Radiation-induced Degradation Research Articles

Optimized radiation-hardened erbium doped fiber amplifiers for long space missions

In this work, we developed and exploited simulation tools to optimize the performances of rare earth doped fiber amplifiers (REDFAs) for space missions. To describe these systems, a state-of-the-art model based on the rate equations and the particle swarm optimization technique is developed in which we also consider the main radiation effect on REDFA: the radiation induced attenuation (RIA). After the validation of this tool set by confrontation between theoretical and experimental results, we investigate how the deleterious radiation effects on the amplifier performance can be mitigated following adequate strategies to conceive the REDFA architecture. The tool set was validated by comparing the calculated Erbium-doped fiber amplifier (EDFA) gain degradation under X-rays at ∼300 krad(SiO2) with the corresponding experimental results. Two versions of the same fibers were used in this work, a standard optical fiber and a radiation hardened fiber, obtained by loading the previous fiber with hydrogen gas. Based on these fibers, standard and radiation hardened EDFAs were manufactured and tested in different operating configurations, and the obtained data were compared with simulation data done considering the same EDFA structure and fiber properties. This comparison reveals a good agreement between simulated gain and experimental data (<10% as the maximum error for the highest doses). Compared to our previous results obtained on Er/Yb-amplifiers, these results reveal the importance of the photo-bleaching mechanism competing with the RIA that cannot be neglected for the modeling of the radiation-induced gain degradation of EDFAs. This implies to measure in representative conditions the RIA at the pump and signal wavelengths that are used as input parameters for the simulation. The validated numerical codes have then been used to evaluate the potential of some EDFA architecture evolutions in the amplifier performance during the space mission. Optimization of both the fiber length and the EDFA pumping scheme allows us to strongly reduce its radiation vulnerability in terms of gain. The presented approach is a complementary and effective tool for hardening by device techniques and opens new perspectives for the applications of REDFAs and lasers in harsh environments.

Radiation resistance of polypropylene composites by incorporating reduced graphene oxide and antioxidant: A comparison study

In this study, polypropylene (PP) composites were fabricated by incorporating reduced graphene oxide (RGO) sheets and antioxidant pentaerythritol tetra [β-(3, 5-di-tert-butyl-4-hydroxyphenyl)-propionate] (AO1010) to comparatively investigate the effect of graphene and antioxidant on the radiation resistance. Morphological observation and X-ray diffraction reveal the uniform dispersion of RGO. The incorporation of antioxidant is beneficial to the improved dispersion and exfoliation of RGO nanosheets in the PP matrix. The melting temperature decreases significantly with increasing irradiation dose, whereas the crystallinity remains almost unchanged for all the samples before and after irradiation. Tensile strength analysis demonstrates that incorporating RGO sheets is more effective for radiation protection at low doses, and adding AO1010 is more applicable to radiation resistance at high doses. Furthermore, the mechanical performance and the decomposition temperature of PP/AO1010/RGO composites by simultaneously incorporating 0.5 wt% AO1010 and 1.0 wt% RGO sheets are higher than that of PP/AO1010 and PP/RGO composites upon gamma irradiation at various doses, indicating an additive effect between RGO and AO1010 in retarding the radiation-induced degradation of PP composites. The intrinsic mechanism of radiation resistance is attributed to the free radical scavenging and oxygen barrier effect. The additive effect between RGO and AO1010 can substantially reduce the number of peroxy radicals and oxygen concentration in the composites, resulting in the remarkable improvement in radiation resistance.

