Diffusivity of 3He atoms in perfect tungsten crystals

Abstract

The diffusivity of 3 He atoms in perfect crystals of tungsten has been studied employing the atomprobe field-ion microscope (FIM) technique. Tungsten FIM specimens were implanted in situ with 300-eV 3He+ ions, to a fluence of 3 X lOIS ions cm -2, at specimen temperatures which ranged from 60 to 110 K. The 3He + ion beam was analyzed magnetically and the ion source was connected to the atom probe through a differentially pumped aperture. At an implantation energy of 300 eV no radiation damage was produced by the implanted 3He atoms. Thus, the state of a tungsten specimen after an implantation consisted of 3 He atoms with an initial depth distribution that was determined solely by the range profile of the low-energy ions. Isothermal annealing experiments between 90 and 110 K were employed to study the kinetics of recovery of the implanted 3He atoms; at 60 K the 3He atoms are immobile. This data, in combination with a suitable diffusion model, was used to determine-for the first time-the diffusivity [D'He (T)] and the enthalpy change of migration of 3 He atoms (.::1h ~e ) in tungsten. The quantity D'He(T) is given by the Arrhenius expression: D'He(T) = (5.4 ± ~086)x 10-3 exp( -0.28 eV /kT}cm2 S-I.The value of.::1h ~e is approximately the same as for.::1h ~e (0.24--0.32 eV). D'He (T) is compared with the diffusivity values of IH and self-interstitial atoms in tungsten-the self-interstitial atoms are considerably more mobile than 3He or 4He atoms at the same temperature, as are the IH atoms.

The Depths of Hydrogen and Helium Bubbles in Tungsten: A Comparison

“…35,68,69 Experimental data on the interstitial lattice location of helium in metals are scarce. However, atomistic simulations of helium atoms in several BCC metals~vandium, iron, molybdenum, and tungsten!…”

“…2 E, where E is the energy of the incident atom and m 1 , m 2 are the masses of the lattice atom and the projectile, respectively. 35 72#, the minimum helium energy for damage production is E ϭ 503 6 12 eV. Because of the closeness of the ion energy value of 510 eV to the threshold energy, we first checked with SRIM~Ref.…”

“…Experimentally determined migration prefactors and activation energies for hydrogen and helium were used. 30,35 Initially, several square side lengths were tried. In the end, minimum lengths for which the bubble depths remained approximately constant were chosen for the high-fluence simulations.…”

Helium Nano-Bubble Evolution in Aging Metal Tritides

“…Thus, this shape is likely a consequence of this discreet nature of the nucleation process and the fact that the bubbles are immobile. A useful fit to this normalized distribution function is provided by the expression Fb(R),, = -.0069 + 1.560/R -127.9/R2 + 5341/R3, (17) where R(A). Some additional bubble nucleation may occur later in life, beyond the current range of the NMR data.…”

Substrate temperature and ion kinetic energy effects on first steps of He+ implantation in tungsten: Experiments and simulations

“…He is well known to be very mobile in W even at room temperature [42,43] and it is highly probable that interstitial isolated He atoms and small clusters are able to migrate and reach the substrate surface to escape. In other words MD At high fluence, differences are observed depending on the kinetic energy.…”