Post-irradiation Thermal Treatment Research Articles

Effects of laser pretreatment on the formation of nanostructured carbon on the surface of chlorinated polyvinyl chloride under high-power ion beam irradiation

The features of formation of surface morphology of chlorinated polyvinyl chloride (pure and with the addition of the catalyst - ferrocene) under the influence of a high-power ion beam of nanosecond duration after the preliminary pulsed laser treatment of the polymer surface have been investigated. It was found that the morphology of the irradiated surface of chlorinated polyvinyl chloride after pulsed laser surface pretreatment differs significantly from the morphology of the irradiated surface of chlorinated polyvinyl chloride after a preliminary stationary heat treatment. For pure chlorinated polyvinyl chloride, pulsed laser pretreatment with increasing power leads to an increase in the porosity of the surface layer after high-power ion beam irradiation, whereas different surface morphologies, including fibers (including polymer fibers) of different diameters, can be obtained for the pre-stationary post-irradiation thermal treatment of this polymer. Pre-stationary thermal pretreatment of chlorinated polyvinyl chloride with the addition of ferrocene (Fe(C5H5)2) leads to a decrease in the diameter of formed carbon nanofibers (with an increase in the treatment temperature). During the pulsed laser pretreatment, an increase in the porosity of the treated layer and a slight increase in the proportion of nanofibers of larger diameter are observed. To explain the obtained differences for pulsed laser and stationary thermal pretreatment, the effect of polymer heating rate on the features of chlorinated polyvinyl chloride decomposition was analyzed.

The Role of Si Self‐interstitial Atoms in the Formation of Electrically Active Defects in Reverse‐Biased Silicon n+–p Diodes upon Irradiation with Alpha Particles

Results of a study of changes in electrical characteristics of n+–p diodes on boron‐doped epi‐silicon induced by irradiation with alpha particles under applied reverse bias voltages are presented. It is found that the irradiation results in a significantly lower introduction rate of carrier‐compensating radiation‐induced defects (RIDs) in the space charge region of the reverse‐biased structures compared with those in the neutral base region and in similar diodes irradiated without bias. The dominant hole and electron emission signals in the capacitance transient spectra of the irradiated diodes are characterized and identified with energy levels of some known RIDs in moderately doped p‐type Si:B. Changes in concentration of the defects are monitored after postirradiation minority carrier injection and thermal treatments. It is argued that the observed effect of the reduced concentration of RIDs in the space charge regions of the diodes is related mainly to some specific features of the silicon self‐interstitials (ISi): a very strong dependence of their thermal stability on the charge state and a highly enhanced mobility in p‐type Si under minority carrier injection conditions. The activation energy of electron emission from the doubly positively charged state of ISi is determined.

Coupled irradiation-temperature effects on induced point defects in germanosilicate optical fibers

We investigated the combined effects of temperature and X-rays exposures on the nature of point defects generated in Ge-doped multimode optical fibers. Electron paramagnetic resonance (EPR) results on samples X-ray irradiated at 5 kGy(SiO2), employing different temperatures and dose rates, are reported and discussed. The data highlight the generation of the Ge(1), Ge(2), E′Ge and E′Si defects. For the Ge(1) and Ge(2), we observed a decrease in the induced defect concentrations for irradiation temperatures higher than ~450 K, whereas the E′ defects feature an opposite tendency. The comparison with previous post-irradiation thermal treatments reveals peculiar effects of the temperature increase during the irradiation. Such difference, confirmed also by online radiation-induced attenuation measurements, has to be considered for practical use of these fibers in a mixed environment. Importantly, even if post-irradiation fading should be considered, the Ge(1) and Ge(2) concentrations measured by postmortem EPR experiments in room-temperature-irradiated samples are quite representative of the concentrations induced in the temperature range 230–450 K regardless of the investigated dose rate. The enhancement of the E′ content can be related to the simultaneous generation of this defect with non-bridging oxygen hole center from strained bonds implying a relevant modification of the defects generation/formation processes in the host glass matrix.

