Radiation Blistering Research Articles

VITA high flux neutron source for various applications

A high flux neutron source based on a vacuum-insulated tandem accelerator (VITA) and a lithium target has been proposed and developed at the Budker Institute of Nuclear Physics in Novosibirsk, Russia. We describe VITA which provides a dc proton/deuteron beam with an energy within a range of 0.6–2.3 MeV with a current from 1 nA to 10 mA. VITA is also capable of producing α-particles through the 7Li(p,α)α and 11B(p,α) α α reactions, 478 keV photons through the 7Li(p,p ′ γ)7Li reaction and positrons through the 19F(p,e+e−)16O reaction. We present several applications of this source: boron neutron capture therapy, nuclear cross sections determination, lithium target study, radiation blistering of metals during proton implantation and the radiation testing of promising materials.

3 KeV H<sub>2</sub><sup>+</sup> Irradiation to Li/Pd/Cu Trilaminar Neutron Production Target for BNCT

For the purpose of avoiding the radiation blistering of the lithium target for neutron production in BNCT (Boron Neutron Capture Therapy) device, trilaminar Li target, of which palladium thin layer was inserted between cupper substrate and Li layer, was newly designed. The Li/Pd/ Cu trilaminar structures of the synthesized target were characterized under 3keV H2 + irradiation by XPS and XAFS technique, which provides structural/electronic properties of solids, and information about the local structure, such as the nature and number of surrounding atoms and inter-atomic distances. The following conclusions were derived; Pd­Cu physical bonding was produced between the Pd and Cu interface by electro-less plating Pd deposition on a high purity Cu plate. From the XAFS observation of white line of Pd, the Pd L3 edge jump was found after H2 + irradiation, this fact indicates increase of hole density in Pd 4d-band. 0.9eV chemical shift was also observed in Pd L3 white line for monolayer and 1µm Pd/Cu samples, which will affect the quality of the Li/Pd/Cu target due to the formation of PdHx in palladium insert layer.

Synthesis of lithium nitride for neutron production target of BNCT by in situ lithium deposition and ion implantation

To achieve high performance of BNCT (Boron Neutron Capture Therapy) device, Li3N/Li/Pd/Cu four layered Li target was designed and the structures of the synthesized four layered target were characterized by X-ray photoelectron spectroscopy. For the purpose of avoiding the radiation blistering and lithium evaporation, in situ vacuum deposition and nitridation techniques were established for in situ production and repairing maintenance of the lithium target.Following conclusions were derived:(1)Uniform lithium layer of a few hundreds nanometer was formed on Pd/Cu multilayer surface by in situ vacuum deposition technique using metallic lithium as a source material.(2)Lithium nitrides were formed by in situ nitridation reaction by the implantation of low-energy nitrogen ions on the deposited lithium layer surface. The chemical states of the nitridated zone were close to the stoichiometric lithium nitride, Li3N.(3)This nitridated zone formed on surface of four layered lithium target is stable for a long time in air condition. The in situ nitridation is effective to protect lithium target from degradation by unfavorable reactions.

In-situ vacuum deposition technique of lithium on neutron production target for BNCT

For the purpose of avoiding the radiation blistering of the lithium target for neutron production in BNCT (Boron Neutron Capture Therapy) device, trilaminar Li target, of which palladium thin layer was inserted between cupper substrate and Li layer, was newly designed. In-situ vacuum deposition and electrolytic coating techniques were applied to validate the method of fabrication of the Li/Pd/Cu target, and the layered structures of the synthesized target were characterized. In-situ vacuum re-deposition technique was also established for repairing and maintenance for lithium target damaged. Following conclusions were derived;(1) Uniform lithium layers with the thickness from 1.6nm to a few hundreds nanometer were formed on Pd/Cu multilayer surface by in situ vacuum deposition technique using metallic lithium as a source material.(2) Re-deposition of lithium layer on Li surface can be achieved by in situ vacuum deposition technique.(3) Small amount of water and carbonate was observed on the top surface of Li. But the thickness of the adsorbed layer was less than monolayer, which will not affect the quality of the Li target.(4) The formation of Pd-Li alloy layer was observed at the Pd and Li interface. The alloy layer would contribute to the stability of the Li layer.

