Radiation-induced Losses Research Articles

Dose-dependent effects of gamma radiation sterilization on the collagen matrix of human cortical bone allograft and its influence on fatigue crack propagation resistance

Fatigue crack propagation resistance and high-cycle S–N fatigue life of cortical bone allograft tissue are both negatively impacted in a radiation dose-dependent manner from 0 to 25 kGy. The standard radiation sterilization dose of 25–35 kGy has been shown to induce cleavage of collagen molecules into smaller peptides and accumulation of stable crosslinks within the collagen matrix, suggesting that these mechanisms may influence radiation-induced losses in cyclic fracture resistance. The objective of this study was to determine the radiation dose-dependency of collagen chain fragmentation and crosslink accumulation within the dose range of 0–25 kGy. Previously, cortical bone compact tension specimens from two donor femoral pairs were divided into four treatment groups (0 kGy, 10 kGy, 17.5 kGy, and 25 kGy) and underwent cyclic loading fatigue crack propagation testing. Following fatigue testing, collagen was isolated from one compact tension specimen in each treatment group from both donors. Radiation-induced collagen chain fragmentation was assessed using SDS-PAGE (n = 5), and accumulation of pentosidine, pyridinoline, and non-specific advanced glycation end products were assessed using a fluorometric assay (n = 4). Collagen chain fragmentation increased progressively in a dose-dependent manner (p < 0.001). Crosslink accumulation at all radiation dose levels increased relative to the 0 kGy control but did not demonstrate dose-dependency (p < 0.001). Taken together with our previous findings on fatigue crack propagation behavior, these data suggest that while collagen crosslink accumulation may contribute to reduced notched fatigue behavior with irradiation, dose-dependent losses in fatigue crack propagation resistance are mainly influenced by radiation-induced chain fragmentation.

Расчетно-экспериментальная оценка реакции волоконного лазера на импульсное воздействие тормозного излучения

Experiments have been carried out to study the transient radiation-induced absorption in the active core of a double-clad ytterbium fiber and the response of a laser based on it under the impact of pulsed X-rays. It has been found that the time of loss of laser performance (downtime) under pulsed irradiation increases with an increase in the absorbed dose rate of radiation and a decrease in the laser pump power and reaches values of ~1 ms. An analysis of the experimental results shows that the laser response to the action of X-rays pulse is determined by radiation-induced losses in the active fiber core. A experimental-calculated method for estimating the radiation reaction of a laser, based on the results of studies of the active fiber, is proposed.

New optical method to study oxygen activity in flowing liquid

The necessity to study the oxygen activity of aqueous media in the flowing state to solve various problems has been substantiated. It has been found that emitted γ-quanta as a result of decay of 16N nuclei with energy more than 9 MeV cause the formation of additional color centers and reversible optical defects in the fiber. Their appearance leads to increased radiation-induced losses in the optical fiber, which reduce the power of laser radiation transmitted through it. A new optical method has been developed that makes it possible to study the nature of oxygen activity change by the number of γ-quanta emitted by 16N nuclei when the liquid moves along the pipeline. For the first time, the nature of the change in the spectral distribution of the number of 16N nuclei emitted as a result of oxygen activity was investigated, and its features in the current flow were determined. In order to realize long-term studies of oxygen activity, a method was proposed to restore optical properties of fiber in the presence of background radioactive radiation. Keywords:

Maximal single-frequency electromagnetic response

Modern nanophotonic and meta-optical devices utilize a tremendous number of structural degrees of freedom to enhance light–matter interactions. A fundamental question is how large such enhancements can be. We develop an analytical framework to derive upper bounds to single-frequency electromagnetic response, across near- and far-field regimes, for any materials, naturally incorporating the tandem effects of material- and radiation-induced losses. Our framework relies on a power-conservation law for the polarization fields induced in any scatterer. It unifies previous theories on optical scattering bounds and reveals new insight for optimal nanophotonic design, with applications including far-field scattering, near-field local-density-of-states engineering, optimal wavefront shaping, and the design of perfect absorbers. Our bounds predict strikingly large minimal thicknesses for arbitrarily patterned perfect absorbers, ranging from 50–100 nm for typical materials at visible wavelengths to micrometer-scale thicknesses for polar dielectrics at infrared wavelengths. We use inverse design to discover metasurface structures approaching the minimum-thickness perfect-absorber bounds.