Growth of ZnO nanostructures by femtosecond laser irradiation of polycrystalline targets

The formation of LIPSS upon irradiation with ultrashort laser pulses on the surface of polycrystalline ZnO samples and the potential use of irradiated areas as growth patterns for the production of highly ordered nanostructures upon redeposition have been studied. For this purpose, we have performed different sets of irradiation experiments including static irradiation experiments at low and high repetition rates, as well as scanned beam experiments at high repetition rate, this later in order to generate relatively large template regions for nanostructure growth by redeposition. In all cases, LIPSS formation has been achieved in the ZnO polycrystalline surface. Under appropriate irradiation conditions, the material is redeposited rendering a high density of nanostructures with high aspect ratios and good crystal quality. Given the special luminescent properties and applications of ZnO, particular attention has been paid to the luminescence properties after irradiation and after post-irradiation thermal treatments. The observed evolution has been correlated with evolution of point defects in the treated surfaces. Thermal treatments cause significant changes in both the topography and the cathodoluminescent emission, such as the development of laminar structures, the emergence of nucleation centers and the recovery of ultraviolet emission previously quenched as a consequence of irradiation. Interestingly, LIPSS remain after the luminescent recovery by thermal annealing, opening the possibility to control both luminescence properties and grain size while maintaining an ordered structure with a high effective surface area.

Adsorption and Reactions on TiO2: Comparison of N,N-Dimethylformamide and Dimethylamine

Fourier transform infrared spectroscopy has been employed to study the adsorption and reactions of N,N-dimethylformamide (DMF) and dimethylamine (DMA) on powdered TiO2. DMF can be adsorbed in molecular form with the carbonyl interacting with the surface Lewis site (Ti4+) or in dissociative form of OCN(CH3)2. Theoretical adsorption study of rutile (110) points out that the C* and O atoms of OC*N(CH3)2 are bonded at a two-fold-coordinated O site and a five-fold-coordinated Ti site, respectively. The thermal products of DMF/TiO2 are found to be CO and DMA. Photochemical reaction of DMF on TiO2 in O2 generates CO2, HCOO, and NCO. O2 participates in the reaction with its oxygen atoms incorporated into the three products. DMA can be adsorbed in molecular form and imine species on TiO2. Photoirradiation of DMA/TiO2 in O2 generates CO2, HCOO, NCO, and imine species. Interestingly, DMF and OCN(CH3)2 are produced after postirradiation thermal treatment of DMA on TiO2, possibly from the reaction between residual DMA and HCOO photoproduct.

Removal of carbon-14 from irradiated graphite

Approximately 250,000 tonnes of irradiated graphite waste exists worldwide and that quantity is expected to increase with decommissioning of Generation II reactors and deployment of Generation IV gas-cooled, graphite moderated reactors. This situation indicates the need for a graphite waste management strategy. On of the isotopes of great concern for long-term disposal of irradiated graphite is carbon-14 (14C), with a half-life of 5730years. Study of irradiated graphite from some nuclear reactors indicates 14C is concentrated on the outer 5mm of the graphite structure. The aim of the research presented here is to develop a practical method by which 14C can be removed. In parallel with these efforts, the same irradiated graphite material is being characterized to identify the chemical form of 14C in irradiated graphite.A nuclear-grade graphite, NBG-18, and a high-surface-area graphite foam, POCOFoam®, were exposed to liquid nitrogen (to increase the quantity of 14C precursor) and neutron-irradiated (1013neutrons/cm2/s). During post-irradiation thermal treatment, graphite samples were heated in the presence of an inert carrier gas (with or without the addition of an oxidant gas), which carries off gaseous products released during treatment. Graphite gasification occurs via interaction with adsorbed oxygen complexes. Experiments in argon only were performed at 900°C and 1400°C to evaluate the selective removal of 14C. Thermal treatment also was performed with the addition of 3 and 5vol% oxygen at temperatures 700°C and 1400°C. Thermal treatment experiments were evaluated for the effective selective removal of 14C. Lower temperatures and oxygen levels correlated to more efficient 14C removal.

