Author Correction: New insights into microstructure of irradiated beryllium based on experiments and computer simulations.

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New insights into microstructure of irradiated beryllium based on experiments and computer simulations.

The microstructural response of beryllium after neutron irradiation at various temperatures (643-923 K) was systematically studied using analytical transmission electron microscope that together with outcomes from advanced atomistic modelling provides new insights in the mechanisms of microstructural changes in this material. The most prominent feature of microstructural modification is the formation of gas bubbles, which is revealed at all studied irradiation temperatures. Except for the lowest irradiation temperature, gas bubbles have the shape of thin hexagonal prisms with average height and diameter increasing with temperature. A high number density of small bubbles is observed within grains, while significantly larger bubbles are formed along high-angle grain boundaries (GB). Denuded zones (DZ) nearly free from bubbles are found along both high- and low-angle grain boundaries. Precipitations of secondary phases (mainly intermetallic Al-Fe-Be) were observed inside grains, along dislocation lines and at GBs. EDX analysis has revealed homogeneous segregation of chromium and iron along GBs. The observed features are discussed with respect to the available atomistic modelling results. In particular, we present a plausible reasoning for the abundant formation of gas bubbles on intermetallic precipitates, observation of various thickness of zones denuded in gas bubbles and precipitates, and their relation to the atomic scale diffusion mechanisms of solute-vacancy clusters.

First simultaneous detection of helium and tritium inside bubbles in beryllium.

Electron energy loss spectroscopy (EELS) was applied to detect and analyze quantitatively helium (He) and tritium (3H) enclosed inside bubbles in irradiated beryllium. Both gases were formed in beryllium under neutron irradiation as a consequence of neutron-induced transmutation reactions. They were detected for the first time as pronounced peaks at 13.0 eV for 3H and 22.4 eV for He in EELS spectra collected from flat hexagonal bubbles. An adhesion of 3H or formation of thin beryllium hydride layers on the internal basal surfaces was observed. The number densities of both gases were estimated using electron scattering cross-section and intensities obtained from EELS spectra. The number density values estimated for various bubbles fluctuate from 4 to 15 at/nm3 for He and from 4 to 10 molecules/nm3 for 3H2. Lower gas number density was measured inside large bubbles. The observed higher density of tritium at inner walls of bubbles seems to confirm very recent ab initio calculations of the interaction of hydrogen isotopes with beryllium surfaces.