Showing papers by "Varian Associates published in 2009"

Overview of a cyber-enabled wireless monitoring system for the protection and management of critical infrastructure systems

Abstract: The long-term deterioration of large-scale infrastructure systems is a critical national problem that if left unchecked, could lead to catastrophes similar in magnitude to the collapse of the I-35W Bridge. Fortunately, the past decade has witnessed the emergence of a variety of sensing technologies from many engineering disciplines including from the civil, mechanical and electrical engineering fields. This paper provides a detailed overview of an emerging set of sensor technologies that can be effectively used for health management of large-scale infrastructure systems. In particular, the novel sensing technologies are integrated to offer a comprehensive monitoring system that fundamentally addresses the limitations associated with current monitoring systems (for example, indirect damage sensing, cost, data inundation and lack of decision making tools). Self-sensing materials are proposed for distributed, direct sensing of specific damage events common to civil structures such as cracking and corrosion. Data from self-sensing materials, as well as from more traditional sensors, are collected using ultra low-power wireless sensors powered by a variety of power harvesting devices fabricated using microelectromechanical systems (MEMS). Data collected by the wireless sensors is then seamlessly streamed across the internet and integrated with a database upon which finite element models can be autonomously updated. Life-cycle and damage detection analyses using sensor and processed data are streamed into a decision toolbox which will aid infrastructure owners in their decision making.

Characterization of vapor-deposited Lu2O3:Eu3+ scintillator for x-ray imaging applications

Abstract: The europium-doped lutetium oxide (Lu 2 O 3 :Eu) transparent optical ceramic has excellent scintillation properties, namely very high density (9.5 g/cm 3 ), high effective atomic number (67.3), light output comparable to thallium-doped cesium iodide (CsI:Tl), and emission wavelength (610 nm) for which silicon-based detectors have a very high quantum efficiency. If microcolumnar films of this material could be fabricated, it would find widespread use in a multitude of highspeed imaging applications. However, the high melting point of over 2400°C makes it extremely challenging to make microcolumnar films of this material. We have recently fabricated and characterized microcolumnar films of Lu 2 O 3 :Eu. These results are presented in this paper.

Lu2SiO5:Ce optical ceramic scintillator

Abstract: Lutetium oxyorthosilicate (Lu 2 SiO 5 :Ce 3+ , commonly known as LSO) is a scintillator of choice for medical imaging applications such as Positron Emission Tomography (PET) because of its high light output, high gamma ray stopping power and fast response. In the current study, phase-pure LSO ceramics were obtained with a high degree of optical transparency and excellent scintillation properties. These LSO optical ceramics were prepared by combining nanotechnology with a sinter-HIP approach. We found that the densities of the LSO ceramics increased with increasing sintering temperature, which corresponds to a systematic decrease in porosity as found by SEM examination. The residual pores were found to segregate at grain boundaries after sintering, and were essentially removed by subsequent hot isostatic pressing (HIPing), which raised the density to essentially the value characteristic of the single crystal and produced polycrystalline LSO ceramics with a high degree of transparency. Under excitation a 22 Na source such specimens displayed a light output as high as 30,100 ph/MeV. The LSO ceramics showed an energy resolution of 15% (FWHM) at 662 keV ( 137 Cs source) and a fast scintillation decay of 40 ns due to the 5d → 4f transition of Ce 3+ . The excellent scintillation and optical properties make LSO ceramic a promising candidate for future gamma-ray spectroscopy as well as medical imaging applications.