253 research outputs found

    The 26th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting

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    This document is a compilation of technical papers presented at the 26th Annual PTTI Applications and Planning Meeting. Papers are in the following categories: (1) Recent developments in rubidium, cesium, and hydrogen-based frequency standards, and in cryogenic and trapped-ion technology; (2) International and transnational applications of Precise Time and Time Interval technology with emphasis on satellite laser tracking, GLONASS timing, intercomparison of national time scales and international telecommunications; (3) Applications of Precise Time and Time Interval technology to the telecommunications, power distribution, platform positioning, and geophysical survey industries; (4) Applications of PTTI technology to evolving military communications and navigation systems; and (5) Dissemination of precise time and frequency by means of GPS, GLONASS, MILSTAR, LORAN, and synchronous communications satellites

    Contributions of precision engineering to the revision of the SI

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    All measurements performed in science and industry are based on the International System of Units, the SI. It has been proposed to revise the SI following an approach which was implemented for the redefinition of the unit of length, the metre, namely to define the SI units by fixing the numerical values of so-called defining constants, including c, h, e, k and NA. We will discuss the reasoning behind the revision, which will likely be put into force in 2018. Precision engineering was crucial to achieve the required small measurement uncertainties and agreement of measurement results for the defining constants

    Neutron Detection by Scintillation of Noble-Gas Excimers

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    Neutron detection is a technique essential to homeland security, nuclear reactor instrumentation, neutron diffraction science, oil-well logging, particle physics and radiation safety. The current shortage of helium-3, the neutron absorber used in most gas-filled proportional counters, has created a strong incentive to develop alternate methods of neutron detection. Excimer-based neutron detection (END) provides an alternative with many attractive properties. Like proportional counters, END relies on the conversion of a neutron into energetic charged particles, through an exothermic capture reaction with a neutron absorbing nucleus (10B, 6Li,3He). As charged particles from these reactions lose energy in a surrounding gas, they cause electron excitation and ionization. Whereas most gas-filled detectors collect ionized charge to form a signal, END depends on the formation of diatomic noble-gas excimers (Ar2*, Kr2*, Xe2*). Upon decaying, excimers emit far-ultraviolet (FUV) photons, which may be collected by a photomultiplier tube or other photon detector. This phenomenon provides a means of neutron detection with a number of advantages over traditional methods. This thesis investigates excimer scintillation yield from the heavy noble gases following the boron-neutron capture reaction in 10B thin-film targets. Additionally, the thesis examines noble-gas excimer lifetimes with relationship to gas type and gas pressure. Experimental data were collected both at the National Institute of Standards and Technology (NIST) Center for Neutron Research, and on a newly developed neutron beamline at the Maryland University Training Reactor. The components of the experiment were calibrated at NIST and the University of Maryland, using FUV synchrotron radiation, neutron imaging, and foil activation techniques, among others. Computer modeling was employed to simulate charged-particle transport and excimer photon emission within the experimental apparatus. The observed excimer scintillation yields from the 10B(n,α)7Li reaction are comparable to the yields of many liquid and solid neutron scintillators. Additionally, the observed slow triplet-state decay of neutron-capture-induced excimers may be used in a practical detector to discriminate neutron interactions from gamma-ray interactions. The results of these measurements and simulations will contribute to the development and optimization of a deployable neutron detector based on noble-gas excimer scintillation

