Varian Associates

About: Varian Associates is a based out in . It is known for research contribution in the topics: Beam (structure) & Amplifier. The organization has 2160 authors who have published 2591 publications receiving 46002 citations.

Long-wavelength photoemission cathode

Abstract: A long wavelength photoemitter, for example a III-V semiconductor, having a work function reduction activation layer thereon, with means for overcoming the energy barrier between the semiconductor conduction band edge and the vacuum comprising means for thermally energizing the photoexcited electrons in the conduction band from a lower energy level therein to a higher "metastable" energy level in which they may reside for a sufficient time such that the electrons can pass with high probability from the elevated energy level into the vacuum over the energy barrier. In one embodiment, promotion of electrons to this higher energy level in the conduction band results from proper selection of the semiconductor alloy with conduction band levels favoring such room temperature thermal excitation. In another embodiment, a Schottky barrier is formed between the semiconductor emitter surface and the activation layer, by means of which an internal electric field is applied to the cathode resulting in high effective electron temperature for energy level transfer analogous to the intervalley electron transfer process of the Gunn effect. In yet other embodiments, composite semiconductor bodies are fabricated in which one region may advantageously be designed for efficient absorption of long-wavelength photons, and another for efficient operation of the promotion mechanism, which together assure a high quantum efficiency. Other properties of the biased promotion layer may be used to minimize emission of electrons which have been excited by purely thermal means, thus providing a low dark current, usually considered to be incompatible with long-wavelength infrared response.

Transparent garnet ceramic scintillators for gamma-ray detection

Abstract: Lanthanide gallium/aluminum-based garnets have a great potential as host structures for scintillation materials for medical imaging. Particularly attractive features are their high density, chemical radiation stability and more importantly, their cubic structure and isotropic optical properties, which allow them to be fabricated into fully transparent, highperformance polycrystalline optical ceramics. Lutetium/gadolinium aluminum/gallium garnets (described by formulas ((Gd,Lu)3(Al,Ga)5O12:Ce, Gd3(Al,Ga)5O12:Ce and Lu3Al5O12:Pr)) feature high effective atomic number and good scintillation properties, which make them particularly attractive for Positron Emission Tomography (PET) and other γ- ray detection applications. The ceramic processing route offers an attractive alternative to single crystal growth for obtaining scintillator materials at relatively low temperatures and at a reasonable cost, with flexibility in dimension control as well as activator concentration adjustment. In this study, optically transparent polycrystalline ceramics mentioned above were prepared by the sintering-HIP approach, employing nano-sized starting powders. The properties and microstructures of the ceramics were controlled by varying the processing parameters during consolidation. Single-phase, high-density, transparent specimens were obtained after sintering followed by a pressure-assisted densification process, i.e. hot-isostatic-pressing. The transparent ceramics displayed high contact and distance transparency as well as high light yield as high as 60,000-65,000 ph/MeV under gamma-ray excitation, which is about 2 times that of a LSO:Ce single crystal. The excellent scintillation and optical properties make these materials promising candidates for medical imaging and γ-ray detection applications.

The relative signs of geminal and vicinal proton spin coupling constants

Abstract: The 60 Mc/s proton resonance spectrum of 2,3-dibromopropionic acid is reported and analysed as an ABC system. The relative signs of the geminal and vicinal coupling constants observed have been determined by the double irradiation method and confirmed by experiments at 15·086 Mc/s. The two types of coupling constant are found to have opposite signs and to be large, the geminal one being ∓9·9 c.p.s. and the vicinal ones ±10·8 c.p.s. and ±4·6 c.p.s.

Nmr sample cell

Abstract: The present invention relates to improving the sensitivity of an NMR system for electrically conductive (polar) NMR samples. Many NMR samples use water or a salt solution of water or other electrically conductive liquid as a solvent for biologically active materials. When such a sample is placed in the probe coil of an NMR spectrometer, electrical losses in the conductive material lowers the Q of the receiving circuit and thereby reduces the sensitivity of the spectrometer. These electrical losses can be greatly reduced by breaking up the current paths within the sample. This can be achieved by a special sample cell that compartmentalizes the sample with electrical insulating material reducing the electrical current paths.

High-power microwave excited plasma discharge lamp

Abstract: A high-power microwave plasma discharge lamp is disclosed. The lamp includes a ceramic tube filled with gas and closed at one end by a window transparent to the optical radiation output of the lamp. The ceramic tube extends through a cavity resonator excited with microwave energy for exciting a plasma discharge within the lamp.