Modeling of H/D isotope-exchange in crystalline beryllium

Matveev, D.; Linsmeier, Ch.; Dittmar, T.; Hansen, P.; Koslowski, H. R.

doi:10.1016/j.nme.2019.100682

Journal Article

FZJ-2019-03040

Modeling of H/D isotope-exchange in crystalline beryllium

Matveev, D. (Corresponding author)FZJ* ; Hansen, P.FZJ* ; Dittmar, T.FZJ* ; Koslowski, H. R.FZJ* ; Linsmeier, C.FZJ*

2019
Elsevier Amsterdam [u.a.]

Nuclear materials and energy 20, 100682 - (2019) [10.1016/j.nme.2019.100682]

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Please use a persistent id in citations: http://hdl.handle.net/2128/22208 doi:10.1016/j.nme.2019.100682

Abstract: A reaction-diffusion model with surface occupation dependent desorption [D. Matveev et al., Nucl. Instr. Meth. B 430 (2018) 23–30] has been updated to handle multiple hydrogen species to simulate hydrogen/deuterium isotope-exchange experiments performed on polycrystalline beryllium samples under ultra-high vacuum laboratory conditions. In the experiments subsequent exposures of a sample to hydrogen and deuterium ion beams in direct and reverse implantation order were followed by thermal desorption spectroscopy measurements under a constant heating rate of 0.7 K/s. The recorded signals of masses 2 to 4 (H2, HD and D2) indicate that the second implanted isotope dominates clearly the low temperature release stage ( ≈ 450 K), while both isotopes show a comparable contribution to the high temperature desorption stage ( ≈ 700 K) with only minor effect of the implantation order attributed to a slightly deeper penetration of deuterium compared to hydrogen. Simulations of the implantation and subsequent thermal desorption of hydrogen isotopes are performed to assess the atomic processes behind the isotope-exchange. Simulations were performed under the assumption that the low temperature release stage is attributed to hydrogen/deuterium atoms retained on effective open surfaces (e.g. interconnected porosity) represented in the simulations by a surface with an effective surface area exceeding the nominal exposed surface area by a factor up to 100. Kinetic de-trapping from vacancies with multiple trapping levels and enhanced desorption at surface coverages close to saturation are addressed in the model as possible mechanisms promoting the isotope-exchange. Simulation results suggest the applicability of the model to describe isotope-exchange processes in crystalline beryllium and give a qualitative explanation of the observed experimental facts.

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