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Feb 2009

Volume 80, Issue 2, Articles (02xxxx)

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Design and estimated performance of a new neutron guide system for the NCNR expansion project

J. C. Cook

Rev. Sci. Instrum. 80, 023101 (2009); http://dx.doi.org/10.1063/1.3077144 (10 pages) | Cited 6 times

Online Publication Date: 11 February 2009

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An integral part of the National Institute of Standards and Technology Center for Neutron Research (NCNR) expansion project is the addition of five cold neutron guide tubes serving multiple experimental stations in an expanded guide hall. The guides have curved-straight arrangements in the horizontal plane, employing horizontally or vertically defocusing and focusing sections in some cases to improve transmission efficiency or for beam reshaping. The horizontally curved sections eliminate direct lines of sight between the source and the experimental stations, and the outer (concave) surfaces generally have higher critical angles than the inner (convex) surfaces. These features result in well-filtered cold neutron beams with no intensity losses at shorter wavelengths with respect to curved guides having the higher critical angle coatings on both surfaces. For all guides the critical angle of the outer coating of the curved section is selected to achieve a desirable characteristic wavelength, consistent with the instrument requirements. On guides where the scattering-plane beam divergence must be strictly limited, the inner radial coatings of the curved sections and the side coatings and lengths of the final straight sections are chosen to produce the desired beam divergence while the outer radial coating is selected so as to obtain a spatial-angular uniformity of the transmitted beam that is not achievable using a curved guide alone. The long-wavelength transmission of such guides tends to exceed that of equivalent straight guides using crystal filters.
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28.50.Dr Research reactors
03.75.Be Atom and neutron optics

A versatile electron-ion coincidence spectrometer for photoelectron momentum imaging and threshold spectroscopy on mass selected ions using synchrotron radiation

Gustavo A. Garcia, Héloïse Soldi-Lose, and Laurent Nahon

Rev. Sci. Instrum. 80, 023102 (2009); http://dx.doi.org/10.1063/1.3079331 (12 pages) | Cited 32 times

Online Publication Date: 13 February 2009

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We present a photoelectron-photoion coincidence (PEPICO) spectrometer named DELICIOUS II which combines a velocity map imaging apparatus with a Wiley–McLaren time of flight analyzer for the study of gas phase samples in interaction with the synchrotron radiation (SR). This versatile system is capable of providing photoelectron images on mass-selected compounds with kinetic energy resolutions of ΔE/E = 5% and a 17 eV bandwidth, as well as threshold photoelectron spectra with a measured resolution of 0.8 meV, as demonstrated on the 3p−1 ionization of argon. This instrument is also employed for threshold PEPICO experiments, allowing the selection of the parent ion’s internal state with sub-meV resolution for light masses (<40 amu) and with typically 2 meV resolution for a mass of 100 amu and with a mass resolving power above 200. The continuous operation of the extraction fields and the independence from the electron’s time of flight are well adapted to the quasicontinuous multibunch mode of the SR. This, together with the high transmission of both the electron and ion detection, allows a high coincidence counting rate and facilitates the subtraction of false coincidences. We illustrate the spectrometer’s coincidence principle of operation with examples from the valence photoionization of an Ar+Xe mixture and of CF4.
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07.81.+a Electron and ion spectrometers
07.75.+h Mass spectrometers

2E1 Ar17+ decay and conventional radioactive sources to determine efficiency of semiconductor detectors

Emily Lamour, Christophe Prigent, Benjamin Eberhardt, Jean Pierre Rozet, and Dominique Vernhet

Rev. Sci. Instrum. 80, 023103 (2009); http://dx.doi.org/10.1063/1.3077284 (7 pages) | Cited 4 times

Online Publication Date: 17 February 2009

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Although reliable models may predict the detection efficiency of semiconductor detectors, measurements are needed to check the parameters supplied by the manufacturers, namely, the thicknesses of dead layer, beryllium window, and crystal active area. The efficiency of three silicon detectors has been precisely investigated in their entire photon energy range of detection. In the zero to a few keV range, we developed a new method based on the detection of the 2E1 decay of the metastable Ar17+ 2s→1s transition. Very good theoretical knowledge of the energetic distribution of the 2E1 decay mode enables precise characterization of the absorbing layers in front of the detectors. In the high-energy range (>10 keV), the detector crystal thickness plays a major role in the detection efficiency and has been determined using a 241Am source.
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29.40.Gx Tracking and position-sensitive detectors
29.40.Wk Solid-state detectors
29.25.Rm Sources of radioactive nuclei
23.20.Lv γ transitions and level energies
27.40.+z 39 ≤ A ≤ 58

Principle, calibration, and application of the in situ alkali chloride monitor

Christer Forsberg, Markus Broström, Rainer Backman, Elin Edvardsson, Shahriar Badiei, Magnus Berg, and Håkan Kassman

Rev. Sci. Instrum. 80, 023104 (2009); http://dx.doi.org/10.1063/1.3081015 (4 pages) | Cited 6 times

Online Publication Date: 20 February 2009

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The extended use of biomass for heat and power production has caused increased operational problems with fouling and high-temperature corrosion in boilers. These problems are mainly related to the presence of alkali chlorides (KCl and NaCl) at high concentrations in the flue gas. The in situ alkali chloride monitor (IACM) was developed by Vattenfall Research and Development AB for measuring the alkali chloride concentration in hot flue gases (≲650 °C). The measurement technique is based on molecular differential absorption spectroscopy in the UV range. Simultaneous measurement of SO2 concentration is also possible. The measuring range is 1–50 ppm for the sum of KCl and NaCl concentrations and 4–750 ppm for SO2. This paper describes the principle of the IACM as well as its calibration. Furthermore, an example of its application in an industrial boiler is given.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
89.60.-k Environmental studies
84.60.Rb Thermoelectric, electrogasdynamic and other direct energy conversion
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables

Chromatic-free spatially resolved optical emission spectroscopy diagnostics for microplasma

Li-Guo Zhu, Wen-Cong Chen, Xi-Ming Zhu, Yi-Kang Pu, and Ze-Ren Li

Rev. Sci. Instrum. 80, 023105 (2009); http://dx.doi.org/10.1063/1.3079379 (4 pages) | Cited 3 times

Online Publication Date: 27 February 2009

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A chromatic-free spatially resolved diagnostic system for microplasma measurement is proposed and demonstrated, which consists of an optical chromatic-free microscope mirror system, an electron multiplying charge coupled device (EMCCD), and bandpass filters. The diagnostic system free of chromatic aberrations with a spatial resolution of about 6 μm is achieved. The factors that limit the resolution of this diagnostic system have been analyzed, which are optical diffraction, the pixel size of the EMCCD, and the thickness of the microplasma. In this paper, the optimal condition for achieving a maximum resolution power has been analyzed. With this diagnostic system, we revealed the spatial nonuniformity of a microwave atmospheric-pressure argon microplasma. Furthermore, the spatial distribution of the time-averaged effective electron temperature has been estimated from the intensity distributions of 750.4 and 415.8 nm emissions.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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