    Aspects on measuring electrical current utilizing magnetic zero-flux technique

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    The utilization of high accuracy measurements of electrical quantities is a prerequisite for the development of modern society. Generally, measurements serve different purposes and hence the criteria for the measurement equipment and method are different. For example, the demands are mild if the application is the continuous monitoring of the power grid, more finely tuned for measuring methods used in research and development, and often challenging in the case of certified measuring methods adequate for calibration and accreditation. RISE Research Institutes of Sweden (former SP Technical Research Institute of Sweden) is appointed the National Metrology Institute by the Swedish government for electrical quantities and continuously develops and provides measurement technology for the different needs governed by application.The magnetic zero-flux technique is a non-contact measurement method for electrical AC and DC current and its design principle enables accurate measurements over a large current range. Its advantages come however with the price of a complex but sophisticated design. The zero-flux technique has been utilized for many decades, and there are a number of manufacturers providing commercial systems with somewhat different features.This project is devoted to the further investigation and advancement of some metrological aspects of the magnetic zero-flux technique for AC. Practical laboratory tests on a state-of-the-art zero-flux system are used to create a picture of its properties at higher frequencies than its manufacturer has provided detailed specifications for. Focus is to determine how sensitive the measurement results are to practical arrangements and limitations of the measurement setup. A method and guide to how different configurations of the measurement setup affect the measured results in different frequency ranges is provided. Utilizing this characterization, practical set-ups can be made, as optimal as possible for the frequency range of interest, avoiding time-consuming focus on aspects not relevant for the specific application.The identified aspects of interest are: (i) identifying the source of the measurement error in the zero-flux system’s design and, if possible, minimizing this error by design adjustments, (ii) measurement error and measurement uncertainty of a zero-flux system in presence of geometric asymmetry and disturbance from return or nearby conductors, (iii) simultaneous measurements of sinusoidal signals of different amplitudes, frequencies and phase angles, (iiii) detection of sub-synchronous events, and (v) non-steady state phenomena, like for example transients in the drive line of electrical vehicles. In this thesis, aspects (i) and (ii) above are in focus. Some conclusions can be drawn based on the performed study concerning aspect (iiii), whereas aspects (iii) and (v) remain out of its scope.The initial step of this project was the choice of a generally applicable method for characterization and evaluation of a zero-flux system. The method chosen is the combination of a coaxial primary current path, or as near coaxial as was practically convenient, and a Digital Sampling Watt Meter (DSWM). The method can be utilized for the characterization and evaluation of other zero-flux systems. An investigation was performed to decide from which part of the construction the phase angle error stems. The performed characterization allowed compensating for the errors, making the measurement accuracy greatly improved. Two modifications to the circuitry of the zero-flux systems were introduced and evaluated, both of which yielded improvement of its high frequency characteristics up to 100 kHz. Also the accuracy within the low frequency range (from 10 – 50 Hz) was improved by one of the modifications.The error of a zero-flux measuring system depends on the positioning of its sensor around the conductor carrying the measured current and the geometry of the primary current path. The total error increases with frequency, but which geometric factor that is the most important one varies with frequency. In this study, utilizing sinusoidal primary current, it was found that for 50 Hz, tilt of the sensor and positioning of the connection point for the measurement and zero-flux control cable (rotation) caused the largest effects on the scale factor. De-centring and the distances to different parts of the return conductor were less important in the 50 Hz case. For 25 kHz, de-centring and rotation were the main contributors to scale factor change, while tilt had the smallest measured effect. The total contribution from sensor positioning in the magnetic field to the expanded measurement uncertainty was estimated to 0.0024 % in the 50 Hz case, to 0.0040 % for 1 kHz, to 0.14 % for 10 kHz, and to 0.41 % for 25 kHz

    Synthesis, Characterization, and Spectroscopy of Lanthanide-Doped Inorganic Nanocrystals; Radiant Flux and Absolute Quantum Yield Measurements of Upconversion Nanocrystals, and Fabrication of a Fiber-Optic Radiation Detector Utilizing Synthetically Optimized, Linearly Responsive Nanoscintillators

