The active electron optics suite at Magnox Electric's Berkeley Centre has a VG HB501 FEGSTEM and a FE-sourced Auger Microprobe (a Fisons Microlab-F) which are routinely used for grain boundary chemistry studies in a variety of highly active austenitic and ferritic steels and nickel base alloys.

In a number of investigations sufficient grain boundary data have been obtained to allow a meaningful comparison between the two instruments to be made. It has been established that for the overwhelming majority of materials and conditions there exists a reasonable correlation between the two sets of compositional (on-boundary) data.

This paper presents this correlation and gives a simple theoretical description justifying the relationship between the raw data from the instruments. Examples are given of materials and conditions for which the correlation cannot be established and this leads to a discussion of the usefulness of the availability of the correlation.

To improve the ability to predict radiation-induced segregation (RIS) in austenitic Fe-Cr-Ni alloys, a model for predicting RIS is developed which calculates diffusion parameters based on local atomic configuration. Comparisons of RIS measurements in austenitic iron-base and nickelbase Fe-Cr-Ni alloys with calculations using the Perks vacancy-driven RIS model have shown that to accurately predict segregation trends, composition specific diffusion parameters must be used. This requirement limits the ability of the Perks model to predict segregation in Fe-Cr-Ni alloys for which no prior segregation measurements exist. To overcome this limitation, the improved model calculates migration energies using pair interaction energies to account for composition dependent diffusivities. The advantages of this approach are that a single set of input parameters can be used to describe a wide range of bulk alloy compositions, and the effects of local order can be easily incorporated into the calculations. A description of the model is presented, and model calculations are compared to segregation data to show that significant trends in the measured segregation data can be modeled using a single set of input parameters.

Intergranular impurity segregation induced during neutron irradiation (9.8 × 1024 n/mr at 438 °C) and thermal ageing has been studied in V-20 wt.% Ti alloys undoped, P doped and S doped all containing residual C and O. Neutron irradiation induced intergranular segregation and desegregation of S in undoped and S doped alloys, respectively. Thermal ageing resulted in a large increase in the S segregation in the undoped and S doped alloys. However, all unirradiated, aged and irradiated P doped alloys showed negligible S segregation. The vanadium alloys had smaller P segregation, compared to the S segregation in the undoped and S doped alloys. The irradiation and ageing enhanced the P segregation in a different fashion depending on the alloys. The grain boundary enrichment of C, O and Ti was reduced during the irradiation but promoted by the thermal ageing. The underlying mechanisms controlling intergranular impurity segregation caused by irradiation or thermal ageing are discussed in light of the impurity solubility change and dynamic interaction of defect and impurity fluxes.

The effects of Ne and Sc implantation on radiation-induced segregation (RIS) in Ni- 9at.%Al were studied in-situ utilizing the high-voltage electron microscopeffandem accelerator facility at Argonne National Laboratory. A highly-focused 900-keV electron beam generated radial defect fluxes which, in turn, induced the transport of Al atoms toward the center of the electronirradiated area via the inverse-Kirkendall effect. The radial segregation rate of Al atoms was monitored by measuring the diameter of the γ′-Ni3Al zone which formed in the Al-enriched area during irradiation. Ne and Sc implantation effects on RIS were investigated at 550°C, while Ne effects were also examined at 625°C to determine the influence of temperature on the ability of Ne to act as defect trapping sites, causing RIS suppression. It was found that the RIS suppression effect of Ne increased with increasing irradiation temperature, and that Sc had a small RIS suppression effect which increased with increasing Sc implantation dose. Ne bubbles which formed during implantation are believed to be responsible for its strong suppression effect.

Radiation-induced segregation (RIS) has been implicated as a potential contributor to irradiation assisted stress corrosion cracking in light water reactor core components. To better understand changes to grain boundary chemistry during irradiation, RIS was measured in ultra-high purity (UHP) 304 stainless steel using Auger electron spectroscopy (AES). Variations in measured grain boundary concentration, both within a sample and between samples, are reduced by refinements in both the radiation and the AES techniques. These refinements include improvements in temperature control, uniformity of sample-to-sample dose, grain boundary acceptance criteria, amount of intergranular fracture, and amount of beam current used in analysis. AES measurements on samples irradiated at 400°C to 1.0 dpa show how implementing the technique refinements reduces the variability in the measured concentrations. Additionally, measurements from regions of ductile tearing in samples irradiated to 0.1 and 1.0 dpa at 400°C, to 1.0 dpa at 200°C, and from unirradiated samples show that sensitivity factors must be determined to obtain the most accurate measurement of grain boundary composition.