Simulations of radiation effects on erbium–ytterbium co-doped fiber amplifiers for space applications

An improved model of erbium–ytterbium codoped fiber amplifier (EYDFA) considering the effects of radiation is proposed. In this model, terms of radiation-induced losses are introduced into power propagation equations, combined with the simplified rate equations to simulate radiation effects on EYDFA performances related to space missions. A method for recovering background losses and radiation-induced losses of EYDFA is illustrated. Numerical simulation tools are based on a homemade particle swarm optimization procedure. In the experimental aspect, two amplifiers of the same type were irradiated with Co60 gamma rays up to a total dose of 10 and 50 krad, respectively. Compared with the experimental data, the curve of output power drawn by the model is in good agreement with the experimentally measured values, validating the validity of the theoretical model. Using this method that combined experimental testing of online monitoring with theoretical simulation provides a new way to evaluate the performance degradation of commercial amplifiers in a radiation environment.

193 nm excimer laser-induced color centers in Yb3+/Al3+/P5+-doped silica glasses

Yb3+, Yb3+/Al3+, and Yb3+/P5+ co-doped silica glasses, as well as pure silica, Al3+, and P5+ single-doped silica glasses, were prepared using a sol–gel method combined with high-temperature sintering. The glasses were irradiated with a 193 nm ArF excimer laser for different durations. The species of the 193 nm laser-induced color centers were identified by radiation-induced absorption (RIA), in-situ photoluminescence (PL), and continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopic techniques. To obtain the RIA and CW-EPR characteristics of each color center, the Gaussian decomposition of RIA and the line-shape simulation of the CW-EPR spectra were performed. The formation mechanism of the color centers was correlated with the glass microscopic structure, which was obtained by nuclear magnetic resonance (NMR) spectroscopy. The results show that the oxygen hole center and the Yb2+ ion pairs are primarily responsible for the radiation-induced darkening, and their formation is highly dependent on the charge balance between the Yb3+ ion and its ligand. This work provides insights into the underlying mechanism of pump light and/or external radiation-induced optical losses in Yb3+-doped silica fibers.

Simulating the Lunar Environment: Partial Weightbearing and High-LET Radiation-Induce Bone Loss and Increase Sclerostin-Positive Osteocytes.

Exploration missions to the Moon or Mars will expose astronauts to galactic cosmic radiation and low gravitational fields. Exposure to reduced weightbearing and radiation independently result in bone loss. However, no data exist regarding the skeletal consequences of combining low-dose, high-linear energy transfer (LET) radiation and partial weightbearing. We hypothesized that simulated galactic cosmic radiation would exacerbate bone loss in animals held at one-sixth body weight (G/6) without radiation exposure. Female BALB/cByJ four-month-old mice were randomly assigned to one of the following treatment groups: 1 gravity (1G) control; 1G with radiation; G/6 control; and G/6 with radiation. Mice were exposed to either silicon-28 or X-ray radiation. (28)Si radiation (300 MeV/nucleon) was administered at acute doses of 0 (sham), 0.17 and 0.5 Gy, or in three fractionated doses of 0.17 Gy each over seven days. X radiation (250 kV) was administered at acute doses of 0 (sham), 0.17, 0.5 and 1 Gy, or in three fractionated doses of 0.33 Gy each over 14 days. Bones were harvested 21 days after the first exposure. Acute 1 Gy X-ray irradiation during G/6, and acute or fractionated 0.5 Gy (28)Si irradiation during 1G resulted in significantly lower cancellous mass [percentage bone volume/total volume (%BV/TV), by microcomputed tomography]. In addition, G/6 significantly reduced %BV/TV compared to 1G controls. When acute X-ray irradiation was combined with G/6, distal femur %BV/TV was significantly lower compared to G/6 control. Fractionated X-ray irradiation during G/6 protected against radiation-induced losses in %BV/TV and trabecular number, while fractionated (28)Si irradiation during 1G exacerbated the effects compared to single-dose exposure. Impaired bone formation capacity, measured by percentage mineralizing surface, can partially explain the lower cortical bone thickness. Moreover, both partial weightbearing and (28)Si-ion exposure contribute to a higher proportion of sclerostin-positive osteocytes in cortical bone. Taken together, these data suggest that partial weightbearing and low-dose, high-LET radiation negatively impact maintenance of bone mass by lowering bone formation and increasing bone resorption. The impaired bone formation response is associated with sclerostin-induced suppression of Wnt signaling. Therefore, exposure to low-dose, high-LET radiation during long-duration spaceflight missions may reduce bone formation capacity, decrease cancellous bone mass and increase bone resorption. Future countermeasure strategies should aim to restore mechanical loads on bone to those experienced in one gravity. Moreover, low-doses of high-LET radiation during long-duration spaceflight should be limited or countermeasure strategies employed to mitigate bone loss.

