Entwicklung und Validierung neuartiger Ansätze zur verlässlichen Datenanalyse in der digitalen Positronenlebensdauerspektroskopie (PALS)

Die Positronenlebensdauerspektroskopie (PALS) ist eine hoch-sensitive Methode zur zerstörungsfreien Untersuchung der Mikrostruktur in den verschiedensten Klassen von Materialien. Da die akkurate Zerlegung der Lebensdauerspektren ein schlecht konditioniertes Problem beschreibt, bedarf ihre quantitative Analyse als wesentliche Voraussetzung der Aufnahme qualitativ hochwertiger Daten. Dazu wurden im Rahmen dieser Arbeit zwei softwareseitige Ansätze unter Verwendung eines digitalen Setups verfolgt, wobei beide Ansätze eine vergleichbare Spektrenqualität liefern. Die Basis hochqualitativer Lebensdauerspektren ermöglichte es ferner, einen neuartigen Ansatz zur Auswertung heranzuziehen, der sich von den herkömmlichen Analysemethoden in der PALS grundlegend unterscheidet. Die Verwendung eines k-NN Klassifikators erlaubt dabei eine quantitative Betrachtung ab einer Statistik von 5000 Ereignissen, was zukünftig bereits mit einem Laborsetup eine in-situ Charakterisierung realisierbar macht.Positron-Annihilation-Lifetime-Spectroscopy (PALS) provides a powerful technique for non-destructive microstructure investigations in a broad field of material classes. Since the accurate decomposition of lifetime spectra describes an ill-conditioned problem, their quantitative analysis requires high-quality data acquisition as an essential prerequisite. This was realized in the present work by two software-based approaches using a digital setup, with both techniques providing comparable spectra quality. The basis of high-quality lifetime spectra enabled a novel approach to be used for analysis, which is fundamentally different from conventional analysis methods in PALS. Exploiting k-NN classification has demonstrated a feasible analysis starting from a statistic of 5000 events. In the future, this enables a quantitative in-situ characterization by using laboratory setup

Update (v1.3) to DLTPulseGenerator: A library for the simulation of lifetime spectra based on detector-output pulses

In the last two updates v1.1 and v1.2 of DLTPulseGenerator library, we provided the simulation of distributed specific lifetimes and the simulation of lifetime spectra consisting of non-Gaussian distributed and linearly combined Instrument Response Functions (IRF). In this update v1.3, the DLTPulseGenerator library was modified to account for additional hardware influences, which significantly modify the ideal shape of a detector output-pulse defined previously by a log-normal distribution function. These influences mainly originate from the electronic parts, which accomplish the conversion of the analog voltage signal into digital numbers, i.e. the A/D converter (ADC). Eventually, this provides the modeling of authentic detector output-pulses, which leads to a spectra simulation under more realistic conditions

Update (v1.2) to DLTPulseGenerator: A library for the simulation of lifetime spectra based on detector-output pulses

In the last update of DLTPulseGenerator library (v1.1), we realised the simulation of distributed specific lifetimes as can be found for the lifetimes of positrons (PALS) in porous materials due to the pore size distribution.However, in this update v1.2, the DLTPulseGenerator library was modified to allow the simulation of lifetime spectra consisting of non-Gaussian distributed and linearly combined Instrument Response Functions (IRF), since a Gaussian shaped instrumental response of a lifetime spectroscopy setup more likely represents an approximation as it reflects the experimentally obtained results. Eventually, this provides an improved modeling of the experimental instrumental response and, finally, leads to a more realistic simulation of lifetime spectra

DDRS4PALS: a software for the acquisition and simulation of lifetime spectra using the DRS4 evaluation board

