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The areal density and the depth distribution of3He trapped in Ni as a function of the bombarding fiuence was measured in the energy range of 1–25 keV and at angles of incidence between 0 and 85° using nuclear reaction analysis. At fluences below saturation a linear relation is found between the areal density and the fiuence. From its slope the trapping and reflection coefficients can be determined.

It has recently been suggested that the diffusion/permeation of hydrogen implanted in Mo and Ni is strongly enhanced by the formation of stable and mobile hydrogen-self interstitial atom complexes.This suggestion is based partly on observations of a strong influence of these complexes on implanted He profiles. We present measurements showing this effect to be negligible.

Simultaneous measurements have been made of blister formation and gas re-emission during bombardment of Ni with 8-40 keV 3He+ at room temperature. It is shown that re-emission and blister formation start at the same critical fluence. An initial peak in the re-emission rate is correlated to a step in the total number of blisters. A more detailed analysis of the experimental data shows that the area contributing to gas re-emission is much larger than the blister area. This suggests the formation of an interconnected layer below the surface in which cracks at blister sites provide gas emission channels to the surface.

Trapping of helium after implantation at energies of 8 to 150 keV and fluences up to 1019 He-ions/cm2 in nickel at room temperature is studied by measuring the thermal desorption spectra during linear heating up to 1000°C. At several annealing stages the trapped helium is measured by means of the nuclear reaction 3He(d, α)H and the target surface is observed by laser scattering and with the scanning electron microscope.The thermal desorption spectra depend strongly on the implantation fluence but only slightly on the implantation energy, indicating a similar trapping of He in the lattice for the implantation energies used here, The temperature at which desorption starts decreases with increasing fluence. Above the critical fluence for blistering an additional low temperature (150°C) desorption maximum is found.The desorption peak at 150°C can be approximated theoretically with a single jump desorption process of first order and a Gaussian distribution of activation energies around 1 eV. The measurements indicate that at higher temperatures (>300°C) helium desorption is partly due to the opening of helium bubbles at the target surface.

A small fraction of the α-particles produced in a future (D, T)-fusion plasma will escape directly and hit some areas of the surrounding solid walls with their full energy, while the majority will be confined in the magnetic field, slowed down in the plasma and reach the first wall with about the same energy distribution as the other plasma particles.During bombardment of a solid by energetic α-particles the implanted surface layers undergo several modifications leading finally to a rough surface with a spongy microstructure. Some of these modifications, i.e. blistering and flaking, are only observed if the critical gas concentration builds up first at some depth below the surface. This condition is met only if simultaneous erosion by sputtering stays below a certain limit. In fusion devices with loss fractions of ≲ 1% high energy α-particles and a plasma temperature near the first wall above some 10 eV, blistering and flaking are likely to be avoided.

Although hard hydrocarbon layers prepared by glow discharge (a-C:H/D films) display hydrogen contents similar to those observed in graphite saturated by hydrogen implantation, the hydrogen-recycling behaviour of both films appears to be significantly different. This is concluded from isotopic exchange measurements during 8 keV D+ and 11 keV H+ irradiation of hydrogenated and deuterated layers. The a-C:H/D films display a strong initial depletion, which gives slowly way for a resaturation at increasing ion fluence. In the case of saturated carbon the initial depletion appears much weaker or is even missing. This difference may be explained qualitatively by different binding states in the films resulting from the different conditions of preparation.

The release of 4He implanted to saturation with an energy of 15 keV in polycrystalline Ni by subsequent 3He implantation with equal energy has been measured between 295 and 1053 K. The fraction of 4He that can be exchanged is shown to decrease with increasing temperature up to T≲800 K. At T>800 K, however, it increases drastically. The results can be interpreted by assuming He trapping in two subsystems: gas bubbles and He-vacancy complexes. At sufficiently high density of the complexes He atoms can move along interlinked chains of complexes in "relay-race" type of motion in which each individual He-atom moves only one step and an atom from the complex nearest to the surface is released into the vacuum. At T > 900 K all complexes should be thermally dissociated. In this case bubble migration may be the mechanism responsible for He re-emission.

The trapping of 5 keV deuterium in ∼ 165 and ∼ 4000 nm thick BeO films grown by thermal oxidation on Be substrates was investigated at different temperatures using the D(3He,H)4He nuclear reaction. The ratio of implanted D to BeO molecules obtained at saturation is 0.24 to 0.34. The D migrates from its end of range location and distributes itself uniformly in the BeO film. With increasing implant temperature the BeO layer flakes from the Be substrate. The distribution of D in BeO films at high concentrations is not consistent with diffusivity measurements at low concentrations of T in BeO.

Minimum yield of backscattered protons and H-atoms with primary energies of 50-150 keV from a well annealed Nb single crystal has been measured in single and double alignment as a function of emerging energy at different temperatures. From these data minimum yield as a function of depth has been calculated, assuming electronic energy losses only. The results are compared to analytical equations for minimum yield in single and double alignment. These equations were obtained from Lindhard's theory of electronic and nuclear multiple scattering in single crystals. It was assumed that transverse energy increases steadily with penetration depth, diffusion being neglibible. At higher energies the agreement between theory and experiment is good in <100> single alignment. In <110> single alignment and at lower energies experimental values are about a factor of 2 higher. In double alignment there is a discrepancy of nearly one order of magnitude, which probably must be attributed to lattice defects.