Dexamethasone Protects Against Radiation-induced Loss of Auditory Hair Cells In Vitro.

Dexamethasone (DXM) protects against radiation-induced loss of auditory hair cells (HCs) in rat organ of Corti (OC) explants by reducing levels of oxidative stress and apoptosis. Radiation-induced sensorineural hearing loss (HL) is progressive, dose-dependent, and irreversible. Currently, there are no preventative therapeutic modalities for radiation-induced HL. DXM is a synthetic steroid that can potentially target many of the pathways involved in radiation-induced ototoxicity. Whole OC explants were dissected from 3-day-old rat cochleae exposed to specific dosages of single-fraction radiation (0, 2, 5, 10, or 20 Gy), were either untreated or treated with DXM (75, 150, 300 μg/mL), and then cultured for 48 or 96 hours. Confocal microscopy for oxidative stress (CellRox, 48 h) and apoptosis (TUNEL assay, 96 h) and fluorescent microscopy for viable HC counts (fluorescein isothiocyanate-phalloidin, 96 h) were performed. Analysis of variance and Tukey post hoc testing were used for statistical analysis. Radiation exposure initiated dose-dependent losses of inner and outer HCs, predominantly in the basal turns of the OC explants. DXM protected against radiation-induced HC losses in a dose-dependent manner. DXM significantly reduced levels of oxidative stress and apoptosis in radiation-injured OC explants (p < 0.001). Radiation-initiated HC losses were dose-dependent in OC explants. DXM treatment protected explant HCs against radiation-initiated losses by decreasing the levels of oxidative stress and apoptosis. DXM may potentially be a therapeutic modality for preventing radiation-induced HL; further in vivo studies are necessary.

Fabrication of ultrathin impurity source to minimize radiation-induced losses in photosensitive films of CdS

The formation of a lead arachidate film was studied at interfaces of an aqueous solution of lead nitrate with the air and with a solid hydrophilic substrate. The efficiency of lead transfer onto a semiconductor substrate by the horizontal lift method was estimated. Optimal conditions of the fabrication of lead arachidate monolayers with minimum oxygen content were found in order to use these layers as an impurity source for CdS. It was shown that an optimal relationship between the photosensitivity of CdS films and losses induced by accelerated electrons is attained due to the formation of PbS precipitates with the radius of at least 3 nm in a topmost layer with the thickness of about the depth of maximal energy dissipation of the ionizing radiation.

Development of radiation-resistant optical fiber for application to observation and laser spectroscopy under high radiation dose

In the Fukushima Daiichi Nuclear Power Station, it is necessary to survey the locations and conditions of fuel debris inside reactor pressure vessels or primary containment vessels under water and radiation environment in preparation for removing fuel debris. An optical fiber is well known for features such as signal transmission, light weight, superior insulation performance, water resistance and electromagnetic noise resistance. These features allow the optical fiber to simplify the instrumentation systems for in-vessel inspection, as long as provide that the optical fiber can be used under high radiation dose environment. The radiation resistance of an optical fiber was improved by increasing the amount of hydroxyl up to 1000 ppm in pure silica fiber. The improved optical fibers were irradiated with γ-ray up to 1 × 106 Gy using a 60Co source. They indicated a large peak around 600 nm and a peak tail from ultraviolet region, but no large absorption in infrared region except a hydroxyl absorption peak of 945 nm. We have confirmed that the optical fiber containing 1000 ppm hydroxyl has enough radiation resistance for radiation-induced transmission losses, and the infrared imaging is effective for observation under high radiation doses.

Effects of γ-radiation on Yb-doped fiber

Yb-doped double-clad fibers are prepared through a conventional modified chemical-vapor deposition technique and solution doping method: each fiber contains a core of around 10 μm in diameter. These fibers are divided into groups under 60Co γ radiations of different doses, and we investigate the fiber absorption spectra and laser spectral properties before and after irradiation. Experimental results show that with increasing the irradiation dose the absorption of the fiber after irradiation increases significantly in the visible region, we believe that the enhancement of optical fiber absorption in the visible region may be due to the color center defects existing already in the fiber (such ODC (Ⅱ)) and the color center defects produced by the irradiation (E'center, POR and Yb2+ions). We also analyze slope efficiencies, bare efficiencies, and transmission characteristics of the fiber before and after laser irradiation. Finally, we use the power-law to fit the radiation-induced losses of the fiber under different radiation doses, and the results obtained in this paper provide a theoretical basis for studying the anti-radiation of optical fibers.