The dose dependence of radiation-induced segregation (RIS) is investigated for proton irradiated ultra high-purity (UHP) 304L stainless steel and Fe-20Cr-24Ni. Grain boundary compositions were measured in samples irradiated with 3.2 MeV protons at 400°C to doses ranging from 0.1 to 3.0 dpa. RIS measurements were made using scanning transmission electron microscopy with energy dispersive x-ray spectroscopy (STEM/EDS) and compared to results from Auger electron spectroscopy (AES). Comparison of the dose dependence for HP-304L and Fe- 20Cr-24Ni shows that RIS is alloy specific. The approach to steady-state Cr depletion was observed to be more rapid in the alloy with higher Ni content. Fe-2OCr-24Ni reaches a steady-state Cr depletion level by 0.5 dpa, and the amount of Cr depletion in HP-304L SS is still increasing between 1.0 and 3.0 dpa. RIS in the stainless steel alloys irradiated with 3.2 MeV protons is comparable to that in neutron irradiated steels of similar composition.

Measurement of minor element compositions at irradiated grain boundaries in austenitic stainless steels indicates that Si is the only element that significantly responds to radiation-induced segregation. Other minor elements, such as P or S, do not exhibit elevated grain boundary concentrations after irradiation. A rate theory evaluation of segregation is in accord with ioninduced Si enrichment, but reveals complexities in the interpretation of extrapolating behavior from ion-irradiation to neutron-irradiation behavior. The model calibrated to measured high-rate, ioninduced segregation greatly overestimates measured low-rate, neutron-irradiation segregation of Si.

Secondary ion mass spectrometry and Rutherford backscattering/channeling analysis have been used to study the segregation of Au at moving Si-SiO2 interfaces during bombardment of Si with 15 keV O- ions. Essentially 100% of the Au is found to segregate at a bombardment temperature of 250°C, whereas only partial segregation occurs for room temperature bombardment. Up to 10 monolayers of Au can be segregated in disordered Si behind an SiO2 layer at 250°C. These results are discussed in terms of ion-assisted migration of Au in disordered Si and extremely low solubilities of Au in SiO2.

Ion-beam-induced amorphization of a wide variety of ceramic materials has been investigated using in situ TEM at the HVEM-Tandem Facility at Argonne National Laboratory with 1.5 MeV Kr+ or Xe+ ions at temperatures between 20 to 1000 K. The critical amorphization temperatures and the activation energies associated with the expitaxial recovery of displacement cascades during irradiation have been determined from the temperature dependence of the critical amorphization dose. The results for phases in the A12 O3-MgO-SiO2 system suggested a parallel in the kinetics between ion-beam-induced amorphization and glass formation. Based on a cascade quenching model, a semiempirical parameter, S, which can easily be calculated from both structural and chemical parameters of a material, has been developed to predict the susceptibility of ceramics to amorphization. The critical amorphization temperature, above which irradiationinduced amorphization cannot be completed, is closely related to the glass transition temperature. The ratio between glass transition and melting temperatures can also be used to predict the susceptibility of a ceramic material to amorphization, equivalent to the Debye temperature criterion.

The amorphization of silicon carbide due to ion and electron irradiation is reviewed with emphasis on the temperature dependent critical dose for amorphization. The effect of ion mass and energy on the threshold dose for amorphization is summarized showing only a weak dependence near room temperature. Results are presented for 0.56 MeV silicon ions implanted into single crystal 6H-SiC as a function of temperature and ion dose. From this, the critical dose for amorphization is found as a function of temperature at depths well separated from the implanted ion region. Results are compared with published data generated using electron and xenon irradiating species. High resolution TEM analysis is presented for the Si ion series showing the evolution of elongated amorphous islands oriented such that their major axis is parallel to the free surface. This suggests that surface or strain effects may be influencing the apparent amorphization threshold. Finally, a model for the temperature threshold for amorphization is described using the Si ion irradiation flux and the fitted interstitial migration energy which was found to be ∼0.56 eV. This model successfully explains the difference in the temperature-dependent amorphization behavior of SiC irradiated with 0.56 MeV silicon ions at 1×10-3 dpa/s and with fission neutrons irradiated at 1×10-6 dpa/s irradiated to 1 5 dpa in the temperature range of ∼340 ±10K.

