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An extension of the online implantation chamber used for emission Mössbauer Spectroscopy (eMS) at ISOLDE/CERN that allows for quick removal of samples for offline low temperature studies is briefly described. We demonstrate how online eMS data obtained during implantation at temperatures between 300 K and 650 K of short-lived parent isotopes combined with rapid cooling and offline eMS measurements during the decay of the parent isotope can give detailed information on the binding properties of the Mössbauer probe in the lattice. This approach has been applied to study the properties of Sn impurities in ZnO following implantation of 119In (T½ = 2.4 min). Sn in the 4+ and 2+ charge states is observed. Above T > 600 K, Sn2+ is observed and is ascribed to Sn on regular Zn sites, while Sn2+ detected at T < 600 K is due to Sn in local amorphous regions. A new annealing stage is reported at T ≈ 550 K, characterized by changes in the Sn4+ emission profile, and is attributed to the annihilation of close Frenkel pairs. [ABSTRACT FROM AUTHOR]

This study analyses the performance of residential buildings in the town of Hveragerði in South Iceland during the 29 May 2008 Mw 6.3 Ölfus Earthquake. The earthquake occurred very close to the town, approximately 3-4 km from it. Ground shaking caused by the earthquake was recorded by a dense strong-motion array in the town. The array provided high-quality three-component ground acceleration data which is used to quantify a hazard scenario. In addition, surveys conducted in the town in the aftermath of the earthquake have provided information on macroseismic intensity at various locations in the town. Detailed information regarding the building stock in the town is collected, and their seismic vulnerability models are created by using building damage data obtained from the June 2000 South Iceland earthquakes. Damage to buildings are then simulated by using the scenario hazard and vulnerability models. Damage estimates were also obtained by conducting a survey. Simulated damage based on the scenario macroseismic intensity is found to be similar to damage estimated from survey data. The buildings performed very well during the earthquake-damage suffered was only 5 % of the insured value on the average. Correlation between actual damage and recorded ground-motion parameters is found to be statistically insignificant. No significant correlation of damage was observed, even with macroseismic intensity. Whereas significant correlation was observed between peak ground velocity and macroseismic intensity, neither of them appear to be good indicators of damage to buildings in the study area. This lack of correlation is partly due to good seismic capacity of buildings and partly due to the ordinal nature of macroseismic intensity scale. Consistent with experience from many past earthquakes, the survey results indicate that seismic risk in South Iceland is not so much due to collapse of buildings but rather due to damage to non-structural components and building contents. [ABSTRACT FROM AUTHOR]

Emission Mössbauer spectroscopy has been utilised to characterize dilute Fe impurities in In O following implantation of Mn ( T = 1.5 min.) at the ISOLDE facility at CERN. From stoichiometry considerations, one would expect Fe to adopt the valence state 3 + , substituting In , however the spectra are dominated by spectral lines due to paramagnetic Fe. Using first principle calculations in the framework of density functional theory (DFT), the density of states of dilute Fe and the hyperfine parameters have been determined. The hybridization between the 3d-band of Fe and the 2p band of oxygen induces a spin-polarized hole on the O site close to the Fe site, which is found to be the cause of the Fe state in In O. Comparison of experimental data to calculated hyperfine parameters suggests that Fe predominantly enters the 8b site rather than the 24d site of the cation site in the Bixbyite structure of In O. A gradual transition from an amorphous to a crystalline state is observed with increasing implantation/annealing temperature. [ABSTRACT FROM AUTHOR]

