 °C in an acid medium, The mean size of the maghemite particles calculated from the X-ray diffractogram was around 5.7 nm. Mössbauer spectroscopy measurements at room temperature show their superparamagnetic behavior. Furhermore, Mössbauer measurements were carried out at 77 K and 4.2 K in order to find the typical hyperfine fields of the maghemite. Magnetite phase was not found. FC and ZFC magnetization curves measured at 500 Oe indicate a blocking temperature of 105.3 K. The magnetization measurements also show almost zero coercivity at RT. TEM images show nanoparticles with diameter smaller than 10 nm, which are in good agreement with the X-ray pattern and the fitting of the magnetization data.
PubDate: 2014-01-01

• Whiteness process of tile ceramics: using a synthetic flow as a modifier agent of color firing
• Abstract: Abstract Synthetic flow is proposed as a modifier agent of color firing in tile ceramic mass during the sinterization process, turning the red color firing into whiteness. Therefore, the 57Fe Mössbauer spectroscopy was used to understand how the interaction of the iron element in the mechanism of color firing mass occurs in this system. The results suggest that the change of color firing can be alternatively due to two main factors: (i) diluting the hematite content in the sample because of the use of synthetic flow and (ii) part of the hematite is converted in other uncolored crystal structures, which makes the final color firing lighter.
PubDate: 2014-01-01

• Mössbauer study of a Fe3O4/PMMA nanocomposite synthesized by sonochemistry
• Abstract: Abstract Magnetite nanoparticles of 10 nm average size were synthesized by ultrasonic waves from the chemical reaction and precipitation of ferrous and ferric iron chloride (FeCl3 · 6H2O y FeCl2 · 4H2O) in a basic medium. The formation and the incorporation of the magnetite in PMMA were followed by XRD and Mössbauer Spectroscopy. These magnetite nanoparticles were subsequently incorporated into the polymer by ultrasonic waves in order to obtain the final sample of 5 % weight Fe3O4 into the polymethylmethacrylate (PMMA). Both samples Fe3O4 nanoparticles and 5 % Fe3O4/PMMA nanocomposite, were studied by Mössbauer spectroscopy in the temperature range of 300 K–77 K. In the case of room temperature, the Mössbauer spectrum of the Fe3O4 nanoparticles sample was fitted with two magnetic histograms, one corresponding to the tetrahedral sites (Fe3 + ) and the other to the octahedral sites (Fe3 +  and Fe2 + ), while the 5 % Fe3O4/PMMA sample was fitted with two histograms as before and a singlet subspectrum related to a superparamagnetic behavior, caused by the dispersion of the nanoparticles into the polymer. The 77 K Mössabuer spectra for both samples were fitted with five magnetic subspectra similar to the bulk magnetite and for the 5 % Fe3O4/PMMA sample it was needed to add also a superparamagnetic singlet. Additionally, a study of the Verwey transition has been done and it was observed a different behavior compared with that of bulk magnetite.
PubDate: 2014-01-01

• Mössbauer and X-ray study of the Fe 65 Ni 35 invar alloy obtained by mechanical alloying
• Abstract: Abstract Fe65Ni35 samples were prepared by mechanical alloying (MA) with milling times of 5, 6, 7, 10 and 11 h, using a ball mass to powder mass ratio of 20:1 and at 280 rpm. The samples were characterized by X-ray diffraction (XRD) and transmission 57Fe Mössbauer spectrometry. The X-ray diffraction pattern showed the coexistence of one body centered cubic (BCC) and two face centered cubic (FCC1 and FCC2) structural phases. The lattice parameters of these phases did not change significantly with the milling time (2.866 Å, 3.597 Å and 3.538 Å, respectively). After 10 h of milling, the X-ray diffraction pattern showed clearly the coexistence of these three phases. Hence, Mössbauer spectrometry measurements at low temperatures from 20 to 300 K of this sample were also carried out. The Mössbauer spectra were fitted using a model with three components: the first one is a hyperfine magnetic field distributions at high fields, related to the BCC phase; the second one is a hyperfine magnetic field distribution involving low hyperfine fields related to a FCC phase rich in Ni, and the third one is a singlet related to a FCC phase rich in Fe, with paramagnetic behavior. As proposed by some authors, the last phase is related with the antitaenite phase.
PubDate: 2014-01-01