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    <p>The ability to interrogate structure-function photophysical properties on lanthanide-doped nanoscale materials will define their utility in next-generation applications and devices that capitalize on their size, light-conversion efficiencies, emissive wavelengths, syntheses, and environmental stabilities. The two main topics of this dissertation are (i) the interrogation of laser power-dependent quantum yield and total radiant flux metrics for a homogeneous, solution phase upconversion nanocrystal composition under both continuous wave and femtosecond-pulsed excitation utilizing a custom engineered absolute measurement system, and (ii) the synthesis, characterization, and power-dependent x-ray excited scintillation properties of [Y<sub>2</sub>O<sub>3</sub>; Eu] nanocrystals, and their integration into a fiber-optic radiation sensing device capable of in vivo dosimetry.</p><p>Presented herein is the laser power-dependent total radiant flux and absolute quantum yield measurements of homogeneous, solution-phase [NaYF<sub>4</sub>; Yb (15%), Er (2%)] upconversion nanocrystals, and further compares the quantitative total radiant flux and absolute quantum yield measurements under both 970 nm continuous-wave and 976 nm pulsed Ti-Sapphire laser excitation (140 fs pulse-width, 80 MHz). This study demonstrates that at comparable excitation densities under continuous-wave and fs-pulsed excitation from 42 - 284 W/cm<super>2</super>, the absolute quantum yield, and the total radiant flux per unit volume, are within a factor of two when spectra are integrated over the 500 - 700 nm wavelength regime. This study further establishes the radiant flux as the true unit of merit for quantifying emissive output intensity of upconverting nanocrystals for application purposes, especially given the high uncertainty in solution phase upconversion nanocrystal quantum yield measurements due to their low absorption cross-section. Additionally, a commercially available bulk [NaYF<sub>4</sub>; Yb (20%), Er (3%)] upconversion sample was measured in the solid-state to provide a total radiant flux and absolute quantum yield standard. The measurements were accomplished utilizing a custom-engineered, multi-detector integrating sphere measurement system that can measure spectral sample emission in Watts on a flux-calibrated (W/nm) CCD-spectrometer, enabling the direct measurement of the total radiant flux without need for an absorbance or quantum yield value. </p><p>Also presented is the development and characterization of a scintillating nanocrystalline composition, [Y<sub>2-x</sub>O<sub>3</sub>; Eu<sub>x</sub>, Li<sub>y</sub>], in which Eu and Li dopant ion concentrations were systematically varied in order to define the most emissive compositions under specific x-ray excitation conditions. It is shown that these optimized [Y<sub>2-x</sub>O<sub>3</sub>; Eu<sub>x</sub>, Li<sub>y</sub>] compositions display scintillation responses that: (i) correlate linearly with incident radiation exposure at x-ray energies spanning from 40 - 220 kVp, and (ii) manifest no evidence of scintillation intensity saturation at the highest evaluated radiation exposures [up to 4 Roentgen per second]. X-ray excitation energies of 40, 120, and 220 kVp were chosen to probe the dependence of the integrated emission intensity upon x-ray exposure-rate in energy regimes where either the photoelectric or the Compton effect governs the scintillation mechanism on the most emissive [Y<sub>2-x</sub>O<sub>3</sub>; Eu<sub>x</sub>, Li<sub>y</sub>] composition, [Y<sub>1.9</sub>O<sub>3</sub>; Eu<sub>0.1</sub>, Li<sub>0.16</sub>]. These experiments demonstrate for nanoscale [Y<sub>2-x</sub>O<sub>3</sub>; Eu<sub>x</sub>], that for comparable radiation exposures, when scintillation is governed by the photoelectric effect (120 kVp excitation), greater integrated emission intensities are recorded relative to excitation energies where the Compton effect regulates scintillation (220 kVp excitation). </p><p>The nanoscale [Y<sub>1.9</sub>O<sub>3</sub>; Eu<sub>0.1</sub>, Li<sub>0.16</sub>] was further exploited as a detector material in a prototype fiber-optic radiation sensor. The scintillation intensity from a [Y<sub>1.9</sub>O<sub>3</sub>; Eu<sub>0.1</sub>, Li<sub>0.16</sub>]-modified optical fiber tip, recorded using a CCD-photodetector or a Si-photodiode, was correlated with radiation exposure using a Precision XRAD 225Cx small-animal image guided radiation therapy (IGRT) system, an orthovoltage cabinet-irradiator, and a clinical X-ray Computed Tomography (CT) machine. For all x-ray energies tested from 80 - 225 kVp, this near-radiotransparent device recorded scintillation intensities that tracked linearly with total radiation exposure, highlighting its capability to provide alternately accurate dosimetry measurements for both diagnostic imaging and radiation therapy treatment. Because Si-based CCD and photodiode detectors manifest maximal sensitivities over the emission range of nanoscale [Y<sub>1.9</sub>O<sub>3</sub>; Eu<sub>0.1</sub>, Li<sub>0.16</sub>], the timing speeds, sizes, and low power-consumption of these devices, coupled with the detection element's linear dependence of scintillation intensity with radiation dose, demonstrates the opportunity for next-generation radiation exposure measuring devices for in/ex vivo applications that are ultra-small, inexpensive, and accurate.</p>Dissertatio

