Radiation-induced Absorption Research Articles

Detection of X-Rays Radiation Effect on Radiation Sensors Based on Optical Fiber Technology

This study aims to investigate the characteristics of optical fiber sensors under X-rays radiation. The Radiation-Induced Absorption (RIA) and Radiation-Induced Refractive-Index Change (RIRIC) in the UV-VIS domain were investigated. Single and multi-mode optical fibers (SMFs & MMFs) have been used for this purpose. The outer diameters of these fibers were reduced from (125 to 50 and 55μm for SMF and MMF respectively) via chemical etching process then dipped into (3 wt % concentration) of germanium (Ge) solution to produce the sensing part of the fibers. Due to the applied X-rays radiation, an attenuation of the spectrum and a redshift in peak wavelength were achieved. Both sensors show good responsivity to the applied radiation and the MMFs sensors showed higher wavelength shifting as compared to SMFs sensors.

Radiation resistance of single-mode optical fibres with view to in-reactor applications

Single-mode optical fibres (SMFs) are required for ITER in-vessel applications as transport fibres to deliver the signal at wavelength λ = 1.55 µm from/to optical fibre sensors. The paper describes the first comparison study of radiation resistance of six pure-silica-core SMFs of different manufacturers performed in the process of fission-reactor irradiation in the conditions corresponding to the whole ITER lifetime (fast-neutron fluence, flux, γ-dose and dose rate of up to 1.8·1020n/cm2, 1.08·1014n/(cm2·s), 2.32 GGy and 1.39 kGy/s, respectively, temperature of 170–190 °C and vacuum pumping). Polyimide- and acrylate-coated SMFs failed mechanically during the irradiation; therefore, only metal-coated fibres can be considered for the in-vessel applications. Induced optical loss in all three metal-coated SMFs (copper- and aluminum-coated ones) at the fast-neutron fluence of 1·1020n/cm2 was found to lie in the range ~1.5–4 dB/m, the lower value of this range allowing the employment of at least 10-m-long transport fibre lengths in the in-vessel applications, assuming the dynamic range of 30 dB. The temperature-dependent microbending optical loss in metal-coated SMFs is discussed, of which the contribution to the total induced loss may be comparable in value to the radiation-induced absorption of light. Neither radiation-induced luminescence, nor Cerenkov emission was detected in the SMFs in the near-infrared range.

Assessment of the Irradiation Exposure of PET Film with Swift Heavy Ions Using the Interference-Free Transmission UV-Vis Transmission Spectra.

This paper presents the results of a study of polyethylene terephthalate (PET) films irradiated with Ar and Kr ions at both normal orientation and an angle of 40° to the normal. Normal irradiation was performed using Ar8+ and Kr15+ ions with an energy of 1.75 MeV/au and fluences in the range (2–500) × 1010 cm−2 for Ar8+ ions and (1.6 − 6.5) × 1010 cm−2 for Kr15+ ions. Kr ions with an energy of 1.2 MeV/au and charges of 13+, 14+, and 15+ were used for angled irradiation. For each Kr ion charge value, three fluence values were used: 5 × 1010, 1 × 1011, and 2.5 × 1011 cm−2. It is well known that irradiation of PET films by swift heavy ions results in a red shift of the UV-vis transmission spectra absorption edge. The experimental transmission spectra exhibit well-defined interference fringes, which obscure the underlying transmission response. Using an existing technique to obtain interference-free transmission curves Tα(λ) for both pristine and irradiated PET film samples, we found that S, the total radiation-induced absorption of light by the PET film, is proportional to the logarithm of the fluence F. In addition to this dependence on the irradiating fluence, we also found that the charge of the irradiating ion has a significant influence on the position of the absorption edge in the UV-vis spectra. This provides experimentally independent evidence to confirm our previous results showing that ion charge has an effect on the post-irradiation state of PET films. We present a physical interpretation of the observed absorption edge red shift in irradiated PET films as being due to the growth of extended conjugated systems via the formation of intermolecular helical structures. Our investigations into the stability of irradiation-induced effects in PET films show that comparison of UV-vis transmission spectra before and after annealing can provide information about the structure of deep traps in PET.