• Comparison of methods to obtain ash from coal of the Southwest of Colombia
• Abstract: Abstract The method for concentration of mineral matter at low temperature (about 250 °C), called Low Temperature Ash (LTA) was applied to a sample of coal from the mine “Las Mercedes” located in Colombia southwestern. This method provides better information about the content of mineral matter in natural coal (NC), removing the organic matter more efficiently without significant transformations of mineral phases present in that coal. These results were observed through Mössbauer spectra and X-ray patterns taken from samples of NC, (LTA) and the conventional method of High Temperature Ash (HTA). The results show that the LTA process provides more representative data of the mineral phases for natural coal than that using the conventional HTA process.
PubDate: 2014-01-01

• Erratum to: Mössbauer analysis of coal coke samples from Samacá, Boyacá, Colombia
• PubDate: 2014-01-01

• Analysis of broadened Mössbauer spectra using simple mathematical functions
• Abstract: Abstract Simulated and experimental broadened Mössbauer spectra are analyzed using several distribution functions. The resolution Hesse and Rübartsch data are reproduced in order to analyze the origin of the oscillations appearing in the recovered distribution function. The lined triangular distribution is used and some of its properties are described. The no implicit nth-nomial distribution function $P\left( x \right)=\left( {a\textrm{Cos}\left( {\pi x} \right)+b\textrm{Sin}\left( {\pi x} \right)} \right)^n$ is introduced, complementing the Window and Hesse and Rübartasch no implicit distribution functions. This new no implicit distribution function gives similar results of those of Window’s method. In addition, the Window method has also been modified by inserting a smoothing factor λ C . For 0 < λ C  < 1 a hyperfine distribution with low resolution may be obtained; for λ C  > 1, the opposite is obtained. The Levenberg-Marquardt algorithm is used to solve the involved Fredholm integral equation rather than the typical second order regularized algorithm. From the extracted hyperfine field distribution functions of the Mössbauer spectra of the amorphous and crystallized Fe70Cr2Si5B16 magnetic alloy the short range atomic order for the amorphous state of this alloy can be inferred.
PubDate: 2014-01-01

• Implementation of a preamplifier-amplifier system for radiation detectors used in Mössbauer spectroscopy
• Abstract: Abstract We report the assembly and testing of a preamplification and amplification system for pulses produced by gaseous radiation detectors commonly used in Mössbauer spectroscopy. The system is composed by a pair of commercial integrated circuits A203 and A206, which operate as charge sensitive preamplifier-shaping amplifier and linear amplifier-low level discriminator, respectively. The integrated circuits were interconnected in the unipolar output mode and placed inside a metallic shielding, which prevents noise amplification for a suitable signal-noise ratio. The system was tested by irradiating a proportional counter LND-45431 with characteristic X rays of 6.3 keV and gamma rays of 14.4 keV emitted by a Mössbauer radioactive source of 57Co (Rh). Unipolar pulses with Gaussian profile were obtained at the output of the linear amplifier, whose amplitudes were close to 0.4 V for 6.3 keV X rays and 1.4 V for 14.4 keV gamma rays. Pulse height spectra showed that the system allows a satisfactory identification of the X-rays and gamma rays emitted by the 57Co source, giving the possibility to make a good selection of the 14.4 keV peak for having a suitable signal-noise ratio in the Mössbauer spectra. Absorption percentages of 14 % were found by taking the Mössbauer spectra of a natural iron absorber. The assembly and tests of the system are presented through this paper.
PubDate: 2014-01-01

• Structural, calorimetric and magnetic properties study of the Cu0,91Fe0,09O system
• Abstract: Abstract In this work the Cu0.91Fe0.09O nanocrystalline system was prepared via the co-precipitation method. Using Mössbauer Spectrometry, X-Ray Diffraction, Vibrating Sample Magnetometry, Thermogravimetry and Differential Scanning Calorimetry, we study the magnetic behavior, and the structural and calorimetric properties of this system. X-ray diffraction shows only the presence of the CuO structural monoclinic phase, suggesting that Cu atoms are substituted by Fe ones. This hypothesis was confirmed by Mössbauer spectrometry at room temperature, because it shows that the spectrum is formed by two doublets, which correspond to Fe + 2 and Fe + 3 sites. Hysteresis cycles obtained by vibrating sample magnetometry detect a soft ferromagnetic behavior at room temperature with coercive fields between 8 and 20 Oe. At T = 20 K the sample shows a hard-magnetic behavior. The thermogravimetry results show a Néel temperature (T N > 440 °C). The differential scanning calorimetry curve show two endothermic peaks in the 90–120 °C range.
PubDate: 2014-01-01