Irradiation-induced nano-voids in strained tin precipitates in silicon

We report on self-assembling of spherically shaped voids in nanometer size strained Sn precipitates after irradiation with He+ ions in different conditions. It is found that high-temperature irradiation induces vacancies which are collected by compressively strained Sn precipitates enhancing of out-diffusion of Sn atoms from the precipitates. Nano-voids formation takes place simultaneously with a β- to α-phase transformation in the Sn precipitates. Post-irradiation thermal treatment leads to the removal of voids and a backward transformation of the Sn phase to β-phase. Strain-enhanced separation of point defects along with vacancy assisted Sn out-diffusion and precipitate dissolution are discussed.

German and Russian Irradiated Reactor Pressure Vessel Steels from PAS Point of View

This paper presents a comparison of commercially used German and Russian reactor pressure vessel steels from the positron annihilation spectroscopy point of view, having in mind knowledge obtained also from other techniques from the last decades. The second generation of Russian reactor pressure vessel steels seems to be fully comparable with German steels and their quality allows prolongation of NPP operating lifetime over projected 40 years. The embrittlement of CrMoV steels is very low due to the dynamic recovery of radiation-induced defects at reactor operating temperatures. Positron annihilation spectroscopy techniques can be e ectively applied for evaluation of microstructural changes caused by extreme external loads by proton implantation, with aim to simulate irradiation and for the evaluation of the e ectiveness of post-irradiation thermal treatments. We used our actual and previous results, collected during last 20 years from measurements of di erent reactor pressure vessel steels in as received , irradiated and post-irradiation annealed state and compare them with the aim to contribute to general knowledge based on experimental positron annihilation spectroscopy data.

Evaluation of the reactor pressure vessel steels by positron annihilation

This paper presents a comparison of commercially used German and Russian reactor pressure vessel steels from the positron annihilation spectroscopy (PAS) point of view, having in mind knowledge obtained also from other techniques from the last decades. The second generation of Russian RPV steels seems to be fully comparable with German steels and their quality allows prolongation of NPP operating lifetime over projected 40years. The embrittlement of CrMoV steels is relatively low due to effect of higher temperature which implies partial in situ annealing of primary microstructural point defects and therefore delays the degradation processes caused by neutron irradiation.PAS techniques can be effectively applied for evaluation of microstructural changes caused by extreme external loads (characterized by high dpa values) by proton implantation, with aim to simulate irradiation and for the evaluation of the effectiveness of post-irradiation thermal treatments. We used our actual and previous results, collected during last 20years from measurements of different RPV-steels in “as received”, irradiated and post-irradiation annealed state and compare them with the aim to contribute to general knowledge based on experimental PAS data.Actual results from irradiated German and Russian steels confirmed that no large voids or vacancy clusters were formed at defined irradiation conditions stated according to the real operational conditions at nuclear power plants. This indicate the fact that vacancy type defects bear hardly any responsibility for radiation-induced hardening and embrittlement of reactor pressure vessel steels and does not affect significantly the long-term operation of nuclear power plants from safety point of view.

Radiation curing of carbon fibre composites

Epoxy/carbon fibre reinforced composites were produced by means of e-beam irradiation through a pulsed 10MeV electron beam accelerator. The matrix consisted of a difunctional epoxy monomer (DGEBA) and an initiator of cationic polymerisation, while the reinforcement was a unidirectional high modulus carbon fibre fabric. Dynamic mechanical thermal analysis was carried out in order to determine the cross-linking degree. The analysis pointed out a nonuniformity in the cross-linking degree of the e-beam cured panels, with the formation of clusters at low Tg (glass transition temperature) and clusters at high Tg. An out-of-mould post irradiation thermal treatment on e-beam cured samples provides a higher uniformity in the network although some slight degradation effects. Mode I delamination fracture toughness and Interlaminar Shear Strength (ISS) were also investigated by means of Double Cantilever Beam (DCB) and Short Beam Shear tests, respectively. Results from this mechanical characterisation allowed to correlate fracture toughness of the bulk matrix resin, cross-linking density and fibre/matrix interaction to the delamination fracture behaviour of the fibre reinforced material.

