Post-irradiation Heat Treatment Research Articles

Defect structures as a function of ion irradiation and annealing in LiNbO3

Ion implantation is commonly utilized during the fabrication of lithium niobate (LiNbO3) acousto- and opto-electronic devices. Mechanistically, implantation creates material defects affecting properties that can be leveraged to create functionality. Enhancing scalability and the repeatability of these implantation protocols therefore necessitates linking process parameters of implantation with those defects created and ultimately the properties imparted by these defects. In response, we systematically examined the effects of ion species (H, He, and N), irradiation energy (150 keV to 2 MeV), implantation fluence (1 × 1012 to 1 × 1018 ions/cm2), and post-irradiation heat treatment (250 to 750 °C) in 128° Y-cut LiNbO3. The resulting defect structures were then analyzed via transmission electron microscopy and Raman spectroscopy. Defect formation suitable for fracture-based processes can be achieved with implantation of He ions, using an implantation fluence of 1 × 1018 ions/cm2 and a heat treatment at 250 or 500 °C. Other irradiation and annealing recipes that mimic material fabrication conditions show the defect evolution in LiNbO3 dependent on irradiation conditions.

Glass transition temperature of Risø B3 radiochromic film dosimeter and its importance on the post-irradiation heating procedure

Full-color development and stability of measured absorbance of the commercially used Risø B3 radiochromic film dosimeter can be achieved by applying a post-irradiation heat treatment procedure, typically at 60 °C for 10 min. However, the choice of post-irradiation heating duration and temperature has only been based on a trial and error method, and thus, the thermal stability of the material has not been fully studied before. We show that B3 film undergoes a rapid thermal decomposition of the PVB polymer base at 400 °C, with an initiation of the process at 70 °C. It means that higher irradiation temperatures, which can occur e.g. at high-dose electron beam irradiation, may cause polymer degradation. We also show that the post-irradiation heating temperature agrees with the polymer material's glass transition temperature as measured by differential scanning calorimetry (DSC). The post-irradiation heating procedure successfully removes the film's thermal history. This can be seen as an endothermic peak in the first heating cycle, which becomes smaller for higher irradiation doses. Glass transition temperatures of irradiated and post-irradiation heated B3 film are lower than those of the non-irradiated film, and decrease with increasing the dose. That implies a probable chain scission or degradation of the base polymer upon irradiation using high dose rates with no irradiation temperature control.

Formation of multicomponent alloy particles in doped ceria under I2+ ion irradiation and thermal annealing

Multicomponent alloys resembling the ε-phase particles in nuclear fuel have the potential to immobilize 99Tc in a stable waste form. Formation of such multicomponent alloys under extreme conditions is studied in a non-activated model system: CeO2 doped with 2 wt.% Mo, 1.5 wt.% Ru, 0.75 wt.% Pd, 0.5 wt.% Re and 0.25 wt.% Rh. The doped CeO2 films were irradiated with I2+ ions (610°C, 1016 and 5×1016 I2+/cm2). For selected samples post-irradiation heat treatment was conducted (900°C, 1100°C). Analytical transmission electron microscopy revealed the formation of 5-20 nm precipitates containing Pd, Mo, and Re sometimes associated with cavities. Iodine was found to segregate to grain boundaries and cracks. After heat treatment at 1100°C, the CeO2 matrix had recrystallized. Precipitates containing Pd, Mo, Re, and Ru were observed near the interface with the polycrystalline yttria-stabilized zirconia substrate. It follows that Pd is the most mobile element, followed by Mo and Re. While irradiation promotes precipitation, high-temperature effects are more significant.