A key challenge in the permanent disposal of high-level waste (HLW), plutonium residues/scraps, and excess weapons plutonium in glass waste forms is the development of predictive models of long-term performance that are based on a sound scientific understanding of relevant phenomena. Radiation effects from β-decay and α-decay can impact the performance of glasses for HLW and Pu disposition through the interactions of the α-particles, β-particles, recoil nuclei, and γ-rays with the atoms in the glass. Recently, a scientific panel convened under the auspices of the DOE Council on Materials Science to assess the current state of understanding, identify important scientific issues, and recommend directions for research in the area of radiation effects in glasses for HLW and Pu disposition. The overall finding of the panel was that there is a critical lack of systematic understanding on radiation effects in glasses at the atomic, microscopic, and macroscopic levels. The current state of understanding on radiation effects in glass waste forms and critical scientific issues are presented.

The ion beam-induced crystalline-to-amorphous transition was studied for crystalline phases in the MgO-A12O3-SiO 2 system. Samples were irradiated with 1.5 MeV Xe+ at temperatures from 15 to 1023 K, and the dose required for amorphization was determined by in situ transmission electron microscopy. Based on a cascade quenching model, we propose that irradiation-induced amorphization is closely related to glass formation. The rate of crystallization from a melt is the controlling factor in determining the susceptibility to amorphization and glass formation. From the analysis of cascade quenching evolution, we have derived a simple relation between amorphization dose and temperature. A quantitative parameter, S0, that describes the susceptibility to amorphization is derived that considers the crystalline structure, field strength, and phase transition temperature.

The behaviour of ZrO2-10%YO1.5-5%ErO1.5-( 10%ThO2) (At %) cubic solid solutions under low and high energy Xe ion irradiation up to a fluence of 1.8·1016 Xe.cm−2 was investigated by TEM. Low energy (60 keV) Xe ions did not yield amorphization. From the observed bubble formation, swelling values of less than one volume per cent were estimated to be 0.19–0.72% during irradiation at room temperature or at high temperature (925 K). Furthermore, no amorphization was obtained by Xe irradiation under extreme conditions such as high energy (1.5 MeV) Xe ion and low temperature (20 K). This confirms the robustness of this material and argues in favour of the selection of zirconia based material as an advanced nuclear fuel for plutonium disposition.

Many crystalline ceramics can be topologically disordered (amorphized) by disordering radiation events involving high-energy collision cascades or (in some cases) successive single-atom displacements. We are interested in both the potential for disorder and the possible aperiodic structures adopted following the disordering event. The potential for disordering is related to connectivity, and among those structures of interest are tetrahedral networks (such as SiO2, SiC and Si3N4) comprising corner-shared tetrahedral units whose connectivities are easily evaluated. In order to study the response of these networks to radiation, we have chosen to model their assembly according to the (simple) local rules that each corner obeys in connecting to another tetrahedron; in this way we easily erect large computer models of any crystalline polymorphic form. Amorphous structures can be similarly grown by application of altered rules. We have adopted a simple model of irradiation in which all bonds in the neighborhood of a designated tetrahedron are destroyed, and we reform the bonds in this region according to a set of (possibly different) local rules appropriate to the environmental conditions. When a tetrahedron approaches the boundary of this neighborhood, it undergoes an optimization step in which a spring is inserted between two corners of compatible tetrahedra when they are within a certain distance of one another; component forces are then applied that act to minimize the distance between these corners and minimize the deviation from the rules. The resulting structure is then analyzed for the complete adjacency matrix, irreducible ring statistics, and bond angle distributions.

