V. Sabelová

Defect Detection in Fe-Cr Alloys with Positron Annihilation Doppler Broadening Spectroscopy

Positron annihilation Doppler broadening spectroscopy (DBS) has been used for the detection of structural defects in Fe-9wt%Cr (Fe-9Cr) alloy in the as-prepared and implanted states. Defects were created by He and H ion implantation with a kinetic energy of 250 keV. DBS is a non-destructive method and is a unique tool for the observation of open volume defects like vacancies and vacancy clusters in solids. A positron beam with variable positron energy was used for the measurement of defect depth profiles up to 1.5 µm. The obtained results provide qualitative and semi-quantitative information about radiation induced defects and their chemical environment. Although the collision damage from helium implantation was one order of magnitude higher than for the case of hydrogen, the changes in S and W parameters are much less significant, probably due to considerably lower mobility of helium in the implanted materials, which results in helium capture by the created open volume defects.

CDBTools - Evaluate Positron Annihilation Coincidence Doppler Broadening Spectrum

CDBTools is a lightweight and easy to use application designed to provide you with an analysis tool for coincidence Doppler broadening (CDB) of the positron annihilation energy spectrum files. This application enables you to analyze the CDB and ratio curves, plots as well as graphs representing the evolution of the orbital electron momentum spectrum. The CDB extraction is provided by selectable filters applied at the diagonal line of the input matrix. To achieve CDB ratio curves with minimal error caused by 511keV peak shift, spectrum curves are recalculated by penalized regression spline.

PALS combined with Charpy-V tests at WWER reactor pressure vessel steels

This paper presents results from our long-term studies of irradiated, commercially used WWER reactor pressure vessel steels. Results from Charpy-V tests and positron annihilation spectroscopy techniques are compared and discussed in details, having in mind actual state of art and other microstructural studies in this area. The optimal region for annealing of irradiation induced defects was analyzed. It was shown that WWER steel with low impurity contents has good radiation stability and operation these reactor pressure vessels could be extended beyond a design lifetime.

QtCDB2 software for coincidence Doppler broadening measurement system

A digital system for the coincidence measurement of Doppler Broadening of positron annihilation (CDB) has been changed to one which is fully software based. Spectrometer is based on two HpGe detectors, HV sources and PC with PCI-9820D digitizer. Detector pulses are digitized directly at the HpGe detector pre-amplifier outputs. The previous external trigger chain was replaced by data processing system with a software trigger. All pulses from detectors are processed by a trapezoid filter. Spectrometer performance was tested and compared in various conditions.

Positron Annihilation Measurements Performed on Oxide-Dispersion Strengthened Steels

This paper is focused on investigation of oxide-dispersion strengthened steels in a basic state (before an experimental treatment) by two positron annihilation techniques – positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy. Three high chromium commercial steels – MA 956, MA 957 and PM 2000 were measured in order to identify and quantify defects in samples as well as to demonstrate defect depth profile in subsurface layers up to 1.6µm. Results indicate presence of di-vacancies in PM 2000, three-vacancies in MA 956 and six-vacancies together with dislocations in MA 957. Positron techniques were supplemented by scanning electron microscopy, which demonstrated also presence of larger defects as pores and different density of precipitates.

Software for Digital Coincidence Doppler Broadening Setup

An advanced digital measurement system for Coincidence Doppler broadening (CDB) technique is presented. Traditional CDB setups are based on shaping amplifiers and multi parameter multi-channel analyzers (MCA). We replaced them by 14-bit data acquisition card (DAQ). Replacing multi-parameter MCA by DAQ was realized also by several groups before, but in our setup the signal shaping tasks are performed digitally by software in a personal computer. Signals from high purity (HP) Ge detectors are sampled at preamplifier outputs. Pulse shaping is realized by a trapezoidal filter.

Thermal Annealing Influence on Ions Implanted Fe-Cr Model Alloys

Abstract. Binary Fe-11.62wt%Cr alloys were investigated in as-received state as well as after a two step helium ion implantation at different energies (100 keV and 250 keV) with doses up to 3.12×1018 cm-2. In order to study changes in alloys in dependence on the temperature, thermal annealing was performed at temperatures of 400, 475, 525 and 600 °C and specimens were afterwards measured by a pulsed low energy positron system (PLEPS). Annealing out of defects at lower temperatures was not as significant as expected, and we also encountered difficulties with defect identification. However, an apparent decrease of defect size was observed in the specimen annealed at a temperature of 600 °C.