[en] New analysis software for selecting and quantifying particles in three-dimensional atom maps has been designed. The selection of solute-rich regions is performed by connecting solute atoms which lie within a fixed distance (d), and taking clusters above a certain minimum number of solute atoms (N_min). Other atoms within some distance L greater than d are taken to belong to the cluster. However, this results in the inclusion of a shell of matrix atoms, which must be removed through an erosion step, to define the final cluster. Data filtered in this way can be used for subsequent quantification of parameters such as size, shape, composition, number density and volume fraction with better accuracy than by manual selection. The choice of d, N_min and L values is discussed and some methods of evaluation of these parameters are proposed. Examples are presented on the application of this new software to the analysis of early stage clustering in an Al-Mg-Si-Cu alloy and a copper-containing steel

[en] Three-dimensional atom probe (3DAP) was used to estimate solute-grain boundary interactions for Nb or Mo in α-Fe. By using the Langmuir-McLean isotherm, effective Gibbs free energies of segregation in α-Fe, ΔG_b, at 800 deg. C were estimated to be -38±2 kJ mol^-1 for Nb and -28±2 kJ mol^-1 for Mo. The apparent width of solute segregation was shown to be broader when the direction of analysis is not perpendicular to the boundary plane, due to limits of the lateral resolution of the 3DAP. However, even taking this effect into account, we measured a width of solute segregation of 1.0-2.0 nm, i.e. extending a few atom layers on both side of grain boundary. In order to represent the actual solute segregation profile, a wedge-shaped interaction potential across grain boundaries was used for the estimation of the interaction from atom probe data. The difference in the solute-grain boundary interaction between Nb and Mo, and the solute distribution within grain boundary is also discussed

[en] The development of nanoscale magnetic materials for applications in information storage systems relies heavily on the ability to engineer the properties of the layered structures from which such materials are fabricated. These properties are strongly dependent on the nature of the interfaces between the individual nanoscale magnetic layers, so knowledge of the interface chemistry is crucial. In this paper, we discuss the application of three-dimensional atom probe analysis to the characterisation of layered magnetic materials, including details of specimen preparation techniques required for this type of analysis. Recent results are presented on the characterisation of interfaces in Co/Cu or CoFe/Cu multilayers, which form part of the read sensor in magnetic recording heads, and Co/Pd multilayers, which are being considered for use as perpendicular recording media

[en] This study describes the equipment implementation of a mobile gamma spectrometry unit using LaBr3 detectors and the process followed to obtain a radiological map of Catalonia (Spain). The mobile unit consists of two 2”x2” LaBr3 scintillation detectors mounted on the top of a 4x4 car. To obtain the preliminary map, the extension of Catalonia was divided in 1425 cells of 5x5 km2. Before starting the measurements, we planned a route to ensure a proper distribution and a minimum quantity of spectra within each cell. The car is equipped with a portable computer to control spectra acquisition and a GPS system that associates a position to each spectrum. Each spectrum is stabilised and calibrated. During the acquisition, the computer placed inside the car shows, in real-time, the value of the ambient dose equivalent and the exact location. Therefore, when the software obtains an unexpected high value, the driver of the car can modify the route to acquire more spectra of the area. The first data set of measurements included 70000 spectra obtained during stable weather conditions and represent the preliminary results of the radiological map, as other data campaigns are currently under preparation. In this study, we present the ambient dose equivalent map of Catalonia and isotopic information of interest, such as punctual detections of 137Cs and 131I and other radionuclides. The origin of these detections is analysed and explained in detail.

[en] An instrument has been developed which is capable of determining the chemical identity and position of atoms within a volume of order (20 nm)³ in a material. Called the position-sensitive atom probe (POSAP), the instrument combines time-of flight mass spectrometry and position-sensitive detection, in the configuration of a short flight path atom probe field-ion microscope. The POSAP makes it possible to reconstruct the three-dimensional nanometre-scale compositional variations in materials, and look at interfaces with sub-nanometre resolution. Apart from the gain in spatial resolution over atom probe analysis in previous designs, the POSAP opens up the possibility of totally new methods of characterisation, based on the morphology of phase microstructure on this scale. The three-dimensional data can also be compared directly with the results of modelling the atomic-scale processes occurring during the ageing of alloys. (author)

[en] Full text of publication follows: Irradiation can induce significant changes on the stability of alloys, such as precipitation in under-saturated solid solutions, precipitate dissolution, anti-coarsening. This paper revisits the formation of Cr-rich precipitates under irradiation conditions in Fe-3-12 at.% Cr alloys as the binary Fe-Cr system is a model system for the low-activation ferritic and ferritic/ martensitic alloys considered as potential structural materials in fusion reactors. The close atomic mass of Fe and Cr and the small strains associated with Cr in Fe make nano-scale chemical variations and small clusters undetectable by current electron microscopy techniques. Atom probe tomography is therefore the technique of choice to study the changes in the Cr distribution induced by irradiation. This paper reports preliminary atom probe tomography results obtained on heavy-ion irradiated binary Fe-3-12at.%Cr alloys indicating Cr clustering even for the lowest Cr-content alloy. (authors)