Измерение температуры электронов плазмы токамака Глобус-М2 методом мультилазерного томсоновского рассеяния

Diagnostics of the plasma electron component by the method of Thomson scattering (TS) of laser radiation makes it possible to reliably measure the spatial distributions of the electron temperature and density. One of the obstacles to the implementation of TS diagnostics in thermonuclear reactors is the distortion of the spectral characteristics of the optical system due to radiation-induced absorption and contamination of optical elements with erosion products of the first wall. As a consequence, the reliability of measurements by the TS method will decrease over time. The paper describes the method of multi-laser Thomson scattering, which will solve this problem. The results of the first experiments on the Globus-M2 tokamak are also presented.

Thermal annealing and transformation of dimer F centers in neutron-irradiated Al2O3 single crystals

The precise study of the thermal annealing of the F2-type dimer defects, being under discussion in the literature for a long time and responsible for the number of absorption bands below 4.5 eV, has been performed in corundum single crystals irradiated by fast neutrons with a fluence of 6.9 × 1018n/cm2. The Gaussian components of the radiation-induced optical absorption with the maxima at 4.08, 3.45 and 2.75 eV have been considered as a measure of the F2, F2+and F22+centers, respectively. In contrast to the F and F+ centers, the concentration of which continuously decreases at the sample heating up to 1100 K, the concentration of dimer defects with different charge states passes the increasing stages above 500 K starting from the F22+centers. The tentative mechanisms of such rise of the F22+centers as well as of the subsequent transformation/rise of dimer centers, F22+→F2+→F2at 650-800 K are considered. The possible sources of carriers needed for the recharging of dimer centers are also analysed on the basis of thermally stimulated luminescence measurements up to ~850 K.

Radiation-induced absorption and photobleaching in erbium Al–Ge-codoped optical fiber

In this work, we analyze the absorption spectra of silica fibers doped with erbium (Er) and usual codoping atoms such as aluminum (Al) and germanium (Ge). This study is performed in the 400 nm to 1000 nm wavelength range. We describe and identify relations between the optical fiber composition and the changes in their absorption spectra after two consecutive processes: a 300-Gy gamma irradiation and then after photobleaching obtained with a 980 nm laser light. Among the results we obtained, we want to emphasize that the creation of Al-related defects, known to be the main origin of radio-darkening in aluminosilicate fibers, depends also on the Al/Er ratio. We also identify a new Al originated trap, different from Al-OHC and not referenced in the existing scientific literature to our knowledge. Its contribution to the RIA seems to be really significant. Moreover, photobleaching appears to be a possible recovery mechanism as the Al-colored centers vanish under 980 nm laser light.

Comparison Study of Radiation-Resistant Polarization-Maintaining PANDA Fibers With Undoped- and N-Doped-Silica Core

For the first time, radiation-induced absorption (RIA) of light is compared in two types of polarization-maintaining PANDA fibers having 1) undoped-silica core and F-doped-silica cladding, or 2) N-doped-silica core and undoped-silica cladding. RIA at λ = 1.55 μm is compared under γ-irradiation and post-irradiation recovery at room temperature (RT) and −60 °C. The post-irradiation RIA decay at RT is used to extrapolate RIA to the postulated end of the PANDA space mission (15 years) with the help of the “nth-order kinetic” model. The RIA extrapolation values for both PANDA types are found to be comparable. RIA spectra are measured in the PANDAs in the spectral range ∼0.5–4 eV in the process of both γ-irradiation and recovery; then the spectra are deconvolved into Gaussians components. The RIA spectra of both PANDA types are found to be composed of inherent and strain-assisted self-trapped holes (STHs), some undoped PANDAs demonstrating, in addition, a long-wavelength RIA tail affecting λ = 1.55 μm. No N-related color centers are revealed. Finally, RIA at λ = 1.55 μm is compared upon pulsed-X-ray irradiation. Undoped PANDAs are found to feature much smaller RIA at RT at post-pulse times larger than ∼40–1000 μs, whereas at smaller times, an N-doped PANDA proved to be superior. At −60 °C and at t > 1 ms, both PANDA types demonstrate approximately equal RIAs. Thus, the experiments showed that the two PANDA types are quite comparable, each type having its own advantages and disadvantages.