• Iron nano-clusters in ytterbium films: a 57Fe Mössbauer spectroscopic study
• Abstract: Abstract We have performed a Mössbauer study on iron clusters that are formed in ytterbium films prepared by vapor co-deposition onto kapton substrates kept at room temperature. The film thicknesses were chosen in a range between 2.5 and 2.8 $\upmu$ m. XRD of the films reveals a mixture of fcc- and hcp-like ytterbium. Iron concentrations were between 0.3 and 5 at %. All samples reveal hyperfine spectra attributed to only two types of iron clusters with well defined hyperfine parameters. The clusters are supposed to be formed at boundaries of hcp- and fcc-like grains. In addition there is found a small contribution from monomeric iron. Spectra taken at 4.2 K reveal a complex distribution of magnetic hyperfine fields. The dynamic origin of the spectral shape is supported by susceptibility data revealing spin-freezing at temperatures below ca. 10 K. This proves that the iron clusters have sizes on the order of nm.
PubDate: 2014-01-01

• Magnetic composites from minerals: study of the iron phases in clay and diatomite using Mössbauer spectroscopy, magnetic measurements and XRD
• Abstract: Abstract Magnetic particles as matrix for enzyme immobilization have been used and due to the enzymatic derivative can be easily removed from the reaction mixture by a magnetic field. This work presents a study about the synthesis and characterization of iron phases into magnetic montmorillonite clay (mMMT) and magnetic diatomaceous earth (mDE) by 57Fe Mössbauer spectroscopy (MS), magnetic measurements and X-ray diffraction (XRD). Also these magnetic materials were assessed as matrices for the immobilization of invertase via covalent binding. Mössbauer spectra of the magnetic composites performed at 4.2 K showed a mixture of magnetite and maghemite about equal proportion in the mMMT, and a pure magnetite phase in the sample mDE. These results were verified using XRD. The residual specific activity of the immobilized invertase on mMMT and mDE were 83 % and 92.5 %, respectively. Thus, both magnetic composites showed to be promising matrices for covalent immobilization of invertase.
PubDate: 2014-01-01

• Fe2+-Mg order–disorder study in orthopyroxenes from São João Nepomuceno (IVA) iron meteorite
• Abstract: Abstract São João Nepomuceno (SJN) is an iron meteorite belonging to IVA chemical group. It consists of Fe-Ni metal matrix and silicate inclusions made of a coarse-grained mixture of tridymite, orthopyroxene and clinopyroxene. In spite of the extensive work performed on the IVA group there is still no consensus about their origin and its thermal history is subject of ongoing debates. In this work, we report preliminary results on Fe2 +  distribution in the non-equivalent octahedral sites in orthopyroxene crystals extracted from São João Nepomuceno in order to infer on the thermal history of this meteorite and therefore acquire more information related to the origin of the IVA iron meteorite group.
PubDate: 2014-01-01

• Mössbauer and vibrational DOS studies of diluted magnetic tin oxides and nano iron oxides
• Abstract: Abstract The magnetic properties and Mössbauer results for SnO2 doped with 57Fe are reviewed, and the values of isomer shift and quadrupole splitting are compared with the results obtained by ab initio calculations. It is concluded that the exchange interactions between oxygen defects and magnetic atoms are responsible for long range magnetic interactions of dilute Fe ions dispersed in SnO2. Fe atom precipitated clusters may be formed in highly Fe doped SnO2 samples by annealing at relatively high temperatures for several hours. The reduction of the particle size to nano-scale dimensions induces magnetization, which can be associated with oxygen defects. We have measured the nuclear inelastic scattering (NIS) spectra of Fe oxides, and 57Fe and (Co or Mn) doped SnO2 synthesized mainly by sol–gel methods and we have derived the vibration density of states (VDOS). The local phonons are sensitive to the presence of precipitated clusters.
PubDate: 2014-01-01