Origin of the visible absorption in radiation-resistant optical fibers

In this work we investigated the point defects at the origin of the degradation of radiation-tolerant optical fibers used in the visible part of the spectrum for plasma diagnostics in radiation environments. For this aim, the effects of γ-ray irradiation up to the dose of 10 MGy(SiO2) and post-irradiation thermal annealing at 550°C were studied for a Fluorine-doped fiber. An absorption peaking around 2 eV is mainly responsible for the measured radiation-induced losses, its origin being currently debated in the literature. On the basis of the unchanging shape of this band with the radiation dose, its correlation with the 1.9 eV photoluminescent band and the thermal treatment results we assign the asymmetric absorption around 2 eV to an unique defect, the NBOHC, instead of a set of various defects.

Air-Induced Recovery of Proton-Exposed Space Materials

T HE fact that materials degrade in space-radiation environments has been studied for decades [1–19] and continues to be an issue of significant importance for space-based systems. Consequently, ground-based simulation of space environmental effects remains an invaluable method for ensuring the performance of any orbital asset, particularly as newmaterials, coatings, and processes are introduced. High-fidelity simulation of space environmental effects requires accurate definition and modeling of the orbital mission exposure, appropriate calculation of the absorbed radiation dose as a function of material thickness, proper simulation of this dose-depth profile in the laboratory, and precise characterization of test-induced changes in material properties. When performing material characterization, in vacuomeasurements are absolutely essential to avoid atmospheric effects on tested materials. Failure to do this can lead to results that are skewed by the too-often-overlooked dynamic of air-induced recovery of radiation-induced degradation, also known as bleaching. For some materials, ignoring the effects of bleaching can easily lead to a significant under estimation of radiation-induced losses and an inaccurate prediction of on-orbit performance. Bleaching is known to occur primarily for thermal control materials [20], and recent work by The Aerospace Corporation has added to the evidence that somematerials, which have been degraded from exposure to simulated space environments, display air-induced recovery behavior. In particular, samples of silverized Teflon, aluminized Kapton, and Z-93P ceramic white paint that were exposed to simultaneous ultraviolet (UV) and electron radiation in a test designed to simulate the conditions present at geosynchronous Earth orbit (GEO) exhibited noticeable bleaching upon subsequent exposure to air. In each case, a portion of the test-induced optical losses was recovered after a brief period ( 2 min) of air exposure. The behavior is material-specific, exhibiting differences in affected spectral region and magnitude of change. The recovery can occur rapidly or over long timescales, with the rate of recovery appearing to depend on material porosity and/or ambient temperature. The spectral response of the three materials is exemplified in Fig. 1. Although air-induced bleaching of optical degradation in some thermal control materials is relatively common, and the effect is not typically observed for materials that are more resistant to the effects of space-radiation exposure, such as solar-cell coverglass.Additional data generated by The Aerospace Corporation, however, indicated that certain coated coverglass materials, namely, those with thin-film coatings of magnesium fluoride (MgF2) and indium tin oxide (ITO), might also be susceptible to bleaching. In another recent GEO simulation, samples of MgF2/ITO-coated 0214 coverglass (0214 refers to the manufacturer-specific type of coverglass substrate) exhibited slight, yet discernible, air-induced recovery of spectral transmittance following simultaneous exposure to UV and electron radiation. Figure 2 shows the material’s spectral response to a short ( 2 min) postirradiation air exposure. Primarily, because of facility limitations, proton exposures at The Aerospace Corporation historically have been performed, usually precedingUV/electron irradiation, in a separate exposure facility: the low-energy accelerator facility (LEAF). The LEAF has a vacuum chamber attached to a linear ion accelerator; the accelerator’s beam is passed through a 30 deg magnetic turn to select the appropriate ion species, and the beam is rastered across the exposure target. The LEAF lacks in vacuo optical measurement capability; thus, air exposure is unavoidable when characterizing proton-induced material changes. Because of this, it is unknown whether, or to what degree, bleaching occurs for proton-irradiated coverglass materials, although it seems reasonable to suspect that somematerials degraded by proton exposure would also exhibit air-induced recovery. Given the apparent bleaching ofUV/electron-induced degradation in MgF2/ITO-coated coverglass and the lack of in vacuo optical measurement capability of the LEAF, this research effort was undertaken to investigate the air-induced response of protonirradiated space materials. Making this possible is The Aerospace Corporation’s newest space environmental effects exposure facility, which had already possessed in vacuo optical measurement capability and now features a variable-energy proton flood gun. This recently enhanced facility makes possible measurements of protonirradiated materials that are free from atmospheric effects and allows Received 21 September 2011; revision received 5 December 2011; accepted for publication 9 January 2012. Copyright © 2012 by The Aerospace Corporation. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. All rights reserved. Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code 0022-4650/12 and $10.00 in correspondence with the CCC. Research Scientist, Materials Science Department, Space Materials Laboratory, 2310 East El Segundo Boulevard, M2-248. Distinguished Scientist, Space Materials Laboratory, 2310 East El Segundo Boulevard, M2-248. JOURNAL OF SPACECRAFT AND ROCKETS Vol. 49, No. 4, July–August 2012