Post-irradiation storage and thermal stability of thermoluminescence glow peaks in LiF:Mg,Cu,Si

Abstract Newly developed LiF:Mg,Cu,Si was found to exhibit no significant fading on room temperature post-irradiation storage up to several months. In view of the wide variation in the reported data of fading of LiF:Mg,Cu,P exhibiting glow curve structure similar to that of LiF:Mg,Cu,Si, a study of the effect of post-irradiation storage and thermal treatments on the deconvoluted glow peaks of LiF:Mg,Cu,Si was undertaken. The decay of inseparable peak-3 by post-irradiation storage or thermal treatments did not indicate any rearrangement in the trap occupation that would affect the response of the main peak (peak-4). A post-irradiation treatment at 125 °C for 10 min was found to be the optimum to eliminate the lower temperature peaks.

The effect of radiation dose on the tensile and impact toughness of highly cross‐linked and remelted ultrahigh‐molecular weight polyethylenes

Several highly cross-linked and remelted ultrahigh-molecular weight polyethylenes (UHMWPE) were introduced in 1998 as bearing materials for orthopaedic implants to achieve superior wear performance. However, gamma radiation and the subsequent postirradiation thermal treatment are associated with decreased mechanical properties such as ductility, toughness, and fatigue strength compared to noncross-linked materials. The purpose of this study was (a) to characterize the toughness (tensile and impact) of highly cross-linked and remelted UHMWPE of varying doses (0-255 kGy) and (b) determine whether a correlation exists between both toughness measures. As radiation dose increased, tensile toughness and impact toughness were shown to decrease in a nonlinear fashion; largely a result of the decrease in ductility, which was also observed. Impact toughness and tensile toughness were also found to be strongly correlated to one another (R(2) = 0.97).

The elimination of free radicals in irradiated UHMWPEs with and without vitamin E stabilization by annealing under pressure

Radiation crosslinking of ultrahigh molecular weight polyethylene (UHMWPE) has been used to decrease the wear of joint implant bearing surfaces. While radiation crosslinking has been successful in decreasing femoral head penetration into UHMWPE acetabular liners in vivo, postirradiation thermal treatment of the polymer is required to ensure the oxidative stability of joint implants in the long term. Two types of thermal treatment have been used: (i) annealing below the melting point preserves the mechanical properties but the residual free radicals trapped in the crystalline regions are not completely eliminated, leading to oxidation in the long-term and (ii) annealing above the melting point (melting) eliminates the free radicals but leads to a decrease in mechanical properties through loss of crystallinity during the melting process. In this study, we hypothesized that free radicals could be reduced by annealing below the melting point under pressure effectively without melting due to the elevation of the melting point. By avoiding the complete melting of UHMWPE, mechanical properties would be preserved. Our hypothesis tested positive in that we found the radiation-induced free radicals to be markedly reduced (below the detection limit of state-of-the-art electron spin resonance) by thermal annealing under pressure in radiation crosslinked virgin UHMWPE and UHMWPE/vitamin-E blends without loss of mechanical properties.

