oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Quantum efficiency of technical metal photocathodes under laser irradiation of various wavelength  [PDF]
F. Le Pimpec,F. Ardana-Lamas,C. P. Hauri,C. Milne
Physics , 2012, DOI: 10.1007/s00339-013-7600-z
Abstract: Quantum efficiency studies for various wavelength and various technical metal surfaces were carried out in a dedicated unbaked vacuum chamber. Copper, magnesium, aluminium and aluminium-lithium photocathodes were irradiated by two different high power, high repetition rate, laser systems. We have observed an emission of electrons for photon energy below the work function of the material. This is explained by multiple photon absorption at the photocathode. We have not observed any degradation of the QE for those materials, but an improvement when irradiating them over a long period of time. This is contrary to observations made in RF photoguns.
Evaluation of various planar gaseous detectors with CsI photocathodes for the detection of primary scintillation light from noble gases  [PDF]
L. Periale,V. Peskov,P. Carlson,T. Francke,C. Iacobaeus,P. Pavlopoulos,F. Pietropaolo,T. Sokolova
Physics , 2001, DOI: 10.1016/S0168-9002(02)01918-6
Abstract: Noble gases and liquids are excellent scintillators and this opens a unique opportunity to directly detect the primary scintillation light produced in these media by photons or particles. This signal can be used for several purposes, for example as a start signal for TPCs or for particles identification. Usually photomultipliers (PMs) are used for the detection of the scintillation light. In our previous work we have demonstrated that costly PMs could be replaced by gaseous detectors with CsI photocathodes . Such detectors have the same quantum efficiency as the best PMs but at the same time are cheap, simple and have high position and time resolutions. The aim of this work is to evaluate various planar type gaseous detectors with CsI photocahodes in order to choose the best one for the detection of the primary scintillation light from noble gases and liquids.
Optical properties of bialkali photocathodes  [PDF]
Dario Motta,Stefan Schoenert
Physics , 2004, DOI: 10.1016/j.nima.2004.10.009
Abstract: The optical properties of the `bialkali' KCsSb and RbCsSb photomultiplier cathodes have been experimentally investigated in the visible range. The measurements carried out include the absolute reflectance at near-normal incidence, the polarization-dependent relative reflectance at various angles and the change in polarization upon reflection from the photocathode. These experimental inputs have been combined with a theoretical model to determine the complex refractive index of the photocathodes in the wavelength range 380 to 680 nm and their thickness. As a result of this work, we derive a model which predicts the fraction of light impinging on a photomultiplier tube that is reflected, absorbed or transmitted, as a function of wavelength and angle, and dependent on the medium to which the photomultiplier is coupled.
Comparison between gradient-doping and uniform-doping GaN photocathodes
梯度掺杂与均匀掺杂GaN光电阴极的对比研究

Wang Xiao-Hui,Chang Ben-Kang,Qian Yun-Sheng,Gao Pin,Zhang Yi-Jun,Guo Xiang-Yang,Du Xiao-Qing,
王晓晖
,常本康,钱芸生,高频,张益军,郭向阳,杜晓晴

物理学报 , 2011,
Abstract: In order to enhance the quantum efficiencies of negative electron affinity (NEA) GaN photocathodes, gradient-doping reflection-mode GaN photocathodes are grown by metal organic chemical vapor deposition (MOCVD)at doping concentrations of 1×1018cm-3, 4×1017cm-3, 2×1017cm-3 and 6×1016cm-3 from the body to the surface, with the thickness of each doping region being about 45nm and the total thickness of GaN 180 nm. The gradient-doping GaN photocathodes are activated in an ultra-high vacuum system and are compared with two kinds of uniform-doping GaN photocathodes whose thicknesses are both 150 nm and doping concentrations are 1.6×1017cm-3 and 3×1018cm-3 separately. The results show that both the photocurrent growth rate and the maximum photocurrent of the gradient-doping GaN photocathodes are greater than those of the uniform-doping GaN in the Cs/O activation process, and the multi-test system measured maximum quantum efficiency of the gradient-doping NEA GaN photocathode is about 56% which is as high as the double of the uniform-doping. Calculations show that the energy band bendings of the gradient-doping GaN photocathodes are 0.024eV, 0.018eV and 0.031eV from the body to the surface, a larger electron drift and diffusion length are gained due to the built-in electric field formed by the energy band bending, because of the 0.073eV total energy band bending the photoelectrons reaching the surface have higher energies and pass through the surface barrier more easily. Therefore the gradient-doping NEA GaN photocathodes have greater quantum efficiencies.