A neutron producing target for BINP accelerator-based neutron source

An innovative accelerator-based neutron source for BNCT has just started operation at the Budker Institute of Nuclear Physics, Novosibirsk. One of the main elements of the facility is a lithium target producing neutrons via the threshold 7Li( p, n) 7Be reaction at 25 kW proton beam with energies of 1.915 MeV or 2.5 MeV. The design of an optimal target and results of the investigation of radiation blistering of the lithium layer were presented at previous NCT Congresses. During the last two years the neutron target has been manufactured, assembled and placed in the facility. Optimization of the target is carried out with the Monte Carlo simulation code MCNP. In this article, the design of the target is discussed, results of all previous investigations are summarized, results of target testing and neutron generation are described, and results of simulation of neutron spectra are presented.

Neutron producing target for accelerator based neutron capture therapy

Pilot innovative accelerator based neutron source for neutron capture therapy of cancer is under construction now at the Budker Institute. One of the main elements of the facility is lithium target producing neutrons via threshold 7Li(p, n)7Be reaction at 10 mA proton beam with energies of 1.915 MeV or 2.5 MeV. In the present report, choice of target was substantiated. The main problems of lithium target were determined to be: 7Be radioactive isotope activation, keeping lithium layer solid, presence of photons resulted from proton inelastic scattering on lithium nuclei, and radiation blistering. The results of thermal testing of target prototype, investigation of radiation blistering and several simulations are presented. It becomes clear that water is preferable for cooling this target, and that the lithium target 10 cm in diameter is able to run up to 25 kW proton beam before melting. The conception of optimal target is proposed: thin and easy to detach metal disk 10 cm in diameter, evaporated with thin layer of pure lithium from the side of proton beam exposure: its back is intensively cooled with turbulent water flow to maintain lithium layer solid. Design of target for the neutron source constructed at BINP is shown. Conceptions of radiation protection and neutrons, γ-rays and α- particles diagnostics are presented. The immediate plans on obtaining epithermal neutron beam are declared.

TEM and SEM studies of radiation blistering in helium-implanted copper

Nanoporous layers produced in metal surfaces by He implantation are of special interest for applications such as catalysis. At high doses nanoporous layer formation can be limited by the onset of radiation blistering. Research into the blistering of metals was stimulated originally by the need to find materials resistant to blistering for use in the first-wall of future nuclear fusion reactors. Blistering was the subject of intensive international study in the two decades centred on 1977. Despite this effort the bubble structures associated with blistering were never determined. In the present work TEM sections have been successfully prepared, by ultramicrotomy, perpendicular to the surface of high dose copper targets. For the first time, in any case of radiation blistering, the bubble structures directly associated with blistering are identified and their depth dependence determined. Local swellings, caused by a bimodal distribution of nanoscale bubbles, are estimated to exceed 150%. Probable answers can now be provided for some longstanding questions from earlier studies.

Tritium barrier development for austenitic stainless steel by its aluminizing in a lithium melt

A technique for obtaining coatings on a 0.12%C/18%Cr/10%Ni/Ti austenitic stainless steel by its aluminizing in melts of the following composition x%Al+(100%− x)%Li( x=3, 10) at the temperature range 870–1070 K for 5–100 h has been developed. An investigation in to the decrease in the tritium penetration through the steel has been carried out. It has been shown that two-side aluminizing of the steel in the 10%Al/90%Li melt at 870 and 970 K for 5 h decreases its tritium permeability by more than three orders of magnitude. Furthermore, aluminizing the steel under these regimes reduces its erosion coefficient by one order of magnitude on average due to radiation blistering, decreases its coefficient of physical sputtering by more than 2.5 times and protects the steel from failure under the action of hydrogen pulsed plasma fluxes with the incident flux specific power up to 4–5·10 10 W m −2 and a pulse duration of 10–50 μs. The mechanisms of decreasing the tritium permeation with regard to the surface relief forming under the treatment have been discussed.