    Traceable multicomponent force and torque measurement

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    Ein Gerät, das für die Messung von Kraft- und Drehmomentvektoren eingesetzt wird und ein Kalibriersystem integriert, wird in dieser Arbeit beschrieben. Die Kräfte und Drehmomente werden auf die Messung von Position, Winkel, elektrischer Spannung, elektrischem Widerstand und Zeit zurückgeführt. Hinsichtlich fundamentaler Naturkonstanten können die Kräfte und Drehmomente auf die Planck Konstante h, die Lichtgeschwindigkeit c und die Frequenz des Hyperfeinübergangs von Caesium [Delta]v_Cs zurückgeführt werden. Das Messprinzip basiert auf dem Prinzip der elektromagnetischen Kraftkompensation und die Kalibrierung auf dem Kibble-Waagen Prinzip. Mehrere Schwierigkeiten und Einschränkungen von traditionellen Kalibrierverfahren für Mehrkomponenten-Kraft- und Drehmomentaufnehmer werden mit diesem System überwunden und neue Möglichkeiten werden vorgeschlagen, wie z.B. die automatische Inprozess-Kalibrierung. Mithilfe einer sorgfältigen Unsicherheitsanalyse wird die erreichbare Unsicherheit für die Kraft- und Drehmomentmessung ausgewertet und die Einschränkungen identifiziert, die durch die verschiedenen Komponenten des Systems verursacht werden. Ein Prototyp wird vorgestellt, der die Kraft- und Drehmomentmessung im Bereich vom 2.2 N und 0.11 N m mit einer relativen Standardmessunsicherheit von 44 ppm bzw. 460 ppm ermöglicht. Weiterhin wurde das System durch die Messung einer bekannten Kraft überprüft, die von einem kalibrierten Testgewicht erzeugt wird. Experimentelle Ergebnisse wurden durch die Anwendung von Mehrkomponentenaufnehmern in der Lorentzkraft-Anemometrie, Mikrobearbeitung und für die Identifikation von Kraft- und Drehmomentmesssystemen erzielt. Auf Verbesserungsmöglichkeiten für die weitere Reduzierung der Unsicherheit bei der Kraft- und Drehmomentmessung mit dem Gerät wird eingegangen.The design of an instrument used to measure force and torque vectors that integrates a calibration system is described. The forces and torques are traced to position, angle, voltage, electrical resistance and time references. In terms of fundamental physical constants, the forces and torques can be traced to the Planck constant h, the speed of light in vacuum c and the hyperfine transition frequency of Caesium Δv_Cs. The measuring strategy used is based on the principle of the electromagnetic force compensation with the calibration based on the Kibble balance principle. Several difficulties and limitations of traditional calibration procedures for multicomponent force and torque transducers are overcome with this system and new features are introduced, such as the automatic in-process calibration. A careful uncertainty analysis is used to determine the achievable uncertainty for both force and torque measurements and identify the limitations caused by the components of the system. A prototype used to measure forces and torques in a range of 2.2 N and 0.11 N m with relative standard uncertainties of 44 ppm and 460 ppm respectively is presented. Considering the literature reviewed in this work, the system presented here exhibits the lowest uncertainty for the multicomponent force measurement. Verifications were performed by measuring a reference force generated by the weight of a calibrated test mass. Experimental results obtained by the application of multicomponent force and torque transducers to the Lorentz force velocimetry, micromachining and the identification of force and torque measuring systems are shown. Improvement possibilities for reducing the uncertainty for the force and torque measurements with the instrument are suggested