Maximum or minimum entropy production? How to select a necessary criterion of stability for a dissipative fluid or plasma

Ten necessary criteria for stability of various dissipative fluids and plasmas are derived from the first and the second principle of thermodynamics applied to a generic small mass element of the system, under the assumption that local thermodynamic equilibrium holds everywhere at all times. We investigate the stability of steady states of a mixture of different chemical species at the same temperature against volume-preserving perturbations. We neglect both electric and magnetic polarization, and assume negligible net mass sources and particle diffusion. We assume that both conduction- and radiation-induced heat losses increase with increasing temperature. We invoke no Onsager symmetry, no detailed model of heat transport and production, no "Extended Thermodynamics," no "Maxent" method, and no "new" universal criterion of stability for steady states of systems with dissipation. Each criterion takes the form of--or is a consequence of--a variational principle. We retrieve maximization of entropy for isolated systems at thermodynamic equilibrium, as expected. If the boundary conditions keep the relaxed state far from thermodynamic equilibrium, the stability criterion we retrieve depends also on the detailed balance of momentum of a small mass element. This balance may include the nablap-related force, the Lorenz force of electromagnetism and the forces which are gradients of potentials. In order to be stable, the solution of the steady-state equations of motion for a given problem should satisfy the relevant stability criterion. Retrieved criteria include (among others) Taylor's minimization of magnetic energy with the constraint of given magnetic helicity in relaxed, turbulent plasmas, Rayleigh's criterion of stability in thermoacoustics, Paltridge 's maximum entropy production principle for Earth's atmosphere, Chandrasekhar' minimization of the adverse temperature gradient in Bénard's convective cells, and Malkus' maximization of viscous power with the constraint of given mean velocity for turbulent shear flow in channels. It turns out that characterization of systems far from equilibrium, e.g., by maximum entropy production is not a general property but--just like minimum entropy production--is reserved to special systems. A taxonomy of stability criteria is derived, which clarifies what is to be minimized, what is to be maximized and with which constraint for each problem.

Radiation-Induced Losses and Emission of Quartz-Polymer Optical Fiber in Bremsstrahlung $\gamma$-Radiation Field

The radiation hardness of a polymer-clad fused-silica core optical fiber is investigated at a dose rate of ~10 R/s with bremsstrahlung photons. Optical transmission recovery rates are measured for different integrated doses in fast (minutes) and slow (hours) time scales. Formation of color centers and their emission characteristics under gamma irradiation are also investigated.

Comparative Study of Pulsed X-Ray and$gamma$-Ray Radiation-Induced Effects in Pure-Silica-Core Optical Fibers