The development of gaseous detectors with solid photocathodes for low temperature  [PDF]
L. Periale,V. Peskov,C. Iacobaeus,T. Francke,B. Lund-Jensen,N. Pavlopoulos,P. Picchi,F. Pietropaolo
Physics , 2004, DOI: 10.1016/j.nima.2004.07.182
Abstract: There are several applications and fundamental research areas which require the detection of VUV light at cryogenic temperatures. For these applications we have developed and successfully tested special designs of gaseous detectors with solid photocathodes able to operate at low temperatures: sealed gaseous detectors with MgF2 windows and windowless detectors. We have experimentally demonstrated, that both primary and secondary (due to the avalanche multiplication inside liquids) scintillation lights could be recorded by photosensitive gaseous detectors. The results of this work may allow one to significantly improve the operation of some noble liquid gas TPCs.
Atomic Hydrogen Cleaning of Polarized GaAs Photocathodes  [PDF]
T. Maruyama,D. -A. Luh,A. Brachmann,J. E. Clendenin,E. L. Garwin,S. Harvey,R. E. Kirby,C. Y. Prescott,R. Prepost
Physics , 2004,
Abstract: Atomic hydrogen cleaning followed by heat cleaning at 450$^\circ$C was used to prepare negative-electron-affinity GaAs photocathodes. When hydrogen ions were eliminated, quantum efficiencies of 15% were obtained for bulk GaAs cathodes, higher than the results obtained using conventional 600$^\circ$C heat cleaning. The low-temperature cleaning technique was successfully applied to thin, strained GaAs cathodes used for producing highly polarized electrons. No depolarization was observed even when the optimum cleaning time of about 30 seconds was extended by a factor of 100.
High Performance Photocathodes based on Molecular Beam Epitaxy Deposition for Next Generation Photo Detectors and Light Sources  [PDF]
Junqi Xie,Marcel Demarteau,Robert Wagner
Physics , 2013,
Abstract: The development of high-performance photocathodes is a key challenge for future accelerator and particle physics applications. In this paper photocathode growth through molecular beam epitaxy is introduced as a promising technique to obtain robust, highly efficient alkali-antimonide based photocathodes. Recent research shows that the quantum efficiency of photocathodes can be significantly enhanced through control of the photocathode crystallinity. Molecular beam epitaxy allows for cost-effective growth of large-area photocathodes with excellent control of the stoichiometry and crystallinity, making photocathodes with peak quantum efficiencies exceeding 35% routine.
Modulation of Mutagenicity of Various Mutagens by Shrimp Flesh and Skin Extracts in Salmonella Test  [PDF]
S. Mehrabian,E. Shirkhodaei
Pakistan Journal of Biological Sciences , 2006,
Abstract: Many mutagens and carcinogens may act through the generation of Reactive Oxygen Species (ROS) in cells that maybe related to cancer. The carotenoid astaxanthin-the red pigment for the attractive coloration in the skin and flesh of shrimp-has attracted considerable interest in recent years because of its superior antioxidative activity to most of the hydrophobic antioxidants. According to the important role of carotenoids in human health, the main carotenoid pigment in flesh and by-products of the different shrimp species from penaeidae family-Astaxanthin-was extracted and separated by thin layer chromatography using silica gel, subsequently. The identifications were confirmed by fourier transform infrared (ET-IR) spectroscopy. The effect of these extracts on mutagenicity and carcinogenicity induced by Sodium Azide and potassium permanganate was investigated in bacterial assay system, i.e., the Ames test with salmonella typhimurium TA100, TA104. These strains have a certain mutation in their histidin operon, which are related to the external histidin source. Such a mutation can be reversed through contact with a diagnostic mutagen, but in shrimp extracts prevented from effect of this mutagen in which, after repeated test series under standardized condition, the anticarcinogenic effect of flesh and skin of shrimp was proven and the shrimp skin showed stronger anticarcinogenic effect in comparison with shrimp flesh. Different shrimp species from penaeidae family indicated similar antricariongenic effects.
Evaluation of hydrogen sulphide test for detection of fecal coliform contamination in drinking water from various sources
DH Tambekar, NB Hirulkar, SR Gulhane, PN Rajankar, SS Deshmukh
African Journal of Biotechnology , 2007,
Abstract: The assessment of H2S field test for detection of potability of drinking water was evaluated by analysing 1050 water samples from various sources at room temperature and at 37oC after 18, 24, and 48 h of incubation. The H2S test showed 100, 84 and 89% correlation with Eijkman test, Membrane Filter Technique (MFT) and Most Probable Number (MPN) test for coliform, respectively. In comparisons with MPN the H2S test showed 84% correlation with open well water, 80% with tube well water and 94% with hotels and restaurants water at room temperature, indicating decrease in efficacy of this test with depth of source of water. The test can be used in the field or in village level without any skilled personnel. Hence the test can be recommended for detection of fecal contamination in drinking water in the field where laboratory facilities are limited.
Test
webmaster id
TEFLIN Journal , 2007,
Abstract: Test
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.