GE Develops Nano Scintillator Materials and Detection Systems

A scintillator is material which exhibits the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e. reemit the absorbed energy in the form of a small flash of light, typically in the visible range.

Scintillator materials can convert high-energy radiation, such as X-rays and gamma rays, into visible light. Scintillators are widely used in detection and non-invasive imaging technologies, such as imaging systems for medical and screening applications. In such systems, high-energy photons typically pass through the person or object undergoing imaging and, on the other side of the imaging volume, impact a scintillator associated with a light detection apparatus. The scintillator typically generates optical photons in response to the high-energy photon impacts. The optical photons may then be measured and quantified by the light detection apparatus, thereby providing a surrogate measure of the amount and location of high-energy radiation incident on the detector. Additionally, scintillators may be useful in systems used to detect radioactive objects, such as contraband or contaminants, and even underground radiation sources which might otherwise be difficult to detect.

General Electric Company (Niskayuna, NY) scientists have developed a scintillation detector using nano-scale particles of a scintillation compound embedded in a plastic matrix. The nano-scale scintillator particles may be made from metal oxides, metal oxyhalides, metal oxysulfides, or metal halides. The particles may be coated with organic compounds or polymers prior to incorporation in the plastic matrix. A technique for matching the refractive index of the plastic matrix with the nano-scale scintillator particles by incorporating nano-scale particles of titanium dioxide was also developed by inventors Sergio Paulo Martins Loureiro, James Scott Vartuli, Brent Allen Clothier, Steven Jude Duclos, Mohan Manoharan, Patrick Roland Lucien Malenfant, Venkat Subramaniam Venkataramani and Clifford Bueno

The scintillator may be coupled with one or more photodetectors to form a scintillation detection system. The scintillation detection system may be adapted for use in X-ray and radiation imaging devices, such as digital X-ray imaging, mammography, computer tomography (Cat Scan), positron emission tomography (PET), or Single photon emission computed tomography (SPECT), or may be used in radiation security detectors or subterranean radiation detectors.  GE’s s scintillator device and materials earned U.S. Patent 7,608,829.

With regard to non-invasive imaging techniques, one of the most important applications for scintillators is in medical equipment for the production of radiographic images using digital detection and storage systems. For example, in current digital X-ray imaging systems, such as CT scanners, radiation from a source is directed toward a subject, typically a patient in a medical diagnostic application. A portion of the radiation passes through the patient and impacts a detector. The surface of the detector converts the radiation to light photons which are sensed. The detector is divided into a matrix of discrete picture elements, or pixels, and encodes output signals based upon the quantity or intensity of the radiation impacting each pixel. Because the radiation intensity is altered as the radiation passes through the patient, the images reconstructed based upon the output signals provide a projection of the patient's tissues similar to those available through conventional photographic film techniques.

Another high-energy radiation based imaging system is positron emission tomography (PET), which generally employs a scintillator-based detector with its pixels typically arranged in a circular array.

Nanostructured Low-Cr Cu-Cr Coatings Provides High Temperature Oxidation Resistance

Southwest Research Institute (San Antonio, TX) scientists Kuang-Tsan Kenneth Chiang, James H. Arps, and Ronghua Wei developed a method of preventing oxidation of copper alloys at high temperatures by deposition of a nano-structured, low-chromium copper-chromium protective coating to copper-alloy components. The coatings are applied by an ion beam assisted, electron beam physical vapor deposition and consist of copper and chromium particles having a diameter of about 10 nm, according to U.S. Patent 7,592,051. The coated copper-alloy components are produced by deposition methods. The coatings may be deposited as one or more discrete layers each of copper and chromium, or alternatively as one or more layers of a copper-chromium mixture. The coatings have a thickness of less than about 25 microns. The so coated copper-containing components exhibit enhanced oxidation resistance at high temperatures

Copper-based alloys and composites are candidate materials for high heat flux structural applications because of their high thermal conductivity and high-temperature strength. Such applications include hot gas walls for combustion chambers and surfaces of nozzle ramps for rocket engines and for the next generation launch vehicles. Other applications include protective coatings for heat exchangers in commercial power generation systems and firearm barrels.

A major limitation to the use of any of these copper-based materials, however, is their rapid oxidation at elevated temperatures. In addition, copper-alloy rocket engine combustion chamber linings have been found to deteriorate when exposed to cyclic reducing/oxidizing (redox) environments, which are a consequence of the combustion process. This deterioration, known as blanching, can be characterized by increased roughness and burn-through sites in the wall of the combustion chamber lining and can seriously reduce the operational lifetime of the combustion chamber. Southwest Research Institute’s coatings display excellent oxidation resistance under high temperature oxidative conditions and perform as well as coatings requiring greater layer thickness and higher levels of chromium.