We have investigated the variation of the optical absorption induced by pulsed (dose rate >108 rad/s) and continuous (<50 rad/s) gamma-ray exposures in pure-silica-core optical fibers. Tested multimode waveguides, designed with well-defined concentrations of hydroxyl groups and chlorine impurity, are possible candidates for integration in the plasma diagnostics of LMJ and ITER facilities. We evaluated their radiation-tolerance to low dose levels (<5times10 4 rad) in the visible and near-infrared parts of the spectrum. We measure the time dependent changes (10-9-10-1 s) of the radiation-induced attenuation (RIA) at fixed wavelengths and we complete these measurements with a spectral (450-1100 nm) analysis of these losses in the time range from 10-2 to 103 s. We compared the responses obtained under transient exposures with measurements done at same dose levels (5times103 rad) with lower dose rate (<102 rad/s). We showed that the radiation-induced changes are strongly dose rate dependent for this kind of optical fibers. Depending on the hydroxyl group concentration in the silica-glass, different point defects are shown to alter the fiber transmission after both irradiation types. The self-trapped holes play a particular role in the transient responses of optical fibers whereas non-bridging oxygen hole centers are mainly responsible for gamma-ray radiation-induced losses. The consequences of these different behaviors for the integration of optical fibers in the LMJ are discussed

Temperature dependence of the transmission loss in KU-1 and KS-4V quartz glasses for the ITER diagnostic window

Quartz glasses of KU-1 and KS-4V are candidate window materials for the ITER optical diagnostics in UV and visible range. The temperature dependence of the radiation-induced transmission losses in UV range has been investigated under γ-ray irradiation for the KU-1 and KS-4V quartz glasses up to 10 MGy. The KU-1 and KS-4V quartz glass samples were irradiated at room temperature, 100, 200 and 300 °C. Dose rate was 0.46–1.1 MGy, and 2.6 Gy/s from 1.1 to 10.4 MGy. It was confirmed that there is no significant loss in wavelength range longer than 350 nm for both window materials. Transmission loss in KU-1 is larger than that in KS-4V under temperature below 200 °C. KU-1 has large temperature dependence. On the other hand, temperature dependence is not clear in KS-4V above 100 °C. Prominent recover of the transmission loss was not observed after irradiation for each sample. From the transmission loss point of view, KS-4V is better window material than KU-1 at temperature below 200 °C. KU-1 is available at 300 °C.

Gamma and UV Radiation-Induced Color Centers in Optical Fibers

Radiation-induced losses and paramagnetic centers were investigated in phosphorusdoped and P-free multimode germanosilicate optical fibers after g-rays (~1 MeV) and ultraviolet (5 eV) exposures. After both types of irradiation, the same defects seem to be responsible of the fiber absorption in the spectral range 400 to 1650 nm. In particular, the P1 centers and the Phosphorus Oxygen Hole centers are created in both cases in the phosphorus-doped fibers and explain the high permanent radiation-induced attenuation levels observed in this fiber type. Luminescence and electron spin resonance measurements (77 K, ~9.38 GHz) on irradiated samples confirm that the GeE’, SiE’ and NBOHC defects are also generated in the different irradiated samples. From this study, it seems that the pertinence of a multimode fiber for nuclear space or civil applications could be estimated through low-cost ultraviolet measurements.

Radial distribution of attenuation in gamma-irradiated single-mode optical fibers

In this letter, a method to determine the radial distribution of attenuation in single-mode optical fibers is proposed. This method is based on guided mode power and loss measurements for different fiber packaging. The most accurate radial attenuation distribution is calculated from experimental results. This approach allows localizing the absorbing or scattering defects along the radial cross section of fibers. As an example, a γ-irradiated germanosilicate fiber is studied at three different wavelengths. Through correlation with fiber chemical analysis, the contributions of each dopant to the permanent radiation-induced losses can be identified and quantified. At 980 nm, phosphorus-related color centers are the origin of induced losses, whereas for shorter wavelengths the influence of germanium-related color centers on fiber behavior becomes dominant.

Properties of phosphorus-related defects induced by γ-rays and pulsed X-ray irradiation in germanosilicate optical fibers

Time dependent radiation-induced attenuation changes of germanosilicate (∼13 wt%) optical fibers have been measured under steady-state γ-ray and pulsed X-ray irradiations. Particularities of phosphorus (P)-codoped cladding fibers for these environments are presented. For each irradiation type, spectral attenuation measurements show that permanent radiation-induced losses at 1.55 μm are due to the infrared absorption band of P 1 centers. We assume that particular kinetics of recovery and an increase of attenuation measured for P-codoped fibers, after pulsed X-ray irradiation, are induced by a charge retrapping phenomenon from phosphorous oxygen hole (POH) centers to P 1 ones. With this mechanism, we explain the P-codoped fiber characteristics after both types of irradiation. Our study shows that the effect of P-related color centers is increased when the P-codoped cladding (∼0.3 wt%) contains also germanium (∼0.3 wt%).