Fe emission Mössbauer spectroscopy has been applied to study the lattice location and properties of Fe in gadolinium gallium garnet GdGa O (GGG) single crystals in the temperature interval 300 - 563 K within the extremely dilute (<10 at.%) regime following the implantation ofMn ( T= 1.5 min.) at ISOLDE/CERN. These results are compared with earlier Mössbauer spectroscopy study of Fe-doped gadolinium gallium garnet GdGa O(GGG), with implantation fluences between 8×10 and 6×10 atoms cm. Three Fe components are observed in the emission Mössbauer spectra: (i) high spin Fe located at damage sites due to the implantation process, (ii) high spin Fe at substitutional tetrahedral Ga sites, and (iii) interstitial Fe, probably due to the recoil imparted on the daughterFe nucleus in the β decay ofMn. In contrast to high fluenceFe implantation studies the Fe ions are found to prefer the tetrahedral Ga site over the octahedral Ga site. No annealing stages are evident in the temperature range investigated. Despite the very low concentration, high-spin Fe shows fast spin relaxation, presumably due to an indirect interaction between nearby gadolinium atoms. [ABSTRACT FROM AUTHOR]

Emission Mössbauer Spectroscopy following the implantation of radioactive precursor isotope Mn ( T= 1.5 min) into ZnO single crystals at ISOLDE/CERN shows that a large fraction of Fe atoms produced in the Mn beta decay is created as paramagnetic Fe with relatively long spin-lattice relaxation times. Here we report on ZnO pre-implanted with Fe to fluences of 2×10, 5×10 and 8 × 10 ions/cm in order to investigate the dependence of the paramagnetic relaxation rate of Fe on fluence. The spectra are dominated by magnetic features displaying paramagnetic relaxation effects. The extracted spin-lattice relaxation rates show a slight increase with increasing ion fluence at corresponding temperatures and the area fraction of Fe at room temperature reaches a maximum contribution of 80(3)% in the studied fluence range. [ABSTRACT FROM AUTHOR]

States of dilute Fe in SnO have been monitored using Fe emission Mössbauer spectroscopy following implantation of Mn ( T = 85.4 s) in the temperature range from 143 K to 711 K. A sharp annealing stage is observed at ~330 K where the Fe/Fe ratio shows a marked increase. It is suggested that this annealing stage is due to the dissociation of Mn-V pairs during the lifetime of Mn; the activation energy for this dissociation is estimated to be 0.9(1) eV. Fe is found in a paramagnetic state showing spin-lattice relaxation rates consistent with an expected T dependence derived for a Raman process. In addition, a sharp lined doublet in the Mössbauer spectra is interpreted as due to recoil produced interstitial Fe. [ABSTRACT FROM AUTHOR]

A study of the annealing processes and charge state of dilute Fe in rutile TiO2 single crystals was performed in the temperature range 143–662 K, utilizing online 57Fe emission Mössbauer spectroscopy following low concentrations (<10−3 at%) implantation of 57Mn (T1/2 = 1.5 min). Both Fe3+ and Fe2+ were detected throughout the temperature range. Three annealing stages were distinguished: (i) a broad annealing stage below room temperature leading to an increased Fe3+ fraction; (ii) a sharp annealing stage at ∼330 K characterized by conversion of Fe3+ to Fe2+ and changes in the hyperfine parameters of Fe2+, attributed to the annealing of Ti vacancies in the vicinity of the probe atoms; and (iii) an annealing stage in the temperature range from 550 to 600 K, where all Fe ions are transformed to Fe3+, attributed to the annealing of the nearby O vacancies. The dissociation energy of MnTi–VO pairs was estimated to be 1.60(15) eV. Fe2+ is found in an environment where it can probe the lattice structure through the nuclear quadrupole interaction evidencing the extreme radiation hardness of rutile TiO2. Fe3+ is found in a paramagnetic state with slow spin–lattice relaxation which follows a ∼Tn temperature dependence with 4.1 < n < 6.3 at T > 350 K. [ABSTRACT FROM AUTHOR]