    The 25th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting

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    Papers in the following categories are presented: recent developments in rubidium, cesium, and hydrogen-based frequency standards, and in cryogenic and trapped-ion technology; international and transnational applications of precise time and time interval (PTTI) technology with emphasis on satellite laser tracking networks, GLONASS timing, intercomparison of national time scales and international telecommunication; applications of PTTI technology to the telecommunications, power distribution, platform positioning, and geophysical survey industries; application of PTTI technology to evolving military communications and navigation systems; and dissemination of precise time and frequency by means of GPS, GLONASS, MILSTAR, LORAN, and synchronous communications satellites

    Development of Traceable Capabilities in Non-Contact Thermal Metrology

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    Accurate temperature measurement is crucial in industry to reduce waste and environmental impact. Industrial use of Radiation Thermometers (RTs) is becoming increasingly common due to their wide market availability, fast response time, large temperature ranges, and their ability to measure temperature without contact. With this growth in use, accurate RT measurements that are traceable to the International Temperature Scale of 1990 (ITS-90) are a growing requirement. Traceable calibrations are usually performed using horizontal Blackbody Cavity Radiation Sources (BCRSs). In the work presented, a unique vertical bath-based BCRS, constructed in-house at the National Standards Authority of Ireland (NSAI), was compared over the range from -30 °C to 150 °C, against a suite of conventional horizontal bath-based BCRSs in overseas National Metrology Institutes (NMIs) and against a previous iteration of this new vertical design. Vertical bath-based BCRSs are more flexible and economical to use than horizontal BCRSs and can take advantage of existing calibration equipment. In the comparison of BCRSs, it was found that the vertical orientation was comparable to within 0.25 °C of standard horizontal cavities for the range from -30 °C to 150 °C. It was concluded that the vertical configuration is an economical alternative for calibration of RTs within the range assessed. A conservative evaluation of the uncertainty of measurement found that it ranged from ±0.34 °C to ±0.66 °C (� = 2). Alongside this comparison, the calibration of direct-reading, handheld Infrared RTs (often simply referred to as IRTs) was investigated. These are lower-cost instruments that read directly in temperature and do not give access to the unprocessed detector signal. IRTs are the most common type of RT used in industry. IRTs are known to suffer from poor Size-of-Source Effects (SSEs), which introduce errors caused by scattered radiation from outside the IRT’s nominal target area. Variation in readings due to changes in proximity of the detector to the source – the Distance Effect (DE) – has also been found to cause significant errors in IRTs. In the present work, best practice calibration procedures and uncertainty budgets were investigated for IRTs using a case study instrument. The instrument was calibrated over the range from -30 °C to 900 °C, and its SSE and Distance Effect (DE) were measured. The test case IRT’s SSE was measured at three different temperatures to determine its true field of view. The IRT was also tested at five target distances and using a variety of radiation sources to calibrate it and determine its DE. The IRT was found to exceed its specification by 3.7 °C when measuring an 800 °C BCRS and was out of specification across most of the rest of its range. At 500 °C, the IRT reading was found to vary by 1.75 °C across a 500 mm range of distances. The IRT reading was also found to drift by up to 2 °C when kept exposed to a 500 °C source for an hour. The case study of the IRT highlighted the importance of providing detailed calibration conditions, particularly regarding calibration geometry, IRT housing temperature, and exposure duration. As well as aiding in the establishment of a fit-for-purpose high-level non-contact calibration capability at NSAI, the work presented details a method by which other NMIs can inexpensively develop RT calibration facilities without custombuilt baths
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