Characterization of a silicate glass as a high dose dosimeter

Commercial silicate glass has been investigated as a possible high dose dosimeter using an UV–vis spectrophotometer. Glass samples were irradiated by 60Co γ rays and the results compared with those obtained with 3.4 and 8.4 MeV electron beams. The irradiated samples showed rapid fading at room temperature immediately after irradiation. In order to improve the stability of absorbance, glass samples were submitted to post-irradiation thermal treatments (150 °C for 20 min). The influences of the dose, type and energy of the ionizing radiation on the fading characteristics and on the response of the irradiated and thermally treated glasses were studied. Dependence of the glass response on the temperature during gamma irradiation in the range −3 to 80 °C is reported. The reproducibility to reuse glass dosimeter by thermal bleaching the radiation induced colour centres at 300 °C for 30 min was also investigated. Calibration curves in the range 0.1–17 kGy were obtained by using in-plant calibration techniques against transfer standard alanine dosimeters in the Tunisian semi-industrial gamma irradiation facility.

Properties of ZnO nanocrystals prepared by radiation method

Zinc oxide nanoparticles were prepared by irradiation of aqueous solutions containing zinc(II) ions, propan-2-ol, polyvinyl alcohol, and hydrogen peroxide. Zinc oxide was found in solid phase either directly after irradiation, or after additional heat treatment. Various physicochemical parameters, including scintillation properties of prepared materials, were studied. After decomposition of impurities and annealing of oxygen vacancies, the samples showed intensive emission in visible spectral range and well-shaped exciton luminescence at 390–400 nm. The best scintillating properties had zinc oxide prepared from aqueous solutions containing zinc formate as initial precursor and hydrogen peroxide. Size of the crystalline particles ranged from tens to hundreds nm, depending on type of irradiated solution and post-irradiation thermal treatment.

Comparison of neutron and gamma irradiation effects on KU1 fused silica monitored by electron paramagnetic resonance

Electron paramagnetic resonance (EPR) studies have been carried out on KU1 fused silica irradiated with neutrons at fluences 10 21 and 10 22 n/m 2, and gamma-ray doses up to 12 MGy. The effects of post-irradiation thermal annealing treatments, up to 850 °C, have also been investigated. Paramagnetic oxygen-related defects (POR and NBOHC) and E′-type defects have been identified and their concentration has been measured as a function of neutron fluence, gamma dose and post-irradiation annealing temperature. It is found that neutrons at the highest fluence generate a much higher concentration of defects (mainly E′ and POR, both at concentrations about 5 × 10 18 spins/cm 3) than gamma irradiations at the highest dose (mainly E′ at a concentration about 4 × 10 17 spins/cm 3). Moreover, for gamma-irradiated samples a lower treatment temperature (about 400 °C) is required to annihilate most of the observed defects than for neutron-irradiated ones (about 600 °C).

UHMWPE for arthroplasty: past or future?

Wear debris related osteolysis is recognised as being the main cause of failure in joint replacements based on UHMWPE inserts. However, many solutions and “new” polyethylenes have been suggested in order to address this issue. This review discusses “historical” issues associated with UHMWPE, such as oxidation, sterilization method and storage, as well as “new” topics, such as crosslinking and stabilization. The final aim is to aid orthopaedic surgeons in their selection of polyethylene inserts and in the information given to the patients. The main problem for the polymer is degradative oxidation, which is caused by the combination of the irradiation used for sterilization and oxygen, and which leads to a decrease in wear resistance and mechanical properties. Irradiation and packaging in the absence of oxygen can only reduce the oxidation, while sterilization with gas (EtO or gas plasma) is the only method that effectively eliminates it. Manufacturing processes are of great relevance to the clinical duration and must be considered by surgeons. Crosslinked polyethylene has been developed for joint inserts due to its superior wear resistance compared to conventional UHMWPE; to prevent the oxidation, crosslinked polyethylene requires post-irradiation thermal treatment, which reduces its mechanical properties and which depends on the producer. Several good clinical results from the use of crosslinked acetabular cups have reported at mid-term, while early results for knee replacements are also encouraging. Recently, the use of the antioxidant vitamin E (alpha-tocopherol) has been introduced for joint prostheses in order to prevent the oxidation of both crosslinked and noncrosslinked UHMWPE.