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.

Accurate modeling of radiation-induced absorption in Er-Al-doped silica fibers exposed to high-energy ionizing radiations.

We offer here an accurate quantitative model of the RIA (radiation-induced absorption) at low dose-rate (below 1 kGy) that experience the most common erbium-doped fibers (Ge-Al-Er-doped silica) under radiations. It addresses the degradation mechanisms of the glass fiber, especially the influence of its doping elements versus its sensitivity to radiations. Moreover, it depends mainly on macroscopic quantities coming from literature or experiments. For these two reasons, it is a reliable and efficient tool for the engineering of erbium-doped fibers (erbium-free fibers too) exposed to ionizing radiations and is validated in this paper by comparing the modelisation results to RIA experiments on 14 Er-doped optical fiber samples, in which composition changes a lot from one sample to another (in the range 0-25%wt for Ge, 0-10%wt for Al and 0-1500ppm for Er).

Kinetics of Radiation-Induced Optical Absorption Spectra in LPX-100, -200 Protective Glasses

The results of studies of the kinetics of radiation-induced optical absorption spectra of commercially produced glasses LPX-100 and -200 (Lemer Pax Co., France) after γ-irradiation to 1 MGy in the wavelength range 320–1000 nm are reported. The restoration of light transmission was monitored for 120 days. The linear coefficients of attenuation of γ-radiation by glasses were measured using a KRONA-II-04 γ-spectrometer with OSGI standard radiation sources 60Co (1.173 and 1.333 MeV) and 137Cs (0.661 MeV). The experimental data make it possible to determine with adequate accuracy the applicability of the studied glasses under other conditions of irradiation. A brief comparative analysis of the results obtained for TK100 and TF103 glasses by other authors is given.

Radiation-Induced Absorption of Light in Undoped-Silica-Core Optical Fibers in the Near-Infrared Range: Effect of Drawing Conditions

Eight identical undoped-silica-core, fluorosilicate-cladding preforms have been drawn into optical fibers under different drawing regimes (temperature T, tension, and speed). Next, the fibers have been γ-irradiated, with radiation-induced absorption (RIA) of light measured at the wavelength λ = 1.55 µm and at the dose of 2.5 kGy (7.4–7.6 Gy/s). RIA is found to strongly increase with an increase in T, which proves to be the main drawing parameter determining the fiber radiation resistance. It is established that the RIA dependence on T−1 is exponential.

Electron beam irradiation and thermal-induced effects on the spectral properties of BAC-Al in Bi/Er codoped aluminosilicate fibers

The effect of electron irradiation (5-140 kGy) on the spectral properties of bismuth active centers (BACs) in Bi/Er codoped aluminosilicate fibers (BEDFs) has been studied. It is revealed that the near-infrared (NIR) emitting BACs exhibit high radiation resistance, evidenced by the negligible change in the saturable absorption and on-off gain of BACs. In contrast, the radiation-induced absorption (RIA) increases sharply with the increasing radiation dose. The contribution of each of the defects to the RIA level has been analyzed, and it is found to be mainly linked to the generation of Al-OHC in the Al2O3-SiO2 host. Furthermore, the thermal annealing on the irradiated BEDFs has also been investigated, revealing the higher thermal stability of BACs due to the thermal bleaching of Al-OHC. This is the first time that the BACs show good resistance to the strong electron irradiation.

Enhanced Radiation Resistance of Pure-Silica-Core Polarization-Maintaining PANDA Optical Fibers

Radiation-induced absorption (RIA) is investigated at $ \lambda = {1.55}~ \mu \text{m}$ in technologically improved pure-silica-core (PSC) PANDAs, in which we minimized drawing-induced silica network strain. The results of the steady-state $\gamma $ - and pulsed-X-ray irradiations are compared with those obtained earlier on former, non-optimized PSC PANDAs. It is found that the technological improvements have resulted in nearly complete suppression of the most deleterious RIA band at ~1 eV to drastically improve the radiation resistance of the PSC PANDAs.

