Radiation Endurance Research Articles

Properties of ultraviolet phosphor for ion-beam-induced fluorescent microscopy technology

Abstract In this study, we have investigated the ultraviolet (UV) fluorescence properties of a phosphor (YPO4:Gd) sample from the irradiation of a scanning proton beam to evaluate its usefulness as a staining agent of ion-beam-induced fluorescence microscopy (IBIF). The phosphor was prepared using a co-precipitation method. Owing to the irradiation, the sample exhibited UV fluorescence with a peak wavelength of 312 nm. In the emission spectrum, the FWHM of the UV peak ≈ 6 nm. The light emission in the UV region and the narrow peak bandwidth are characteristics that are effective at minimizing the background fluorescence and allow high-sensitivity IBIF imaging. Moreover, it was confirmed that the phosphor had a considerable radiation endurance. In addition, we successfully obtained IBIF images and elemental maps simultaneously for a test sample containing YPO4:Gd powder. These results demonstrate that the prepared phosphor is suitable for IBIF.

Effects of Gamma Radiation on Resonant and Antiresonant Characteristics of Piezoelectric Wafer Active Sensors

This paper presents gamma radiation effects on resonant and antiresonant characteristics of piezoelectric wafer active sensors (PWAS) for structural health monitoring (SHM) applications to nuclear-spent fuel storage facilities. The irradiation test was done in a Co-60 gamma irradiator. Lead zirconate titanate (PZT) and Gallium Orthophosphate (GaPO4) PWAS transducers were exposed to 225 kGy gamma radiation dose. First, 2 kGy of total radiation dose was achieved with slower radiation rate at 0.1 kGy/h for 20; h then the remaining radiation dose was achieved with accelerated radiation rate at 1.233 kGy/h for 192 h. The total cumulative radiation dose of 225 kGy is equivalent to 256 years of operation in nuclear-spent fuel storage facilities. Electro-mechanical impedance and admittance (EMIA) signatures were measured after each gamma radiation exposure. Radiation-dependent logarithmic sensitivity of PZT-PWAS in-plane and thickness modes resonance frequency (∂(fR)/∂( logeRd)) was estimated as 0.244 kHz and 7.44 kHz, respectively; the logarithmic sensitivity of GaPO4-PWAS in-plane and thickness modes resonance frequency was estimated as 0.0629 kHz and 2.454 kHz, respectively. Therefore, GaPO4-PWAS EMIA spectra show more gamma radiation endurance than PZT-PWAS. Scanning electron microscope (SEM) and X-ray diffraction method (XRD) was used to investigate the microstructure and crystal structure of PWAS transducers. From SEM and XRD results, it can be inferred that there is no significant variation in the morphology, the crystal structure, and grain size before and after the irradiation exposure.

Reliability assessment and failure mode analysis of MEMS accelerometers for space applications

In the present work, the reliability assessment of capacitive MEMS accelerometers of 3 different suppliers (codenamed A, B, and C) for their use in space applications was performed. The developed reliability assessment testing program addressed specific severities of space missions, such as mechanical shocks and vibrations during take-off and rocket stages separation, high temperature gradients and radiation endurance during in-orbit operation. The main aim of the testing was to evaluate the robustness and reliability limits of MEMS devices by overstressing their specific properties through dedicated tests. Typical failures modes were analyzed and root-causes identified on the devices' subsystem level: MEMS structure, ASIC, interconnecting wires, and package. Overall results of the performed reliability assessment tests and failure mode analyses suggest that the most specific MEMS components, namely the microstructures, do not themselves constitute the failure causes. Following the observations, other components, e.g. interconnects, ASIC or packaging, exhibit lower reliability limits to the specific stresses of the space harsh conditions. Comparative analysis of three accelerometers from various suppliers (designs A, B, and C) suggests the design A (in a hermetic ceramic package) to exhibit the best overall reliability for space-specific application conditions. Design B also shows good robustness. However, its non-hermetic packaging makes it unsuitable for the direct use for space applications in the current state. Utilization of a hermetic package and improvement of the wire-bonding temperature resistance would significantly improve this design. Accelerometers of supplier C (in a hermetic ceramic package) have a trend of occasional “infant mortality” early failures. It is therefore very important to perform burn-in and initial pre-screening for these devices. Another strong weak point for this design is related to a low radiation endurance, which shall be significantly improved.

