The irradiation of metals by energetic particles causes significant degradation of the mechanical properties1,2, most notably an increased yield stress and decreased ductility, often accompanied by plastic flow localization. Such effects limit the lifetime of pressure vessels in nuclear power plants3, and constrain the choice of materials for fusion-based alternative energy sources4. Although these phenomena have been known for many years1, the underlying fundamental mechanisms and their relation to the irradiation field have not been clearly demonstrated. Here we use three-dimensional multiscale simulations of irradiated metals to reveal the mechanisms underlying plastic flow localization in defect-free channels. We observe dislocation pinning by irradiation-induced clusters of defects, subsequent unpinning as defects are absorbed by the dislocations, and cross-slip of the latter as the stress is increased. The width of the plastic flow channels is limited by the interaction among opposing dislocation dipole segments and the remaining defect clusters.

Multiscale modelling of plastic flow localization in irradiated materials

The last decades brought impressive progress in synthesizing and studying properties of nuclides located very far from the beta stability line. Among the most fundamental properties of such exotic nuclides, the ones usually established first are the half-life, possible radioactive decay modes, and their relative probabilities. When approaching limits of nuclear stability, new decay modes set in. First, beta decays are accompanied by emission of nucleons from highly excited states of daughter nuclei. Second, when the nucleon separation energy becomes negative, nucleons start being emitted from the ground state. A review of the decay modes occurring close to the limits of stability is presented. The experimental methods used to produce, identify, and detect new species and their radiation are discussed. The current theoretical understanding of these decay processes is reviewed. The theoretical description of the most recently discovered and most complex radioactive process---the two-proton radioactivity---is discussed in more detail.

Radioactive decays at limits of nuclear stability

Comparison of empirical interatomic potentials for iron applied to radiation damage studies

Comparative study of radiation damage accumulation in Cu and Fe

Irradiation of solids with energetic particles results in the reorganization of constituent target atoms, i.e., ion beam mixing (IM). At low temperatures, IM is characterized by prompt (10 −10 s) diffusion processes which are localized in the vicinity of the displacement cascade. Mixing at low temperatures can cause the system to depart far from the equilibrium state. At elevated temperatures, the diffusion of radiation-induced defects extends the mixing to longer times and greater distances. These delayed IM processes tend to return the system toward equilibrium. Recent experimental progress has led to a qualitative understanding of the fundamental aspects of IM in both temperature regimes. This has been achieved through systematic measurements of the influence of temperature, dose, dose-rate, cascade energy density and chemical interactions on IM. The results of these experiments will be reviewed and compared to IM models based on collisional, thermal spike and radiation-enhanced diffusion processes. The relation of IM to other fundamental radiation damage effects will also be discussed.

Fundamental aspects of ion beam mixing

The technique of transmission electron microscopy has been used to study neutron irradiation damage in α -iron. Foils were irradiated to a fission neutron dose of ∼ 2 × 1020 cm−2 at 60°c and the effects of annealing up to 500°c on the micro-hardness and structure were studied. The irradiated foils contained visible point defect clusters which remained unchanged on annealing up to 300°c. Above 300°c the size of clusters remained fairly constant but the number decreased steadily until they had all disappeared after annealing at 500°c. The micro-hardness also remained unchanged up to 300°c and then recovered steadily until it returned to the unirradiated value at 500°c. The results of a diffraction analysis carried out on loops in annealed foils indicated that their Burgers vector was in a ⟨111⟩ direction and that both interstitial and vacancy loops were present. It is suggested that the visible clusters in the irradiated iron are interstitial in nature, the vacancies being trapped by interstitial i...

An electron microscope study of neutron irradiation damage in alpha-iron

Molybdenum, ranging in resistivity ratio (ρ293°K/ρ4·2°K) from 150 to 8000, has been neutron irradiated at 77°K and 473°K to integrated fission doses of ∼1020 n. cm−2 ∼7 × 1019 n. cm−2, respectively. A detailed electron microscope study has been made of the damage structures both before and after a post-irradiation anneal of one hour at 1173°K. It is found that the defect cluster topology in the irradiated specimens is a sensitive function of both material purity and irradiation temperature. A model has been discussed specifically to explain the topology of interstitial clusters in which impurity assisted nucleation dominates.

Neutron irradiation damage in molybdenum: Part II. The influence of crystal perfection and irradiation temperature on the damage structure and its annealing behaviour

An electron microscope study has been made of vacancy loops formed as a result of displacement cascade collapse in molybdenum irradiated with 60 keV self-ions. The experiments were directed towards exposing two aspects of this process. Firstly, the influence of material purity was investigated by comparing the structures generated in three crystals, one being of high purity, the second containing a significantly higher level of substitutional impurities and the third doped specifically with nitrogen. The results demonstrated that nitrogen in solution was the most effective in reducing both the number of visible vacancy loops formed by cascade collapse and the fraction of vacancies surviving in the cascades to form loops. The second major aspect studied was the influence of irradiation temperature on vacancy loop formation in the high purity crystal. In this case the number of visible loops decreased sharply with temperature over the range studied, i.e. up to 535°C. The decrease is shown to follow...

B. L. Eyre

Papers

An electron microscope study of neutron irradiation damage in alpha-iron

Neutron irradiation damage in molybdenum: Part II. The influence of crystal perfection and irradiation temperature on the damage structure and its annealing behaviour

The influence of material purity and irradiation temperature on self-ion damage in molybdenum

The damage structure formed in molybdenum by irradiation in a fast reactor at 650°c

Neutron irradiation damage in molybdenum. part iv. a quantitative correlation between irradiated and irradiated-annealed structures.