1.55-μm-light absorption induced by pulsed-X-ray radiation in pure-silica-core fiber: Effects of light power and temperature

Pure-silica-core F-doped-silica cladding fiber (“pure silica fiber”, PSF) is subjected to eight pulsed-X-ray irradiations (pulse duration of 20 ns, mean photon energy of ~5 MeV). In each pulse, the probe light power at the wavelength λ = 1.55 μm is either 10 mW, or 33–40 μW, the irradiation temperature being also varied among pulses from −80 to +85 °C. Post-pulse decay of radiation-induced absorption (RIA) in the PSF is measured at λ = 1.55 μm in the subsecond scale and, in four typical cases, is approximated in the framework of the second-order-kinetic model to separate RIA due to inherent and strain-assisted self-trapped holes (STHs). Post-pulse RIA time evolution is found to be qualitatively different at the different probe light powers. At the 33–40-μW power, RIA is virtually wholly described by inherent STHs with some admixture of strain-assisted ones only at the highest temperature of +85 °C. At the 10-mW power, the RIA temporal run is found to be composed of two clear-cut successive domains due to inherent and strain-assisted STHs regardless of temperature. An enhanced probe light power and enhanced temperature are found to have a similar influence on the STHs of the two classes: they partly suppress the inherent STHs and promote the occurrence of the strain-assisted ones. A physical mechanism is proposed for the latter effect. Basic principles for selecting the best-suited probe light power at λ = 1.55 μm with regard to the application specifications are proposed.

Prediction of Radiation-Induced Light Absorption in Optical Fibers with an Undoped Silica Core for Space Applications

Radiation-induced absorption (RIA) of light in five isotropic optic fibers (OFs) with a core of undoped silica glass (SiO2) and a fluorosilicate cladding and one birefringent OF of the “PANDA” type of the same chemical composition was measured at a wavelength λ = 1.55 μm under γ-irradiation to a dose of 1 kGy (∼ 1 Gy/s), 15–45 min after completion of irradiation, and in a few months at temperatures +25 and –60°C. An extrapolation of the RIA after irradiation in the framework of the kinetic model of the nth order, which gave a forecast of the RIA for isotropic OFs of ∼1.1 and ∼ 0.3 ± 0.1 dB/km at –60 and +25°C, respectively, was made to assess the RIA at the end of a 15-year mission in space. It has been concluded that it is possible to use at least 4–5 km of OF in space under conditions of temperature variation within ±60°C at a maximum dose of 1 kGy and a mission duration of 15 years. It has also been established that the RIA will not have been higher in the birefringent OF than in the isotropic ones by the end of such a mission.

Characterization of ion radiation-induced damage in polyimide by wavelength-scanning and dual-wavelength laser photoacoustic spectroscopy

In this paper, photoacoustic spectroscopy (PAS) was presented to characterize the ion radiation-induced damage in the polyimide (PI). We demonstrated a mathematical model of monochromatic light excited photoacoustic (PA) pressure in ion radiation damaged PI. A dual-wavelength PA relative amplitude difference linear dependence on ion irradiation fluence was proposed to quantitatively determine the ion radiation damage in PI. The ion radiation-induced optical absorption modifications of PI films radiated by different fluence of ions were measured by means of wavelength-scanning (400 nm-800 nm) PAS and dual-wavelength (405 nm, 808 nm) laser PAS methods. The results indicated that the optical absorption of PI material was obviously enhanced with the increase of radiated ion fluence. The PA relative amplitude difference induced by laser at the wavelength of 405 nm and 808 nm showed approximate linear dependence on the radiation fluence of nitrogen ions, which was a good agreement with the theoretical model. PAS approaches have the merits of high specificity and sensitivity to the ion radiation-induced damage in PI material and provide a reliable tool to evaluate the damage quantitatively.