Design and qualification tests of a robotic joint module for tokamak in-vessel manipulator use

PurposeThis paper aims to present the design and a prototype experiment of a robotic joint module for tokamak in-vessel manipulator-related research; the results will promote the adaptation of current in-vessel inspection manipulator to achieve full tokamak in-vessel environment compatibility.Design/methodology/approachA flexible metallic bellow-enclosed working chamber is used to protect the main servo drive components, the active cooling method for high temperature protection and the servo control structure simplification for high radiation endurance. A joint module prototype is manufactured and tested under a similar in-vessel environmental condition for extreme condition protection validation and basic servo control ability evaluation.FindingsThe joint module prototype successfully survived the similar in-vessel environment tests and proved good mobility via closed-loop servo control. A conceptual design of a serial linkage manipulator with joint module structure is proposed for future in-vessel inspection manipulator development.Originality/valueThe proposed joint module uses common industrial servo components to achieve its full extreme in-vessel environment compatibility. Different from traditional metallic bellow application in a vacuum environment to produce a linear movement result, the proposed joint module aims to achieve rotating movement directly from the metallic bellow structure, thereby reducing the joint structure space requirement, simplifying the vacuum environment movement transmission structure and increasing the vacuum environment compatibility degree.

Temperature Dependence of the Seebeck Coefficient in Zinc Oxide Thin Films

Thermoelectric devices are reliable tools for converting waste heat into electricity as they last long, produce no noise or vibration, have no moving elements, and their light weight makes them suitable for the outer space usage. Materials with high thermoelectric figure of merit (zT) have the most important role in the fabrication of efficient thermoelectric devices. Metal oxide semiconductors, specially zinc oxide has recently received attention as a material suitable for sensor, optoelectronic and thermoelectric device applications because of their wide direct bandgap, chemical stability, high-energy radiation endurance, transparency and acceptable zT. Understanding the thermoelectric properties of the undoped ZnO thin films can help design better ZnO-based devices. Here, we report the results of our experimental work on the thermoelectric properties of the undoped polycrystalline ZnO thin films. These films are deposited on alumina substrates by thermal evaporation of zinc in vacuum followed by a controlled oxidation process in air carried out at the 350-500 °C temperature range. The experimental setup including gradient heaters, thermometry system and Seebeck voltage measurement equipment for high resistance samples is described. Seebeck voltage and electrical resistivity of the samples are measured at different conditions. The observed temperature dependence of the Seebeck coefficient is discussed.

Radiation endurance in Al2O3 nanoceramics

The lack of suitable materials solutions stands as a major challenge for the development of advanced nuclear systems. Most issues are related to the simultaneous action of high temperatures, corrosive environments and radiation damage. Oxide nanoceramics are a promising class of materials which may benefit from the radiation tolerance of nanomaterials and the chemical compatibility of ceramics with many highly corrosive environments. Here, using thin films as a model system, we provide new insights into the radiation tolerance of oxide nanoceramics exposed to increasing damage levels at 600 °C –namely 20, 40 and 150 displacements per atom. Specifically, we investigate the evolution of the structural features, the mechanical properties, and the response to impact loading of Al2O3 thin films. Initially, the thin films contain a homogeneous dispersion of nanocrystals in an amorphous matrix. Irradiation induces crystallization of the amorphous phase, followed by grain growth. Crystallization brings along an enhancement of hardness, while grain growth induces softening according to the Hall-Petch effect. During grain growth, the excess mechanical energy is dissipated by twinning. The main energy dissipation mechanisms available upon impact loading are lattice plasticity and localized amorphization. These mechanisms are available in the irradiated material, but not in the as-deposited films.

Are Nanoporous Materials Radiation Resistant?

The key to perfect radiation endurance is perfect recovery. Since surfaces are perfect sinks for defects, a porous material with a high surface to volume ratio has the potential to be extremely radiation tolerant, provided it is morphologically stable in a radiation environment. Experiments and computer simulations on nanoscale gold foams reported here show the existence of a window in the parameter space where foams are radiation tolerant. We analyze these results in terms of a model for the irradiation response that quantitatively locates such window that appears to be the consequence of the combined effect of two length scales dependent on the irradiation conditions: (i) foams with ligament diameters below a minimum value display ligament melting and breaking, together with compaction increasing with dose (this value is typically ∼5 nm for primary knock on atoms (PKA) of ∼15 keV in Au), while (ii) foams with ligament diameters above a maximum value show bulk behavior, that is, damage accumulation (few hundred nanometers for the PKA's energy and dose rate used in this study). In between these dimensions, (i.e., ∼100 nm in Au), defect migration to the ligament surface happens faster than the time between cascades, ensuring radiation resistance for a given dose-rate. We conclude that foams can be tailored to become radiation tolerant.