Toward the Development of an InSb-Based Neutron-Resistant Hall Sensor

We describe a study concerning two irradiation series of InSb thin films in the form of Hall structures, using the natural neutron spectrum of a thermal-type fission reactor. We used mono- and polycrystalline InSb thin films with various levels of donor doping. The range of electron concentration values of the samples (from $10^{{16}}$ to $10^{{18}}$ cm $^{{-3}}$ ) allowed us to study the impact of predominant thermal neutrons on various InSb structures. Preirradiation long-term annealing of the samples at high temperatures ensured the thermal stabilization of the electrical parameters and made it possible to assess only defects introduced by neutrons in postirradiation heat treatments, without the influence of postevaporation defects. Neutron fluences of $8.7\times 10^{ {17}}$ cm $^{ {-2}}$ and $1.2\times 10^{ {18}}$ cm $^{ {-2}}$ were applied sequentially, and the total fluence was above $2\times 10^{ {18}}$ cm $^{ {-2}}$ . Annealing at high temperatures was performed after each irradiation process to estimate the quantity of donors created and to remove defects arising in the InSb structure. The results demonstrate the possibility of application of the InSb thin film in neutron-resistant Hall sensor (NRHS) for modern technological settings: fusion and fission reactors, particle accelerators, cosmic, and other scientific research.

The effects of swift Xe ion bombardment on the amorphous structure of a VITROPERM type alloy

Influence of swift Xe ion irradiation (ion energy of 11.1 MeV/u, ion fluences from 2.5 × 1012 to 1.0 × 1013 ions/cm2) on the local structural arrangement of a VITROPERM alloy is investigated using synchrotron-based X-ray diffraction, Fe and Nb K-edge X-ray absorption spectroscopy, and 57Fe Mössbauer spectroscopy techniques. The obtained data show an increase of structural disordering due to ion bombardment. However, no alterations in pairwise interatomic lengths are observed. The irradiation-induced structural modifications can be removed by an appropriate post-irradiation heat treatment. We suggest that the microscopic origin of changes induced by the swift heavy ions could be similar to the structural modifications caused by severe plastic deformation.

Investigating the thermal stability of irradiation-induced damage in a zirconium alloy with novel in situ techniques

Zr alloys exhibit irradiation-induced growth and hardening which is associated with the defects and dislocation loops that form during irradiation. In this study, state-of-the-art in-situ synchrotron X-ray diffraction (SXRD) and transmission electron microscopy (TEM) techniques were used to investigate the stability of dislocation loops in two proton-irradiated Zr-Fe binary alloys in real time. Complementary data from both techniques show rapid annealing of a-loops occurs between 300 °C and 450 °C. Line profile analysis was performed on the SXRD patterns using the convoluted multiple whole profile analysis tool, to calculate the change in a-loop line density as a function of post-irradiation heat treatment temperature and time. At temperatures below 300 °C, no significant decrease in a-loop density was detected when held for 1 h at temperature. From this SXRD experiment, we calculate the effective activation energy for the annealing process as 0.46 eV. On-axis in-situ STEM imaging was used to directly observe a-loop mobility during heating cycles and confirm that a-loops begin to glide in the trace of the basal plane at ∼200 °C in a thin foil specimen. Such a-loop gliding events, leading to annihilation at the foil's surfaces, became more frequent between 300 and 450 °C.

The effect of helium irradiation on the thermal evolution of the microstructure of nc‐ZrN

AbstractZrN is a candidate material for use as inert matrix fuel host for the burn‐up of plutonium and other minor actinides, waste products commonly present in spent nuclear fuel. These materials will operate within the nuclear reactor core and will therefore be subject to various types of radiation, high temperatures and a corrosive environment. Ceramics employed in the nuclear reactor environment will accumulate helium via (n, α) reactions. Nanocrystalline ZrN irradiated with 30 keV He to fluences between 1016 and 5×1016 cm–2to simulate the effects of alpha particle irradiation. The He irradiated sam‐ ples were annealed at temperatures between 600 and 1000 °C and were analysed using TEM and selected area diffraction. The results indicated that post irradiation heat treatment induces exfoliation at a depth that corresponds to the end‐of‐range of 30 keV He ions. TEM analysis of He suggests that nanocrystalline ZrN is prone to the formation of He blisters which may ultimately lead material failure. The results also suggest that the doping of nc‐ZrN with He aids the transformation from a nanocrystalline to microcrystalline state during heat treatment. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Raman spectroscopic study of remelting and annealing-induced effects on microstructure and compressive deformation behavior of highly crosslinked UHMWPE for total hip arthroplasty