[en] Partitioning behaviour of alloying elements during the primary crystallisation of both Fe₁₈Co₆₀Nb₆B₁₆ and Fe₃₉Co₃₉Nb₆B₁₅Cu₁ alloys has been studied using three-dimensional atom probe (3DAP). Cu rich clusters were found in the Cu-containing alloy, and they provided nucleation sites for the primary α-Fe(Co) particles. In the Cu clusters, concentration of both Fe and Co was greatly decreased. In both Cu-containing and Cu-free alloys Nb and B were depleted in the α-Fe(Co) particles and enriched in the remaining amorphous phase. However, Co concentration in the α-Fe(Co) was the same as the remaining amorphous phase. Based on the 3DAP analysis, the phase volume fraction has been estimated

[en] The microstructure and phase chemistry of melt-spun nanocomposite Pr_9.7Fe_76.6Co_7.8B_5.9 and Pr_9.2Fe_69.4Co_15.4B_6.0 ribbons have been studied using three-dimensional atom probe (3DAP) and transmission electron microscopy. The microstructure of these alloys consists of two phases, bcc α-Fe--Co and tetragonal Pr₂(FeCo)₁₄B. Practically all of the B and Pr atoms are rejected from the α-Fe--Co phase and are concentrated into the 2/14/1 hard magnetic phase. However, no significant difference of Co concentration between the two phases is observed. From the measured Co concentration in the 2/14/1 phase, it is explained why the effect of Co content on Curie temperature (T_c) is greater in the nanocomposite alloys than in single phase alloys. Predictions of T_c for the nanocomposite alloys based on the 3DAP composition data show excellent agreement with experimental measurements. Copyright 2001 American Institute of Physics

[en] The Catalan Environmental Radiological Surveillance Network consists of different types of scintillation gamma spectrometry detectors for the continuous and real-time automatic measurement of environmental radiation. The Network has a total of 35 monitors that obtain spectra every 10 minutes: 23 direct measurement monitors (13 with LaBr3(Ce), 5 SrI2(Eu) and 5 NaI (Tl) detectors), 10 particulate filter monitors (9 with LaBr3(Ce) detectors and 1 with SrI2(Eu)) and 2 river water monitors. A method for the automatic and real-time quantification of the activity concentration of artificial, natural and NORM isotopes was developed and tested in the laboratory. The uncertainties in the activity concentrations, as well as the corresponding detection limits, were calculated applying the ISO-11929 standard. The developed and validated method that is exposed in the present study will be implemented shortly in all the stations of the Network. The method is based on the analysis by spectral regions or ROIs (Regions of Interest). The method eliminates from the ROIs of the artificial (or NORM) isotopes of study the contributions due to emissions of natural isotopes (overlapping and Compton radiation), the ambient background, the possible intrinsic background of the detector and the contributions of other possible isotopes. As a result, an equation is generated for each isotope that allows us to obtain its net activity concentration (Bq/m3). This procedure is applied to determine the activity concentration of isotopes of natural origin (212Pb, 214Pb and 214Bi), artificial (131I, 137Cs and 60Co) and NORM (234Th). The method successfully eliminates the contribution of natural elements, intrinsic background and Compton contribution, both in situations with high and low activity of natural isotopes. Therefore, it allows obtaining the net activity concentration of the artificial isotopes of interest and eliminates the presence of false positives that could be produced by the presence of natural isotopes.

[en] Atom probe tomography (APT) analysis and hardness measurements have been used to characterise the early stages of precipitation in three Al–Mg–Si alloys with different Cu contents (Al–0.51 at.%Mg–0.94 at.%Si, with 0.01 at.%, 0.06 at.%, or 0.34 at.% Cu). A range of single and multi- stage heat treatments were chosen to evaluate the changes in precipitation processes. Three ageing temperatures were investigated, 298 K (natural ageing), 353 K (pre-ageing) and 453 K (automotive paint-bake conditions). The Cu content had significant effects on the microstructural evolution within the alloy. Formation of clusters which can act as precursors of elongated precipitates during paint-baking was found to be enhanced with increasing Cu content. This improved the paint-bake hardening response and mitigated the deleterious effects of natural ageing. Cu was present in all precipitates in the highest Cu-containing alloy. These precipitates were believed to be precursors to the Q′ phase. Mechanisms for the effects of Cu on precipitation kinetics are proposed.