The lattice locations and electronic configurations of Fe in 57Co/57Fe implanted ZnO (to (5-6) × 1014 Fe/cm-2) have been studied by 57Fe Mössbauer emission spectroscopy. The spectra acquired upon room temperature implantation show ∼20% of the probe atoms as Fe2+ on perturbed Zn sites and the remaining fraction as Fe2+ in damage sites of interstitial character. After annealing at 773 K, ∼20% remain on crystalline sites, while the damage fraction has partly disappeared and instead a ∼30% fraction occurs as high-spin Fe3+, presumably in precipitates. This suggests that precipitation of Co/Fe in ZnO likely takes place at relatively low temperatures, thus explaining some of the discrepancies in the literature regarding magnetic properties of 3d metal-doped ZnO. [ABSTRACT FROM AUTHOR]

The valence state and annealing reactions of Mn/Fe in single crystalline α-AlO have been determined following low fluence (<10 cm) 60 keV implantations of Mn (T = 1.5 min) and emission Mössbauer spectroscopy on the Fe daughter nuclei in the temperature range from 110-700 K. At 110 K, most probe atoms are found in the Fe state in amorphous surroundings due to the implantation damage. A fraction of the Fe is found in cubic environment, possibly nano-precipitates of η-AlO. This site is found to disappear from the spectra above 500 K. Annealing of the damage sites at increasing temperatures leads first to increased incorporation of the probe atoms as Fe on Al sites, and, above room temperature, also as Fe. The Fe sub-spectrum is masked by slow paramagnetic relaxations following a T dependence, as expected for a two-phonon Raman process. Our data is consistent with data from Co and Fe implantations, suggesting a general increase in the average Fe valence state with lower implantation dose and negligible annealing reactions at room temperature. [ABSTRACT FROM AUTHOR]

Ion implantation provides a precise method of incorporating dopant atoms in semiconductors, provided lattice damage due to the implantation process can be annealed and the dopant atoms located on regular lattice sites. We have undertaken Fe emission Mössbauer spectroscopy measurements on GaAs and GaP single crystals following implantation of radioactive Mn ions, to study the lattice sites of the implanted ions, the annealing of implantation induced damage and impurity-vacancy complexes formed. The Mössbauer spectra were analyzed with four spectral components: an asymmetric doublet (D1) attributed to Fe atoms in distorted environments due to implantation damage, two single lines, S1 assigned to Fe on substitutional Ga sites, and S2 to Fe on interstitial sites, and a low intensity symmetric doublet (D2) assigned to impurity-vacancy complexes. The variations in the extracted hyperfine parameters of D1 for both materials at high temperatures ( T > 400 K) suggests changes in the immediate environment of the Fe impurity atoms and different bonding mechanism to the Mössbauer probe atom. The results show that the annealing of the radiation induced damage is more prominent in GaAs compared to GaP. [ABSTRACT FROM AUTHOR]

We present a method to describe the temperature dependence of emission Mössbauer spectra showing slow spin-lattice relaxations of Fe in MgO single crystals, obtained after implantation of Mn at ISOLDE/CERN. The analysis is based on the Blume-Tjon model for the line-shape of relaxing paramagnetic sextets with the spin relaxation rate, τ as a parameter. The temperature dependent spin relaxation rate of Fe in MgO is found to increase to ~10 s at 647 K by assuming a relaxation rate of τ < 10 s at 77 K. The results are in accordance with those obtained by electron paramagnetic resonance spectroscopy demonstrating the possibility of retrieving spin-lattice relaxation rates of dilute Fe from emission Mössbauer spectroscopy of Mn/Fe-implanted oxides. [ABSTRACT FROM AUTHOR]

Emission Mössbauer spectroscopy on Fe fed by Mn ions implanted in the metal oxides ZnO, MgO and AlO has been performed. The implanted ions occupy different lattice sites and charge states. A magnetic part of the spectra in each oxide can be assigned to Fe ions in a paramagnetic state with unusually long relaxation time observable to temperatures up to several hundreds Kelvin. Earlier expectations that the magnetic spectra could correspond to an ordered magnetic state could not be confirmed. A clear decision for paramagnetism and against an ordered magnetic state was achieved by applying a strong magnetic field of 0.6 Tesla. The relaxation times deduced were compared to spin-lattice relaxation times from electron paramagnetic resonance (EPR). [ABSTRACT FROM AUTHOR]

