1. The effect of nanocrystalline microstructure on deuterium transport in displacement damaged tungstenSabina Markelj, Thomas Schwarz-Selinger, Mitja Kelemen, Esther Punzón Quijorna, Janez Zavašnik, Andreja Šestan, David Dellasega, Gabriele Alberti, Mateo Passoni, 2023, izvirni znanstveni članek Povzetek: The influence of grain boundaries (GBs) on the deuterium (D) transport and the creation of defects in nanocrystalline tungsten (W) films deposited on a W substrate was studied. Samples with three different grain sizes were produced for this purpose: a sample with a film having nanometer-size grains, a sample with hundred nanometer-grained film and a sample with micrometer-grained film. Samples were irradiated by 20 MeV W ions at 300 K to create displacement damage and exposed to 300 eV D ions at 450 K to populate the created and any pre-existing defects. The D transport and retention was assessed by measuring D depth profiles after certain exposure times by nuclear reaction analysis (NRA) using a 3He ion beam. From the final D concentration in the damaged area we could determine the concentration of defects that trap hydrogen, showing that the sample with the smallest grain size had the highest D concentration and it decreases with the increase of the grain size. Therefore, in nanocrystalline tungsten irradiated at 300 K, GBs do not improve radiation resistance, which would lead to fewer defects. For the first time, we show experimentally, that D transport is faster inside the nanometer-grained sample as compared to the micrometer-grained sample, meaning that D atoms have enhanced bulk diffusion along GBs. Accidentally, the film thickness was so thin that the W irradiation reached the interface between the W film and substrate, where NRA showed enhanced retention of oxygen. At that depth, two times higher D concentration was observed compared to D concentration in the damaged area in the middle of the film indicating on defect stabilization due to the presence of oxygen.
Ključne besede: grain boundaries, deuterium, tungsten, transport, displacement damage
Objavljeno v DiRROS: 12.12.2025; Ogledov: 753; Prenosov: 472
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2. Deuterium retention and transport in ion-irradiated tungsten exposed to deuterium atoms : role of grain boundariesSabina Markelj, Janez Zavašnik, Andreja Šestan, Thomas Schwarz-Selinger, Mitja Kelemen, Esther Punzón Quijorna, Gabriele Alberti, Mateo Passoni, David Dellasega, 2024, izvirni znanstveni članek Povzetek: The influence of grain boundaries on deuterium (D) retention and transport was investigated in nanocrystalline tungsten (W) by exposing the samples to sub eV D atoms. Thin tungsten films with nanometer-sized grains were produced by pulsed laser deposition on tungsten substrates. Their grain size was increased up to one micrometer by thermal annealing in vacuum up to 1223 K. Irradiation damage was created by 20 MeV W ions at 290 K. The transmission electron microscopy analysis showed one order of magnitude larger dislocation density in nanometer-grained samples compared with the larger-grained samples. The samples were after W irradiation exposed to 0.3 eV D atoms at 600 K. D retention and D depth profiles were measured by nuclear reaction analysis. In the as-deposited nanometer-grained samples, D populated the damaged region more than three times faster than in the samples with larger grains, indicating that grain-boundaries increase D transport through the material. The concentration of defects was assessed by the final D concentration in the samples. The sample with a smallest grain size showed slightly larger D concentration in the irradiated area, but the difference in the D concentration is not substantial between different-grained samples. A large D concentration in the non-irradiated nanometer-grained sample was measured which is an indication for a high defect density in the initial material. From our observations, it can be postulated that the nanocrystalline microstructure did not substantially influence the generation of irradiation-induced defects by defect annihilation at grain boundaries.
Ključne besede: deuterium, tungsten, grain boundaries, transport, displacement damage, retention
Objavljeno v DiRROS: 12.12.2025; Ogledov: 730; Prenosov: 530
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3. Influence of near-surface helium on the deuterium retention and uptake in tungstenSabina Markelj, Thomas Schwarz-Selinger, Andreja Šestan, Janez Zavašnik, Mitja Kelemen, 2025, izvirni znanstveni članek Povzetek: The effect of near-surface helium (He) on deuterium (D) retention and uptake into the bulk of tungsten (W) was investigated. To quantify the He influence on D uptake, He was implanted close to the surface with 3 keV energy at different fluences and different temperatures. 20 MeV W irradiation was performed at room temperature after He implantation to create defects within the first 2.3 µm. Samples were then exposed to a low flux, low energy (300 eV/D) D ion beam at 450 K. The defects created by W ions trap penetrating D and make it hence possible to quantify D transport into depth below the He layer using 3He nuclear reaction analysis. Elastic recoil detection analysis enabled us to measure the D and He concentration depth profiles near the surface. Results show that D gets preferentially retained where He is implanted with D concentrations up to 10 at.%. At the same time D uptake beyond the He zone is reduced by a factor of 15 compared to a He-free W sample.