Novel system for pulse radiolysis with multi-angle light scattering detection (PR-MALLS) – concept, construction and first tests

Time-resolved pulse radiolysis, utilizing short pulses of high-energy electrons from accelerators, is an effective method for rapidly generating free radicals and other transient species in solution. Combined with fast time-resolved spectroscopic detection (typically in the ultraviolet/visible/near-infrared), it is invaluable for monitoring the reactivity of species subjected to radiolysis on timescales ranging from picoseconds to seconds. When used for polymer solutions, pulse radiolysis can be coupled with light-scattering detection, creating a powerful tool for kinetic and mechanistic analysis of processes like degradation or cross-linking of macromolecules. Changes in the light scattering intensity (LSI) of polymer solutions are indicative of alterations in the molecular weight and/or in the radius of gyration, i.e., the dimensions and shape of the macromolecules. In addition to other detection methods, LSI technique provides a convenient tool to study radiation-induced alterations in macromolecules as a function of time after the pulse. Pulse radiolysis systems employing this detection mode have been so far constructed to follow light scattered at a single angle (typically the right angle) to the incident light beam. Here we present an advanced pulse radiolysis & multi-angle light-scattering-intensity system (PR-MALLS) that has been built at IARC and is currently in the phase of optimization and testing. Idea of its design and operation is described and preliminary results for radiation-induced degradation of pullulan as well as polymerization and crosslinking of poly(ethylene glycol) diacrylate are presented. Implementation of the proposed system provides a novel research tool, which is expected to contribute to the expansion of knowledge on free-radical reactions in monomer- and polymer solutions, by delivering precise kinetic data on changes in molecular weight and size, and thus allowing to formulate or verify reaction mechanisms. The proposed method is universal and can be applied for studying both natural and synthetic polymers. The developed system can be also valuable in studies of the border of biology and medicine, especially on radical reactions of biopolymers and their conformational transitions. Furthermore, capability to follow fast changes in mass and dimensions of nanobjects may be of significant importance for nanoscience and nanotechnology.

Characterization of microporous ECTFE membrane after exposure to different liquid media and radiation

Changes in the properties of microfiltration (MF) membranes exposed to acids, bases and organic solvents used in semiconductor processing are of interest. Microfiltration membranes used for sterilization in beverage, biotechnology and pharmaceutical industries are sterilized by gamma radiation among others. Irradiation-induced degradation in membrane properties should be known. Microporous membranes of ethylene chlorotrifluoroethylene (ECTFE) membranes subjected to caustic soaking, organic solvent soaking and γ-irradiation were characterized extensively and compared with widely-used polyvinylidene fluoride (PVDF) membranes for selected properties. ECTFE membrane swellings by seven solvents including tri-n-octylamine (TOA) were much larger than those of nonporous ECTFE films. Scanning electron microscopy, atomic force microscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) indicated significant defects in TOA-soaked membranes. Thermogravimetric analysis (TGA) and DSC confirmed TOA presence in membrane pores. Solvents THF (tetrahydrofuran), toluene, acetonitrile and TOA decreased Young's modulus by 6–30%. ECTFE membranes resisted plasticization by these solvents: glass transition temperature variations were limited. In TOA-treated membranes, XRD indicated more significant defects in PVDF membranes. Treatment with NaOH solutions showed no effect on contact angle and bubble point pressure (BPP). Only 3M caustic solution reduced liquid entry pressure by 13.8 kPag. ECTFE membranes showed greater hydrophobicity, stronger wetting resistance and better ability to maintain hydrophobicity vis-à-vis PVDF membranes. ECTFE membranes subjected to γ-radiation (up to 45 kGy) showed almost no effect on morphology, porosity and Young's modulus. Slight variations were observed in BPP, melting enthalpy obtained via DSC and energy loss measured in dielectric relaxation spectroscopy.

Gamma and Electron NIEL Dependence of Irradiated GaAs

In GaAs material, the radiation-induced degradations are demonstrated to vary according to the nonionizing energy loss (NIEL). But some discrepancies are still observed between experimental degradation measurements and predicted NIELs. The used displacement threshold energy varies, from one author to another, from 10 up to 25 eV. A measurement made with 60Co gamma rays is used to investigate the relevance of the NIEL scaling law for both electrons and gamma rays.

REMOVAL OF CRYSTAL VIOLET DYE FROM AQUEOUS SOLUTION BY GAMMA IRRADIATION

In this study the radiation-induced degradation of crystal violet (CV) dye under various experimental conditions has been investigated. D0.5, D0.9 and D0.99 values suggests that lower doses are required for 50%, 90% and 99% removal of CV dye when the sample solution contains excessive amount of •OH radicals. The removal efficiency of CV dye in terms of G-values was also calculated under each reaction conditions. The results showed that •OH radicals are playing effective role in the degradation of CV dye as compared to eaq‒ and •H radicals. The gamma irradiation process effectively degraded CV dye at all pH values. The organic byproducts were examined and accordingly degradation pathway was proposed.