Three-dimensional crystallographic morphologies were studied by means of confocal/polarized Raman spectroscopy as developed upon manufacturing in three different types of first and second generation highly crosslinked UHMWPE (HXLPE) acetabular liners. The impact of such microstructural characteristics on the deformation behavior of the liners was also evaluated and discussed from the viewpoint of molecular chain mobility. All the investigated liners showed similar microstructural transitions within the first 35 μm below their surfaces in terms of crystallinity, molecular orientation, and crystalline anisotropy. Interestingly, different postirradiation heat treatments (remelting or annealing in single step or in sequential steps) led to clear differences in the subsurface microstructure among the three liners. Remelted liner possessed both lower bulk crystallinity and degree of molecular orientation as compared to the annealed liners. Sequentially, irradiated/annealed liner showed the highest degree of crystallinity and orientation among the studied liners. The peculiar microstructure of this latter liner exhibited the highest restoring (shape-recovery) force against the applied uniaxial strain. Accordingly, the present study suggests that the sequential irradiation and annealing offers an efficient way to obtain microstructure quite suitable for attaining high creep resistance. However, all the investigated liners exhibited the significantly low values of surface anisotropy, which could be equally efficient in minimizing strain-softening-assisted wear phenomena.

The effect of He and swift heavy ions on nanocrystalline zirconium nitride

Recent studies have shown that swift heavy ion irradiation may significantly modulate hydrogen and helium behaviour in some materials. This phenomenon is of considerable practical interest for ceramics in general and also for candidate materials for use as inert matrix fuel hosts. These materials will accumulate helium via (n, α) reactions and will also be subjected to irradiation by fission fragments. Cross-sectional transmission electron microscopy and scanning electron microscopy was used to study nanocrystalline ZrN irradiated with 30keV He to fluences between 1016 and 5×1016cm−2, 167MeV Xe to fluences between 5×1013 and 1014cm−2 and also 695MeV Bi to a fluence of 1.5×1013cm−2. He/Bi and He/Xe irradiated samples were annealed at temperatures between 600 and 1000°C and were analysed using SEM, XTEM and selected area diffraction. The results indicated that post irradiation heat treatment induces exfoliation at a depth that corresponds to the end-of-range of 30keV He ions. SEM and XTEM analysis of He/Xe irradiated samples revealed that electronic excitation effects, due to Xe ions, suppress helium blister formation and consequently the exfoliation processes. He/Bi samples however do not show the same effects. This suggests that nanocrystalline ZrN is prone to the formation of He blisters which may ultimately lead material failure. These effects may however be mitigated by electronic excitation effects from certain SHIs.

PL and DLTS Analysis of Carbon-Related Centers in Irradiated P-Type Cz-Si

Photoluminescence (PL) and deep level transient spectroscopy (DLTS) have been used to investigate carbon related defects in p–type Cz–Si induced by proton irradiation. The interstitial carbon–interstitial oxygen (CiOi) level in DLTS and the corresponding C–line (789.5 meV) in PL spectra are detected in as–irradiated samples. Formations of the so–called P–line at 767 meV in PL and a new defect level at about 0.39 eV above the valence band edge, Ev, in the DLTS spectra are observed in the annealed samples. The evolution of the CiOiand Ev+0.39 eV levels in DLTS and also the C– and P– lines in PL upon post–irradiation heat–treatment is investigated, showing that the intensity of the CiOilevel decreases with heat–treatment, which is consistent with the PL data for the C–line. The intensity of the Ev+0.39 eV level is enhanced and then saturates with annealing duration. We tentatively assign this level to the interstitial carbon–oxygen dimer (CiO2i).

Phonon transport assisted by inter-tube carbon displacements in carbon nanotube mats

Thermal transport in carbon nanotube (CNT) mats, consisting of randomly networked multi-walled carbon nanotubes (MWNTs), is not as efficient as in an individual CNT because of the constrained tube-to-tube phonon transport. Through experiments and modeling, we discover that phonon transport in CNT mats is significantly improved by ion irradiation, which introduces inter-tube displacements, acting as stable point contacts between neighboring tubes. Inter-tube displacement-mediated phonon transport enhances conductivity, while inter-tube phonon-defect scattering reduces conductivity. At low ion irradiation fluence, inter-tube thermal transport enhancement leads to thermal conductivity increase by factor > 5, while at high ion irradiation fluence point defects within tubes cause a decrease in thermal conductivity. Molecular dynamics simulations support the experimentally obtained results and the proposed mechanisms. Further conductivity enhancement in irradiated mats was obtained by post-irradiation heat treatment that removes majority of the defects within the tubes without affecting thermally stable inter-tube displacements.

