Positron annihilation lifetime spectroscopy at a superconducting electron accelerator

The Helmholtz-Zentrum Dresden-Rossendorf operates a superconducting linear accelerator for electrons with energies up to 35 MeV and average beam currents up to 1.6 mA. The electron beam is employed for production of several secondary beams including X-rays from bremsstrahlung production, neutrons, and positrons. The secondary positron beam after moderation feeds the Monoenergetic Positron Source (MePS) where positron annihilation lifetime (PALS) and positron annihilation Doppler-broadening experiments in materials science are performed in parallel. The adjustable repetition rate of the continuous-wave electron beams allows matching of the pulse separation to the positron lifetime in the sample under study. The energy of the positron beam can be set between 0.5 keV and 20 keV to perform depth resolved defect spectroscopy and porosity studies especially for thin films

Positron annihilation lifetime spectroscopy at a superconducting electron accelerator

The Helmholtz-Zentrum Dresden-Rossendorf operates a superconducting linear accelerator for electrons with energies up to 35 MeV and average beam currents up to 1.6 mA. The electron beam is employed for production of several secondary beams including X-rays from bremsstrahlung production, neutrons, and positrons. The secondary positron beam after moderation feeds the Monoenergetic Positron Source (MePS) where positron annihilation lifetime (PALS) and positron annihilation Doppler-broadening experiments in materials science are performed in parallel. The adjustable repetition rate of the continuous-wave electron beams allows matching of the pulse separation to the positron lifetime in the sample under study. The energy of the positron beam can be set between 0.5 keV and 20 keV to perform depth resolved defect spectroscopy and porosity studies especially for thin films

Positron annihilation lifetime spectroscopy at a superconducting electron accelerator

The Helmholtz-Zentrum Dresden-Rossendorf operates a superconducting linear accelerator for electrons with energies up to 35 MeV and average beam currents up to 1.6 mA. The electron beam is employed for production of several secondary beams including X-rays from bremsstrahlung production, neutrons, and positrons. The secondary positron beam after moderation feeds the Monoenergetic Positron Source (MePS) where positron annihilation lifetime (PALS) and positron annihilation Doppler-broadening experiments in materials science are performed in parallel. The adjustable repetition rate of the continuous-wave electron beams allows matching of the pulse separation to the positron lifetime in the sample under study. The energy of the positron beam can be set between 0.5 keV and 20 keV to perform depth resolved defect spectroscopy and porosity studies especially for thin films

Vývoj radiačního poškození v čistém W a slitině W-Cr-Hf způsobené 5 MeV Au ionty v širokém rozsahu dpa

Čistý W a slitina W-Cr-Hf, které jsou perspektivními materiály pro jaderné fúzní reaktory, jako je DEMO, byly ozářeny při pokojové teplotě 5 MeV ionty Au2+ s dávkami mezi 4 × 10e14 a 1,3 × 10e16 ionty.cm-2 za účelem vytvoření různých úrovní poškození mřížky od jednotek až po desítky dpa. Odlišný charakter akumulace radiačního poškození, mikrostruktura a povaha defektů byly pozorovány u čistého W i slitin W-Cr-Hf, přičemž tyto slitiny vykazovaly zajímavou schopnost reorganizace poškození a snížení velikosti defektu při vyšších dávkách iontů, jak bylo stanoveno pozitronovou anihilační spektroskopií. (PAS). Vysoká míra radiačního poškození v ozařované vrstvě byla prokázána ve vzorcích W již při nižších dávkách Au-iontů ve srovnání se vzorky W-Cr-Hf, kde se poškození stupňovitě zvyšovalo s rostoucí dávkou Auiontů. Zřetelná akumulace defektů byla doprovázena odlišnou distribucí implantovaných Au-iontů v ozařované vrstvě stanovenou sekundární iontovou hmotnostní spektrometrií (SIMS), stejně jako tepelné vlastnosti ukázaly následné zhoršení hloubky v dobré shodě s Au koncentračními hloubkovými profily. TEM potvrdila výše uvedená zjištění, kde podpovrchová vrstva vykazovala po ozáření uvolnění defektů, maximum hustoty dislokační smyčky bylo identifikováno v hloubce podle predikovaného maxima dpa (posun částic na atom) pro nižší dávku Au-iontů. Kromě toho TEM ukazuje, že struktura pásu hustoty dislokací se objevila ve vzorcích W-Cr-Hf vykazujících pásmo defektů s vysokou hustotou podle projektovaného rozsahu Au-iontů současně s další vrstvou s většími izolovanými dislokacemi vyjádřenými ve větší hloubce jako rostoucí funkce dávky Au-iontů. Takový jev nebyl u W vzorků pozorován.Pure W and W-Cr-Hf alloy which are prospective materials for nuclear fusion reactors, such as DEMO, were irradiated at room temperature with 5 MeV Au2+ ions with fluences between 4 × 10e14 and 1.3 × 10e16 ions.cm-2 to generate various levels of lattice damage from about units up to tens of dpa. The distinct character of radiation damage accumulation, microstructure and defect nature have been observed in both pure W and W-Cr-Hf alloys, the latter exhibited interesting ability of damage reorganisation and defect size decrease at the higher ion fluences as determined by positron annihilation spectroscopy (PAS). High radiation damage rate in the irradiated layer has been evidenced in the W samples already at the lower Au-ion fluences compared to W-Cr-Hf samples, where the damage increased in steps with the increasing Au-ion fluence. The distinct defect accumulation was accompanied with the different Au-ion implanted distribution in the irradiated layer determined by Secondary Ion Mass Spectrometry (SIMS) as well as the thermal properties have shown the consequent worsening in the depth in good agreement with the Au-depth concentration profiles. TEM corroborated above mentioned findings, where the sub-surface layer exhibited defect release after the irradiation, the maximum of dislocation loop density has been identified in the depth according the predicted dpa (displacement particles per atom) maximum for the lower Au-ion fluences. Moreover, TEM shows the dislocation density band structure appeared in W-Cr-Hf samples exhibiting the high density defect band according the projected range of the Au-ions simultaneously with the additional layer with larger isolated dislocations pronounced in the higher depth as a growing function of Au-ion fluence. Such phenomenon was not observed in W samples