• Enhancing vibration measurements by Mössbauer effect
• Abstract: Abstract The measurement of the Mössbauer effect in a system excited with a periodic perturbation can provide information about it. For that purpose, the Mössbauer absorption of a source-absorber set which hyperfine parameters are well known, is measured at a constant relative velocity (i.e. at a defined spectral energy). The resulting Mössbauer absorption periodic signal provides information of the sample ac perturbation response. This approach has been used time ago to measure small tympanic vibrations (mechanical perturbations). In this work we present an extension of the vibration experiments, by measuring them at various absorber-source relative velocities within a constant-velocity strategy. As a demonstration test, the frequency response of a piezoelectric diaphragm in the 100 Hz–5 kHz range is obtained with a custom electronic counter. The experiments are performed using a 57Co(Rh) source and a 25- $\upmu$ m-thick stainless-steel absorber fixed to a piezoelectric diaphragm. Phase shifts and amplitude vibrations with velocities in the range from 1.5 $\upmu$ m/s to 20 mm/s are well characterized, extending the linearity limit well beyond the earlier suggested one of 1 mm/s.
PubDate: 2014-01-01

• Chairmen and committees
• PubDate: 2014-01-01

• Effect of boron in Fe 70 Al 30 nanostructured alloys produced by mechanical alloying
• Abstract: Abstract The substitution of aluminum by boron in the Fe70Al30 system prepared by high energy ball milling is studied when the B content ranged from 0 up to 20 at. %, and the milling times were 24, 48 and 72 h. X-ray diffraction (XRD) patterns of Fe70Al30 showed a predominant bcc structural phase with a lattice parameter larger than that of α-Fe. A second (tetragonal) phase arose with the addition of boron. It is associated to the existence of (Fe, Al)2B, although the values of the lattice parameters are slightly different from those found in the literature. This phase shows high stability; its lattice parameters and the Mössbauer parameters do not show notable variations, either with milling time or composition. It was also evidenced that an increase of boron content and of milling time produced a decrease of the lattice parameter of the Fe-Al bcc structure. This is in agreement with the small atomic radius of boron in comparison with that of aluminum. This also allows boron to occupy interstitial sites in the lattice, increasing the grain size and giving rise to the ductile character of the alloy. On the other hand, 300 K transmission Mössbauer spectra (TMS) were fitted, for low boron concentrations (<8 at.%), with a hyperfine field distribution (HFD) associated with the bcc phase. For high boron content (≥8 at.%), a magnetic component related to the tetragonal phase is added and its broadened lines are attributed to the disordered character of Fe2B, probably induced by the milling process.
PubDate: 2014-01-01

• Trap-assisted studies of odd, neutron-rich isotopes from Tc to Pd
• Abstract: Abstract We review the present and future of trap-assisted structure studies of odd, neutron-rich Tc, Ru, Rh and Pd isotopes at the limits of present experimental techniques. These nuclei of refractory elements are produced in light-particle induced fission and filtered by their mass number with the IGISOL mass separator. Further mass separation with the JYFLTRAP Penning trap system provides a clean, monoisotopic beam perfectly suited for precise nuclear spectroscopy. Connecting the IGISOL and the JYFLTRAP facilities to the recently installed MCC30/15 cyclotron opens new prospects for post-trap spectroscopy of very exotic, neutron-rich nuclei.
PubDate: 2014-01-01

• Fast life-time measurements on fission products
• Abstract: Abstract Ultra Fast Timing has been applied at the IGISOL facility since more than a decade ago with the aim to systematically study nano- and subnanosecond lifetimes in the neutron-rich nuclei from the A~110 region. Over this period two generations of crystals and photomultipliers have been introduced, which allowed to study more complex level schemes populated in β decay. The IGISOL facility provides unique capabilities to study the A~110 region not matched elsewhere in the world.
PubDate: 2014-01-01

• Decay spectroscopy of neutron-rich nuclei with A ≃ 100
• Abstract: Abstract We review structure data obtained by decay spectroscopy of neutron-rich nuclei of mass close to 100. Emphasis is put on the contribution of experiments at IGISOL in the nineties. They confirmed the earlier postulated shape coexistence in the fast shape-transition region between N = 58 (spherical ground states and low collectivity) and N = 60 (strong axial deformation). A detailed spectroscopic study of the A = 99 chain established the upper-Z limit of the N = 56 shell closure region with 99Nb, owing to striking similarities with 97Y. A consequence of the N = 56 closure is that the s 1/2 odd-neutron becomes the ground state of the most neutron-rich N = 57 isotones, starting with 99Mo, instead of the degenerated d 5/2 and g 7/2 subshells familiar in the tin region. Consequences on the change of spin on astrophysical r-process calculations are briefly discussed. Finally, we say a few words about neutron-rich rhodium and palladium isotopes near the neutron midshell where regular and intruder states coexist very close to each other.
PubDate: 2014-01-01

• An IGISOL portrait
• PubDate: 2014-01-01

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