Pre-gamma dose thermoluminescence characteristics of muscovite mica

In the present research work, sensitization characteristics of the 180°C thermoluminescence peak of muscovite mica have been studied. The sensitization factor (S/S0) as a function of post-irradiation heat treatment, pre-dose and duration of heat treatment has been investigated. A pre-dose of 2kGy followed by heat treatment at 500°C for 1h is found to be the optimum condition for sensitizing the muscovite samples. The thermoluminescence glow curve structure of unsensitized and sensitized mica is nearly the same but a great improvement in the sensitivity has been observed after sensitization. The thermoluminescence response curves for unsensitized and sensitized mica samples exhibit linear behavior in the range 5–25kGy. Analysis of the thermoluminescence glow curves and calculation of trapping parameters (activation energy and frequency factor) for individual deconvoluted peaks for 25kGy gamma irradiated of unsensitized and sensitized mica have been done using glow curve deconvolution software.

Experimental study and numerical modelling of the irradiation damage recovery in zirconium alloys

Neutron irradiation damage in zirconium alloys used as fuel cladding tubes for Pressurized Water Reactors in the nuclear industry consists mainly in a high density of small prismatic dislocation loops. During post-irradiation heat treatment thermal annealing of loops occurs. This phenomenon has been investigated by transmission electron microscopy and microhardness tests. It has been shown that the loop density decreases while their mean size increases. Furthermore it was demonstrated that only vacancy loops remain present in the material after a long term annealing at high temperature. A mechanism based on vacancies diffusion has been proposed to explain the loop evolution during annealing. A cluster dynamic model, originally developed to compute the evolution of the microstructure under irradiation, has been adapted to the modelling of the annealing for zirconium alloys. This physically based model reproduces the loop size and density evolution during a large variety of heat treatments and also provides a better understanding of the mechanisms involved in the loop recovery.

Characterization of a power bipolar transistor as high-dose dosimeter for 1.9–2.2 MeV electron beams

Results of the characterization studies on a power bipolar transistor investigated as a possible radiation dosimeter under laboratory condition using electron beams of energies from 2.2 to 8.6 MeV and gamma rays from a 60Co source and tested in industrial irradiation plants having high-activity 60Co γ-source and high-energy, high-power electron beam have previously been reported. The present paper describes recent studies performed on this type of bipolar transistor irradiated with 1.9 and 2.2 MeV electron beams in the dose range 5–50 kGy. Dose response, post-irradiation heat treatment and stability, effects of temperature during irradiation in the range from –104 to +22 °C, dependence on temperature during reading in the range 20–50 °C, and the difference in response of the transistors irradiated from the plastic side and the copper side are reported. DLTS measurements performed on the irradiated devices to identify the recombination centres introduced by radiation and their dependence on dose and energy of the electron beam are also reported.

Electron-beam modification of the near-surface layers of photosensitive glasses

Electron-beam treatment of photosensitive silicate glasses doped with silver or copper ions leads to the formation of metal nanoparticles in the near-surface layer of a sample. The characteristics of this layer depend on the type of metal ions, pre- and postirradiation heat treatments, charge distribution, and conditions for the removal of electrons from the surface. A certain spatial profile of charge distribution can lead to the formation of lenslike structures with a thickness of 200–400 nm.