Many applications of high temperature superconductors, HTS, require the presence of lattice defects in the material structure to suppress the motion of magnetic vortices and enhance the critical current density, Jc. The microstructure of Tl2Ba2CaCu2O8-δ (T1–2212) thin films which have extended defects induced by high energy Au and Cu ion irradiation is studied using high resolution transmission electron microscopy, HRTEM, with slow scan digital imaging. In order to optimize the HTS properties and better analyze the consequent microstructural modification, the fluence is varied. At moderate fluences, resulting in ∼4% reduction of the superconducting transition, large enhancements of Jc, and vortex pinning potential are observed. The density and microstructure of isolated defects and surrounding structure will be discussed and compared to damage profiles calculated using the TRIM code. Correlation will be made between the HRTEM results and the changes in HTS properties.

The effects of irradiation with thermal neutrons on LiNbO3 single crystals doped with Hf and Hf,Mg were studied with ion beam and hyperfme interaction techniques, using Hf as a probe. In crystals where Hf occupies both Li and Nb sites, the fraction in Nb sites is strongly reduced after irradiation. The initial situation is recovered after thermal annealing at 973 K, in air.

Scanning Auger microscopy (SAM) and reflected electron energy loss microscopy (REELM) have been used to study the chemical modifications induced by 10-keV electron bombardment at the surface of the alkali halides: LiF, NaF, NaCl and KI. Auger spectra show that the alkali-to-halogen surface ratio increases with irradiation time, although they provide no conclusive evidence as to the chemical nature of the damage layer. Conversely, REELM analysis clearly reveals the formation of alkali metal through the occurrence of characteristic bulk plasmon peaks and surface plasmon peaks, which can also be used to image the lateral distribution of the damage layer to nearly submicron spatial resolution. Some unexpected signals are observed, deriving from combination of surface plasmon excitations with bulk plasmon excitations, and tentatively interpreted as arising from the inhomogeneous morphology of the alkali metal layer.

A noncontact, nondestructive method is used to determine viscoelastic and thermal transport properties of a DuPont Kapton film before and after neutron irradiation to determine the changes that would be expected to occur in a nuclear reactor environment. The results demonstrate general capabilities for non-destructive evaluation (NDE) of radiation-induced material degradation. The specific application demonstrated is evaluation of insulation materials to be used in a superconducting magnet design in the International Thermonuclear Experimental Reactor (ITER).

There are two main components to the irradiation spectrum which need to be considered inradiation effects studies on nonmetals, namely the primary knock-on atom energy spectrum and ionizing radiation. The published low-temperature studies on A12O3 and MgO suggest that the defect production is nearly independent of the average primary knock-on atom energy, in sharp contrast to the situation for metals. On the other hand, ionizing radiation has been shown to exert a pronounced influence on the microstructural evolution of both semiconductors and insulators under certain conditions. Recent work on the microstructure of ion-irradiated ceramics is summarized, which provides evidence for significant ionization-induced diffusion. Polycrystalline samples of MgO, A12O3, and MgAl2O4 were irradiated with various ions ranging from 1 MeV H+ to 4 MeV Zr+ ions at temperatures between 25 and 650°C. Cross-section transmission electron microscopy was used to investigate the depth-dependent microstructure of the irradiated specimens. Dislocation loop nucleation was effectively suppressed in specimens irradiated with light ions, whereas the growth rate of dislocation loops was enhanced. The sensitivity to irradiation spectrum is attributed to ionization-induced diffusion. The interstitial migration energies in MgAl2O4 and A12O3 are estimated to be ≤0.4 eV and ≤0.8 eV, respectively for irradiation conditions where ionization-induced diffusion effects are expected to be negligible.

Radiation damage of amorphous Si (a- Si) under 17 MeV- proton bombardment has been studied, measuring particle- induced conductivity(PIC) and photoconductivity(PC). The in- situ measurements have been conducted to focus on the structural flexibility and the metastable nature, inherent in the amorphous structure. While the PC (with weak illumination) has a fast response and reversible nature, the PIC has a long time- constant ∼60 s, followed by a persistent conductivity for more than ∼103 s. Both the PIC and the PC remain fairly stable against further irradiation, comparing to crystalline Si (c-Si), but they decay in the higher fluence region. A large part of the decayed PC recovers after annealing at 450 K. The results of a- Si are compared with those of c- Si. It is suggested that, in the lower fluence region, a-Si is more resistant against proton irradiation than c- Si, relaxing the atomic displacements, and the excited conductivities gradually decay with accumulation of the dangling bonds.