Ključne besede: deuterium retention, displacement damage
Objavljeno v DiRROS: 11.12.2025; Ogledov: 778; Prenosov: 418
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4. Deuterium retention in tungsten, tungsten carbide and tungsten-ditungsten carbide compositesPetra Jenuš, Anže Abram, Saša Novak, Mitja Kelemen, Matic Pečovnik, Thomas Schwarz-Selinger, Sabina Markelj, 2023, izvirni znanstveni članek Povzetek: The selection of the most suitable material for the EU DEMO divertor is still underway. Current research focuses on the development of tungsten-based materials for plasma-facing applications. In addition to other requirements, the candidate material must also exhibit low intrinsic hydrogen isotope retention. To verify the suitability of the tungsten carbide-containing materials, we examined the effect of carbon in the form of carbide or free carbon on deuterium (D) retention. The samples were consolidated by Field Assisted Sintering (FAST) and examined in terms of phase composition and microstructure before the d-retention studies. The Nuclear Reaction Analysis (NRA) technique was used to determine the depth distribution of D after the exposure to D plasma (fluence of 1.3 × 1024 D/m2 and 1.3 × 1025 D/m2 and an exposure temperature of 370 K and 523 K, respectively). Thermal Desorption Spectroscopy (TDS) was used to measure the D desorption spectra. The surfaces of samples exposed to D plasma were also examined in terms of microstructure by scanning electron microscopy. The study has shown that apart from the d-fluence and exposure temperature, the materials’ composition plays a vital role in d-retention, accompanied by blisters and pillar formation. The lowest d-retention was observed for tungsten and the highest in the W-W2C composite. The blisters and pillars were formed in these two materials but not in the WC, which also contains free carbon. At higher D fluence, approximately 15 to 20-times more blisters and pillars were formed in the W-W2C composite than in the tungsten prepared by the same method. The results suggest that the number of defects causing higher d-retention is the highest in W-W2C. On the other hand, the absence of surface irregularities in the WC-C sample after D retention studies indicates that the cause for higher D retention does not lie in the carbides, but, presumably, the microstructural and crystal lattice defects govern the D retention in tungsten-tungsten carbide systems.
Ključne besede: tungsten, (di)tungsten carbide, deuterium, nuclear reaction analysis, thermal desorption spectroscopy
Objavljeno v DiRROS: 03.09.2025; Ogledov: 930; Prenosov: 526
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5. Characterizing the groundwater flow regime in a landslide recharge area using stable isotopes: a case study of the Urbas landslide area in NW SloveniaKatja Koren Pepelnik, Luka Serianz, Mitja Janža, 2022, izvirni znanstveni članek Povzetek: Slope stability strongly depends on the prevailing hydrological and hydrogeological conditions. The amount and intensity of precipitation and changing groundwater levels are important landslide triggering factors. Environmental tracers, including the chemical and stable isotope compositions of precipitation and groundwater, were used to gain insight into the groundwater dynamics of the Urbas landslide. The landslide is situated in a mountainous area with steep slopes and high precipitation amount and poses a high risk for the safety of the Koroška Bela settlement that lies downstream. The stable isotope analyses of oxygen-18 (18O) and deuterium (2H) in the precipitation and groundwater were used to estimate the groundwater mean residence time and the average altitude of the landslide recharge area. This information will help to plan and prioritize remedial landslide measures aiming to reduce the recharge of the landslide body and, thus, lower the risk of transformation of the sliding material into debris flow. The results of the chemical analysis of samples taken from springs and a piezometer show a Ca–HCO3 water type. This indicates low water–rock interaction in a landslide area composed of Upper Carboniferous and Permian clastic rocks and points to upper laying carbonate rocks and scree deposits as the main recharge area. Water samples for stable isotope analyses of δ18O and δ2H were collected from a rain gauge, springs, and a piezometer over a two-year period (2018–2020). The estimated mean recharge altitude of the groundwater at sampling points was from approximately 1700 to 1800 m a.s.l. with a mean residence time of 2–5 months.
Ključne besede: landslide, groundwater, stable isotopes, oxygen-18, deuterium, hydrogeology, recharge dynamic
Objavljeno v DiRROS: 16.03.2022; Ogledov: 3037; Prenosov: 996
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