Lifetime techniques are applied to diverse fields of study including materials sciences, semiconductor physics, biology, molecular biophysics and photochemistry. Here we present DDRS4PALS, a software for the acquisition and simulation of lifetime spectra using the DRS4 evaluation board (Paul Scherrer Institute, Switzerland) for time resolved measurements and digitization of detector output pulses. Artifact afflicted pulses can be corrected or rejected prior to the lifetime calculation to provide the generation of high-quality lifetime spectra, which are crucial for a profound analysis, i.e. the decomposition of the true information. Moreover, the pulses can be streamed on an (external) hard drive during the measurement and subsequently downloaded in the offline mode without being connected to the hardware. This allows the generation of various lifetime spectra at different configurations from one single measurement and, hence, a meaningful comparison in terms of analyzability and quality. Parallel processing and an integrated JavaScript based language provide convenient options to accelerate and automate time consuming processes such as lifetime spectra simulations

Update (v1.1) to DLTPulseGenerator: A library for the simulation of lifetime spectra based on detector-output pulses

In this update, the DLTPulseGenerator library was extended to allow the simulation of spectra consisting of non-discrete and distributed specific lifetimes, which follow a Gaussian, Lorentzian/Cauchy or Log-Normal distribution function. Typically, distributions of specific lifetimes are found for the lifetimes of positrons in porous materials due to the pore size distributions

DLTPulseGenerator: a library for the simulation of lifetime spectra based on detector-output pulses

The quantitative analysis of lifetime spectra relevant in both life and materials sciences presents one of the ill-posed inverse problems and, hence, leads to most stringent requirements on the hardware specifications and the analysis algorithms. Here we present DLTPulseGenerator, a library written in native C++ 11, which provides a simulation of lifetime spectra according to the measurement setup. The simulation is based on pairs of non-TTL detector output-pulses. Those pulses require the Constant Fraction Principle (CFD) for the determination of the exact timing signal and, thus, the calculation of the time difference i.e. the lifetime. To verify the functionality, simulation results were compared to experimentally obtained data using Positron Annihilation Lifetime Spectroscopy (PALS) on pure tin

Data on pure tin by Positron Annihilation Lifetime Spectroscopy (PALS) acquired with a semi-analog/digital setup using DDRS4PALS

Positron annihilation lifetime spectroscopy (PALS) provides a powerful technique for non-destructive microstructure investigations in a broad field of material classes such as metals, semiconductors, polymers or porous glasses. Even though this method is well established for more than five decades, no proper standardization for the used setup configuration and subsequent data processing exists. Eventually, this could lead to an insufficiency of data reproducibility and avoidable deviations. Here we present experimentally obtained and simulated data of positron lifetime spectra at various statistics measured on pure tin (4N-Sn) by using a semi-analog/digital setup, where the digital section consists of the DRS4 evaluation board, “Design and performance of the 6 GHz waveform digitizing chip DRS4” [1]. The analog section consists of nuclear instrument modules (NIM), which externally trigger the DRS4 evaluation board to reduce the digitization and, thus, increase the acquisition efficiency. For the experimentally obtained lifetime spectra, 22Na sealed in Kapton foil served as a positron source, whereas 60Co was used for the acquisition of the prompt spectrum, i.e. the quasi instrument response function. Both types of measurements were carried out under the same conditions. All necessary data and information regarding the data acquisition and data reduction are provided to allow reproducibility by other research groups

The Li stance on precipitation in Al–Li-based alloys: an investigation by X-ray Raman spectroscopy

Decomposition and precipitation processes in a binary Al–Li alloy and a technical Al–Li–Cu–Mg alloy were investigated using differential scanning calorimetry and X-ray Raman spectroscopy (XRS). The formation of ’ and T1 precipitates in the Al–Li and the T8 heat-treated Al–Li–Cu–Mg alloy, respectively, was confirmed using DSC. The XRS measurements complemented by simulated spectra allowed for probing specifically Li and its environment within the Al matrix. Based on linear combination fits of the XRS spectra, the relative contributions of ′ and T1 precipitates were quantified. These results are in agreement with estimates of the relative amount of Li taking part in the precipitation process. Difficulties and limitations of the application of XRS to Al alloy systems are also discussed