New radiation colour centre in germanosilicate glass fibres

We have investigated radiation-induced absorption (RIA) of light in five optical fibres with a germanosilicate core and a light-reflecting cladding made of undoped silica glass in the visible and near-IR ranges under γ-irradiation to a dose of 1 kGy at temperatures from −60 to +60 °C. The concentration of GeO2 in the cores of the studied fibres ranged from 3.5 to 50 mol%. It is found that the RIA dependences on temperature for optical fibres having been lightly or heavily doped by germanium are different. An increase in RIA with increasing temperature for heavily doped fibres is associated with an increase in the absorption intensity of the GeX centre due to thermal decay of Ge(1) centre. It is found that, in fibres lightly doped by germanium, RIA in the near-IR range is determined mainly by a previously unknown radiation colour centre (RCC) called the GeY centre, with a maximum of the absorption band at a wavelength of ∼900 nm (1.38 eV), a half-width of 495 nm (0.71 eV), and an activation energy of 0.15 eV. It is established that the concentrations of GeX and GeY centres differently depend on the irradiation temperature and the content of germanium in silica glass: the concentration of GeX centres increases and the concentration of GeY centers, on the contrary, decreases with increasing temperature and GeO2 concentration in the core. Thus, in accordance with its spectral position, the GeY centre represents the main RCC limiting the radiation resistance of standard telecommunication fibres with a small addition of germanium (3.5 mol % of GeO2).

Light Absorption Induced in Undoped-Silica-Core Panda-Type Birefringent Optical Fiber by Pulsed Action of Ionizing Radiation

The evolution of radiation-induced absorption (RIA) of light at λ = 1.55 μmis compared after pulsed action of ionizing radiation at different probe light power in an undoped-silica-core Panda-type birefringent optical fiber and in an isotropic optical fiber drawn from the same preform before embedding the stress-applying rods.High efficiency of RIA photobleaching by the probe light at λ = 1.55 μm is revealed in the birefringent fiber.

Effects of high dose gamma irradiation on the optical properties of Eu3+ doped zinc sodium bismuth borate glasses for red LEDs

Interaction of 10ZnO-5Na2O-10Bi2O3–74.3B2O3-0.7Eu2O3 glasses exposed to high dose gamma rays were investigated using XRD, FTIR, absorption, photoluminescence followed by thermally and optically stimulated luminescence studies. XRD analysis confirmed the amorphous nature of glasses post-irradiation. Variation in FTIR spectra revealed, structural deformation of borate groups as a result of high dose gamma irradiation. Enhanced glass absorbance and red shift in absorption edge were observed with the increase in gamma dose. Further, radiation-induced absorption coefficient confirmed the trapped charges in the forbidden energy gap supported by Tauc's plot and Urbach energy. Photoluminescence (PL) study demonstrated quenching of luminescence intensity at higher gamma doses. Lifetime of metastable 5D0 state of Eu3+ ions were estimated by the decay curves and color purity was calculated using 1931 CIE chromaticity coordinates (x,y). Thermally and optically stimulated luminescence studies reassured the existence of charges in trap centers due to irradiation. TL glow curve exhibited two broad emission peaks with the corresponding temperature being at 490 K and 625 K. Distinct TL peaks of the material and their kinetic parameters (E, S, τ and b) were determined via Computerized Glow Curve Deconvolution (CGCD) method. Linear behaviour obtained through the dose response of the glass (0.25–3 kGy) proved their suitability for dosimetric application in the food irradiation zones in addition to red LEDs (< 1 kGy).

Observation of radiation-induced absorption of self-trapped holes in Ge-doped silica fiber in near infrared range at reduced temperature

Short-lived radiation-induced absorption (RIA) of light peaking at wavelengths >1700 nm has been revealed in a γ-irradiated (≤1 kGy) heavily (50 mol% GeO2) Ge-doped silica optical fiber (Ge-doped fiber) at low temperatures (≤−30 °C). This RIA is found to closely resemble in properties the known RIA due to inherent self-trapped holes (STHs) in undoped-silica-core optical fibers (same spectral range, low thermostability, non-monotonic evolution with dose, shift of the peak wavelength with temperature, Arrhenius dependence on temperature, growth of the activation energy in the course of irradiation and recovery). The STH-like RIA is found not to occur in more lightly Ge-doped fibers and in a Bi-codoped Ge-doped fiber with the same (50 mol%) GeO2 concentration. A possible microscopic structure of the STH in heavily Ge-doped fibers is discussed.