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Optimization of Positron-Lifetime Measurement Geometry Based on Geant4 Simulation

100%
Saro M., Petriska M., Slugeň V.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1634-1636
EN
Proper choice of measuring geometry and experimental setup of nuclear instrumentation modules and photomultipliers is a key element which affects substantial positron lifetime measurement properties: count rate and time resolution. An adequate compromise must be found, when it comes to geometry of measurement. The optimal geometry using three detector layout is inspected in this paper. During our work, we concentrated on the simulation of XP2020Q photomultipliers and the BaF₂ scintillator material. The Geant4 simulation allows to estimate an influence of the measuring geometry on detection efficiency and to choose the most appropriate crystals dimensions and positions. As mentioned in paper of Bečvaŕ et al., slight changes in geometry result in distortion or improvement of measured results. Experimental results already showed, changes of start crystals dimensions can result in significant increase in count rate of three-detector measurement.
2
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Effect of the Initial Microstructure on Defect Evolution in Neutron Irradiated Fe-Cr-C Alloys

88%
Brodziansky T., Slugeň V., Sojak S., Petriska M., Konstantinović M.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1590-1592
EN
The irradiation-induced evolution of vacancy type defects in various iron-chromium model alloys and high chromium ferritic/martensitic steels have been studied using coincidence Doppler broadening spectroscopy. Specimens were neutron irradiated to 0.11 dpa at two different temperatures, 290°C and 450°C. It has been found that the microstructure (ferrite vs. ferrite/martensite), more precisely distribution of dissolved carbon within the matrix, is one of the key factor that affect response of the materials to neutron irradiation. Presence of dissolved carbon within the matrix leads to formation of stable and immobile carbon-vacancy complexes which act as traps for irradiation induced vacancies and therefore, leading to increased formation of vacancy clusters. Impact of carbon-vacancy complexes on defects evolution during neutron irradiation is relevant only for certain irradiation temperatures.
3
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German and Russian Irradiated Reactor Pressure Vessel Steels from PAS Point of View

64%
Slugeň V., Hein H., Sojak S., Pecko S., Šimeg Veterníková J., Petriska M., Sabelová V., Bartošová I., Stacho M.
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vol. 125
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issue 3
726-728
EN
This paper presents a comparison of commercially used German and Russian reactor pressure vessel steels from the positron annihilation spectroscopy point of view, having in mind knowledge obtained also from other techniques from the last decades. The second generation of Russian reactor pressure vessel steels seems to be fully comparable with German steels and their quality allows prolongation of NPP operating lifetime over projected 40 years. The embrittlement of CrMoV steels is very low due to the dynamic recovery of radiation-induced defects at reactor operating temperatures. Positron annihilation spectroscopy techniques can be effectively applied for evaluation of microstructural changes caused by extreme external loads by proton implantation, with aim to simulate irradiation and for the evaluation of the effectiveness of post-irradiation thermal treatments. We used our actual and previous results, collected during last 20 years from measurements of different reactor pressure vessel steels in "as received", irradiated and post-irradiation annealed state and compare them with the aim to contribute to general knowledge based on experimental positron annihilation spectroscopy data.
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