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A digital VCSEL driver has been designed, simulated and assessed under radiation, using discrete SiGe HBTs. The circuit tolerates high levels of gamma radiation, up to 12 MGy, features less than 2% drift in the forward current of the VCSEL and operates well above 10 MHz. The output duty cycle shows no notable degradation at 200 kHz, enabling the design of robust analog and digital communication systems using pulse-width-modulation (PWM) schemes. [ABSTRACT FROM AUTHOR]

The fiber Bragg gratings (FBGs) inside photonic crystal fibers (PCFs) having high fiber birefringence, such as in PCF with butterfly shape microstructure, are characterized by two Bragg peaks. The spectral distance between these two peaks is not affected by a change of temperature or by a longitudinally applied strain, but this spectral separation evolves when the sensor is subjected to a transversal strain. This makes such FBGs inscribed in highly birefringent PCFs very interesting for structural health monitoring of civil structures, as well as for operation in harsh environments such as the ones associated with the nuclear industry. In this paper, we monitor the radiation-induced Bragg wavelength shift (RI-BWS) of the punctual sensor and the radiation-induced attenuation in the fiber used for its inscription up to a dose of 1.5 MGy(SiO2). Even if we observe a RI-BWS for both Bragg peaks, the spectral distance between them only slightly evolves, of less than 10 pm. These gratings are then very promising sensors for the structural health monitoring of nuclear facilities. [ABSTRACT FROM AUTHOR]

The effect of gamma-radiation on the spectral characteristics of FBGs has been studied experimentally. The FBGs were fabricated in optical fibers with a GeO2 concentration in the core in a range from several to 99 mol.%. Various pre- and post-fabrication treatments were applied with the aim to improve the radiation tolerance of the FBGs. The best result was obtained for a Type ha annealed grating written in SM310 fiber, where the Bragg peak shift saturated at a 12 pm level and an amplitude change of 0.04 dB with the maximal dose of about 50 kGy. [ABSTRACT FROM AUTHOR]

We characterized the responses of three erbium-doped fibers with slightly different concentrations of rare-earth ions (240-290 ppm) and Al2O3 (7-10 wt.%) during proton and γ-ray exposures. We have simultaneously measured the radiation-induced attenuation (RIA) around the Er3+ ion pumping wavelength (980 nm) and the associated changes of the Er3+ emission around 1530 nm. The three erbium-doped fibers show similar radiation responses. All fibers exhibit RIA levels between 9 × 10-3 and 1.7 × 10-2 dB m-1 Gy-1 at 980 nm and between 4 × 10-3 and 1.1 × 10-2 dB m-1 Gy-1 at 1530 nm. Protons and -y-rays lead to similar radiation damages, with small differences between the protons of different energies (50 MeV and 105 MeV). Furthermore, we have performed online measurements of the spectral dependence of RIA from 600 to 1600 nm and offline measurements from 1200 to 2400 nm. The three fibers exhibit the same spectral response. Losses decrease monotonically from the visible to the infrared part of the spectrum. We have performed spectral decomposition of these RIA curves with the help of absorption bands previously associated with radiation-induced point defects. Our analysis shows that the main part of the RIA (600-1700 nm) in erbium-doped glass can be explained by the generation of Al-related point defects. The other defects related to the germanium and phosphorus doping of the silica seem to have a lower contribution to the induced losses. The Er3+ ion properties seem to be mainly unaffected by proton exposure, suggesting a solvation shell around the Er3+ ion formed by Al2O3 species. [ABSTRACT FROM AUTHOR]

Abstract: Diagnostic components and heating and current drive systems will be used within the vacuum vessel of the future fusion reactors, and especially in ITER. They will have to withstand harsh conditions in terms of neutron and gamma radiations, temperatures, applied voltages and vacuum. In order to study the degradation phenomena of the insulation and window materials and to qualify prototype systems, a representative environment must be available to perform reliable evaluation tests. A multi-purpose irradiation facility has been therefore designed to fit the BR2 experimental fission reactor in Mol, Belgium. This reloadable facility allows a full control of the irradiation conditions (up to 1014ncm−2 s−1 and 500°C) in a vacuum or inert atmosphere, with in-situ bias and measurement capabilities. [Copyright &y& Elsevier]

Abstract: Several single mode silica-based fibers with different levels of erbium concentrations have been tested under 60Co gamma radiation. Irradiation has been performed at a dose-rate of ∼30Gy/h to a total dose of ∼2kGy. Transmission spectra were measured in situ in a spectral range from 1250 to 1630nm. The measurements show no detectable change in the Er-ions luminescence and absorption spectrum profiles, while a significant (∼dB/m/kGy at 1530nm) increase in transmission losses is attributed to the silica host matrix modifications. This conclusion is drawn based on the post-irradiation photo-luminescence analyzes realized with a confocal micro-spectrometer (514.5nm excitation, P ∼2mW). [Copyright &y& Elsevier]

Abstract: We investigated pulsed-X-ray-induced attenuation in two pure-silica-core (PSC) optical fibers with low-chloride (Cl) and different hydroxyl (OH) contents. We measured at room temperature the temporal (100ms–1000s) and spectral (0.73–3.1eV) variation of the induced optical absorption after a 1MeV X-ray pulse in both low- and high-OH PSC multi-mode fiber samples. A component of the transient loss in the low-OH sample was found to comprise absorption bands at 1.63 and 1.88eV (760 and 660nm) arising from self-trapped holes (STHs). Already known to be unstable at room temperature, STHs appear to play a key role in the transient responses of low-OH/low-Cl pure-silica-core fibers in the visible/near-infrared part of the spectrum. [Copyright &y& Elsevier]

Raman Distributed Temperature Sensors (RDTS) are attractive for the monitoring of large structures in nuclear power plants such as containment structures and coolant loop systems. We demonstrate the high radiation tolerance of a Raman distributed fiber optic temperature sensor, up to total gamma doses in excess of 300 kGy, using a double-ended configuration and commercially-available optical fibers. [ABSTRACT FROM AUTHOR]

The radiation tolerance testing of materials or opto-electronic components in a nuclear reactor requires a careful determination of the different components of the mixed gamma-neutron field. While the characterization of the neutron field can be performed using, for example, activation foils and validated by Monte-Carlo computation codes, the experimental measurement of the in-reactor gamma dose rate requires the use of costly ionization chambers. In this paper, we evaluate the possibility of using Red Perspex from Hanvell Technologies for routine gamma dosimetry in mixed gamma neutron field. Self-powered gamma detectors and ionization chambers were used as reference dosimeters. We show that the accuracy of the Red 4034 dosimeter's is better than 10% in mixed gamma-neutron fields. [ABSTRACT FROM AUTHOR]