Radiation Response and Adaptive Control-Based Degradation Mitigation of MEMS Accelerometers in Ionizing Dose Environments

This paper investigates the effects of gamma radiation on the operation of commercially available capacitive microelectromechanical accelerometers intended for use in robotic systems deployed for nuclear disaster remediation. Radiation-induced accelerometer degradation is examined in terms of its effects on the input–output relationship of ADXL325 accelerometers (Analog Devices, Inc., Norwood, Massachusetts, USA) prior to sensor failure. Results show a moderate increase in sensor nonlinearity as well as significant, non-monotonic changes to accelerometer axis sensitivity and zero- $g$ bias. Both part-to-part variation and axis-to-axis variation within individual accelerometers are observed. The effects of the observed accelerometer degradation on the performance of a simple robotic manipulator that relies on acceleration feedback are evaluated in simulation. Additionally, using tools derived from adaptive control theory, this paper presents a real-time recalibration technique for mitigating the effects of the measured accelerometer degradation on the performance of robotic systems that can be applied in-field, without the knowledge of the degradation mechanisms. An example implementation of this technique is also evaluated. Results suggest that control-based strategies for mitigating hardware degradation may be able to extend the useful operating lifetime of non-radiation-hardened sensors in robotic systems deployed in extreme radiation environments.

Efficiency of La-doped TiO2 calcined at different temperatures in photocatalytic degradation of β-blockers

Photocatalytic activity of titania–based photocatalysts doped with 1% La has been tested in UVA radiation-induced degradation of two β-blockers – metoprolol tartrate (MET) and propranolol hydrochloride (PRO). Photocatalysts have been synthesized by sol–gel process followed by calcination at various temperatures in the range of 450–750°C. The great impact of calcination temperature on the structural, compositional and morphological properties of prepared catalysts has been revealed by XRPD, SEM, BET and Raman scattering measurements. Doped catalysts calcined at 450–650°C, with dominant anatase phase and developed mesoporous structure, have displayed higher photocatalytic performance than much less porous samples calcined at 700–750°C, with sodium hexatitanate as dominant phase. Also, La-doped anatase sample has shown higher efficiency in degradation of MET and PRO in comparison with the efficiency of undoped TiO2 nanopowders calcined at same temperatures. The quenching effects of various scavengers suggest that the major role in degradation of MET may be attributed to reactive radicals, whereas photogenerated holes are mainly responsible for degradation of PRO. Applying density functional theory (DFT) calculations, we analyzed fundamental structural and electronic properties (total and polar surface areas, frontier molecular orbitals, optoelectronic properties and average local ionization energy surfaces) of MET and PRO molecules, which are of significance for the understanding of more effective degradation of PRO in comparison with MET.

Gamma irradiation-induced complete degradation and mineralization of phenol in aqueous solution: Effects of reagent

This study aims to gain new insight into phenol degradation and mineralization in aqueous solution using ionizing radiation to control its radiolytic elimination under various experimental conditions and to present the different radical reactions involved in water radiolysis. The most obvious finding of this study is that the combination of a reagent, i.e., O3, H2O2, N2O, O2, or S2O82−, with γ-rays effectively enhances the radiolytic system for phenol degradation or mineralization. Radiolytic yield is higher with H2O2 than with S2O82−. For the γ-ray/free O2, γ-ray/H2O2, γ-ray/S2O82−, γ-ray/N2O, and γ-ray/N2 systems, the absorbed doses for 90% phenol elimination are 1.7, 0.85, 1.65, 1.2, and 6.4kGy, respectively; in contrast, phenol can be decomposed totally and directly via reaction with molecular ozone. The lowest dose constant for phenol removal is determined for γ-ray/HCO3−. 89% of mineralization is reached for an absorbed dose of 10kGy with a γ-ray/S2O82− combination.