Carbon fiber composites cured by γ‐radiation‐induced polymerization of an epoxy resin matrix

AbstractThe use of ionizing radiation in order to initiate polymerization of suitable monomers has found increased interest in the last two decades due to its several advantages. In this work, carbon fiber composites through gamma radiation polymerization of epoxy matrices have been produced for aerospace and advanced automotive applications. Composite samples were produced by irradiation at room temperature using different radiation doses and, as reference, thermal curing of the same epoxy resin formulations was also carried out. Furthermore, some irradiated samples were subjected to postirradiation thermal curing to complete the polymerization reactions. The properties of the cured materials were studied by dynamic mechanical thermal analysis and mechanical flexural tests. Also the effect of moisture absorption on the thermal properties was investigated. The results indicate that irradiation at room temperature gives rise to different cross‐link densities of the epoxy matrix depending on the total absorbed dose. Postirradiation thermal treatment makes the materials more “homogeneous,” resulting also in a higher glass transition temperature. Moreover, thermal analysis performed on irradiated samples, cut in both parallel and perpendicular directions to the fibers, has shown fiber‐‐matrix interactions that are less intensive in comparison to thermally cured samples. The water absorption data show a plasticization effect of moisture on the epoxy matrix, causing a significant reduction of Tg. Flexural tests reveal a marked effect of postirradiation thermal curing on the less cross‐linked samples, reflecting the higher efficiency of the thermal treatment on more mobile reactive species. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 27:163–171, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20127

Influence Of Growth Conditions on Irradiation Induced Defects in 4H-SiC

Nitrogen doped 4H-SiC epitaxial layers grown by hot-wall chemical vapor deposition were investigated by Deep Level Transient Spectroscopy after irradiation with 6 MeV electrons at room temperature. This study is focusing on the influence of nitrogen doping and C/Si ratio on the behaviour of the Z1,2 and EH6,7 levels which occur in already as-grown material but are substantially enhanced by electron and ion irradiation. It was found that both the Z1,2 and EH6,7 concentrations increase with both the nitrogen doping and the C/Si ratio. However, while the Z1,2 concentration increases during post-irradiation thermal treatment the opposite holds for the EH6,7 level especially in silicon rich samples. On the basis of these results, the influence of carbon and nitrogen on the formation of the Z1,2 complex is reconfirmed and a possible identity of the EH6,7 defect is discussed.

Hydrogen in Zircaloy-4: effects of the neutron irradiation on the hydride formation

X-ray diffraction patterns of neutron irradiated Zircaloy-4 samples were obtained at the Brazilian Synchrotron Light Laboratory (LNLS) to study the effects of the fast neutron fluxes and post-irradiation thermal treatments on the zirconium hydride evolution. The high intensity and resolution of the synchrotron beam allowed to detect the (111)δ and (220)δ diffraction peaks of the ZrH1.5 + x (0 ≤ x≤ 0.16) δ-phase in unirradiated Zircaloy-4 samples having a hydrogen concentration as low as 0.2 at.% (20 wppm). Then, irradiated samples, that were taken from the Zircaly-4 core components of the argentine HWPR Atucha I Nuclear Power Plant (CNA-1) were studied with that radiation to detect the diffraction peaks of ZrH1.5 + x δ-phase particles precipitated in samples having hydrogen isotope concentration lower than 2 at.% (220 wppm). A significant increment of the (111)δ and (220)δ peak areas were observed at room temperature after post-irradiation thermal treatments at 600 °C during 4 h. These results indicate that after the annealing a hydrogen concentration between 35 to 70 wppm, which were apparently absent in the irradiated samples has precipitated at room temperature as zirconium hydrides. That amount was estimated from a (220)δ peak area versus the bulk H concentration regression line, made with unirradiated samples. These results get support to a hydrogen trapping hypothesis proposed in previous works. In addition, it has been shown that the zirconium hydride that precipitate in the irradiated samples have the equilibrium δ-ZrH1.5 + x cubic crystalline structure.