The He gas bubble superlattice in Cu: Analysis of structural variants in {110} grains

The spatial ordering of helium gas bubbles (diameter ~ 2 nm) produced in polycrystalline copper by 30 keV He + irradiation at 300 K was studied using TEM. Transmission electron micrographs of the bubble array in 〈110〉 grains have been analysed for B along 〈110〉 in the Cu matrix. That the bubble superlattice is in the same orientation as the host metal matrix (the m orientation) has long been considered to be an important feature of bubble ordering. However, in a striking result, we have found that a high proportion of the ordered bubble array consists of structural variants which have orientations different from m. Both the spatial characteristics and frequency of occurrence of the structural variants have been determined. Examination of these features of the bubble array show considerable promise in clarifying the mechanism leading to bubble lattice formation and radiation blistering.

Radiation blistering in inconel-625 due to 100 keV helium ion irradiation

The objective of this study was to determine whether the change of angle of incidence of an ion beam impinging on surface blisters during their growth phase (before exfoliation) could influence the blister skin thickness and the blister crater depth. Polished, polycrystalline Inconel-625 samples were irradiated at room temperature and at normal incidence to the major sample surface with 100 keV helium ions to a total dose of 6.24 × 10 18 ions/cm 2 . The results revealed that many exfoliated blisters leave craters which have two or three concentric pits. The blister skin thickness near the center of the blister was found to agree well with the calculated projected range of 100 keV He ions in nickel. However, the blister skin thickness of some exfoliated blisters along the edge of the fracture surface showed different thicknesses. A model is proposed to explain the observed blister crater/blister skin fracture features in terms of a change of angle of incidence of the incident ions to the surface during the growth phase of surface blisters.

Influence of external action and structural factors on radiation blistering

Abstract A survey of experimental results is presented, pertaining to radiation blistering of a considerable number of materials (stainless steels, alloys with high nickel content, alloys of refractory metals) under helium ion irradiation with energies of 20–100 keV under conditions corresponding to the plasma-wall interaction: bombardment at various angles of incidence and cyclic irradiation in a wide spectrum of ion incidence angles; influence of external action, including thermocycling; influence of preceding neutron and proton irradiation. It has been shown that external factors have a complex influence on blister parameters and erosion coefficients of materials. A study has been carried out on the influence of aluminium coatings, alloying additions, phase state of material and microstructure on the nature and degree of surface erosion. Complex influence of element and phase composition, as well as microstructural changes during heat treatment and welding on radiation erosion have been established.

Surface erosion of stressed materials under high energy helium ion irradiation

Experiments on the influence of external mechanical loading on radiation blistering and flaking of stainless steel and aluminium were carried out. An increase in the critical dose for blistering or flaking of materials was observed when the level of stress increased from zero up to the yield point in a particular temperature range. This phenomenon is discussed in the frame of enhanced capture of helium atoms by bent dislocations in the presence of external mechanical loading. Some supplementary experiments supported the possibility of a dislocation-based mechanism.

Bubble structures in He+irradiated metals

Abstract Transmission electron microscopy is used to investigate the spatial arrangement of gas bubbles produced in the metals, Cu, Ni, Au, stainless steel and Ti irradiated with He+ at temperatures ∼ 300 K. For metals having a high degree of crystalline perfection within grains, a gas bubble superlattice is formed at high He doses in every case investigated. A study is made of the growth of bubbles on an existing superlattice (formed in a prior He+ irradiation) in Cu under (i) 1 MeV electron irradiation and (ii) in-situ heating in the electron microscope. The changes in bubble structure with depth in Cu for a He dose Φ near Φc (the critical dose for radiation blistering) are investigated. The development of the bubble structure and the microstructure at depths near the mean projected range is studied as a function of He dose. Electron diffraction from the super-lattice in Cu for B along , , , and in the host matrix reveals some unusual but reproducible features in the diffracti...

Anomalous deflection of irradiated cantilevers undergoing blistering

Plates which are implanted with ions that segregate to form gaseous occlusions may show a succession of net surface compressional stress and net tensional stress as radiation blistering occurs and the surface exfoliates. Data are given for 140-keV helium ion bombardments of Synroc B, a ceramic compact intended for the incorporation and storage of radioactive wastes, and two of its constituents: perovskite and zirconolite.