Development and Characterization of Photoinduced Acrylamide-Grafted Polylactide Films for Biomedical Applications

Surface grafting of biodegradable/biocompatible polylactide (PLA) films by a UV-assisted reaction has been developed by employing a hydrophilic acrylamide (Am) monomer, an N,N′-methylenebisacrylamide (MBAm) cross-linker, and a camphorquinone (CQ)/N,N′-dimethylaminoethylmethacrylate (DMAEMA) photoinitiator/coinitiator system. The accomplishment of the process is confirmed by FTIR and XPS analyses. Physicochemical changes of the grafted PLA films are evaluated in terms of chemical structures, radiation-induced degradation followed by crystallization, morphology, thermal properties, and mechanical behavior. The results reveal that a low degree of PLA degradation through chain scission is observed in both blank and grafted PLA films. This generates more polar chain ends that can further induce crystallization. Results from contact angle measurements indicate that the grafted films have higher hydrophilicity and pH-responsive behavior. The incorporation of PAm on the film’s surface and the induced crystallization lead to improvements in certain aspects of mechanical properties of the films. The materials have high potential for use in biomedical and environmental applications, such as cell culture substrates or scaffolds or pH-sensitive absorbents.

Displacement Damage in Bipolar Junction Transistors: Beyond Messenger-Spratt

Bipolar junction transistors (BJTs) with relatively large feature sizes, typical of older technologies and high-voltage devices, are susceptible to recombination in the neutral base region when they are damaged by atomic displacement. This results in gain degradation, which, as originally described by Messenger and Spratt, can be modeled as an increase in the ratio of BJT base to collector current ( $1/\beta $ ) when the device is exposed to high energy particles (e.g., neutrons). While this also occurs in smaller devices and in those intended for operation at lower voltages, recombination in the emitter-base depletion region typically dominates the radiation-induced gain degradation in these devices. This is a consequence of the recombination rate being highest in regions where the electron and hole concentrations are approximately equal. Recombination in the neutral base and emitter-base depletion region exhibit different dependences on applied voltage, base doping and neutral base width. These dependences result in inaccuracies in the standard Messenger-Spratt equation, even for devices with base widths as large as $\sim 10~\mu \text {m}$ . This paper presents a physics-based modification of the equation which provides a much better fit to experimental data, particularly at low voltages.

Impact of 2 MeV Proton Irradiation on the Large-Signal Performance of Ka-Band GaN HEMTs

GaN high electron mobility transistors (HEMTs) have shown the potential to be extremely tolerant of the space radiation environment. To understand whether this radiation tolerance extends to millimeter wave GaN technology nodes, we have investigated the performance of discrete devices made with a commercial Ka-band AlGaN/GaN HEMT process after exposure to 2 MeV proton irradiation. In addition, we evaluate the large signal RF performance to enable the extraction of relevant device metrics (output power, gain, PAE) and understand how this performance compares to existing models for radiation-induced degradation of DC and pulsed I-V parameters.

The treatment of aniline in aqueous solutions by gamma irradiation

AbstractA laboratory investigation of the radiation-induced degradation of aniline by gamma irradiation is the subject of this paper. During the inquiry, several aqueous samples with aniline concentrations of 25, 50, 75, 100 and 200 mg/L were irradiated for 5, 10, 15, 20, 25 and 30 h, respectively, by a

Analysis of TID Process, Geometry, and Bias Condition Dependence in 14-nm FinFETs and Implications for RF and SRAM Performance