Evaluation of sequentially crosslinked ultra‐high molecular weight polyethylene

This study was undertaken to investigate the effect of crosslinking ultra-high molecular weight polyethylene (UHMWPE) in a sequential manner to the final desired dose and to compare the results to single-dose crosslinking. To verify these results, an explanted, commercially available, sequentially crosslinked component was characterized. Finally, additional tensile testing was conducted to determine if tensile-sample thickness has a significant effect on the mechanical properties of UHMWPE. Based upon this well-controlled study with the same starting material, there is no apparent benefit of sequential crosslinking over crosslinking by single dose in any of the mechanical, thermophysical, physical, or oxidative properties evaluated in this study. In contrast, the soak temperature of the postirradiation heat treatment was more influential and exhibited statistically significant effects on the stability, structure, and properties of the resultant material. Compared to virgin material, crosslinking always resulted in decreases in tensile strength, elongation, and impact strength. These results were confirmed by characterization of a retrieved, sequentially crosslinked (X3) cup. All of the metrics derived for the retrieved cup were virtually identical to the sequential- and single-dose-crosslinked materials produced in this study. Examination of the effect of tensile-sample thickness demonstrated that there are significant effects on the resultant properties. In particular, the ultimate tensile strength of UHMWPE can be elevated by conducting tensile tests with thin specimens.

Embrittlement of RPV steels: An atom probe tomography perspective

Atom probe tomography has played a key role in the understanding of the embrittlement of neutron irradiated reactor pressure vessel steels through the atomic level characterization of the microstructure. Atom probe tomography has been used to demonstrate the importance of the post weld stress relief treatment in reducing the matrix copper content in high copper alloys, the formation of ∼2-nm-diameter copper-, nickel-, manganese- and silicon-enriched precipitates during neutron irradiation in copper containing RPV steels, and the coarsening of these precipitates during post irradiation heat treatments. Atom probe tomography has been used to detect ∼2-nm-diameter nickel-, silicon- and manganese-enriched clusters in neutron irradiated low copper and copper free alloys. Atom probe tomography has also been used to quantify solute segregation to, and precipitation on, dislocations and grain boundaries.

Synergistic effect of combination of Irganox 1010 and zinc stearate on thermal stabilization of electron beam irradiated HDPE/EVA both in hot water and oven

Thermo-oxidative stability of HDPE/EVA blends can be considerably increased by combination of a high-molecular weight phenolic antioxidant and zinc stearate. In this work, the post-irradiation thermal stability of HDPE/EVA blends has been studied. High-density polyethylene and its blends with ethylene-vinylacetate copolymer in both pure form and mixed with Irganox 1010 and zinc stearate were exposed to electron beam radiation at doses between 80 and 150 kGy, at room temperature, in air. In order to evaluate the thermal stability of the samples, post-irradiation heat treatments were done in both hot water bath at 95 °C and in an oven at 140 °C. The mechanical properties and changes in the chemical structure were determined during thermal aging in hot water and oven. The gel content was enhanced by increasing EVA concentration in all applied doses. The stabilized blends have lower gel content than the unstabilized samples. From the results of heat aging treatments it was observed that the thermal stability of the unstabilized blend samples was lower than HDPE. Thermal stability of the samples has been improved by incorporation of Irganox 1010 and zinc stearate. Formation of hydroxyl group was insignificant for stabilized samples during heat aging in both conditions. Also, the changes in the value of oxidation induction time (OIT) for the stabilized samples were negligible after prolonged immersion in hot water.

Embedded photonic structures fabricated in photosensitive glass using proton beam writing

In this paper, we present a method that utilizes a focused beam of mega electron volt (MeV) protons to fabricate embedded photonic structures in Foturan™ glass. Both direct modification via proton beam end of range damage and post irradiation heat treatment are used to make the structures. Microfluidic channels with integrated waveguides and optical diffraction gratings are made using this technique.

Ultraviolet-visible absorption spectra of N-doped TiO2 film deposited on sapphire

The optical-response properties of nitrogen(N)-doped titanium dioxide (TiO2) films are investigated by means of a combination of ultraviolet-visible absorption spectroscopy and first-principles density-functional calculations. The TiO2 films were epitaxially grown on the sapphire substrate by the pulsed laser deposition method. The doping of N atoms was achieved by 70keV of N+ ion implantation, followed by postirradiation heat treatment at 550°C for 2h in air. We find that when 5×1016 (1×1017)Nions∕cm2 were implanted into the epitaxially grown TiO2 film, the absorption edge is reproducibly shifted to lower energy by about 0.06 (0.12)eV together with a significant optical absorption extending into the visible-light region. These experimental data can be explained by our calculated band structure of N-doped TiO2, where the bands originating from N 2p states locate above the valence band edge, while the band gap narrowing due to the mixing of N with O 2p states is 0.04eV.