Investigation of the radiation blistering of aluminum alloys during simultaneous irradiation with He+ and D+ ions

Investigation of the radiation blistering of aluminum alloys during simultaneous irradiation with He+ and D+ ions

Temperature dependence of radiation blistering of aluminum alloys in irradiation by helium ions

Temperature dependence of radiation blistering of aluminum alloys in irradiation by helium ions

The onset of radiation blistering as a function of target temperature for D+ irradiated copper

Radiation blistering in 200 keV D+ irradiated copper has been studied for target temperatures in the range 120 to 380 K. Abrupt changes in both the critical dose for blistering and the blister morphology are observed to occur at target temperatures of 195 ± 10 and 300 ± 5 K. For target temperatures in the ranges 120 to 190 K and 300 to 380 K, semi-spherical blisters with a mean diameter of ~5.5 μm are observed to form at fluences of (2.0 ± 0.5) × 1022 and (4 ± 1) × 1022 d/m2, respectively. In the intermediate temperature region, irregularly shaped blisters with a mean diameter of ~1.3 μm are found to form at a fluence of (6 ± 2) × 1021 d/m2. Depth profiles of the implanted deuterium have been obtained. The deuterium concentrations at the onset of blistering are found to be approximately constant over the temperature ranges 120 to 190 K and 190 to 300 K, although a different concentration is observed in each range. For temperatures above 300 K, the deuterium concentration at the onset of blistering is found to decrease with increasing temperature.

The bubble coalescence model of radiation blistering

The existence of overpressurized gas bubbles, and a suitable mechanism for bubble growth during low temperature ion implantations, are the essential ingredients for the validity of a gas-driven blister formation mechanism. In this paper, taking into account the difference between the formation energy of helium interstitials and the free energy change of a bubble per helium atom added, we have theoretically shown that such bubbles indeed exist, and their growth is driven by their bias for vacancies and anti-bias for interstitials which arise because of the overpressure-induced compressive stress field around them. The relations for helium density in bubbles and the bubble overpressure are derived. The role of interbubble interaction and the effect of bubbles on the elastic properties of the material have been taken into account to determine the dose dependence of the integrated lateral stress and the critical conditions for interbubble coalescence/fracture. It is shown that the observed sublinearity and the relief of integrated lateral stress are a natural consequence of the attractive interbubble interaction and do not uniquely relate to the blister formation as considered in the stress model. The derived conditions for coalescence agree well with the available data. It is argued that the present treatment provides a sound theoretical basis for the gas pressure model of radiation blistering.

The gas-bubble superlattice and the development of surface structure in He + and H irradiated metals at 300 K

Transmission electron microscopy (TEM) is used to investigate the spatial arrangement of the small gas bubbles produced at 300 K in several fcc metals including copper and in the hcp metal titanium by 30 keV helium ion irradiation, and in copper by 16 keV proton irradiation. For the fcc metals it is found that the helium gas bubbles lie on a superlattice having a fcc structure with principal axes aligned with those of the metal matrix. The bubble lattice constant, a 1 , measured for a helium fluence just below the critical dose for radiation blistering of the metal surface ( ∼4 × 10 21 He +/m 2) is typically ∼7 nm with bubble diameters typically ∼2 nm. For titanium, similar bubble ordering is seen in samples irradiated to a level of ∼1.5 × 10 22 He +/m 2, with bubble sizes and spacings approximately 50% greater than those for the fcc metals. Pipe-like passages formed by the interconnection of strings of helium gas bubbles are evident in all metals studied. Superlattice formation is also a feature of the hydrogen bubble structure in copper following irradiation to a level of ∼1.3 × 10 23 H +/m 2. At an early stage of bubble development small bubbles (∼2 nm diameter) arranged on a lattice of spacing a 1 ∼ 12 nm are found. The bubble structure evolves further through several well-defined stages before radiation blistering of the surface occurs. Some implications for gas release and for synergistic effects in irradiated surfaces are suggested by these results and by those obtained in other recent experiments.

Formation of Large Blisters on Rolled Mo Surface Bombarded with Hydrogen Ions

Relatively large blisters were observed on the surface of rolled plates of polycrystalline molybdenum bombarded with hydrogen ions at energies of 160 eV or greater. Some blisters have a skin thickness about 2 orders of magnitude larger than the projected range of implanted ions, thus being distinguished from those of usual radiation blistering. The formation of such large blisters depends on the texture of the metal specimen, and may be attributed to the high pressure gas produced by the recombination of hydrogen atoms at the site of the defects originating in the fabrication of the specimen.