Total ionizing dose results are provided, showing the effects of different threshold adjust implant processes and irradiation bias conditions of 14-nm FinFETs. Minimal radiation-induced threshold voltage shift across a variety of transistor types is observed. Off-state leakage current of nMOSFET transistors exhibits a strong gate bias dependence, indicating electrostatic gate control of the sub-fin region and the corresponding parasitic conduction path are the largest concern for radiation hardness in FinFET technology. The high- $V_{\textit {th}}$ transistors exhibit the best irradiation performance across all bias conditions, showing a reasonably small change in off-state leakage current and $V_{\textit {th}}$ , while the low- $V_{\textit {th}}$ transistors exhibit a larger change in off-state leakage current. The “ worst-case” bias condition during irradiation for both pull-down and pass-gate nMOSFETs in static random access memory is determined to be the on-state ( $V_{\textit {gs}}=V_{\textit {dd}}$ ). We find the nMOSFET pull-down and pass-gate transistors of the SRAM bit-cell show less radiation-induced degradation due to transistor geometry and channel doping differences than the low- $V_{\textit {th}}$ transistor. Near-threshold operation is presented as a methodology for reducing radiation-induced increases in off-state device leakage current. In a 14-nm FinFET technology, the modeling indicates devices with high channel stop doping show the most robust response to TID allowing stable operation of ring oscillators and the SRAM bit-cell with minimal shift in critical operating characteristics.

Gamma radiolysis of anion exchange resins based on 4-vinylpyridine in aqueous solution

Radiation-induced degradation of the weakly and strongly 4-vinylpyridine basic ion exchange resins by gamma radiolysis was investigated in the presence of air and liquid water. This study is focused on evaluating the radiolytic gases (H2, CO, CO2 and CH4) and liquid products (water-solute TOC and NH4 +). The weakly basic resin yielded lower amounts of H2 and CO and higher amounts of CO2 than those of the strongly basic resin. Moreover, the strong basic resin tended to yield greater amounts of NH4 +. Resins were characterized by the FTIR spectroscopy technique and the results showed that the resins structures are relatively stable.

Prediction of the photoluminescence of In0.53Ga0.47As/InP irradiated by 1 MeV electron

Minimizing the impact of radiation-induced degradation on light source and optoelectronic devices based on the In0.53Ga0.47As/InP (InGaAs/InP) plays an important role in their applications. The first objective of this work is to measure the photoluminescence (PL) intensity of InGAs/InP before and after electron radiation. Electron fluence (0–9×1014electrons/cm2)-dependent PL of InGaAs/InP in the range of free- and bound-exciton emission is presented. The experimental results show that the PL intensity of InGaAs/InP is decreased with increasing fluence and more electron-induced defects occurred in the InGaAs/InP hetero-junction than in the InGaAs/InP quantum well. The wavelength dependence of the PL intensity was then fitted using the “Asym2Sig” equation as an asymmetric double sigmoidal function, and the coefficients obtained show reasonable agreement with the experimental data. The strongest bound-exaction line with a width (full width at half-maximum) exhibited a thermal activation energy of approximately 0.71eV for the InGaAs/InP hetero-junction, while it was not observed of InGaAs/InP quantum well. Moreover, the influence of fluence on the PL intensity was explained with the mathematical method in this work, which enables the prediction of the PL intensity of InGaAs/InP through wavelength and fluence.

Ionizing radiation exposure reveals instability of purified domains in polymer/fullerene solar cells

Solar cells based on conjugated polymer and fullerene blends exhibit morphology-dependent stability towards ionizing radiation exposure. Blend thin film solar cells of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C60-butyric acid methyl ester (PCBM) were irradiated up to 1Mrad with X-rays (10–60KeV) and investigated with resonance Raman and photocurrent/photovoltage modulation spectroscopy and imaging. Bulk blend morphological characteristics were pre-selected by controlling film processing conditions (i.e., solvent and thermal annealing). As-cast P3HT/PCBM devices with a large fraction of a well-mixed phase display improvements in performance upon application of post-irradiation annealing treatments. On the other hand, devices annealed prior to irradiation showed irreversible performance degradation that could not be recovered following annealing treatments after exposure. Resonance Raman spectroscopy and imaging following irradiation up to 1Mrad reveals virtually no changes in the P3HT structural and packing integrity for both types of devices. Intensity modulated photocurrent/photovoltage spectroscopy measurements indicate that radiation-induced performance degradation is concentrated in the vicinity of device contacts, evident from large alterations in charge extraction kinetics. We propose that charge transfer from the aluminum cathode leads to formation of a space charge zone which becomes more pronounced in devices with greater phase purification (i.e., larger PCBM crystallites in the vicinity of the cathode). Importantly, well-mixed P3HT/PCBM regions, which are more plentiful in as-cast devices, appear to mitigate radiation-induced performance degradation since application of post-irradiation annealing treatments restores device performances to pristine levels. Our results suggest that greater morphological stability, such as polymer/fullerene systems forming co-crystals, is key for suppressing performance losses from ionizing radiation exposure.