We analyse a new optimization-based approach for feature selection that uses the nested partitions method for combinatorial optimization as a heuristic search procedure to identify good feature subsets. In particular, we show how to improve the performance of the nested partitions method using random sampling of instances. The new approach uses a two-stage sampling scheme that determines the required sample size to guarantee convergence to a near-optimal solution. This approach therefore also has attractive theoretical characteristics. In particular, when the algorithm terminates in finite time, rigorous statements can be made concerning the quality of the final feature subset. Numerical results are reported to illustrate the key results, and show that the new approach is considerably faster than the original nested partitions method and other feature selection methods. [ABSTRACT FROM AUTHOR]

This preliminary study aims to investigate a M w 6.3 earthquake that occurred in South Iceland on Thursday 29 May 2008 at 15:45 UTC. The epicentre was in the Olfus District between the towns of Selfoss and Hveragerdi. This study examines the data recorded and the damage observed immediately after the event. Horizontal accelerations of up to 80%g were recorded in the epicentral region and there is visual evidence that the vertical acceleration exceeded 1 g. The PGA data is compared to a ground motion estimation model developed for the South Iceland earthquakes in June 2000. In general the basic properties of this event are found to be similar to the characteristics of the South Iceland earthquakes in June 2000. The duration of strong-motion is short and the intensity attenuates rapidly with increasing distance. The earthquake action resisted by buildings in the near fault area is inspected through evaluation of elastic as well as inelastic response spectra. The vast majority of structures seemed to withstand the strong-motion fairly competently and without significant visual damage due firstly to the low-rise, predominantly reinforced concrete or timber, style of buildings. Secondly, the short duration of strong-motion contributed to the endurance of structures. [ABSTRACT FROM AUTHOR]

The impact of the June 2000 South Iceland earthquakes has been assessed applying data collected in field surveys and strong-motion recordings from the Icelandic Strong-Motion Network. The areas within approximately 20 km of the causative faults suffered considerable damage, including transportation and utility systems as well as buildings, both with regard to structure and inventories. Ground subsidence and dislocations were significant in the near-fault zone. Aftershocks and permanent displacements of building foundations resulted in progressive structural damage. By introducing holistic measures derived from the acceleration data, a fair correlation was achieved between the obtained earthquake intensities and the recorded accelerations. The measures adopted were square root of the sum of the squares (SRSS) values of peak ground acceleration (PGA) and the trace of the Arias intensity tensor. It was found that the overall attenuation tended to be more rapid than reflected by common strong-motion models reported in the literature. There is no simple explanation for this behaviour but it is reasonable to suggest that it can be partly attributed to the heterogeneous and fractured crust that is characteristic of Icelandic geology. [ABSTRACT FROM AUTHOR]

A theoretical attenuation model of earthquake-induced ground motion is presented and discussed. This model is related directly to physical quantities such as source and wave motion parameters. An attenuation formula for rms acceleration of ground motion is derived and verified using acceleration data from moderate-sized earthquakes recorded in Iceland from 1986 to 1997. The source parameters and the crustal attenuation are computed uniformly for the applied earthquake data. Furthermore, attenuation formulas for peak ground acceleration are put forward. [ABSTRACT FROM AUTHOR]

Prompted by the generally poor understanding of the nature of magnetic phenomena in 3d-metal doped ZnO, we have undertaken on-line 57Fe Mössbauer spectroscopy on ZnO single crystals in an external magnetic field of 0.6 T, following the implantation of radioactive 57Mn ions at room temperature. The Mössbauer spectra of the dilute Fe impurities are dominated by sextets whose angular dependence rules out an ordered magnetic state (which had been previously proposed) but are well accounted for on the basis of Fe3+ paramagnetic centers on substitutional Zn sites with unusually long relaxation times (>20 ns). [ABSTRACT FROM AUTHOR]