Study of the electrical parameters degradation of GaAs sub-cells for triple junction space solar cells by computer simulation

In this paper, a theoretical study of the electrical parameters degradation of different n-type GaAs sub-cells for InGaP/GaAs/Ge triple junction solar cells irradiated with 1 and 5 MeV electrons has been performed by means of computer simulation. Effects of base carrier concentration upon the maximum power point, short-circuit current, open circuit voltage, diffusion current, recombination current and series resistance of these devices have been researched using the displacement damage dose method, the one-dimensional PC1D device modeling program and a home-made numerical code based on genetic algorithms. The radiative recombination lifetime, damage constant for minority-carrier lifetime and carrier removal rate models for GaAs sub-cells have been used in the simulations. An analytical model has been proposed, which is useful to describe the radiation-induced degradation of diffusion current, recombination current and series resistance. Results obtained in this work can be used to predict the radiation resistance of solar cells over a wide range of energies.

Mechanisms of Radiation-Induced Degradation of CFCl3 and CF2Cl2 in Noble-Gas Matrixes: An Evidence for "Hot" Ionic Channels in the Solid Phase.

The X-ray-induced transformations of simple chlorofluorocarbons (CFCl3 and CF2Cl2) in solid noble-gas matrixes (Ne, Ar, Kr, and Xe) at 7 K were studied in order to elucidate basic mechanisms of the radiation-chemical degradation with possible implications for stratospheric and extraterrestrial ice chemistry. The decomposition of parent molecules and formation of products were monitored by FTIR spectroscopy, and the identification was supported by ab initio calculations at the CCSD(T) level. It was shown that the ionic reaction channels were predominating in most cases (except for CF2Cl2/Xe system). The primary radical cations (CFCl3+• and CF2Cl2+•) are either stabilized in matrixes or undergo fragmentation to yield the corresponding secondary cations (CFCl2+, CCl3+, CF2Cl+) and halogen atoms. The probability of fragmentation through different channels demonstrates a remarkable matrix dependence, which was explained by the effect of excess energy resulting from the exothermic positive hole transfer from matrix atoms to freon molecules. A qualitative correlation between "hot" ionic fragmentation at low temperatures and gas-phase ion energetics was found. However, dissociative electron attachment leads to formation of neutral radicals (CFCl2• or CF2Cl•) and chloride anions. One more possible way of dissociative electron attachment in the case of CF2Cl2 is formation of CF2•• and Cl2-•. A general scheme of the radiation-induced processes is proposed.

Effects of electron beam irradiation on thermal and mechanical properties of poly(lactic acid) films

The purpose of this study is to examine the effect of electron-beam (EB) radiation on biodegradable polylactic acid (PLA), and to understand radiation-induced degradation mechanisms. PLA films were irradiated between 0 and 120 kGy and physical properties were characterized by means of GPC, DSC, DMA and tensile drawing. It was shown that degradation of PLA under EB leads to a random chain scission responsible for a reduction of the molar mass. These molar mass changes affect glass transition temperature Tg, degree of crystallinity, and mechanical properties. It was found that Tg, stress and strain at break decrease with increasing irradiation dose, whereas the degree of crystallinity increases up to 45 kGy then decreases. Cross-linking Gx and chain scission Gs values of PLA revealed that chain scission reactions at lower dose predominate over cross-linking. DMA results exhibit an exothermal re-crystallization for neat and irradiated samples, which disappears with increasing heating rate. These results were confirmed by DSC measurements. Ductile-brittle transition was determined as function of EB-dose and crosshead speed. A change of physico-chemical and mechanical properties was evidenced during application of a dose of 45 kGy.